Aliphatic Polycarbonate-Based Solid-State Polymer Electrolytes for Advanced Lithium Batteries: Advances and Perspective

Block Copoly (Ester-Carbonate) Electrolytes for LiFePO4|Li Batteries with Stable Cycling Performance

To address the challenges posed by the narrow oxidation decomposition potential window and the characteristic of low ionic conductivity at room temperature of solid polymer electrolytes (SPEs), carbon dioxide (CO2), epichlorohydrin (PO), caprolactone (CL), and phthalic anhydride (PA) were employed in synthesizing di-block copolymer PCL-b-PPC and PCL-b-PPCP. The carbonate and ester bonds in PPC and PCL provide high electrochemical stability, while the polyether segments in PPC contribute to the high ion conductivity. To further improve the ion conductivity, we added succinonitrile as a plasticizer to the copolymer and used the copolymer to assemble lithium metal batteries (LMBs) with LiFePO4 as the cathode. The LiFePO4/SPE/Li battery assembled with PCL-b-PPC electrolyte exhibited an initial discharge-specific capacity of 155.5 mAh·g-1 at 0.5 C and 60 °C. After 270 cycles, the discharge-specific capacity was 140.8 mAh·g-1, with a capacity retention of 90.5% and an average coulombic efficiency of 99%, exhibiting excellent electrochemical performance. The study establishes the design strategies of di-block polymer electrolytes and provides a new strategy for the application of LMBs.

Progress of Polymer Electrolytes Worked in Solid-State Lithium Batteries for Wide-Temperature Application

Solid-state Li-ion batteries have emerged as the most promising next-generation energy storage systems, offering theoretical advantages such as superior safety and higher energy density. However, polymer-based solid-state Li-ion batteries face challenges across wide temperature ranges. The primary issue lies in the fact that most polymer electrolytes exhibit relatively low ionic conductivity at or below room temperature. This sensitivity to temperature variations poses challenges in operating solid-state lithium batteries at sub-zero temperatures. Moreover, elevated working temperatures lead to polymer shrinkage and deformation, ultimately resulting in battery failure. To address this challenge of polymer-based solid-state batteries, this review presents an overview of various promising polymer electrolyte systems. The review provides insights into the temperature-dependent physical and electrochemical properties of polymers, aiming to expand the temperature range of operation. The review also further summarizes modification strategies for polymer electrolytes suited to diverse temperatures. The final section summarizes the performance of various polymer-based solid-state batteries at different temperatures. Valuable insights and potential future research directions for designing wide-temperature polymer electrolytes are presented based on the differences in battery performance. This information is intended to inspire practical applications of wide-temperature polymer-based solid-state batteries.

Opening and Constructing Stable Lithium-ion Channels within Polymer Electrolytes

Lithium-ion batteries play an integral role in various aspects of daily life, yet there is a pressing need to enhance their safety and cycling stability. In this study, we have successfully developed a highly secure and flexible solid-state polymer electrolyte (SPE) through the in situ polymerization of allyl acetoacetate (AAA) monomers. This SPE constructed an efficient Li+ transport channel inside and effectively improved the solid-solid interface contact of solid-state batteries to reduce interfacial impedance. Furthermore, it exhibited excellent thermal stability, an ionic conductivity of 3.82×10-4 S cm-1 at room temperature (RT), and a Li+ transport number (tLi+) of 0.66. The numerous oxygen vacancies on layered inorganic SiO2 created an excellent environment for TFSI- immobilization. Free Li+ migrated rapidly at the C=O equivalence site with the poly(allyl acetoacetate) (PAAA) matrix. Consequently, when cycled at 0.5C and RT, it displayed an initial discharge specific capacity of 140.6 mAh g-1 with a discharge specific capacity retention rate of 70 % even after 500 cycles. Similarly, when cycled at a higher rate of 5C, it demonstrated an initial discharge specific capacity of 132.3 mAh g-1 while maintaining excellent cycling stability.

Electrochemical recycling of polymeric materials

Polymeric materials play a pivotal role in our modern world, offering a diverse range of applications. However, they have been designed with end-properties in mind over recyclability, leading to a crisis in their waste management. The recent emergence of electrochemical recycling methodologies for polymeric materials provides new perspectives on closing their life cycle, and to a larger extent, the plastic loop by transforming plastic waste into monomers, building blocks, or new polymers. In this context, we summarize electrochemical strategies developed for the recovery of building blocks, the functionalization of polymer chains as well as paired electrolysis and discuss how they can make an impact on plastic recycling, especially compared to traditional thermochemical approaches. Additionally, we explore potential directions that could revolutionize research in electrochemical plastic recycling, addressing associated challenges.

In-Situ Cross-linked F- and P-Containing Solid Polymer Electrolyte for Long-Cycling and High-Safety Lithium Metal Batteries with Various Cathode Materials

The practical application of lithium metal batteries (LMBs) has been hindered by limited cycle-life and safety concerns. To solve these problems, we develop a novel fluorinated phosphate cross-linker for gel polymer electrolyte in high-voltage LMBs, achieving superior electrochemical performance and high safety simultaneously. The fluorinated phosphate cross-linked gel polymer electrolyte (FP-GPE) by in-situ polymerization method not only demonstrates high oxidation stability but also exhibits excellent compatibility with lithium metal anode. LMBs utilizing FP-GPE realize stable cycling even at a high cut-off voltage of 4.6 V (vs Li/Li+) with various high-voltage cathode materials. The LiNi0.6Co0.2Mn0.2O2|FP-GPE|Li battery exhibits an ultralong cycle-life of 1200 cycles with an impressive capacity retention of 80.1 %. Furthermore, the FP-GPE-based batteries display excellent electrochemical performance even at practical conditions, such as high cathode mass loading (20.84 mg cm-2), ultrathin Li (20 μm), and a wide temperature range of -25 to 80 °C. Moreover, the first reported solid-state 18650 cylindrical LMBs have been successfully fabricated and demonstrate exceptional safety under mechanical abuse. Additionally, the industry-level 18650 cylindrical LiMn2O4|FP-GPE|Li4Ti5O12 cells demonstrate a remarkable cycle-life of 1400 cycles. Therefore, the impressive electrochemical performance and high safety in practical batteries demonstrate a substantial potential of well-designed FP-GPE for large-scale industrial applications.

Alternatives to fluorinated binders: recyclable copolyester/carbonate electrolytes for high-capacity solid composite cathodes

Optimising the composite cathode for next-generation, safe solid-state batteries with inorganic solid electrolytes remains a key challenge towards commercialisation and cell performance. Tackling this issue requires the design of suitable polymer binders for electrode processability and long-term solid-solid interfacial stability. Here, block-polyester/carbonates are systematically designed as Li-ion conducting, high-voltage stable binders for cathode composites comprising of single-crystal LiNi0.8Mn0.1Co0.1O2 cathodes, Li6PS5Cl solid electrolyte and carbon nanofibres. Compared to traditional fluorinated polymer binders, improved discharge capacities (186 mA h g-1) and capacity retention (96.7% over 200 cycles) are achieved. The nature of the new binder electrolytes also enables its separation and complete recycling after use. ABA- and AB-polymeric architectures are compared where the A-blocks are mechanical modifiers, and the B-block facilitates Li-ion transport. This reveals that the conductivity and mechanical properties of the ABA-type are more suited for binder application. Further, catalysed switching between CO2/epoxide A-polycarbonate (PC) synthesis and B-poly(carbonate-r-ester) formation employing caprolactone (CL) and trimethylene carbonate (TMC) identifies an optimal molar mass (50 kg mol-1) and composition (wPC 0.35). This polymer electrolyte binder shows impressive oxidative stability (5.2 V), suitable ionic conductivity (2.2 × 10-4 S cm-1 at 60 °C), and compliant viscoelastic properties for fabrication into high-performance solid composite cathodes. This work presents an attractive route to optimising polymer binder properties using controlled polymerisation strategies combining cyclic monomer (CL, TMC) ring-opening polymerisation and epoxide/CO2 ring-opening copolymerisation. It should also prompt further examination of polycarbonate/ester-based materials with today's most relevant yet demanding high-voltage cathodes and sensitive sulfide-based solid electrolytes.

Nitrile-functionalized Poly(siloxane) as Electrolytes for High-Energy-Density Solid-State Li Batteries

In the quest to replace liquid Li-ion electrolytes with safer and non-toxic solid counterparts for Li-ion batteries, polysiloxane polymers have attracted considerable attention as they offer low glass transition temperatures, stability with metallic lithium, and versatility in chemical functionalization of the backbone. Herein, we present the synthesis of Li-ion conductive polysiloxane-based polymers functionalized with 60 % nitrile groups per chain unit. The synthesis procedure is based on the reaction of poly-(dimethylsiloxane-co-methylvinylsiloxane) polymer with 2-cyanoethanethiol, followed by the addition of lithium bis (trifluoromethanesulfonyl) imide. The presented polysiloxane-based polymers exhibit exceptionally high ionic conductivity up to 0.375 mS cm-1 at 60 °C and Li+ ion transfer number of 0.73, one of the highest reported for polymer Li-ion conducting electrolytes. Their electrochemical performance was evaluated in both symmetrical and full-cell configurations to test the utility of synthesized polymers as electrolytes in Li-ion batteries.

Polymeric Electrolytes for Solid-state Lithium Ion Batteries: Structure Design, Electrochemical Properties and Cell Performances

Solid-state electrolytes are key to achieving high energy density, safety, and stability for lithium-ion batteries. In this Review, core indicators of solid polymer electrolytes are discussed in detail including ionic conductivity, interface compatibility, mechanical integrity, and cycling stability. Besides, we also summarize how above properties can be improved by design strategies of functional monomers, groups, and assembly of batteries. Structures and properties of polymers are investigated here to provide a basis for all-solid-state electrolyte design strategies of multi-component polymers. In addition, adjustment strategies of quasi-solid-state polymer electrolytes such as adding functional additives and carrying out structural design are also investigated, aiming at solving problems caused by simply adding liquids or small molecular plasticizer. We hope that fresh and established researchers can achieve a general perspective of solid polymer electrolytes via this Review and spur more extensive interests for exploration of high-performance lithium-ion batteries.

Demonstration of a Gel-Polymer Electrolyte-Based Electrochromic Device Outperforming Its Solution-Type Counterpart in All Merits: Architectural Benefits of CeO2 Quantum Dot and Nanorods

For years, solution-type electrochromic devices (ECDs) have intrigued researchers' interest and eventually rendered themselves into commercialization. Regrettably, challenges such as electrolyte leakage, high flammability, and complicated edge-encapsulation processes limit their practical utilization, hence necessitating an efficient alternate. In this quest, although the concept of solid/gel-polymer electrolyte (SPE/GPE)-based ECDs settled some issues of solution-type ECDs, an array of problems like high operating voltage, sluggish response time, and poor cycling stability have paralyzed their commercial applicability. Herein, we demonstrate a choreographed-CeO2-nanofiller-doped GPE-based ECD outperforming its solution-type counterpart in all merits. The filler-incorporated polymer electrolyte assembly was meticulously weaved through the electrospinning method, and the resultant host was employed for immobilizing electrochromic viologen species. The filler engineering benefits conceived through the tuned shape of CeO2 nanorod and quantum dots, along with the excellent redox shuttling effect of Ce3+/Ce4+, synchronously yielded an outstanding class of GPE, which upon utilization in ECDs delivered impressive electrochromic properties. A combination of features possessed by a particular device (QD-NR/PVDF-HFP/IL/BzV-Fc ECD) such as exceptionally low driving voltage (0.9 V), high transmittance change (ΔT, ∼69%), fast response time (∼1.8 s), high coloration efficiency (∼339 cm2/C), and remarkable cycling stability (∼90% ΔT-retention after 25,000 cycles) showcased a striking potential in the yet-to-realize market of GPE-based ECDs. This study unveils the untapped potential of choreographed nanofillers that can promisingly drive GPE-based ECDs to the doorstep of commercialization.

Feasibility of Multifunctional Cellulose-Based Polysalt as a Polymer Matrix for Li Metal Polymer Batteries

Li metal secondary batteries known for their high energy and power density are the much-awaited energy storage systems owing to the high specific capacity of Li metal. However, due to the instability of Li metal with common Li-ion battery electrolytes, a combination with a polymer electrolyte seems to be an effective strategy to alleviate the safety issues of employing Li metal and provide design conformity to the system. Current trends show improvements in different aspects, such as improving ionic conductivity, single-ion conductivity, mechanical stability, and electrochemical stability. A combination of all these properties has been a bottleneck for the development of polymer electrolytes for safe and efficient operation of all solid-state batteries. Herein, a multifunctional polysalt has been synthesized from green and sustainable materials, namely, ethyl cellulose, plasticized with adiponitrile, that contributes to meeting the critical properties enabling high compatibility with Li metal and a quasi-single-ion-conducting property while simultaneously acting as a matrix/filler for efficient operation of the cells. This multifunctional polymer matrix inhibits further decomposition of nitrile-based plasticizers on Li metal anodes with the formation of a favorable Li metal anode interface, thus enabling the utilization of high-voltage stable nitrile-based plasticizers (4.2 V) to be implemented as an electrolyte component for realization of high-voltage Li metal anode polymer batteries.

Investigation of the sodium-ion transport mechanism and elastic properties of double anti-perovskite Na3S0.5O0.5I

Sodium-rich anti-perovskites have unique advantages in terms of composition tuning and electrochemical stability when used as solid-state electrolytes in sodium-ion batteries. However, their Na+ transport mechanism is not clear and Na+ conductivity needs to be improved. In this paper, we investigate the stability, elastic properties and Na+ transport mechanisms of both the double anti-perovskite Na3S0.5O0.5I and anti-perovskite Na3OI. The results indicate that the NaI Schottky defect is the most favorable intrinsic defect for Na+ transport and due to the substitution of S2- for O2-, Na3S0.5O0.5I has stronger ductility and higher Na+ conductivity compared to Na3OI, despite the electrochemical window being slightly narrower. Divalent alkaline earth metal dopants can increase the Na+ vacancy concentration, while impeding Na+ migration. Among the dopants, Sr2+ and Ca2+ are the optimal dopants for Na3S0.5O0.5I and Na3OI, respectively. Notably, the Na+ conductivity of the non-stoichiometric Na3S0.5O0.5I at room temperature is 1.2 × 10-3 S cm-1, indicating its great potential as a solid-state electrolyte. Moreover, strain effect calculations show that biaxial tensile strain is beneficial for Na+ transport. Our work reveals the sodium-ion transport mechanism and elastic properties of double anti-perovskites, which is of great significance for the development of solid-state electrolytes.

Applications of Polymer Electrolytes in Lithium-Ion Batteries: A Review

Polymer electrolytes, a type of electrolyte used in lithium-ion batteries, combine polymers and ionic salts. Their integration into lithium-ion batteries has resulted in significant advancements in battery technology, including improved safety, increased capacity, and longer cycle life. This review summarizes the mechanisms governing ion transport mechanism, fundamental characteristics, and preparation methods of different types of polymer electrolytes, including solid polymer electrolytes and gel polymer electrolytes. Furthermore, this work explores recent advancements in non-aqueous Li-based battery systems, where polymer electrolytes lead to inherent performance improvements. These battery systems encompass Li-ion polymer batteries, Li-ion solid-state batteries, Li-air batteries, Li-metal batteries, and Li-sulfur batteries. Notably, the advantages of polymer electrolytes extend beyond enhancing safety. This review also highlights the remaining challenges and provides future perspectives, aiming to propose strategies for developing novel polymer electrolytes for high-performance Li-based batteries.

Regulating Steric Hindrance of Porous Organic Polymers in Composite Solid-State Electrolytes to Induce the Formation of LiF-Rich SEI in Li-Ion Batteries

Lithium fluoride (LiF) at the solid electrolyte interface (SEI) contributes to the stable operation of polymer-based solid-state lithium metal batteries. Currently, most of the methods for constructing lithium fluoride SEI are based on the design of polar groups of fillers. However, the mechanism behind how steric hindrance of fillers impacts LiF formation remains unclear. This study synthesizes three kinds of porous polyacetal amides (PAN-X, X=NH2 , NH-CH3 , N-(CH3 )2 ) with varying steric hindrances by regulating the number of methyl substitutions of nitrogen atoms on the reaction monomer, which are incorporated into polymer composite solid electrolytes, to investigate the regulation mechanism of steric hindrance on the content of lithium fluoride in SEI. The results show that bis(trifluoromethanesulfonyl)imide (TFSI- ) will compete for the charge without steric effect, while excessive steric hindrance hinders the interaction between TFSI- and polar groups, reducing charge acquisition. Only when one hydrogen atom on the amino group is replaced by a methyl group, steric hindrance from the methyl group prevents TFSI- from capturing charge in that direction, thereby facilitating the transfer of charge from the polar group to a separate TFSI- and promoting maximum LiF formation. This work provides a novel perspective on constructing LiF-rich SEI.

Highly Conductive Polyoxanorbornene-Based Polymer Electrolyte for Lithium-Metal Batteries

This present study illustrates the synthesis and preparation of polyoxanorbornene-based bottlebrush polymers with poly(ethylene oxide) (PEO) side chains by ring-opening metathesis polymerization for solid polymer electrolytes (SPE). In addition to the conductive PEO side chains, the polyoxanorbornene backbones may act as another ion conductor to further promote Li-ion movement within the SPE matrix. These results suggest that these bottlebrush polymer electrolytes provide impressively high ionic conductivity of 7.12 × 10-4 S cm-1 at room temperature and excellent electrochemical performance, including high-rate capabilities and cycling stability when paired with a Li metal anode and a LiFePO4 cathode. The new design paradigm, which has dual ionic conductive pathways, provides an unexplored avenue for inventing new SPEs and emphasizes the importance of molecular engineering to develop highly stable and conductive polymer electrolytes for lithium-metal batteries (LMB).

Magnesium Polymer Electrolytes Based on the Polycarbonate Poly(2-butyl-2-ethyltrimethylene-carbonate)

Magnesium electrolytes based on a polycarbonate with either magnesium tetrakis(hexafluoroisopropyloxy) borate (Mg(B(HFIP)₄)₂) or magnesium bis(trifluoromethanesulfonyl)imide (Mg(TFSI)₂) for magnesium batteries were prepared and characterized. The side-chain-containing polycarbonate, poly(2-butyl-2-ethyltrimethylene carbonate) (P(BEC)), was synthesized by ring opening polymerization (ROP) of 5-ethyl-5-butylpropane oxirane ether carbonate (BEC) and mixed with Mg(B(HFIP)₄)₂ or Mg(TFSI)₂ to form low- and high-salt-concentration polymer electrolytes (PEs). The PEs were characterized by impedance spectroscopy, differential scanning calorimetry (DSC), rheology, linear sweep voltammetry, cyclic voltammetry, and Raman spectroscopy. A transition from classical salt-in-polymer electrolytes to polymer-in-salt electrolytes was indicated by a significant change in glass transition temperature as well as storage and loss moduli. Ionic conductivity measurements indicated the formation of polymer-in-salt electrolytes for the PEs with 40 mol % Mg(B(HFIP)₄)₂ (HFIP40). In contrast, the 40 mol % Mg(TFSI)₂ PEs showed mainly the classical behavior. HFIP40 was further found to have an oxidative stability window greater than 6 V vs Mg/Mg²⁺, but showed no reversible stripping-plating behavior in an Mg||SS cell.

Solid-State Electrolytes in Lithium-Sulfur Batteries: Latest Progresses and Prospects

Solid-state lithium-sulfur batteries (SSLSBs) have attracted tremendous research interest due to their large theoretical energy density and high safety, which are highly important indicators for the development of next-generation energy storage devices. Particularly, safety and "shuttle effect" issues originating from volatile and flammable liquid organic electrolytes can be fully mitigated by switching to a solid-state configuration. However, their road to thecommercial application is still plagued with numerous challenges, most notably the intrinsic electrochemical instability of solid-state electrolytes (SSEs) materials and their interfacial compatibility with electrodes and electrolytes. In this review, a critical discussion on the key issues and problems of different types of SSEs as well as the corresponding optimization strategies are first highlighted. Then, the state-of-the-art preparation methods and properties of different kinds of SSE materials, and their manufacture, characterization and performance in SSLSBs are summarized in detail. Finally, a scientific outlook for the future development of SSEs and the avenue to commercial application of SSLSBs is also proposed.

Quasi-Solid Polymer Electrolyte with Multiple Lithium-Ion Transport Pathways by In Situ Thermal-Initiating Polymerization

Solid polymer electrolytes (SPEs) are considered to be attractive candidates for rechargeable batteries on account of their high safety and flexible processability. However, the restricted polymer segmental dynamics limit the Li⁺ conduction of SPEs. Herein, a composite electrolyte membrane was prepared via in situ thermal-initiating polymerization of diethylene glycol diacrylate (DEGDA) in a poly(vinylidene fluoride) frameworks (PVDF FMs) electrospun in advance. As a quasi-solid polymer electrolyte (QSPE), it provides multiple transport highways for Li⁺ built by the C═O or C-O or C═O/C-O groups in poly(diethylene glycol) diacrylate (PDEGDA), respectively, proved by density functional theory calculations together with the high-resolution ⁷Li solid-state nuclear magnetic resonance spectra. Since the interaction between Li⁺ and C═O is weaker than that between Li⁺ and C-O, Li⁺ tends to move along C═O dominating paths in PDEGDA/PVDF FMs QSPEs, even skipping back to C═O nodes from the original C-O dominating way. Multiple transport patterns facilitate Li⁺ migration within PDEGDA/PVDF FMs QSPEs, contributing to the ionic conductivity of 1.41 × 10^-4 S cm^-1 at 25 °C and the Li⁺ transference number of 0.454. Ascribing to the wetting capability of the monomer to the electrodes in use, compatible electrolyte/electrode interfaces with low interface resistance and compact cells were acquired by the in situ polymerization. Protective lithiated oligomers (RCOOLi) and LiF are enriched at the Li anode surface, promoting a lasting stable Li plating/stripping over 2000 h. By applying the QSPEs in LiFePO₄ cell, a capacity of 157.7 mAh g^-1 with almost 100% coulombic efficiency during 200 cycles is achieved at 25 °C.

"Pore-Hopping" Ion Transport in Cellulose-Based Separator Towards High-Performance Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have great potential for large-scale energy storage. Cellulose is an attractive material for sustainable separators, but some key issues still exist affecting its application. Herein, a cellulose-based composite separator (CP@PPC) was prepared by immersion curing of cellulose-based separators (CP) with poly(propylene carbonate) (PPC). With the assistance of PPC, the CP@PPC separator is able to operate the cell stably at high voltages (up to 4.95 V). The "pore-hopping" ion transport mechanism in CP@PPC opens up extra Na⁺ migration paths, resulting in a high Na⁺ transference number (0.613). The separator can also tolerate folding, bending and extreme temperature under certain circumstances. Full cells with CP@PPC reveal one-up capacity retention (96.97 %) at 2C after 500 cycles compared to cells with CP. The mechanism highlights the merits of electrolyte analogs in separator modification, making a rational design for durable devices in advanced energy storage systems.

Segmental Motion Adjustment of the Polycarbonate Electrolyte for Lithium-Metal Batteries

Carbonyl oxygen atoms are the primary active sites to solvate Li salts that provide a migration site for Li ions conducting in a polycarbonate-based polymer electrolyte. We here exploit the conductivity of the polycarbonate electrolyte by tuning the segmental motion of the structural unit with carbonyl oxygen atoms, while its correlation to the mechanical and electrochemical stability of the electrolyte is also discussed. Two linear alkenyl carbonate monomers are designed by molecular engineering to combine methyl acrylate (MA) and the commonly used ethylene carbonate (EC), w/o dimethyl carbonate (DMC) in the structure. The integration of the DMC structural unit in the side chain of the in situ constructed polymer (p-MDE) releases the free motion of the terminal EC units, which leads to a lower glass-transition temperature and higher ionic conductivity. While pure polycarbonates are normally fragile with high Young's modulus, such a prolonged side chain also manipulates the flexibility of the polymer to provide a mechanical stable interface for Li-metal anode. Stable long-term cycling performance is achieved at room temperature for both LiFePO₄ and LiCoO₂ electrodes based on the p-MDE electrolyte incorporated with a solid plasticizer.

Thermally Stable Polymer-Rich Solid Electrolyte Interphase for Safe Lithium Metal Pouch Cells

Serious safety risks caused by the high reactivity of lithium metal against electrolytes severely hamper the practicability of lithium metal batteries. By introducing unique polymerization site and more fluoride substitution, we built an in situ formed polymer-rich solid electrolyte interphase upon lithium anode to improve battery safety. The fluorine-rich and hydrogen-free polymer exhibits high thermal stability, which effectively reduces the continuous exothermic reaction between electrolyte and anode/cathode. As a result, the critical temperature for thermal safety of 1.0 Ah lithium-LiNi_0.5 Co_0.2 Mn_0.3 O₂ pouch cell can be increased from 143.2 °C to 174.2 °C. The more dangerous "ignition" point of lithium metal batteries, the starting temperature of battery thermal runaway, has been dramatically raised from 240.0 °C to 338.0 °C. This work affords novel strategies upon electrolyte design, aiming to pave the way for high-energy-density and thermally safe lithium metal batteries.

Buffering Volume Change in Solid-State Battery Composite Cathodes with CO2-Derived Block Polycarbonate Ethers

Polymers designed with a specific combination of electrochemical, mechanical, and chemical properties could help overcome challenges limiting practical all-solid-state batteries for high-performance next-generation energy storage devices. In composite cathodes, comprising active cathode material, inorganic solid electrolyte, and carbon, battery longevity is limited by active particle volume changes occurring on charge/discharge. To overcome this, impractical high pressures are applied to maintain interfacial contact. Herein, block polymers designed to address these issues combine ionic conductivity, electrochemical stability, and suitable elastomeric mechanical properties, including adhesion. The block polymers have "hard-soft-hard", ABA, block structures, where the soft "B" block is poly(ethylene oxide) (PEO), known to promote ionic conductivity, and the hard "A" block is a CO₂-derived polycarbonate, poly(4-vinyl cyclohexene oxide carbonate), which provides mechanical rigidity and enhances oxidative stability. ABA block polymers featuring controllable PEO and polycarbonate lengths are straightforwardly prepared using hydroxyl telechelic PEO as a macroinitiator for CO₂/epoxide ring-opening copolymerization and a well-controlled Mg(II)Co(II) catalyst. The influence of block polymer composition upon electrochemical and mechanical properties is investigated, with phosphonic acid functionalities being installed in the polycarbonate domains for adhesive properties. Three lead polymer materials are identified; these materials show an ambient ionic conductivity of 10 ^-4 S cm^-1, lithium-ion transport (t_Li+ 0.3-0.62), oxidative stability (>4 V vs Li^+/Li), and elastomeric or plastomer properties (G' 0.1-67 MPa). The best block polymers are used in composite cathodes with LiNi_0.8Mn_0.1Co_0.1O₂ active material and Li₆PS₅Cl solid electrolyte-the resulting solid-state batteries demonstrate greater capacity retention than equivalent cells featuring no polymer or commercial polyelectrolytes.

Bifunctional Solid-State Copolymer Electrolyte with Stabilized Interphase for High-Performance Lithium Metal Battery in a Wide Temperature Range

Solid-state polymer electrolytes (SPEs) are expected to guarantee safe and durable operations of lithium metal batteries (LMBs). Herein, inspired by the salutary poly(vinyl ethylene carbonate) (PVEC) component in the solid electrolyte interphase, cross-linking vinyl ethylene carbonate and ionic liquid copolymers were synthesized by in-situ polymerization to serve as polymer electrolyte for LMBs. On one hand, due to rich ester bonds of PVEC, Li⁺ could transfer by coupling/decoupling with oxygen atoms. On the other hand, the imidazole ring of ionic liquid could facilitate the dissociation of lithium salt to promote the free movement of Li⁺ . The bifunctional component synergistically increased the ionic conductivity of the SPE to 1.97×10^-4  S cm^-1 at 25 °C. Meanwhile, it also showed a wide electrochemical window, superior mechanical properties, outstanding non-combustibility, and excellent interfacial compatibility. The bifunctional copolymer-based LiFePO₄ batteries could normally operate at 0 to 60 °C, making them a promising candidate for wide-temperature-rang LMBs.

Solid Polymer Electrolytes for Lithium Batteries: A Tribute to Michel Armand

In a previous publication, a tribute to Michel Armand was provided, which highlighted his outstanding contribution to all aspects of research and development of lithium-metal and lithium-ion batteries. This area is in constant progress and rather than an overview of the work of Armand et al. since the seventies, we mainly restrict this review to his contribution to advances in solid polymer electrolytes (SPEs) and their performance in all-solid-state lithium-metal batteries in recent years.

Exovinylene Cyclic Carbonates: Multifaceted CO2 -Based Building Blocks for Modern Chemistry and Polymer Science

Carbon dioxide is a renewable, inexhaustible, and cheap alternative to fossil resources for the production of fine chemicals and plastics. It can notably be converted into exovinylene cyclic carbonates, unique synthons gaining momentum for the preparation of an impressive range of important organic molecules and functional polymers, in reactions proceeding with 100 % atom economy under mild operating conditions in most cases. This Review summarizes the recent advances in their synthesis with particular attention on describing the catalysts needed for their preparation and discussing the unique reactivity of these CO₂ -based heterocycles for the construction of diverse organic building blocks and (functional) polymers. We also discuss the challenges and the future perspectives in the field.

Improving Cyclability of All-Solid-State Batteries via Stabilized Electrolyte-Electrode Interface with Additive in Poly(propylene carbonate) Based Solid Electrolyte

In this study, tetraethylene glycol dimethyl ether (TEGDME) is demonstrated as an effective additive in poly(propylene carbonate) (PPC) polymers for the enhancement of ionic conductivity and interfacial stability and a tissue membrane is used as a backbone to maintain the mechanical strength of the solid polymer electrolytes (SPEs). TEGDME in the PPC allows the uniform distribution of conductive LiF species throughout the cathode electrolyte interface (CEI) layer which plays a critically important role in the formation of a stable and efficient CEI. In addition, the high modulus of SPEs suppresses the formation of a protrusion-type CEI on the cathode. The SPE with the optimized TEGDME content exhibits a high ionic conductivity of 0.89 mS cm^-1 , an adequate potential stability of up to 4.89 V, and a high Li-ion transference number of 0.81 at 60 °C. Moreover, the Li/SPE/Li cell demonstrates excellent cycling stability for 1650 h, and the Li/SPE/LFP full cell exhibits an initial reversible capacity of 103 mAh g^-1 and improved stability over 500 cycles at a rate of 1 C. The TEGDME additive improves the electrochemical properties of the SPEs and promotes the creation of a stable interface, which is crucial for ASSLIBs.

para-Aminobenzoic acid-capped hematite as an efficient nanocatalyst for solvent-free CO2 fixation under atmospheric pressure

Utilization of carbon dioxide by converting it into value-added chemicals is a sustainable remedy approach that stipulates abundant, cheap, non-toxic and efficient catalytic materials. In this study, we have demonstrated the use of para-aminobenzoic acid-capped hematite (PABA@α-Fe₂O₃) as an efficient nanocatalyst for the conversion of epoxides to cyclic carbonates utilizing CO₂. The developed PABA@α-Fe₂O₃ nanocatalyst along with a cocatalyst, tetrabutylammonium iodide (TBAI), was able to convert a variety of epoxide substrates into their corresponding cyclic carbonates under atmospheric pressure and solvent-free conditions. The efficient catalytic activity of the material is attributed to the synergistic effect between α-Fe₂O₃ and the amine group of the PABA molecule present on the surface. Furthermore, the recyclability study and post-catalytic analysis revealed that the developed catalyst can be used for multiple catalytic cycles due to the stable and robust nature of the nanocatalyst. The choice of the PABA@α-Fe₂O₃ nanocatalyst is indeed a sustainable approach from the CO₂ capture and utilization point of view.

The role of coordination strength in solid polymer electrolytes: compositional dependence of transference numbers in the poly(ε-caprolactone)-poly(trimethylene carbonate) system

Both polyesters and polycarbonates have been proposed as alternatives to polyethers as host materials for future polymer electrolytes for solid-state lithium-ion batteries. While being comparatively similar functional groups, the electron density on the coordinating carbonyl oxygen is different, thereby rendering different coordinating strength towards lithium ions. In this study, the transport properties of poly(ε-caprolactone) and poly(trimethylene carbonate) as well as random copolymers of systematically varied composition of the two have been investigated, in order to better elucidate the role of the coordination strength. The cationic transference number, a property well-connected with the complexing ability of the polymer, was shown to depend almost linearly on the ester content of the copolymer, increasing from 0.49 for the pure poly(ε-caprolactone) to 0.83 for pure poly(trimethylene carbonate). Contradictory to the transference number measurements that suggest a stronger lithium-to-ester coordination, DFT calculations showed that the carbonyl oxygen in the carbonate coordinates more strongly to the lithium ion than that of the ester. FT-IR measurements showed the coordination number to be higher in the polyester system, resulting in a higher total coordination strength and thereby resolving the paradox. This likely originates in properties that are specific of polymeric solvent systems, e.g. steric properties and chain dynamics, which influence the coordination chemistry. These results highlight the complexity in polymeric systems and their ion transport properties in comparison to low-molecular-weight analogues, and how polymer structure and steric effects together affect the coordination strength and transport properties.

Recent Advances and Perspectives on the Polymer Electrolytes for Sodium/Potassium-Ion Batteries

Owing to the low cost of sodium/potassium resources and similar electrochemical properties of Na⁺ /K⁺ to Li⁺ , sodium-ion batteries (SIBs) and potassium-ion batteries (KIBs) are regarded as promising alternatives to lithium-ion batteries (LIBs) in large-scale energy storage field. However, traditional organic liquid electrolytes bestow SIBs/KIBs with serious safety concerns. In contrast, quasi-/solid-phase electrolytes including polymer electrolytes (PEs) and inorganic solid electrolytes (ISEs) show great superiority of high safety. However, the poor processibility and relatively low ionic conductivity of Na⁺ and K⁺ ions limit the further practical applications of ISEs. PEs combine some merits of both liquid-phase electrolytes and ISEs, and present great potentials in next-generation energy storage systems. Considerable efforts have been devoted to improving their overall properties. Nevertheless, there is still a lack of an in-depth and comprehensive review to get insights into mechanisms and corresponding design strategies of PEs. Herein, the advantages of different electrolytes, particularly PEs are first minutely reviewed, and the mechanism of PEs for Na⁺ /K⁺ ion transfer is summarized. Then, representative researches and recent progresses of SIBs/KIBs based on PEs are presented. Finally, some suggestions and perspectives are put forward to provide some possible directions for the follow-up researches.

Solid Polymer Electrolytes with High Conductivity and Transference Number of Li Ions for Li-Based Rechargeable Batteries

Smart electronics and wearable devices require batteries with increased energy density, enhanced safety, and improved mechanical flexibility. However, current state-of-the-art Li-based rechargeable batteries (LBRBs) use highly reactive and flowable liquid electrolytes, severely limiting their ability to meet the above requirements. Therefore, solid polymer electrolytes (SPEs) are introduced to tackle the issues of liquid electrolytes. Nevertheless, due to their low Li⁺ conductivity and Li⁺ transference number (LITN) (around 10^-5 S cm^-1 and 0.5, respectively), SPE-based room temperature LBRBs are still in their early stages of development. This paper reviews the principles of Li⁺ conduction inside SPEs and the corresponding strategies to improve the Li⁺ conductivity and LITN of SPEs. Some representative applications of SPEs in high-energy density, safe, and flexible LBRBs are then introduced and prospected.

Interface Issues and Challenges in All-Solid-State Batteries: Lithium, Sodium, and Beyond

Owing to the promise of high safety and energy density, all-solid-state batteries are attracting incremental interest as one of the most promising next-generation energy storage systems. However, their widespread applications are inhibited by many technical challenges, including low-conductivity electrolytes, dendrite growth, and poor cycle/rate properties. Particularly, the interfacial dynamics between the solid electrolyte and the electrode is considered as a crucial factor in determining solid-state battery performance. In recent years, intensive research efforts have been devoted to understanding the interfacial behavior and strategies to overcome these challenges for all-solid-state batteries. Here, the interfacial principle and engineering in a variety of solid-state batteries, including solid-state lithium/sodium batteries and emerging batteries (lithium-sulfur, lithium-air, etc.), are discussed. Specific attention is paid to interface physics (contact and wettability) and interface chemistry (passivation layer, ionic transport, dendrite growth), as well as the strategies to address the above concerns. The purpose here is to outline the current interface issues and challenges, allowing for target-oriented research for solid-state electrochemical energy storage. Current trends and future perspectives in interfacial engineering are also presented.

Macromolecular Design of Lithium Conductive Polymer as Electrolyte for Solid-State Lithium Batteries

In the development of solid-state lithium batteries, solid polymer electrolyte (SPE) has drawn extensive concerns for its thermal and chemical stability, low density, and good processability. Especially SPE efficiently suppresses the formation of lithium dendrite and promotes battery safety. However, most of SPE is derived from the matrix with simple functional group, which suffers from low ionic conductivity, reduced mechanical properties after conductivity modification, bad electrochemical stability, and low lithium-ion transference number. Appling macromolecular design with multiple functional groups to polymer matrix is accepted as a strategy to solve the problems of SPE fundamentally. In this review, macromolecular design based on lithium conducting groups is summarized including copolymerization, network construction, and grafting. Meanwhile, the construction of single-ion conductor polymer is also focused herein. Moreover, synergistic effects between the designed matrix, lithium salt, and fillers are reviewed with the objective to further improve the performance of SPE. At last, future studies on macromolecular design are proposed in the development of SPE for solid-state batteries with high energy density and durability.

Coupling a Sponge Metal Fibers Skeleton with In Situ Surface Engineering to Achieve Advanced Electrodes for Flexible Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are regarded as promising next-generation energy storage systems, however, the uncontrollable dendrite formation and serious polysulfide shuttling severely hinder their commercial success. Herein, a powerful 3D sponge nickel (SN) skeleton plus in situ surface engineering strategy, to address these issues synergistically, is reported, and a high-performance flexible LSB device is constructed. Specifically, the rationally designed spray-quenched lithium metal on the SN matrix (solid electrolyte interface (SEI)@Li/SN), as dendrite inhibitor, combines the merits of the 3D lithiophilic SN skeleton and the in situ formed SEI layer derived from the spray-quenching process, and thereby exhibits a steady overpotential within 75 mV for 1500 h at 5 mA cm^-2 /10 mA h cm^-2 . Meanwhile, in situ surface sulfurization of the SN skeleton hybridizing with the carbon/sulfur composite (SC@Ni₃ S₂ /SN) serves as efficient lithium polysulfide adsorbent to catalyze the overall reaction kinetics. COMSOL Multiphysics simulations and density functional theory calculations are further conducted to explore the underlying mechanisms. As a proof of concept, the well-designed SEI@Li/SN||SC@Ni₃ S₂ /SN full cell shows excellent electrochemical performance with a negative/positive ratio in capacity of ≈2 and capacity retention of 99.82% at 1 C under mechanical deformation. The novel design principles of these materials and electrodes successfully shed new light on the development of flexible LSBs.

Rational Design of Ion Transport Paths at the Interface of Metal-Organic Framework Modified Solid Electrolyte

Solid-state lithium batteries have attracted great attention owing to their potential advantages in safety and energy density. Among various solid electrolytes, solid polymer electrolyte is promising due to its good viscoelasticity, lightweight, and low-cost processing. However, key issues of solid polymer electrolyte include poor ionic conductivity and low Li⁺ transference number, which limit its practical application. Herein, a new-type of ultraviolet cross-linked composite solid electrolyte (C-CSE), composed of ZIF-based ionic conductor (named ZIL) and polymer, is designed with enhanced ion transport. The ZIL is composed of ZIF-8 and ionic liquid, which can provide C-CSE with fast ion transport paths. Moreover, the proper pore size of ZIF-8 can restrict the migration of embedded ionic liquid and thus construct a solid-liquid transport interface between polymer chains and ZIF-8, which could achieve fast ion transport. In addition, ultraviolet irradiation can decrease the crystallization of C-CSE and thus increase the amorphous region. Consequently, the C-CSE show excellent electrochemical performance including high ionic conductivity of 0.426 mS cm^-1 at 30 °C, high Li⁺ transference number of 0.67, and good Li|Li compatibility cycle over 1040 h. Experimental and computational results indicate that diffusion energy barrier of Li⁺ through ZIF-8 is smaller than that of polymer chains, which reveals a new Li⁺ transport mechanism between polymer chains and ZIL, from "chain-chain-chain" to "chain-ZIL-chain". This work demonstrates rational design of ion transport paths at the interface of solid electrolyte could facilitate the development of solid-state lithium batteries as a promising novel strategy.

Solvent-Free Method Prepared a Sandwich-like Nanofibrous Membrane-Reinforced Polymer Electrolyte for High-Performance All-Solid-State Lithium Batteries

Solid polymer electrolytes (SPEs) with the advantages of high safety, low volatility, and the ability to suppress Li dendrites are highly desirable to be used in next generation high-safety and high-energy lithium-ion batteries. The exploration of SPEs with superior comprehensive properties has received extensive attention for high-performance all-solid-state batteries (ASSBs). Herein, a sandwich-like nanofibrous membrane-reinforced poly-caprolaclone diol and trimethyl phosphate (TMP) composite polymer electrolyte (CPE) has been designed by a facile "solvent-free" solution-casting method. Specifically, the flame-retardant TMP is employed as a plasticizer, which can improve the ionic conductivity effectively. The as-prepared solid electrolyte exhibits superior comprehensive performance in terms of high ionic conductivity, wide electrochemical window, good compatibility with lithium metal, and superior thermal stability. Furthermore, the assembled Li//LiFePO₄ ASSBs with this solid CPE show outstanding cycling stability and high average discharge capacity at room temperature (30 °C). Undoubtedly, our study provides a new facile method and a qualified solid electrolyte material for next generation high-performance ASSBs.

Intertwined Nanosponge Solid-State Polymer Electrolyte for Rollable and Foldable Lithium-Ion Batteries

Herein, we report a straigthforward procedure to prepare an excellent intertwined nanosponge solid-state polymer electrolyte (INSPE) for highly bendable, rollable, and foldable lithium-ion batteries (LIBs). The mechanically reliable and electrochemically superior INSPE is conjugated with intertwined nanosponge (IN) poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) and ion-conducting polymer electrolyte (PE) containing poly(ethylene glycol) diacrylate (PEGDA), succinonitrile (SCN) plasticizer, and lithium bis(trifluoromethanesilfonyl)imide (LiTFSI). The conjugated INSPE has both high strength with great flexibility (tensile strength of 2.1 MPa, elongation of 36.7%), and excellent ionic conductivity (1.04 × 10^-3 S·cm^-1, similar to the values of liquid electrolytes). As a result of such special combination, the as-prepared INSPE retains almost 100% of its ionic conductivity when subjected to many types of severe mechanical deformations. Therefore, the INSPE is successfully applied to bendable, rollable, and foldable LIBs that show excellent energy storage performance despite the intense mechanical deformations.

Polymerized Ionic Liquid-Containing Interpenetrating Network Solid Polymer Electrolytes for All-Solid-State Lithium Metal Batteries

The practical application of lithium metal batteries (LMBs) with high energy density is hindered by uneven lithium deposition during battery cycling. To mitigate this process, in this work, an interpenetrating polymer network solid polymer electrolyte (IPN SPE) is prepared by introducing a polymerized ionic liquid (PIL), poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)imide to a polyhedral oligomeric silsesquioxane-poly(ethylene glycol)-based network SPE. Compared with the virgin SPE, the newly developed IPN SPE exhibited improved ionic conductivity, excellent lithium dendrite resistance, and superior battery performance, which was attributed to the homogeneous, immobilized ion network provided by the PIL-containing IPN. Furthermore, the effects of ionic conductivity and homogenized ion distribution were quantitatively delineated by galvanostatic cycling and polarization measurements at current densities that were below and above the estimated Sand's critical current density based on the Chazalviel model. Full battery tests also showed excellent discharge capacity, cycle life, and Coulombic efficiency. Our results suggest that the PIL-containing IPN SPEs provide a promising system for stabilizing lithium electrodeposition and fabricating high-performance LMBs.