Dense inorganic electrolyte particles as a lever to promote composite electrolyte conductivity

Highly efficient ion-transport "polymer-in-ceramic" electrolytes boost stable all-solid-state Li metal batteries

"Polymer-in-ceramic" (PIC) electrolytes are widely investigated for all-solid-state batteries (ASSBs) due to their good thermal stability and mechanical performance. However, achieving fast and diversified lithium-ion transport inside the PIC electrolyte and uniform Li+ deposition at the electrolyte/Li anode interface simultaneously remains a challenge. Besides, the effect of ceramic particle size on Li+ transport and Li anodic compatibility is still unclear, which is essential for revealing the enhanced mechanism of the performance for PIC electrolytes. Herein, PIC with moderate ceramic size and contents are prepared and studied to strike a balance between ionic conductivity and anodic compatibility. Through moderate filler-filler interfacial impedance and appropriate surface roughness, a particle size of 17 μm is optimized to facilitate homogeneous Li+ flux on anode and enhance Li+ conductivity of the electrolyte. The PIC electrolyte with ceramic particle size of 17 μm achieves a high lithium ion transference number (0.74) and an ionic conductivity of 4.11 × 10-4 S cm-1 at 60 °C. The Li/PIC/Li symmetric cell can stably cycle for 2800 h at 0.2 mA cm-2 with 0.2 mAh cm-2. Additionally, the Li/PIC/LiFePO4 cell also delivers a superior cycling performance at 0.5C, a high capacity retention of 93.28% after 100 cycles and 83.17% after 200 cycles, respectively.

Tuning Ceramic Surface to Minimize the Ionic Resistance at the Interface between PEO- and LATP-Based Ceramic Electrolyte

New battery technologies are currently under development, and among them, all-solid-state batteries should deliver better electrochemical performance and enhanced safety. Composite solid electrolytes, combining a solid polymer electrolyte (SPE) and a ceramic electrolyte (CE), should then provide high ionic conductivity coupled to high mechanical stability. To date, this synergy has not yet been reached due to the complexity of the Li-ion transport within the hybrid solid electrolyte, especially at the SPE/CE interface currently considered the limiting step. Yet, there is no proper kinetic model to elucidate the parameters influencing this interfacial barrier. The limited understanding of the SPE/CE interface can be partly explained by scattered SPE/CE interface resistances reported in the literature as well as the lack of systematic studies. Herein, we propose a systematic study of the effect on the SPE/CE interfacial resistance of chemical and thermal treatments of a model LATP-based ceramic based on a methodology relying on electrochemical impedance spectroscopy (EIS) and X-ray photoemission spectroscopy (XPS). The results provide different levers for the optimization of this interface and valuable insights into experimental precautions needed to obtain more reproducible results.

A Fluoride-Rich Solid-Like Electrolyte Stabilizing Lithium Metal Batteries

To address the problems associated with Li metal anodes, a fluoride-rich solid-like electrolyte (SLE) that combines the benefits of solid-state and liquid electrolytes is presented. Its unique triflate-group-enhanced frame channels facilitate the formation of a functional inorganic-rich solid electrolyte interphase (SEI), which not only improves the reversibility and interfacial charge transfer of Li anodes but also ensures uniform and compact Li deposition. Furthermore, these triflate groups contribute to the decoupling of Li+ and provide hopping sites for rapid Li+ transport, enabling a high room-temperature ionic conductivity of 1.1 mS cm-1 and a low activation energy of 0.17 eV, making it comparable to conventional liquid electrolytes. Consequently, Li symmetric cells using such SLE achieve extremely stable plating/stripping cycling over 3500 h at 0.5 mA cm-2 and support a high critical current up to 2 mA cm-2. The assembled Li||LiFePO4 solid-like batteries exhibit exceptional cyclability for over 1 year and a half, even outperforming liquid cells. Additionally, high-voltage cylindrical cells and high-capacity pouch cells are demonstrated, corroborating much simpler processibility in battery assembly compared to all-solid-state batteries.

An Ultrathin Composite Polymer Electrolyte Dual-Reinforced by a Polymer of Intrinsic Microporosity (PIM-1) and Poly(tetrafluoroethylene) (PTFE) Porous Membrane

The performances of solid-state polymer electrolytes are urgently required to be further improved for high energy density lithium metal batteries. Herein, a highly reinforced ultrathin composite polymer electrolyte (PLPP) is successfully fabricated in a large scale by densely filling the well-dispersed mixture of polyethylene oxide (PEO), Li-salt (LiTFSI) and a polymer of intrinsic microporosity (PIM-1) into porous poly(tetrafluoroethylene) (PTFE) matrix. Based on the macro-plus-micro synergistic enhancement of the PTFE with excellent mechanical properties and the soluble PIM-1 with suitable functional groups, the PLPP electrolyte exhibits excellent properties including mechanical stress, thermal stability, lithium-ion transference number, voltage window and ionic conductivity, which are all superior to the typical PEO/LiTFSI electrolytes. As a result, the Li/PLPP/Li symmetric cell can stably cycle for > 2000 h, and the LiFePO4/PLPP/Li full cell exhibits excellent rate performance (>10 C) and high cycling stability with an initial capacity of 158.8 mAh g-1 and a capacity retention of 78.8% after 300 cycles. In addition, the excellent mechanical properties as well as the wide voltage window reasonably result in the stable operation of full cells with either high-loading cathode up to 28.1 mg cm-2 or high voltage cathode with high energy density.

Lithium-Ion Transport and Exchange between Phases in a Concentrated Liquid Electrolyte Containing Lithium-Ion-Conducting Inorganic Particles

Understanding Li+ transport in organic-inorganic hybrid electrolytes, where Li+ has to lose its organic solvation shell to enter and transport through the inorganic phase, is crucial to the design of high-performance batteries. As a model system, we investigate a range of Li+-conducting particles suspended in a concentrated electrolyte. We show that large Li1.3Al0.3Ti1.7P3O12 and Li6PS5Cl particles can enhance the overall conductivity of the electrolyte. When studying impedance using a cell with a large cell constant, the Nyquist plot shows two semicircles: a high-frequency semicircle related to ion transport in the bulk of both phases and a medium-frequency semicircle attributed to Li+ transporting through the particle/liquid interfaces. Contrary to the high-frequency resistance, the medium-frequency resistance increases with particle content and shows a higher activation energy. Furthermore, we show that small particles, requiring Li+ to overcome particle/liquid interfaces more frequently, are less effective in facilitating Li+ transport. Overall, this study provides a straightforward approach to study the Li+ transport behavior in hybrid electrolytes.

Typology of Battery Cells - From Liquid to Solid Electrolytes

The field of battery research is bustling with activity and the plethora of names for batteries that present new cell concepts is indicative of this. Most names have grown historically, each indicative of the research focus in their own time, e.g. lithium-ion batteries, lithium-air batteries, solid-state batteries. Nevertheless, all batteries are essentially made of two electrode layers and an electrolyte layer. This lends itself to a systematic and comprehensive approach by which to identify the cell type and chemistry at a glance. The recent increase in hybridized cell concepts potentially opens a world of new battery types. To retain an overview of this dynamic research field, each battery type is briefly discussed and a systematic typology of battery cells is proposed in the form of the short and universal cell naming system AAM XEBCAM (AAM: anode active material; X: L (liquid), G (gel), PP (plasticized polymer), DP (dry polymer), S (solid), H (hybrid); EB: electrolyte battery; CAM: cathode active material). This classification is based on the principal ion conduction mechanism of the electrolyte during cell operation. Even though the presented typology initiates from the research fields of lithium-ion, solid-state and hybrid battery concepts, it is applicable to any battery cell chemistry.

1.89 $ kg-1 Lake-Water-Based Semisolid Electrolytes for Highly Efficient Energy Storage

Solid electrolytes with fast ion kinetics and superior mechanical properties are critical to electrochemical energy devices; however, how to design low-cost, high-performance solid electrolytes has become a critical challenge in the energy field, and significant progress has not been achieved until now. Here, lake-water-based semisolid electrolytes with a low cost of 1.89 $ kg^-1 have been put forward for the purpose of market promotion. By virtue of the palygorskite dopants and lake water source, the electrolytes display satisfying mechanical, electrical, and electrochemical properties as well as economic benefits. The application potential of electrolytes has been demonstrated by employing a polyelectrolyte with ionic conductivity of 0.82 × 10^-4 S cm^-1 in flexible supercapacitors. The as-assembled devices give a high energy density of 54.72 Wh kg^-1 and excellent cycling stability with a capacity retention of 94.8% over 20 000 cycles. The flexibility of devices has been verified through 5000 repetitive bending tests. Our work presents insight into the design of flexible solid electrolytes based on cheap and green raw materials.

PMMA-Based Composite Gel Polymer Electrolyte with Plastic Crystal Adopted for High-Performance Solid ECDs

A PMMA-based gel polymer electrolyte (GPE) modified by a plastic crystal succinonitrile (SN) was synthesized using a facile solvent-casting method. The effects of SN additives upon lithium-ion dissociation and ionic conductivity were investigated primarily using Fourier transform infrared spectroscopy and electrochemical impedance spectroscopy, accompanied by other structural characterization methods. The results show that SN is distributed uniformly in the PMMA matrix with a high content and produces vast dipoles that benefit the dissociation of lithium salt. Hence, the SN-modified GPE (SN-GPE) achieves an excellent ionic conductivity of 2.02 mS·cm^-1 and good mechanical properties. The quasi-solid-state ECD fabricated using the SN-GPE exhibits stable cyclability and excellent electrochromic performance, in which the bleaching/coloration response time is 10 s/30 s. These results add significant insight into understanding the inter- and intra-molecular interaction in SN-GPEs and provide a type of practicable high-performance GPE material for solid electrochromic devices.

Rational Design of High-Performance PEO/Ceramic Composite Solid Electrolytes for Lithium Metal Batteries

Composite solid electrolytes (CSEs) with poly(ethylene oxide) (PEO) have become fairly prevalent for fabricating high-performance solid-state lithium metal batteries due to their high Li+ solvating capability, flexible processability and low cost. However, unsatisfactory room-temperature ionic conductivity, weak interfacial compatibility and uncontrollable Li dendrite growth seriously hinder their progress. Enormous efforts have been devoted to combining PEO with ceramics either as fillers or major matrix with the rational design of two-phase architecture, spatial distribution and content, which is anticipated to hold the key to increasing ionic conductivity and resolving interfacial compatibility within CSEs and between CSEs/electrodes. Unfortunately, a comprehensive review exclusively discussing the design, preparation and application of PEO/ceramic-based CSEs is largely lacking, in spite of tremendous reviews dealing with a broad spectrum of polymers and ceramics. Consequently, this review targets recent advances in PEO/ceramic-based CSEs, starting with a brief introduction, followed by their ionic conduction mechanism, preparation methods, and then an emphasis on resolving ionic conductivity and interfacial compatibility. Afterward, their applications in solid-state lithium metal batteries with transition metal oxides and sulfur cathodes are summarized. Finally, a summary and outlook on existing challenges and future research directions are proposed.

Polyzwitterion-SiO2 Double-Network Polymer Electrolyte with High Strength and High Ionic Conductivity

The key to developing high-performance polymer electrolytes (PEs) is to achieve their high strength and high ionic conductivity, but this is still challenging. Herein, we designed a new double-network PE based on the nonhydrolytic sol-gel reaction of tetraethyl orthosilicate and in situ polymerization of zwitterions. The as-prepared PE possesses high strength (0.75 Mpa) and high stretchability (560%) due to the efficient dissipation energy of the inorganic network and elastic characteristics of the polymer network. In addition, the highest ionic conductivity of the PE reaches 0.44 mS cm-1 at 30 °C owning to the construction of dynamic ion channels between the polyzwitterion segments and between the polyzwitterion segments and ionic liquids. Furthermore, the inorganic network can act as Lewis acid to adsorb trace impurities, resulting in a prepared electrolyte with a high electrochemical window over 5 V. The excellent interface compatibility of the as-prepared PE with a Li metal electrode is also confirmed. Our work provides new insights into the design and preparation of high-performance polymer-based electrolytes for solid-state energy storage devices.