Designing Polymer‐in‐Salt Electrolyte and Fully Infiltrated 3D Electrode for Integrated Solid‐State Lithium Batteries

High-Performance Pomegranate-Like CuF2 Cathode Derived from Spent Lithium-Ion Batteries

With the large-scale application of lithium-ion batteries (LIBs), a huge amount of spent LIBs will be generated each year and how to realize their recycling and reuse in a clean and effective way poses a challenge to the society. In this work, using the electrolyte of spent LIBs as solvent, we in situ fluorinate the conductive three-dimensional porous copper foam by a facile solvent-thermal method and then coating it with a cross-linked sodium alginate (SA) layer. Benefiting from the solid-electrolyte interphase (SEI) that accommodating the volume change of internal CuF2 core and SA layer that inhibiting the dissolution of CuF2, the synthesized CuF2@void@SEI@SA cathode with a pomegranate-like structure (yolk-shell) exhibits a large reversible capacity of ~535 mAh g-1 at 0.05 A g-1 and superb cycling stability. This work conforms to the development concept of green environmental protection and comprehensively realizes the unity of environmental, social and economic benefits.

Robust and Adhesive Laminar Solid Electrolyte with Homogenous and Fast Li-Ion Conduction for High-Performance All-Solid-State Lithium Metal Battery

Constructing composite solid electrolytes (CSEs) integrating the merits of inorganic and organic components is a promising approach to developing high-performance all-solid-state lithium metal batteries (ASSLMBs). CSEs are now capable of achieving homogeneous and fast Li-ion flux, but how to escape the trade-off between mechanical modulus and adhesion is still a challenge. Herein, a strategy to address this issue is proposed, that is, intercalating highly conductive, homogeneous, and viscous-fluid ionic conductors into robust coordination laminar framework to construct laminar solid electrolyte with homogeneous and fast Li-ion conduction (LSE-HFC). A 9 µm-thick LSH-HFC, in which poly(ethylene oxide)/succinonitrile is adsorbed by coordination laminar framework with metal-organic framework nanosheets as building blocks, is used here as an example to determine the validity. The Li-ion transfer mechanism is verified and works across the entire LSE-HFC, which facilitates homogeneous Li-ion flux and low migration energy barriers, endowing LSE-HFC with high ionic conductivity of 5.62 × 10-4 S cm-1 and Li-ion transference number of 0.78 at 25 °C. Combining the outstanding mechanical strength against punctures and the enhanced adhesion force with electrodes, LSE-HFC harvests uniform Li plating/stripping behavior. These enable the realization of high-energy-density ASSLMBs with excellent cycling stability when being assembled as LiFePO4/Li and LiNi0.6Mn0.2Co0.2O2/Li cells.

Manipulating the ionic conductivity and interfacial compatibility of polymer-in-dual-salt electrolytes enables extended-temperature quasi-solid metal batteries

Solid polymer electrolytes (SPEs) have shown great promise in the development of lithium-metal batteries (LMBs), but SPEs' interfacial instability and limited ionic conductivity still prevent their widespread applications. Herein, high-concentration hybrid dual-salt "polymer-in-salt" electrolytes (HDPEs) through formulation optimization were facilely prepared to simultaneously boost ionic conductivity, improve interfacial compatibility, and ensure a wide-temperature-range operation with high safety. An optimized electrolyte (HDPE-0.6) shows negligible corrosion to the aluminum current collector after manipulating the salt ratio of lithium bis(trifluoromethane)sulfonimide and lithium bis(oxalato)borate. In addition, HDPE-0.6 has excellent ionic conductivity (i.e., ∼0.536, ∼0.898, and ∼1.28 mS cm-1 at 0, 30, and 60 °C), approaching 1 mS cm-1 at room temperature. Furthermore, HDPE-0.6 exhibits a high lithium transference number of 0.6 and a high electrochemical oxidation stability potential of > 4.8 V vs. Li/Li+. Additionally, due to the formulation of high-concentration thermally stable lithium salts and the employment of flame-retardant trimethyl phosphate as the solvent, HDPE-0.6 has no safety issues. The resultant LiFePO4|HDPE-0.6|Li cell exhibits high discharge capacity, good rate capability, and excellent cycle stability at extended temperatures of 0, 30, and 60 °C. By coupling theoretical calculations and in-depth X-ray photoelectron spectroscopy, we attribute the excellent cycle stability to the formation of a stable interphase. Moreover, our formulation strategy is suitable for the Na3V2(PO4)3//Na battery when replacing the lithium salts with sodium salts (i.e., sodium bis(trifluoromethane)sulfonimide and sodium bis(oxalato)borate) to yield HDPE-0.6-Na, as demonstrated by excellent cycle stability (e.g., 98.6 % of capacity retention after 300 cycles). Our work demonstrates that the as-developed quasi-solid HDPEs are suitable for LMBs and sodium-metal batteries, and HDPEs can function normally in a wide temperature range.

Wide-Temperature and High-Rate Operation of Lithium Metal Batteries Enabled by an Ionic Liquid Functionalized Quasi-Solid-State Electrolyte

The development of high-energy-density solid-state lithium metal battery has been hindered by the unstable cycling of Ni-rich cathodes at high rate and limited wide-temperatures adoptability. In this study, an ionic liquid functionalized quasi-solid-state electrolyte (FQSE) is prepared to address these challenges. The FQSE features a semi-immobilized ionic liquid capable of anchoring solvent molecules through electrostatic interactions, which facilitates Li+ desolvation and reduces deleterious solvent-cathode reactions. The FQSE exhibits impressive electrochemical characteristics, including high ionic conductivity (1.9 mS cm-1 at 30 °C and 0.2 mS cm-1 at -30 °C) and a Li+ transfer number of 0.7. Consequently, Li/NCM811 cells incorporating FQSE demonstrate exceptional stability during high-rate cycling, enduring 700 cycles at 1 C. Notably, the Li/LFP cells with FQSE maintain high capacity across a wide temperature range, from -30 to 60 °C. This research provides a new way to promote the practical application of high-energy lithium metal batteries.

Design of High-Entropy Tape Electrolytes for Compression-Free Solid-State Batteries

Advanced solid electrolytes with strong adhesion to other components are the key for the successes of solid-state batteries. Unfortunately, traditional solid electrolytes have to work under high compression to maintain the contact inside owing to their poor adhesion. Here, a concept of high-entropy tape electrolyte (HETE) is proposed to simultaneously achieve tape-like adhesion, liquid-like ion conduction, and separator-like mechanical properties. This HETE is designed with adhesive skin layer on both sides and robust skeleton layer in the middle. The significant properties of the three layers are enabled by high-entropy microstructures which are realized by harnessing polymer-ion interactions. As a result, the HETE shows high ionic conductivity (3.50 ± 0.53 × 10-4 S cm-1 at room temperature), good mechanical properties (toughness 11.28 ± 1.12 MJ m-3, strength 8.18 ± 0.28 MPa), and importantly, tape-like adhesion (interfacial toughness 231.6 ± 9.6 J m-2). Moreover, a compression-free solid-state tape battery is finally demonstrated by adhesion-based assembling, which shows good interfacial and electrochemical stability even under harsh mechanical conditions, such as twisting and bending. The concept of HETE and compression-free solid-state tape batteries may bring promising solutions and inspiration to conquer the interface challenges in solid-state batteries and their manufacturing.

Dendritic Solid Polymer Electrolytes: A New Paradigm for High-Performance Lithium-Based Batteries

Li-ions battery is widely used and recognized, but its energy density based on organic electrolytes has approached the theoretical upper limit, while the use of organic electrolytes also brings some safety hazards (leakage and flammability). Polymer electrolytes (PEs) are expected to fundamentally solve the safety problem and improve energy density. Therefore, Li-ions battery based on solid PE has become a research hotspot in recent years. However, low ionic conductivity and poor mechanical properties, as well as a narrow electrochemical window limit its further development. Dendritic PEs with unique topology structure has low crystallinity, high segmental mobility, and reduced chain entanglement, providing a new avenue for designing high-performance PEs. In this review, the basic concept and synthetic chemistry of dendritic polymers are first introduced. Then, this story will turn to how to balance the mechanical properties, ionic conductivity, and electrochemical stability of dendritic PEs from synthetic chemistry. In addition, accomplishments on dendritic PEs based on different synthesis strategies and recent advances in battery applications are summarized and discussed. Subsequently, the ionic transport mechanism and interfacial interaction are deeply analyzed. In the end, the challenges and prospects are outlined to promote further development in this booming field.

Interface Engineering of All-Solid-State Batteries Based on Inorganic Solid Electrolytes

All-solid-state batteries (ASSBs) based on inorganic solid electrolytes (SEs) are one of the most promising strategies for next-generation energy storage systems and electronic devices due to the higher energy density and intrinsic safety. However, the poor solid-solid contact and restricted chemical/electrochemical stability of inorganic SEs both in cathode and anode SE interfaces cause contact failure and the degeneration of SEs during prolonged charge-discharge processes. As a result, the increasing interface resistance significantly affects the coulombic efficiency and cycling performance of ASSBs. Herein, we present a fundamental understanding of physical contact and chemical/electrochemical features of ASSB interfaces based on mainstream inorganic SEs and summarize the recent work on interface modification. SE doping, optimizing morphology, introducing interlayer/coating layer, and utilizing compatible electrode materials are the key methods to prevent side reactions, which are discussed separately in cathode/anode-SE interface. We also highlight the constant extra stack pressure applied during ASSB cycling, which is important to the electrochemical performance. Finally, our perspectives on interface modification for practical high-performance ASSBs are put forward.

Influencing Factors on Li-ion Conductivity and Interfacial Stability of Solid Polymer Electrolytes, Exampled by Polycarbonates, Polyoxalates and Polymalonates

The application of solid polymer electrolytes (SPEs) in all-solid-state(ASS) batteries is hindered by lower Li⁺ -conductivity and narrower electrochemical window. Here, three families of ester-based F-modified SPEs of poly-carbonate (PCE), poly-oxalate (POE) and poly-malonate (PME) were investigated. The Li⁺ -conductivity of these SPEs prepared from pentanediol are all higher than the counterparts made of butanediol, owing to the enhanced asymmetry and flexibility. Because of stronger chelating coordination with Li⁺ , the Li⁺ -conductivity of PME and POE is around 10 and 5 times of PCE. The trifluoroacetyl-units are observed more effective than -O-CH₂ -CF₂ -CF₂ -CH₂ -O- during the in situ passivation of Li-metal. Using trifluoroacetyl terminated POE and PCE as SPE, the interfaces with Li-metal and high-voltage-cathode are stabilized simultaneously, endowing stable cycling of ASS Li/LiNi_0.6 Co_0.2 Mn_0.2 O₂ (NCM622) cells. Owing to an enol isomerization of malonate, the cycling stability of Li/PME/NCM622 is deteriorated, which is recovered with the introduce of dimethyl-group in malonate and the suppression of enol isomerization. The coordinating capability with Li⁺ , molecular asymmetry and existing modes of elemental F, are all critical for the molecular design of SPEs.

Al and Ta co-doped LLZO as active filler with enhanced Li+conductivity for PVDF-HFP composite solid-state electrolyte

Battery safety calls for solid state batteries and how to prepare solid electrolytes with excellent performance are of significant importance. In this study, hybrid solid electrolytes combined with organic PVDF-HFP and inorganic active fillers are studied. The modified active fillers of Li_7-x-3yAl_yLa₃Zr_2-xTa_xO₁₂are obtained by co-element doping with Al and Ta when LLZO is synthesized by calcination. And an high room temperature ionic conductivity of 5.357 × 10^-4S cm^-1is exhibited by ATLLZO ceramic sheet. The composite solid electrolyte PVDF-HFP/LiTFSI/ATLLZO (PHL-ATLLZO) is prepared by solution casting method, and its electrochemical properties are investigated. The results show that when the contents of lithium salt LiTFSI and active filler ATLLZO are controlled at 40 wt% and 10%, respectively, the ionic conductivity of the resulting composite solid electrolyte is as high as 2.686 × 10^-4S cm^-1at room temperature, and a wide electrochemical window of 4.75 V is exhibited. The LiFePO₄/PHL-ATLLZO/Li all-solid-state battery assembled based on the composite solid-state electrolyte exhibits excellent cycling stability at room temperature. The cell assembled by casting the composite solid-state electrolyte on the cathode surface shows a discharge specific capacity of 134.3 mAh g^-1and 96.2% capacity retention after 100 cycles at 0.2 C. The prepared composite solid-state electrolyte demonstrates excellent electrochemical performance.

Functional Polymer Materials for Advanced Lithium Metal Batteries: A Review and Perspective

Lithium metal batteries (LMBs) are promising next-generation battery technologies with high energy densities. However, lithium dendrite growth during charge/discharge results in severe safety issues and poor cycling performance, which hinders their wide applications. The rational design and application of functional polymer materials in LMBs are of crucial importance to boost their electrochemical performances, especially the cycling stability. In this review, recent advances of advanced polymer materials are examined for boosting the stability and cycle life of LMBs as different components including artificial solid electrolyte interface (SEI) and functional interlayers between the separator and lithium metal anode. Thereafter, the research progress in the design of advanced polymer electrolytes will be analyzed for LMBs. At last, the major challenges and key perspectives will be discussed for the future development of functional polymers in LMBs.

Stable Interface Chemistry and Multiple Ion Transport of Composite Electrolyte Contribute to Ultra-long Cycling Solid-State LiNi0.8 Co0.1 Mn0.1 O2 /Lithium Metal Batteries

Severe interfacial side reactions of polymer electrolyte with LiNi_0.8 Co_0.1 Mn_0.1 O₂ (NCM811) cathode and Li metal anode restrict the cycling performance of solid-state NCM811/Li batteries. Herein, we propose a chemically stable ceramic-polymer-anchored solvent composite electrolyte with high ionic conductivity of 6.0×10^-4  S cm^-1 , which enables the solid-state NCM811/Li batteries to cycle 1500 times. The Li_1.4 Al_0.4 Ti_1.6 (PO₄ )₃ nanowires (LNs) can tightly anchor the essential N, N-dimethylformamide (DMF) in poly(vinylidene fluoride) (PVDF), greatly enhancing its electrochemical stability and suppressing the side reactions. We identify the ceramic-polymer-liquid multiple ion transport mechanism of the LNs-PVDF-DMF composite electrolyte by tracking the ⁶ Li and ⁷ Li substitution behavior via solid-state NMR. The stable interface chemistry and efficient ion transport of LNs-PVDF-DMF contribute to superior performances of the solid-state batteries at wide temperature range of -20-60 °C.