Lithium Metal Polymer Batteries Research Articles

Hybrid Ceramic Polymer Electrolytes Enabling Long Cycling in Practical 1 Ah‐Class High‐Voltage Solid‐State Batteries with Li Metal Anode

AbstractSolid polymer electrolytes offer a safer alternative to organic liquid electrolytes in high‐voltage lithium metal batteries, yet challenges remain in achieving adequate cyclability, energy density, scalability, and safety. This study presents the cycling performance of 1 Ah high‐voltage lithium polymer batteries featuring a hybrid ceramic polymer electrolyte (HCPE), a lithium metal anode, and a LiNi0.8Mn0.1Co0.1O2 (NMC‐811)‐based positive electrode. The HCPE stands out for its remarkable mechanical properties, with a Young's modulus exceeding 200 MPa at room temperature, providing robust resistance against dendrite formation. The Li||Li symmetric cells exhibited outstanding performance, cycling for over 1000 hours at a capacity of 2 mAh cm−2, highlighting the exceptional attributes of HCPE. Full cell testing is conducted under practical conditions, utilizing various cell configurations, from coin cells to large pouch cells with a 1 Ah capacity, achieving an energy density of nearly 250 Wh kg−1 and promising cyclability with 80% capacity retention after 110 cycles. The study also investigated thermal runaway characteristics, showing comparability with commercial lithium‐ion batteries. This research underscores the scalability and performance of high‐voltage lithium metal polymer batteries, advancing their potential for commercial viability.

Electrochemical Passivation of Aluminum As a Current Collector for Solid-State Polymer Batteries : PEO/LiTFSI Polymer Electrolyte

Investigation of the electrochemical properties and passivation mechanism of aluminum as a current collector for solid-state polymer batteries is carried out. Herein, electrochemical stabilities of Polyethylene glycol (PEO) based solid-state electrolyte containing Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt are proved using electrochemical dynamic- and transient-mode polarization with surface scratching. These results indicate that Al metal undergoes passivation with a layer below 4.5 V vs. Li+/Li. And then Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) reveal double layers are formed during the passivation on Al metal surface, with the outer layer composed of metal fluorides (AlF3) and the inner layer composed of metal oxides (Al2O3). The formation of the AlF3 layer on Al metal surface is attributed to the reaction between Al2O3 and HF following as Al2O3 + 6HF → 2AlF3 + 3H2O. Therefore, successful passivation achieved by the formation of AlF3 on the Al2O3 surface of Al metal facilitates to be widely used as a current collector for lithium metal polymer batteries. Therefore, successful passivation by the formation of AlF3 on the Al2O3 surface of Al metal making it a promising choice for the positive electrode in lithium metal polymer batteries.

Design of a Teflon‐Like Anion for Unprecedently Enhanced Lithium Metal Polymer Batteries

AbstractRechargeable lithium metal polymer batteries (LMPBs) utilizing solid polymer electrolytes (SPEs) have gained increasing attention during the past five decades, owing to the superior flexibility, good process‐ability, and no‐leakage of SPEs versus traditional non‐aqueous liquid and inorganic solid electrolytes. Undoubtedly, among all of the SPE components, salt anions have a significant impact on the overall performances of LMPBs. Yet, lithium bis(trifluoromethanesulfonyl)imide, being commonly applied in the prevailing SPEs shows relatively poor interphasial stability toward lithium metal (Li°) anode, which greatly impedes the long‐term cycling stability of LMPBs. Herein, a Teflon‐like sulfonimide salt, lithium bis(n‐nonafluorobutanesulfonyl)imide (LiNFSI), is ingeniously selected for modulating the properties of solid–electrolyte‐interphases on the anode side, in view of the peculiar film‐forming ability of n‐nonafluorobutanesulfonyl group. In‐depth physical, chemical, and electrochemical characterizations demonstrate that the incorporation of the Teflon‐like anion, NFSI−, results in a remarkably enhanced electrochemical stability between Li° anode and SPEs, with a negligible expense of ionic conductivities. The Teflon‐like sulfonimide anion suggested in this work provides an elegant path toward the wider application of LMPBs in energy storage and electric vehicles in the near future.

Mechanistically Novel Frontal‐Inspired In Situ Photopolymerization: An Efficient Electrode|Electrolyte Interface Engineering Method for High Energy Lithium Metal Polymer Batteries

The solvent‐free in situ polymerization technique has the potential to tailor‐make conformal interfaces that are essential for developing durable and safe lithium metal polymer batteries (LMPBs). Hence, much attention has been given to the eco‐friendly and rapid ultraviolet (UV)‐induced in situ photopolymerization process to prepare solid‐state polymer electrolytes. In this respect, an innovative method is proposed here to overcome the challenges of UV‐induced photopolymerization (UV‐curing) in the zones where UV‐light cannot penetrate, especially in LMPBs where thick electrodes are used. The proposed frontal‐inspired photopolymerization (FIPP) process is a diverged frontal‐based technique that uses two classes (dual) of initiators to improve the slow reaction kinetics of allyl‐based monomers/oligomers by at least 50% compared with the conventional UV‐curing process. The possible reaction mechanism occurring in FIPP is demonstrated using density functional theory calculations and spectroscopic investigations. Indeed, the initiation mechanism identified for the FIPP relies on a photochemical pathway rather than an exothermic propagating front forms during the UV‐irradiation step as the case with the classical frontal photopolymerization technique. Besides, the FIPP‐based in situ cell fabrication using dual initiators is advantageous over both the sandwich cell assembly and conventional in situ photopolymerization in overcoming the limitations of mass transport and active material utilization in high energy and high power LMPBs that use thick electrodes. Furthermore, the LMPB cells fabricated using the in situ‐FIPP process with high mass loading LiFePO4 electrodes (5.2 mg cm‐2) demonstrate higher rate capability, and a 50% increase in specific capacity against a sandwich cell encouraging the use of this innovative process in large‐scale solid‐state battery production.

Lithium Metal Polymer Batteries: Towards Operation at Ambient Temperature

A canonical electrolyte for lithium metal polymer batteries is PEO (Polyethylene Oxide) doped with lithium salts1. Its ionic conductivity is closely related to the local dynamics (Å, ps) of the polymer chains acting as a solid solvent. For good conductive performances, these batteries must be maintained above the melting point of the bulk PEO (TM =60°C).In order to lower this operating temperature, we propose to use one-dimensional nanoscale confinement to downshift the melting point of the confined electrolyte according to ΔTM ≈ 1/d where d is the pore diameter (Gibbs-Thomson effect)².Porous polymer composite membranes based on vertically aligned Carbon NanoTubes (VA-CNTs)3 ,4 seem to be able to meet this ambitious target. The pores are cylindrical (diameter 4nm, length 100µm) and have the particularity of being all macroscopically oriented and parallel.The effect we are seeking is driven by the curvature of the confining pore. It is then critical to ensure that only the interior of the CNTs is the permeable part of the membrane. We have followed by neutron imaging the time dependence of the penetration of the electrolyte within the membrane. We evidence a critical feature we target: only the interior of the CNTs are the permeable moieties of the membrane.As for the PEO dynamics under confinement, the electrolyte’s multiscale transport properties and ionic conductivity are characterized by PFG-NMR at the micrometer scale and Electrochemical Impedance Spectroscopy (EIS) at the macroscopic scale. We report a conductivity gain of one order of magnitude under VA-CNT confinement.Nevertheless, on a multitude of non-connected CNT pores, conductivity fluctuations are not in phase: by such classical spectroscopic techniques, only an averaged conductivity is measured. To complement the spectroscopic approach, we also probe the system by the Voltage Clamp (also called Single Pore) technique. The analysis of the conductivity noise going through a single CNT pore can indeed reveal whether the conductivity under confinement5 is due to an anomalous mobility and/or charge fluctuations.(1) Xue, Z. et al., Poly(Ethylene Oxide)-Based Electrolytes for Lithium-Ion Batteries. J. Mater. Chem. A 2015, 3 (38), 19218–19253.(2) Alba-Simionesco, C. et al., M. Effects of Confinement on Freezing and Melting. J. Phys.: Condens. Matter 2006, 18 (6), R15–R68.(3) Berrod, Q. et al., Enhanced Ionic Liquid Mobility Induced by Confinement in 1D CNT Membranes. Nanoscale 2016, 8 (15), 7845–7848.(4) Zanotti, J.-M. et al., Nanocomposite membranes for electrochemical devices. Patent WO2016151142 A1.(2016)(5) Tasserit, C. et al., Pink Noise of Ionic Conductance through Single Artificial Nanopores Revisited. Phys. Rev. Lett. 2010, 105 (26), 260602. Figure 1

Durable fast-charging lithium metal batteries designed with cross-linked polymer electrolytes and niobate-coated cathode

A durable lithium metal polymer battery with extended cycle-life is designed by exploiting cross-linked poly(trimethylene carbonate) (PTMC) electrolytes and LiNi0.6Mn0.2Co0.2O2 (NMC622) with well-defined protective coating (0.5 wt% of LiNbO3 on the surface layer, <5 nm thickness). The presented materials demonstrate feasibility of faster cycling at rates of 1C and 2C at temperatures of 40 and 60 °C, exhibiting prominent capacity retention of 91% and 80% SOH (state of health) after 500 cycles. At higher cross-linking densities, the introduced quasi-solid polymer electrolytes afford good cycling performance and sufficient suppression of high surface area lithium depositions as well as improved ability of solvent entrapment, hence reflecting a considerable step forward towards achieving all solid-state polymer-based cells.

Multisalt chemistry in ion transport and interface of lithium metal polymer batteries

Solvent-free solid-state polymer electrolytes (SPE) that go beyond the barriers like intrinsic low ionic conductivity, slow ion dynamics, and unstable electrode-electrolyte interphase will be fundamental for realizing the next generation of safe and high-performance lithium metal batteries. Hereby, cross-linked solid polymer electrolyte (XSPE) networks based on multisalt chemistry are synthesized using photopolymerization reaction, which outshine the conventional single salt-based XSPEs. By introducing the multisalt chemistry, an enhanced Li+ ion transport (ionic conductivity and short residence time) via anion mediated transfer (AMT) and improved interfacial characteristics (e.g., stable Li|electrolyte interphase, smooth Li-deposition) are demonstrated. Furthermore, a three-times increase in Li+ ion transference number and nearly one order of magnitude increment in diffusion coefficient are achieved. Using theoretical calculations, we propose an AMT-based ion conduction pathway in multisalt-based XSPEs. Besides, the superior electrochemical performance of multisalt-based XSPEs compared to single salt-based polymer electrolytes in Li-metal polymer batteries (LMPB) using C-LiFePO4 and LiNi0.8Co0.15Al0.05O2 cathodes are successfully demonstrated.

Ionic liquid plasticizers comprising solvating cations for lithium metal polymer batteries

Ternary solid polymer electrolytes (TSPEs) with ionic liquids (ILs) including alkyl-based ammonium cations and low coordinating anions suffer from the lack of Li+ ion coordination by the ILs compared to the immobile polymer backbone, in terms of Li+ ion transport. Thus, solvating ionic liquids (SILs) with an oligo(ethylene oxide) side chain attached onto the cation were prepared to improve the interaction between Li+ and the IL and accelerate Li+ transport in TSPEs. A variety of methods, such as pulsed field gradient nuclear magnetic resonance spectroscopy, Li metal plating/stripping and measurements of Sand's times were used to show that Li+ ion transference numbers increase with the oligo(ethylene oxide) side chain length in SIL-based TSPEs, which results in faster Li+ ion transport and translates into much slower lithium depletion at a given current, thereby delaying the onset of fast dendrite growth of lithium metal.

A Polymer-in-Salt Electrolyte with Enhanced Oxidative Stability for Lithium Metal Polymer Batteries.

The lithium (Li) metal polymer battery (LMPB) is a promising candidate for solid-state batteries with high safety. However, high voltage stability of such a battery has been hindered by the use of polyethylene oxide (PEO), which oxidizes at a potential lower than 4 V versus Li. Herein, we adopt the polymer-in-salt electrolyte (PISE) strategy to circumvent the disadvantage of the PEO-lithium bis(fluorosulfonyl)imide (LiFSI) system with EO/Li ≤ 8 through a dry ball-milling process to avoid the contamination of the residual solvent. The obtained solid-state PISEs exhibit distinctly different morphologies and coordination structures which lead to significant improvement in oxidative stability. P(EO)1LiFSI has a low melting temperature, a high ionic conductivity at 60 °C, and an oxidative stability of ∼4.5 V versus Li/Li+. With an effective interphase rich in inorganic species and a good stability of the hybrid polymer electrolyte toward Li metal, the LMPB constructed with Li||LiNi1/3Co1/3Mn1/3O2 can retain 74.4% of capacity after 186 cycles at 60 °C under the cutoff charge voltage of 4.3 V. The findings offer a promising pathway toward high-voltage stable polymer electrolytes for high-energy-density and safe LMPBs.

An Alternative Composite Polymer Electrolyte for High Performances Lithium Battery

A composite electrolyte consisting of polyethylene-glycol dimethyl-ether (MW 2000 g mol-1), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) conducting salt, lithium nitrate (LiNO3) film-forming additive, and nanometric silica (SiO2) filler, is herein obtained by a scalable solvent casting pathway and thoroughly investigated for application in lithium metal polymer battery. Structure and morphology of the electrolyte are investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively, while its electrochemical features are revealed by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), chronoamperometry, and galvanostatic cycling tests in lithium cell. The room-temperature structure of the composite electrolyte reflects the combination into a complex of the membrane components, while its morphology appears smooth with uniform distribution of salts and ceramic. The electrolyte shows an ionic conductivity over 10-4 S cm-1 above 40 °C promoted by repeated heating and cooling, lithium transference number ranging from 0.22 at 45 °C to 0.27 at 70 °C, low interphase resistance and polarization in lithium cell, and an electrochemical stability window extending above 4.4 V. These optimal features allow the membrane to operate in a lithium cell with LiFePO4 cathode at 50 °C, with specific capacity exceeding 150 mAh g-1 and coulombic efficiency approaching 100% over prolonged cycling. Figure 1

Electrochemical Assessment of Indigo Carmine Dye in Lithium Metal Polymer Technology.

Lithium metal batteries are inspiring renewed interest in the battery community because the most advanced designs of Li-ion batteries could be on the verge of reaching their theoretical specific energy density values. Among the investigated alternative technologies for electrochemical storage, the all-solid-state Li battery concept based on the implementation of dry solid polymer electrolytes appears as a mature technology not only to power full electric vehicles but also to provide solutions for stationary storage applications. With an effective marketing started in 2011, BlueSolutions keeps developing further the so-called lithium metal polymer batteries based on this technology. The present study reports the electrochemical performance of such Li metal batteries involving indigo carmine, a cheap and renewable electroactive non-soluble organic salt, at the positive electrode. Our results demonstrate that this active material was able to reversibly insert two Li at an average potential of ≈2.4 V vs. Li+/Li with however, a relatively poor stability upon cycling. Post-mortem analyses revealed the poisoning of the Li electrode by Na upon ion exchange reaction between the Na countercations of indigo carmine and the conducting salt. The use of thinner positive electrodes led to much better capacity retention while enabling the identification of two successive one-electron plateaus.

Cation-Assisted Lithium-Ion Transport for High-Performance PEO-based Ternary Solid Polymer Electrolytes.

N‐alkyl‐N‐alkyl pyrrolidinium‐based ionic liquids (ILs) are promising candidates as non‐flammable plasticizers for lowering the operation temperature of poly(ethylene oxide) (PEO)‐based solid polymer electrolytes (SPEs), but they present limitations in terms of lithium‐ion transport, such as a much lower lithium transference number. Thus, a pyrrolidinium cation was prepared with an oligo(ethylene oxide) substituent with seven repeating units. We show, by a combination of experimental characterizations and simulations, that the cation's solvating properties allow faster lithium‐ion transport than alkyl‐substituted analogues when incorporated in SPEs. This proceeds not only by accelerating the conduction modes of PEO, but also by enabling new conduction modes linked to the solvation of lithium by a single IL cation. This, combined with favorable interfacial properties versus lithium metal, leads to significantly improved performance on lithium‐metal polymer batteries.

Simultaneous Monitoring of Structural Changes and Phase Distribution of LiFePO4 Along the Cathode Thickness of Li Metal Polymer Battery

Probing the structural changes that electrode materials undergo during electrochemical cycling while monitoring their spatial distribution within the volume gives valuable insights on dynamic processes, i.e. side reactions and evolution of phase migration barriers, often associated to capacity and power limitation. In this work, we present an electrochemical cell to perform spatial and time resolved operando synchrotron X-ray diffraction on Lithium (Li) metal polymer batteries operating at 80 °C. A 3.2 mm diameter battery made of a Li metal anode, a LiFePO4 based cathode, and a solid polymer electrolyte acting as separator, is placed inside a glass-based casing and cycled at a beamline. The cylindrical cell geometry with its small size enables to follow the phase transformations occurring at different states of charge and at different cathode heights. It is possible to create spatially resolved phase distribution plots and to differentiate active material structural changes occurring close to the interface with the electrolyte from those at the current collector vicinity. The results provide a direct observation of the Li diffusion in the LiFePO4 and FePO4 phase distribution. In addition, synchrotron X-ray diffraction computed tomography (XRD-CT) measurements were performed to obtain phase distribution maps at different heights of the battery assembly.

(Invited) Lithium Metal Polymer Batteries: State-of-the-Art of the Technology and Commercial Prospects

BlueSolutions has been commercializing all-solid state batteries since 2011. EVs, buses and stationary applications are the main targets of its research and development program. After more than 15 years, this Bolloré group subsidiary masters all the industrial processes for the production of a unique solid state battery technology. The know-how goes from the transformation of the lithium ingots to the integration of the battery packs within the applications. Importantly, a low-ecological footprint process has been stated for both the positive electrode and the polymer electrolyte manufacturing.In order to get incomparable energy densities, today, all the industrial actors of lithium batteries are hardly working on the lithium metal technology. In this context, BlueSolutions has a unique 10 years feedback regarding both the behavior of this special anode and of the solid-state electrolyte.After having spread the first pack generation for 8 years all-over the world, an optimized 650V battery pack is about to be delivered. It is especially designed for heavy vehicles, such as buses. To match with customers expectations this new generation offers optimized performance and a very long cyclability. In the meanwhile, BlueSolutions has already started working on its future generation products. While the current battery is LFP-based and cycles at a nominal temperature of 80°C, a lot of efforts are dedicated to improve the actual chemistry. Research programs are conducted on the development of a new positive electrode with higher energy density, new polymers that will be compatible with high-voltage materials and which have high conductivity at ambient temperature and optimized lithium electrode. In fine, the goal is to keep the intrinsic safety of the polymer solid electrolyte, while benefiting from the promising performances of new electrode materials.

Trifluoromethyl-free anion for highly stable lithium metal polymer batteries

With the blooming of energy storage systems in e-mobility applications, the research activities of rechargeable lithium metal (Li°) batteries (LMBs) using solid-state electrolytes have been rekindled in recent years in light of stringent demands in terms of safety and energy density which are far beyond the capability of the contemporary lithium-ion batteries (LIBs). Lithium metal polymer (LMP) batteries utilizing solid polymer electrolytes (SPEs) are inherently safe and easy to process, thus becoming in the spotlights of solid-state lithium metal batteries (SSLMBs) technologies. However, the widely used electrolyte salts generally contain the trifluoromethyl (—CF3) group which has very low chemical and biochemical degradability, despite its strong electron-withdrawing ability which is essential for the dissolution and transport of ions in SPEs. In this work, a trifluoromethyl-free anion, bis(difluoromethanesulfonyl)imide {[N(SO2CF2H)2]−, DFSI−}, as an environmentally benign and interfacially favourable anion for high-performance SSLMB is reported. In contrast to the popular bis(trifluoromethanesulfonyl)imide anion {[N(SO2CF3)2]−, TFSI−}, the DFSI-based salt shows more rapid chemical degradation and its SPEs possess higher Li-only conductivity, significantly enhanced stability against Li° electrode, and better cell performance of LMP batteries. The results conveyed in this work may inspire the design of better SPEs, thus enabling a wider practical deployment of SSLMBs.

Improvement of Lithium Metal Polymer Batteries through a Small Dose of Fluorinated Salt.

Introducing a small dose of an electrolyte additive into solid polymer electrolytes (SPEs) is an appealing strategy for improving the quality of the solid-electrolyte-interphase (SEI) layer formed on the lithium metal (Li°) anode, thereby extending the cycling life of solid-state lithium metal batteries (SSLMBs). In this work, we report a new type of SPEs comprising a low-cost, fluorine-free salt, lithium tricyanomethanide, as the main conducting salt and a fluorinated salt, lithium bis(fluorosulfonyl)imide (LiFSI), as the electrolyte additive for enhancing the performance of SPE-based SSLMBs. Our results demonstrate that a homogeneous and stable SEI layer is readily formed on the surface of the Li° electrode through the preferential reductive decomposition of LiFSI, and consequently, the cycle stabilities of Li°||Li° and Li°||LiFePO4 cells are significantly improved after the incorporation of LiFSI as an additive. The intriguing chemistry of the salt anion revealed in this work may expedite the large-scale implementation of SSLMBs in the near future.

Study of the Lithium/Polymer Interface and Conductive Deposits on Lithium Metal Used for Lithium Metal Polymer Batteries.

Lithium metal anode has recently regained tremendous attention in the frame of the development of higher power and energy density lithium batteries for automotive industry. Lithium metal is indeed an ideal anode for lithium batteries due to its high capacity (3860 mAh/g). However, upon high discharge currents, the growth of dendrites leads to cell short cuts and limited coulombic efficiency.This issue had first restrained its practical application in rechargeable batteries for high power applications until the use of solid polymer electrolytes that could mechanically prevent the dendrites from crossing the electrolyte. Among the different families of polymer electrolytes, polyethylene oxide-based (PEO-based) electrolytes have been established as the reference thanks to a reasonable conductivity above 60oC and its ability to form a stable solid electrolyte interphase (SEI) with lithium. Nevertheless, due to the low transference number of POE/LiTFSI electrolytes (t+≈0.15), dendrites or uneven lithium plating are still susceptible to form. Nowadays, many efforts are dedicated to solve these problems by focusing either on the improvement of the electrolyte or on the modification of the lithium-electrolyte interface. Gold layers have been proposed as an alternative to prevent dendrite formation; these gold coatings are used mainly together with ceramic electrolytes in order to improve the interface between Li metal anode and electrolyte. However, their use with polymer electrolytes where dendrite formation is favorable due to low transference number and mechanical strength have not being widely studied. In this presentation, three different coatings will be considered; aluminum (Al), gold (Au) and lithium fluoride (LiF). The choice of Al and Au is based on their ability to form Li-rich alloys while LiF is known to act as an artificial ion conducting SEI. The morphology and physico-chemical properties of the coatings are first characterized by Atomic Force Microscopy (AFM), X-Ray Diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) before evaluation of the interface between POE-based electrolyte and coated Lithium. Eventually stability during long-term cycling in Lithium Metal Polymer batteries is performed and compared to that of cells made using bare Lithium.

An alternative composite polymer electrolyte for high performances lithium battery

A composite electrolyte consisting of polyethylene-glycol dimethyl-ether (MW 2000 g mol−1), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) conducting salt, lithium nitrate (LiNO3) film-forming additive, and nanometric silica (SiO2) filler, is herein obtained by a scalable solvent casting pathway and thoroughly investigated for application in lithium metal polymer battery. Structure and morphology of the electrolyte are investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively, while its electrochemical features are revealed by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), chronoamperometry, and galvanostatic cycling tests in lithium cell. The room-temperature structure of the composite electrolyte reflects the combination into a complex of the membrane components, while its morphology appears smooth with uniform distribution of salts and ceramic. The electrolyte shows an ionic conductivity over 10−4 S cm−1 above 40 °C promoted by repeated heating and cooling, lithium transference number ranging from 0.22 at 45 °C to 0.27 at 70 °C, low interphase resistance and polarization in lithium cell, and an electrochemical stability window extending above 4.4 V. These optimal features allow the membrane to operate in a lithium cell with LiFePO4 cathode at 50 °C, with specific capacity exceeding 150 mAh g−1 and coulombic efficiency approaching 100% over prolonged cycling.

Capacity degradation mechanism and improvement actions for 4 V-class all-solid-state lithium-metal polymer batteries

Abstract Owing to high safety and considerable energy density, rechargeable all-solid-state lithium-metal polymer batteries (ASSLPBs) with organic-inorganic composite solid-state electrolytes (CSSEs) have been recognized as one of the most promising battery systems. However, 4 V or above-class ASSLPBs still suffer serious capacity degradation arising from the complex interface issues between the electrode and electrolyte. Herein, for the first time, we find the oxidation decomposition of TFSI- anion and further interaction with PEO polymer matrix in the LiNi0.8Co0.1Mn0.1LiO2 (NCM811)/CSSEs (PEO-LiTFSI-LAGP)/Li cell, which cause continuous damage to the interfacial stability and persistent capacity degradation. Increasing the ratio of LAGP filler in CSSEs membrane and employing PEO-LiBOB electrolyte in composite cathode were demonstrated effective. As a consequence, the ASSLPBs show high reversibility, and high capacity retention up to 88% (3.0–4.2 V) and 78% (3.0–4.3 V) after 100 cycles with the charge/discharge current density of 30 mA g−1 (35 °C). The understanding on capacity degradation mechanism, along with the positive improvement strategies validly boosts the development and promising application of 4 V-class ASSLPBs.

4-V flexible all-solid-state lithium polymer batteries

Lithium metal polymer batteries have attracted extensive interest spurred by the pursuit of high safety as well as high-energy power sources. In this work, we report, a flexible, all-solid-state lithium metal polymer battery composed of the 4V-class, LiNi1-xCo0.2MnxO2 cathode, lithium anode and PEO10-LiTFSI-PYR14TFSI2 ternary solid polymer electrolyte. Compared with LiNi0.4Co0.2Mn0.4O2, the Ni-rich LiNi0.6Co0.2Mn0.2O2 cathode composite showed considerably more stable cycling performance and C-rate capability, as a result of the more homogeneous particle distribution that provides better electronic and ionic conductivity, and, most important, more stable interfacial impedance with smaller values upon cycling resulting from the formation of quickly stabilized SEI and the significantly alleviated phase transitions. Through the systematic investigation, this work herein provides a valid assessment of the potential use of 4V-class Ni-rich NCM for practical lithium metal polymer batteries.