All-solid-state Lithium-ion Batteries Research Articles

A review of composite solid-state electrolytes for lithium batteries: fundamentals, key materials and advanced structures.

All-solid-state lithium ion batteries (ASSLBs) are considered next-generation devices for energy storage due to their advantages in safety and potentially high energy density. As the key component in ASSLBs, solid-state electrolytes (SSEs) with non-flammability and good adaptability to lithium metal anodes have attracted extensive attention in recent years. Among the current SSEs, composite solid-state electrolytes (CSSEs) with multiple phases have greater flexibility to customize and combine the advantages of single-phase electrolytes, which have been widely investigated recently and regarded as promising candidates for commercial ASSLBs. Based on existing investigations, herein, we present a comprehensive overview of the recent developments in CSSEs. Initially, we introduce the historical development from solid-state ionic conductors to CSSEs, and then summarize the fundamentals including mechanisms of lithium ion transport, key evaluation parameters, design principles, and key materials. Four main types of advanced structures for CSSEs are classified and highlighted according to the recent progress. Moreover, advanced characterization and computational simulation techniques including machine learning are reviewed for the first time, and the main challenges and perspectives of CSSEs are also provided for their future development.

Wet-Chemical Tuning of Li3-x PS4 (0≤x≤0.3) Enabled by Dual Solvents for All-Solid-State Lithium-Ion Batteries.

All-solid-state lithium-ion batteries (ASLBs) employing sulfide solid electrolytes are attractive next-generation rechargeable batteries that could offer improved safety and energy density. Recently, wet syntheses or processes for sulfide solid electrolyte materials have opened opportunities to explore new materials and practical fabrication methods for ASLBs. A new wet-chemical route for the synthesis of Li-deficient Li3-x PS4 (0≤x≤0.3) has been developed, which is enabled by dual solvents. Owing to its miscibility with tetrahydrofuran and ability to dissolve elemental sulfur, o-xylene as a cosolvent facilitates the wet-chemical synthesis of Li3-x PS4 . Li3-x PS4 (0≤x≤0.15) derived by using dual solvents shows Li+ conductivity of approximately 0.2 mS cm-1 at 30 °C, in contrast to 0.034 mS cm-1 for a sample obtained by using a conventional single solvent (tetrahydrofuran, x=0.15). The evolution of the structure for Li3-x PS4 is also investigated by complementary analysis using X-ray diffraction, Raman, and X-ray photoelectron spectroscopy measurements. LiCoO2 /Li-In ASLBs employing Li2.85 PS4 obtained by using dual solvents exhibit a reversible capacity of 130 mA h g-1 with good cycle retention at 30 °C, outperforming cells with Li2.85 PS4 obtained by using a conventional single solvent.

Practical evaluation of energy densities for sulfide solid-state batteries

Abstract All-solid-state Lithium (ion) batteries (ASSLBs) have been widely accepted as the key technology for next-generation energy storage devices, for which sulfide solid electrolyte (SSE) is most promising due to its high ionic conductivity and good mechanical property. For the development of sulfide ASSLBs, their energy densities with different electrode systems at cell level should be calculated as first priority, to rule out exaggerated/misleading reports and enable dedicated solutions to specific material systems with clear energy-density targets/applications. Herein, we evaluate the gravimetric/volumetric energy densities of sulfide ASSBs with practical parameters in a commercialized pouch cell for 8 common cathode/anode systems. The typical spacial distribution modes of solid electrolyte (SE) in electrodes are all considered to further precisely evaluate their effects on energy densities. Results show that for LiCoO2/SSE (50 μm)/Li ASSLB, its gravimetric (volumetric) energy density ranges in 410–280 Wh kg−1 (820-560 Wh L−1), as active material content varies from 96.5 to 67.5 wt%. By providing calculation paradigms of energy densities with practical conditions and reasonable assumptions, this study aims to present an unambiguous understanding in energy density predictions of sulfide ASSBs with real-world conditions.

Spark Plasma Sintering of Lithium Aluminum Germanium Phosphate Solid Electrolyte and its Electrochemical Properties.

Sodium superionic conductor (NASICON)-type lithium aluminum germanium phosphate (LAGP) has attracted increasing attention as a solid electrolyte for all-solid-state lithium-ion batteries (ASSLIBs), due to the good ionic conductivity and highly stable interface with Li metal. However, it still remains challenging to achieve high density and good ionic conductivity in LAGP pellets by using conventional sintering methods, because they required high temperatures (>800 °C) and long sintering time (>6 h), which could cause the loss of lithium, the formation of impurity phases, and thus the reduction of ionic conductivity. Herein, we report the utilization of a spark plasma sintering (SPS) method to synthesize LAGP pellets with a density of 3.477 g cm−3, a relative high density up to 97.6%, and a good ionic conductivity of 3.29 × 10−4 S cm−1. In contrast to the dry-pressing process followed with high-temperature annealing, the optimized SPS process only required a low operating temperature of 650 °C and short sintering time of 10 min. Despite the least energy and short time consumption, the SPS approach could still achieve LAGP pellets with high density, little voids and cracks, intimate grain–grain boundary, and high ionic conductivity. These advantages suggest the great potential of SPS as a fabrication technique for preparing solid electrolytes and composite electrodes used in ASSLIBs.

Enabling high-areal-capacity all-solid-state lithium-metal batteries by tri-layer electrolyte architectures

All-solid-state lithium-ion batteries (ASSLiBs) with metallic lithium (Li) anode, ceramic-type solid-state electrolyte (SSE) and nickel (Ni)-rich cathode offer great promise to deliver high energy density and high safety. However, the low cathode material loading and poor metallic Li/SSE interface are two major challenges. Herein, we design a new tri-layer SSE structure to address the challenges. A porous three-dimensional (3D) Li1·5Al0.5Ge1.5(PO4)3 (LAGP) layer acts as a host for LiNi0·8Mn0·1Co0·1O2 (NCM811) cathode, a thin but dense LAGP layer is employed to conduct ions and block dendrite, and a cross-linked solid-state polymer electrolyte (SPE) of polyethylene glycol bis(amine)-triglycidyl isocyanurate is introduced to the NCM811/LAGP/metallic Li interfaces to ameliorate contact issues. Enabled by such structure, the cathode loading in 3D porous LAGP layer reaches 13 mg cm−2, and delivers a reversible areal capacity of 2.01 mAh cm−2 at 0.1 C and a capacity retention of 70% over 50 cycles, whereas the conventional two-dimensional (2D) electrode only gives a low areal capacity of 0.11 mAh cm−2 and undergoes a rapid capacity fading. The significantly enhanced performance is ascribed to the continuous SSE structure and SSE/electrode interfacial compatibility. Our methodology on SSE construction design can provide a new strategy to develop the ASSLiBs with high energy density.

Visualization of the Interfacial Decomposition of Composite Cathodes in Argyrodite-Based All-Solid-State Batteries Using Time-of-Flight Secondary-Ion Mass Spectrometry

All-solid-state lithium-ion batteries (ASSBs) are expected to represent a future alternative compared to conventional lithium-ion batteries with liquid electrolytes (LIBs). The excellent performanc...

Sheet-type Li6PS5Cl-infiltrated Si anodes fabricated by solution process for all-solid-state lithium-ion batteries

All-solid-state lithium-ion batteries (ASLBs) employing sulfide solid electrolytes are considered a promising alternative to conventional lithium-ion batteries (LIBs) from the perspectives of safety and high energy density. From a practical point of view, the development of sheet-type electrodes employing alternative electrode materials by scalable fabrication is of prime importance. While Si has been extensively studied for next-generation LIBs, reports on ASLBs are scarce. Herein, we fabricate sheet-type Si composite electrodes by infiltrating conventional LIB electrodes with solid electrolytes using a homogeneous Li6PS5Cl-ethanol solution. Further, we systematically investigate effects of the particle size (micro- vs. nano-Si) and polymeric binders (polyvinylidene fluoride vs. polyacrylic acid/carboxymethyl cellulose) on the electrochemical performance of ASLBs under varying external pressures (140, 20, and 5 MPa) upon cycling. Owing to intimate ionic contacts enabled by liquefied solid electrolytes, the Li6PS5Cl-infiltrated Si electrodes show higher capacities of over 3000 mA h g−1 at 0.25 mA cm−2 and 30 °C as compared with conventional dry-mixed electrodes. At 20 MPa, the Si electrodes using micro-Si and polyvinylidene fluoride show marginal degradation of performance. The high energy density of 338 W h kg−1 of LiCoO2/Si ASLBs fabricated using the Li6PS5Cl-infiltrated electrodes is demonstrated, highlighting the prospect of high-energy practical ASLBs.

Slurry‐Fabricable Li+‐Conductive Polymeric Binders for Practical All‐Solid‐State Lithium‐Ion Batteries Enabled by Solvate Ionic Liquids

AbstractFor mass production of all‐solid‐state lithium‐ion batteries (ASLBs) employing highly Li+conductive and mechanically sinterable sulfide solid electrolytes (SEs), the wet‐slurry process is imperative. Unfortunately, the poor chemical stability of sulfide SEs severely restrict available candidates for solvents and in turn polymeric binders. Moreover, the binders interrupt Li+‐ionic contacts at interfaces, resulting in the below par electrochemical performance. In this work, a new scalable slurry fabrication protocol for sheet‐type ASLB electrodes made of Li+‐conductive polymeric binders is reported. The use of intermediate‐polarity solvent (e.g., dibromomethane) for the slurry allows for accommodating Li6PS5Cl and solvate‐ionic‐liquid‐based polymeric binders (NBR‐Li(G3)TFSI, NBR: nitrile−butadiene rubber, G3: triethylene glycol dimethyl ether, LiTFSI: lithium bis(trifluoromethanesulfonyl)imide) together without suffering from undesirable side reactions or phase separation. The LiNi0.6Co0.2Mn0.2O2and Li4Ti5O12electrodes employing NBR‐Li(G3)TFSI show high capacities of 174 and 160 mA h g−1at 30 °C, respectively, which are far superior to those using conventional NBR (144 and 76 mA h g−1). Moreover, high areal capacity of 7.4 mA h cm−2is highlighted for the LiNi0.7Co0.15Mn0.15O2electrodes with ultrahigh mass loading of 45 mg cm−2. The facilitated Li+‐ionic contacts at interfaces paved by NBR‐Li(G3)TFSI are evidenced by the complementary analysis from electrochemical and7Li nuclear magnetic resonance measurements.

High ionic conductivity Y doped Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte

Li1.3Al0.3Ti1.7(PO4)3 is regarded as one of the most promising solid electrolytes for all solid state lithium ion batteries (ASSLIBS). However, its grain boundary conductivity is still low, which reduces the total conductivity of electrolyte. In this work, in order to further improve the electrical conductivity of Li1.3Al0.3Ti1.7(PO4)3, a series of Y doped Li1.3Al0.3-xYxTi1.7(PO4)3 (x = 0, 0.025, 0.05, 0.075 and 0.15) solid electrolytes were synthesized using a modified solid state method. Effects of Y doping content on morphology, phase and electrical conductivity of Li1.3Al0.3Ti1.7(PO4)3 electrolyte materials were systematically investigated. All synthetic electrolyte powders show Nasicon-like structure, well-shaped polyhedral morphology as well as good crystallinity. Y dopant content has a great influence on electrochemical properties of electrolytes. The high total conductivity of 7.8 × 10−4 S/cm at room temperature and a low activation energy of 0.17 eV is obtained for the electrolyte with the Y doping content of 0.075 due to the increasing of grain boundary conductivity, and its electrical conductivity is about 2 times larger than that of the undoped electrolyte. The excellent electrochemical performance is mainly attributed to high electrolyte density which results from the good sintering property of electrolyte materials as well as the existence of YPO4 phase at grain boundaries. Additionally, this electrolyte has a negligible electronic conductivity. These results suggest that Y doped Li1.3Al0.3Ti1.7(PO4)3 can be used as an alternative solid electrolyte for all solid state lithium ion batteries.

Blended cathode materials for all-solid-state Li-ion batteries

In this article, we report the effects of blended cathode materials in all solid-state lithium-ion batteries (ASLBs) with oxide-based inorganic-organic-hybrid electrolytes. A high capacity Ni-rich cathode material was used for high energy density in an ASLB, and LiFePO4, with its robust olivine structure, was added to compensate for the degradation of the Ni-rich cathode material during cycling. In case of the blended cathode, the shortcomings of the parent material can be minimized by blending two cathode materials, and the blending ratio can be tailored to produce stable high energy and power densities. For these reasons, the structure, cycling stability, and rate performance of the blended LiNi0.7Co0.15Mn0.15O2/LiFePO4 cathode material, for use in ASLBs with oxide-based inorganic–organic-hybrid electrolytes, was investigated by powder X-ray diffraction, field-emission scanning electron microscopy, Brunauer–Emmett–Teller sorption experiments, electrochemical impedance spectroscopy, and galvanostatic testing.

Development of the PEO Based Solid Polymer Electrolytes for All-Solid State Lithium Ion Batteries.

Solid polymer electrolytes (SPEs) have attracted considerable attention due to the rapid development of the need for more safety and powerful lithium ion batteries. The prime requirements of solid polymer electrolytes are high ion conductivity, low glass transition temperature, excellent solubility to the conductive lithium salt, and good interface stability against Li anode, which makes PEO and its derivatives potential candidate polymer matrixes. This review mainly encompasses on the synthetic development of PEO-based SPEs (PSPEs), and the potential application of the resulting PSPEs for high performance, all-solid-state lithium ion batteries.

Reversible thixotropic gel electrolytes for safer and shape-versatile lithium-ion batteries

All-solid-state lithium-ion batteries (ASLBs) are receiving considerable attention due to their safety superiority and high energy density (achieved by bipolar configuration). Inorganic solid electrolytes are explored as a key-enabling material of the ASLBs. However, their critical challenges, including grain boundary resistance, interfacial instability with electrode materials and complicated processability, remain yet unresolved. Here, we demonstrate a new class of gel electrolyte with reversible thixotropic transformation and abuse tolerance as an effective and scalable approach to address the aforementioned longstanding issues. The gel electrolyte consists of (fluoropolymer/cellulose derivative) matrix and liquid electrolyte. The reversible thixotropic transformation is realized via sol-gel transition based on Coulombic interaction of the polymer matrix with liquid electrolyte. This unusual rheological feature allows the gel electrolyte to be printed in various forms. In addition, the gel electrolyte shows low crystallinity, thus playing a viable role in delivering high ionic conductivity. Based on understanding of rheological/electrochemical characteristics of the gel electrolyte, we fabricate a form factor-free pouch-type cell assembled with the gel electrolyte using sequential screen-printing process. The resultant cell shows exceptional safety upon exposure to various harsh abuse conditions, along with decent electrochemical performance.

In situ visualization of Li concentration in all-solid-state lithium ion batteries using time-of-flight secondary ion mass spectrometry

Lithium ion batteries (LIBs) are the most important energy storage devices. Novel methods for directly characterizing the behavior of Li ions during battery operations are highly coveted for understanding the fundamental working principles of the batteries and improving their device performances. In this study, we developed a novel method to visualize the change in Li ion distribution in the electrodes of all-solid-state (ASS) LIBs based on the time-of-flight secondary ion mass spectrometry technique with an in situ electrical measurement system. We succeeded in directly visualizing the decrease/increase of Li concentration in the cathode composite electrode during the charging/discharging cycles. Our method paves the way to characterize the fundamental aspects of ASS LIBs for improving device performance, including the evaluation of Li-depleted regions, visualization of the conductive paths and analysis of the causes of device degradation.

Structural changes and their effect on Li-ion conductivity upon quenching of La(1-x)/3LixNbO3 solid electrolytes

La(1-x)/3LixNbO3 (LLNbO) solid solutions constitute a promising family of electrolyte materials for use in all-solid-state lithium-ion batteries (ASSLIBs) because of their good electrochemical stability in contact with Li metal. Even in monocrystalline form, however, their Li-ion conductivities are insufficient for practical use. Post-synthesis heat treatment is a commonly applied technique for modifying nano- and microstructures, and hence properties of materials, although the effect of thermal treatment on A-site deficient layered perovskites is not well understood. Here we combine high temperature in situ X-ray diffraction, atomic-resolution scanning transmission electron microscopy, and molecular dynamics simulations to examine the effect of quenching on LLNbO with Li contents x ≈ 0.05 (Li-poor) and x ≈ 0.1 (Li-rich). Quenching results in a number of nanostructural changes, including weakening of the modulated structure by disordering of La atoms and vacancies within A1 layers, and movement of some La and Li atoms from A1 layers into A2 layers. Rumpling of Nb-O-Nb layers in the [001]p direction also becomes less pronounced and domain boundaries disappear as a result of suppression of NbO6 octahedral tilting. In the case of the Li-poor sample, the Li-ion conductivity decreased by about 66% after quenching, while that of the Li-rich sample increased by about 20%. Thus, despite success in displacing some cations from A1 to A2 layers, the combined effects of quenching failed to increase the Li-ion conductivities to useful levels. More effective means of increasing charge carrier concentrations while decreasing migration barrier energies in LLNbO need to be found if it is to be competitive as a solid electrolyte in ASSLIBs.

Effect of solvated ionic liquids on the ion conducting property of composite membranes for lithium ion batteries

We prepared the polyethylene oxide (PEO)-based composite membrane electrolytes which contained the specialized ionic liquids and the inorganic filler of Li7La3Zr2O12 (LLZO). Mixtures of ionic liquids and tetragonal inorganic fillers were used as additives to prepare composite electrolytes for an application of all solid-state lithium ion batteries (ASLBs). In order to improve the ionic conductivity of composite membranes, we studied the structural change and the electrochemical behaviors as a function of the amounts of solvated ionic liquids (ILs). The addition effect of solvated ILs showed the higher ionic conductivity such as 10−4 S/cm at 55 °C by reducing the crystalline character of polymer based composite, resulting in the enhanced ion conducting property. The hybrid composite membranes were successfully made in flexible form, and have an excellent thermal and electrochemical stability. Finally, the electrochemical performance of the half-cell was evaluated, and it was confirmed that the ion-conducting characteristics were influenced and controlled by the effect of ILs.

Assessment of all-solid-state lithium-ion batteries

All-solid-state lithium-ion batteries (ASSBs) are considered as next generation energy storage systems. A model might be very useful, which describes all contributions to the internal cell resistance, enables an optimization of the cell design, and calculates the performance of an open choice of cell architectures.A newly developed one-dimensional model for ASSBs is presented, based on a design concept which employs the use of composite electrodes. The internal cell resistance is calculated by linking two-phase transmission line models representing the composite electrodes with an ohmic resistance representing the solid electrolyte (separator). Thereby, electrical parameters, i.e. ionic and electronic conductivity, electrochemical parameters, i.e. charge-transfer resistance at interfaces and lithium solid-state diffusion, and microstructure parameters, i.e. electrode thickness, particle size, interface area, phase composition and tortuosity, are considered as the most important material and design parameters. Subsequently, discharge curves are simulated, and energy- and power-density characteristics of all-solid-state cell architectures are calculated. These model calculations are discussed and compared with experimental data from literature for a high power LiCoO2-Li10GeP2S12/Li10GeP2S12/Li4Ti5O12-Li10GeP2S12 cell.

(Invited) Influence of Mechanical Stress on Lithium Chemical Potential in Lithium Ion Battery Electrodes

In solid-state ionic devices, such as all-solid-state lithium ion batteries (ASSLIBs) and solid oxide fuel cells (SOFCs), mechanical stress is introduced at the electrode/electrolyte hetrointerfaces due to differences in the crystal structures and the chemical/thermal expansion coefficients. A mechanical strain at the heterointerface might affect thermodynamic and kinetic properties of the electrodes and the electrolyte, resulting in the performance deterioration or improvement of the devices. Although such a so-called “mechano-electro-chemical coupling effect” has been empirically demonstrated by many researches, the origins of the effect are not fully understood so far. In this presentation, we will discuss the influence of mechanical stress on thermodynamic properties of solid-state ionic materials. As a model case, lithium chemical potential in electrode materials for ASSLIBs under mechanical stress was investigated. A dense thin film electrode of LiCoO2, Li2MnO4 or LiFePO4 was deposited on a plate of solid-state lithium ion conductors, and the variation of the lithium chemical potential in the electrode was evaluated by measuring electromotive force under compressively- and tensely-strained conditions. Electromotive force accompanied by mechanical strain could be clearly observed, demonstrating a “mechano-electro-chemical coupling effect”. The influence of mechanical stress was different depending on the kinds of electrode material. The observed change in the electromotive force could be thermodynamically related to the lithium partial molar volume of the electrodes.

Pseudo zero-strain insertion materials for Li-ion batteries: cross-sectional observations of LiNi1/2Co1/2O2, LiNi1/3Co1/3Mn1/3O2, and LiNi0.8Co0.15Al0.05O2

Constructing robust interfaces between a positive (or negative) electrode and a solid electrolyte is essential for realizing more practical all-solid-state lithium-ion batteries (ALIBs). For the negative electrode, a zero-strain insertion material exists, Li[Li1/3Ti5/3]O4, which indicates a virtually 0% change in lattice volume (ΔV). In contrast, for the positive electrode, no zero-strain insertion material is currently available. In this paper, we observed cross-sections of charged Li x Ni1/2Co1/2O2 (NC11), Li x Ni1/3Co1/3Mn1/3O2 (NCM111), and Li x Ni0.8Co0.15Al0.05O2 (NCA) samples to clarify whether these positive electrode materials are applicable for ALIBs. Hardly any fractures were observed between primary particles in the NC11 and NCM111 samples, while fractures were observed in the NCA sample. This difference was due to the pseudo zero-strain character of the NC11 and NCM111 samples, which have ΔV values of approximately 0%, although their lattice parameters vary with x. Therefore, the ability of NC11 and NCM111 to maintain ionic and electronic contacts with a solid electrolyte makes them ideal positive electrode materials for ALIBs.

Toward practical all-solid-state lithium-ion batteries with high energy density and safety: Comparative study for electrodes fabricated by dry- and slurry-mixing processes

Owing to their potential for greater safety, higher energy density, and scalable fabrication, bulk-type all-solid-state lithium-ion batteries (ASLBs) employing deformable sulfide superionic conductors are considered highly promising for applications in battery electric vehicles. While fabrication of sheet-type electrodes is imperative from the practical point of view, reports on relevant research are scarce. This might be attributable to issues that complicate the slurry-based fabrication process and/or issues with ionic contacts and percolation. In this work, we systematically investigate the electrochemical performance of conventional dry-mixed electrodes and wet-slurry fabricated electrodes for ASLBs, by varying the different fractions of solid electrolytes and the mass loading. This information calls for a need to develop well-designed electrodes with better ionic contacts and to improve the ionic conductivity of solid electrolytes. As a scalable proof-of-concept to achieve better ionic contacts, a premixing process for active materials and solid electrolytes is demonstrated to significantly improve electrochemical performance. Pouch-type 80 × 60 mm2 all-solid-state LiNi0·6Co0·2Mn0·2O2/graphite full-cells fabricated by the slurry process show high cell-based energy density (184 W h kg−1 and 432 W h L−1). For the first time, their excellent safety is also demonstrated by simple tests (cutting with scissors and heating at 110 °C).

Coatable Li4 SnS4 Solid Electrolytes Prepared from Aqueous Solutions for All-Solid-State Lithium-Ion Batteries.

Bulk-type all-solid-state lithium-ion batteries (ASLBs) for large-scale energy-storage applications have emerged as a promising alternative to conventional lithium-ion batteries (LIBs) owing to their superior safety. However, the electrochemical performance of bulk-type ASLBs is critically limited by the low ionic conductivity of solid electrolytes (SEs) and poor ionic contact between the active materials and SEs. Herein, highly conductive (0.14 mS cm-1 ) and dry-air-stable SEs (Li4 SnS4 ) are reported, which are prepared using a scalable aqueous-solution process. An active material (LiCoO2 ) coated by solidified Li4 SnS4 from aqueous solutions results in a significant improvement in the electrochemical performance of ASLBs. Side-effects of the exposure of LiCoO2 to aqueous solutions are minimized by using predissolved Li4 SnS4 solution.