# Prospects of Sulfide-Based Solid-State Electrolytes Modified by Organic Thin Films

Authors: Liyu Liu; Kai Chen; Liguo Zhang; Bong-Ki Ryu
Journal: International Journal of Energy Research
 (2023)

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## Abstract

Lithium-ion batteries are key to tackling today’s energy crisis. In recent years, compared with the research on other components of lithium-ion batteries, the research on solid-state electrolytes is particularly hot. Among various solid-state electrolyte modification measures, we found that the material design of organic/inorganic composite flexible solid-state electrolytes can achieve the best all-solid-state battery cycling performance. Based on the study of sulfide-based organic/inorganic composite solid-state electrolytes, this article firstly introduces the classification of inorganic solid electrolytes and the advantages and disadvantages of each type of materials. At the same time, the research progress of various oxide solid electrolyte materials and sulfide solid electrolyte materials in recent years is introduced as well as the advantages of organic/inorganic composite solid-state electrolyte materials. Then the influencing factors that affect the performance of solid-state electrolytes, such as material lattice, lattice defects, electrolyte interface problems, and electrolyte microcracks, are introduced. Finally, the superiority of the industrial electrochemical performance of the organic/inorganic composite solid electrolyte material and its future prospects are introduced.


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## Body

## 1. Introduction

To cope with the challenges of global warming and energy crisis, the development and utilization of alternative sustainable energy sources is necessary [1]. Electrochemical energy storage systems are important devices for grid stability in dealing with intermittent renewable energy. Lithium-ion batteries (LIBs) are widely used as energy storage devices in electrochemical energy storage systems [2]. And lithium-ion battery technology will achieve the transition from nonrenewable fossil fuels to renewable energy in the field of electric vehicles that replace petroleum power. Moreover, lithium-ion batteries are also widely found in smart electronic devices. In order to further greatly improve the battery performance of LIBs to cater the increasing demand of energy storage, various improvement measures of lithium-ion battery technology have been widely studied [1], such as developing new high-capacity cathode materials [3, 4], adopting metal lithium as anode materials, and replacing traditional organic and aqueous liquid electrolytes with solid-state electrolytes (SSEs). For cathode materials, Zhang et al. studied a multielectron transfer-based conversion reaction type cathode material to increase the energy density by increasing the specific capacity of the electrode [3, 5], and Sun et al. studied a high-nickel cathode material by introducing high-valence elements into cobalt-free layers [6], which can increase the energy of the battery by increasing the working voltage density [7]. For cathode materials, various new anode materials such as alloy-type metal selenium [8, 9] and metal phosphorus [10] have obtained better battery performance. However, lithium metal is the most ideal anode material for LIBs with the lowest potential and the highest capacity. Therefore, the application of metal lithium is the ultimate destination of anode materials for lithium-ion batteries, but the problem of metal lithium dendrites is the key trouble that hinders its application. The metal lithium surface modification technology studied by Cui et al. [11, 12] effectively alleviates the problem of lithium dendrites and takes a huge step towards the application of metal lithium. Among them, the research of solid-state electrolyte is also expected to solve a series of problems of metal lithium as anode material. Traditional liquid electrolytes have a series of problems, for example, the decomposition of SEI at high temperature is accompanied by the release of gas generated by the thermal decomposition of the electrolyte and a series of safety problems due to the generation of dendrites of metallic lithium in the electrolyte. Usually, the anode SEI film begins to decompose when the temperature exceeds 80°C in lithium-ion battery, and the cathode releases flammable gas and oxygen, which is prone to explosion danger; if metallic lithium is used as the anode in the lithium-ion battery [13]. The decomposition and regeneration of the SEI film will occur when the temperature exceeds 70°C, in which a large number of lithium dendrites will be produced, and a short circuit will easily occur at this time. Numerous safety concerns are based on liquid electrolytes [13, 14]. Battery separators are also an important part of lithium-ion batteries. The use of solid electrolytes can eliminate the need for separators. Solid electrolytes with high mechanical strength have better durability than organic separators. Moreover, the cost of separators is generally high, and all-solid-state batteries can save a lot of separator costs. In order to solve the numerous safety issues of liquid electrolytes and reduce battery costs, the research on solid-state electrolytes has been vigorously developed.


## 2. Advantages of Sulfide-Based Organic/Inorganic Composite Solid Electrolyte Materials

Solid-state electrolytes have the following advantages: (1) negligible self-discharge characteristics due to its low electronic conductivity [13]; (2) high power density without concentration polarization at high current densities due to the immobility of the anionic framework [13]; (3) ionic migration number of solid-state electrolytes (approaching 1) is higher than that of liquid electrolytes (about 0.4-0.5) due to the absence of solvation of ions [14]; (4) no mechanism of consumption and aging due to nonvolatile and puny solid-phase reactions with electrodes; (5) high safety due to nonflammability and high thermal conductivity due to its good thermal conductivity; (6) wide voltage window being expected and solution to the dendrite problem being expected. In order to develop solid-state electrolytes with high ionic conductivity, wide potential window, and low interfacial impedance, Liu et al. reported a thin and flexible organic/inorganic composite solid-state electrolyte membrane being prepared by an electrospinning-infusion-hot pressing method (Figure 1). A solid-state electrolyte membrane consisting of a lithium-argyrodite Li6PS5Cl (LPSCl) and a polar poly (vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) framework. Firstly, the pure Li6PS5Cl sample was synthesized by ball milling and annealing process. Secondly, a P(VDF-TrFE)-based electrospun membrane with a tunable pore frame was prepared by selecting the P(VDF-TrFE) with low electronic conductivity and strong polarity. Finally, the Li6PS5Cl slurry with toluene was infiltrated into the P(VDF-TrFE) membrane, followed by removing solvent and pressing in high temperature, to obtain a self-supporting composite solid electrolyte (CSE) film with good mechanical properties (thickness of about 30-40 μm). The ionic conductivity of the composite solid electrolyte film is about 1.19×10−3 S cm-1 at the room temperature, which is attributed to the good ionic conductivity of Li6PS5Cl (about 3.89×10−3 S cm-1). The electronic conductivity of the composite solid electrolyte is 3.39×10−6 mS cm-1 as measured by the DC polarization tests. CV tests of composite solid electrolyte-carbon CSE. In batteries showed that the composite solid electrolyte had a very similar voltage window to Li6PS5Cl, where the cathode potential can be up to 3.09 V vs. Li+/Li. The good interaction between Li6PS5Cl and P(VDF-TrFE) ensures high Li-ion conductivity and good mechanical flexibility of the CSEs. Thereby, excellently improved electrochemical performance is obtained [15]. Moreover, this technology provides a much desired technological path for the development of high-performance SSE materials.Figure 1
Organic/inorganic composite solid-state-electrolyte film. All-solid-state batteries with the novel organic/inorganic composite film, synthesized by Liu et al., exhibit ultralong-cycling performance [15].


## 3. The Important Role of Conductivity in Solid-State Electrolytes

In general, materials with high ionic conductivity must meet the following conditions [14]: (1) possessing a large number of mobile ions; (2) possessing many migration sites for a large number of ions to move; (3) the free energy of move-in location site and move-out location site must be similar to ensure a low migration energy barrier; (4) possessing a relatively open migration channel. The lithium-argyrodite sulfide (Li6PS5Cl studied by Liu et al.) can well cater the above conditions. Solid-state electrolytes can be classified into organic solid electrolytes and inorganic solid electrolytes. Due to the low electrical conductivity, narrow chemical stability potential window, and poor high-temperature chemical stability of organic polymer solid electrolytes, the possibility of future practical application of organic polymer solid electrolytes is slim. Compared with organic solid-state electrolytes, inorganic solid-state electrolytes show good application feasibility due to their high ionic conductivity, wide chemical stability potential window, and good high-temperature chemical stability.Typically, practical all-solid-state batteries (ASSBs) require an internal resistance of less than 40Ω and a cycle efficiency of over 90% at 1°C. The composite interface electrolyte materials synthesized by Liu et al. achieved an excellent internal resistance (0.6-2.7 Ω) and a cycle efficiency close to 100% under long cycling. Generally, the high impedance of the electrolyte is caused by the decrease of the conductivity due to the high thickness of the SSEs and the electrochemical reaction at the electrode/electrolyte interface being hindered. Liu et al. reduced the impedance of the electrolyte by reducing the electrolyte thickness and improving the electrode/electrolyte interface.


## 4. Categories of Solid-State Electrolytes

Generally, inorganic solid-state electrolytes are divided into two categories: oxide type and sulfide type. Further, oxide solid inorganic solid-state electrolytes can be classified into garnet-type, NASICON (Na-superionic conductor)-type, and perovskite-type solid electrolytes. Garnet-type, NASICON-type, and perovskite-type solid electrolytes all have the advantages of high thermal stability, high chemical stability, high voltage stability, etc. [16]. However, they also have the disadvantages of high Young’s modulus, high grain boundary resistance, and low ionic conductivity (garnet-type and NASICON-type, 10−4−10−3 S cm-2; perovskite-type, 10-4 S cm-2).The advantages of sulfide-type electrolytes are as follows: (1) compared with oxygen atoms, sulfur atoms have lower electronegativity and bonding energy for lithium ions and are more prone to migration. (2) The radius of the sulfur atom is larger, which creates a larger channel for the migration of lithium ions. (3) Sulfides are softer and more flexible than oxides. During the cold pressing process, the sulfide particles are in tighter contact, and the boundary contact resistance of the grains is smaller [17]. The organic/inorganic composite solid electrolytes (CSEs) studied by Liu et al. are more suitable for the use of sulfide-based solid-state electrolytes. Compared with oxide-type solid-state electrolytes, sulfide-type solid-state electrolytes have higher ionic conductivity but poorer stability.


## 5. Research Progress of Sulfide-Based Solid-State Electrolytes

The Li-ion conductivity of sulfide SSEs is comparable to that of organic liquid electrolytes (~10-2 S cm-1 at room temperature). Various sulfide materials with high ionic conductivity have been widely developed. For example, Kamaya et al. took the lead in developing Li10GeP2S12 (LGPS) solid-state electrolytes, which showed good ionic conductivity (6×10−3 S cm-1) [18]. And the Li10SnP2S12 solid-state electrolytes published by Lewis et al. in Nature Materials in 2021, show good ionic conductivity (2.1 mS cm-1) [19]. At the same time, the Li9.54Si1.74P1.44S11.7Cl0.3 solid-state electrolytes published in Nature Energy by Kato et al. [20] also exhibit ultragood ionic conductivity (25 mS cm-1). Compared with the above-mentioned sulfide solid-state electrolytes, argyrodites-type Li6PS5X (X=Cl, Br) have received more attention due to its higher Li-ion conductivity and easier to modify [15]. Among them, Wang et al. prepared Li6PS5Cl0.5Br0.5 (LPSCB)/multiwalled carbon nanotube solid-state electrolytes, published in Advanced Energy Materials in 2021 [11], exhibiting excellent long-cycle performance (94% retention of 1000 cycles at 0.7°C) and good conductivity. The Li5.5PS4.5ClBr0.5 material in Chemistry of Materials in 2021 by Patel et al. [21], also has good conductivity performance (17 mS cm-1) and good cycle performance. At the same time, the Li6PS5Cl published by Wang et al. [22], showed a good ionic conductivity (3.15×10−3 S cm-1) and good rate capability. Therefore, ASSBs using argyrodites-type sulfide generally exhibit good cycling and rate performance while having good ionic conductivity. Liu et al. used argyrodites-type sulfide as a research object, precisely because of these electrochemical advantages. Recently, Ye et al. proposed a dynamic crack filling mechanism of the expansion screw effect to prevent lithium dendrite growth in Nature in 2021 [23], which achieved effective suppression of lithium dendrites in solid-state electrolytes. Based on the above concepts, Liu et al. introduced organic composite materials as filling materials to adjust cracks and synthesized an organic/inorganic composite solid-state electrolytes (Li6PS5Cl), which achieved ultrahigh-cycle stability.Recently, similar sulfide-polymer composite solid electrolytes (CSEs) have also made great progress. Among them, Zhang et al. prepared Li6PS5Cl/poly (ethylene oxide) (PEO) composite solid electrolytes, [16] and the assembled LiNi0.7Co0.2Mn0.1O2CSElithium-indium (Li-In) ASSBs achieved good cycling performance (74% capacity retention of 1000 cycles at 60°C). Oh et al. prepared Li6PS5Cl0.5Br0.5 CSEs composited with dry polymer electrolyte-type binders and obtained good Li-ion conductivity (2.2 mS cm–1 at 30°C) and good cycle performance (100 cycles at 0.1°C, 86% capacity retention) in the NCM(LiNixCoyMn1-x-yO2, 0<x, y<1)CSEgraphite ASSBs. Lee et al. prepared Li6PS5Cl-based CSEs composited with a nonaqueous acrylate-based binder and achieved good cycling performance (89% capacity retention of at 1000 cycles at 0.5°C, 60°C) in NCMCSEAg-C ASSBs. However, most of the above works only focus on increasing the energy density of ASSB batteries by reducing the thickness of the CSE layer, whose long-cycle stability and rate performance of ASSBs are not satisfactory. Herein, the organic/inorganic composite solid-state electrolyte film synthesized by Liu et al. maintained good cycling stability under 20,000 cycles.


## 6. Factors Affecting the Performance of Organic/Inorganic Composite Solid-State Electrolytes

### 6.1. The Effect of Crystal Structure on Electrolyte Materials

In inorganic solid-state electrolytes, the crystal structure is also a factor that affects the ionic conductivity of the material. In the face-centered cubic (FCC) lattice, the migration path of lithium ions is from one tetrahedron (T) through the middle octahedron (O) to another tetrahedron (T), which is called the T-O-T migration path. The migration barrier is 0.39 eV. In a body-centered cubic (BCC) lattice, lithium ions migrate directly from one tetrahedron (T1) to the next tetrahedron (T2), which is a T1-T2 pathway with a lower migration barrier (0.19 eV) [24]. In the hexagonal close-packed (HCP) lattice, the lithium-ion migration paths have both a T1-T2 path from one tetrahedron to another tetrahedron and a T-O-T path from one tetrahedron to another tetrahedron via an octahedron path. The two paths alternate and are extremely unstable [25]. In summary, body-centered cubic (BCC) anionic frameworks generally have the best ionic conductivity due to the lowest lithium ion migration barrier. Point defects (Schottky and Frenkel defects) play a key role in ion transport in crystals. Aliovalent doping of lattice materials can result in point defects and structural disorder, the degree of defects can be reflected by nuclear magnetic resonance (NMR). In NMR, broader peaks indicate more disordered structures [14]. Suitable defect and disorder can make diffusion easier. The NMR data of the samples of Liu et al. exhibited suitable peak widths, indicating that the material has relatively good point defects and easy ion diffusion. In addition, more advanced and efficient characterization technology plays a crucial role in promoting the exploration of catalyst physical properties and defects. Typical advanced technologies include electron paramagnetic resonance (EPR) [26], X-ray absorption fine structures (XAFS) [27], and positron annihilation lifetime spectroscopy (PALS) [28], which will more accurately analyze defects and help explore the essential properties of nanomaterials, thereby helping to improve the electrochemical performance of catalysts.The composite electrolyte materials synthesized by Liu et al. have good chemical stability and interfacial compatibility. In FT-IR spectroscopy, the pure P(VDF-TrFE) sample has a polarβ phase due to the presence of TrFE groups. The polar β-phase peaks of the composite electrolyte material are at the similar position, indicating that the polymer structure has not changed in the electrolyte composite. Raman spectroscopy revealed that the Raman peaks associated with PS43-groups in the composite electrolyte material exhibited a broadening effect, which indicated that sulfides can form chemical bonds with P(VDF-TrFE). In addition, a strong peak (85 ppm) corresponding to PS43- was also detected in the P NMR spectra of both samples, further confirming that the sulfide and polymer are bound together. In addition, the authors further confirmed the composite interaction by the density functional theory calculations to simulate the molecular dynamics of organic-inorganic composite interfaces.


### 6.2. The Effects of Electrode/Solid-State Electrolyte Interface

The electrode/solid-state electrolyte interface problem is an important research point [29]. When sulfide materials are paired with cathode materials such as layered LiCoO2, side reactions are prone to occur [30]. For example, PS43- groups in sulfides react with some cathodes (such as layered LiCoO2) to form PO43- groups and metal sulfides [2]. Liu et al. added an organic thin film between the cathode and the sulfide, which effectively alleviated this problem. In addition, the space charge layer is the main cause of the large impedance at the interface between the sulfide and the cathode [31]. Liu et al. employed physically isolating the interface of the electrode and electrolyte to improve interfacial stability, which can effectively suppress the generation of the space charge layer as a buffer layer.


### 6.3. The Effects of Generation and Expansion of Microcracks

In solid-state electrolytes, the generation and expansion of microcracks can accelerate the formation of lithium dendrites, resulting in battery short circuit [24]. Typically, a thicker solid-state electrolyte layer (~0.5-1.2 mm) is required to cope with the generation and expansion of microcracks during the pressing process [15]. This strategy not only increases the cost but also reduces the overall energy density of the battery. To obtain thin sulfide SSE films, Liu et al. adopted a strategy of compounding with polymers, effectively reducing the thickness of the solid-state electrolyte. In addition, coupled with the relative flexibility of sulfide, the P(VDF-TrFE)/Li6PS5Cl composite electrolyte material synthesized by Liu et al. possesses good flexibility and bendability, which can be applied in flexible devices [13].


### 6.4. The Effect of Electrical Conductivity on Material Performance

Conductivity is an important parameter in battery research systems. It is a measure of ease of charge transfer within a substance. Conductivity (σ) is the reciprocal of resistivity (σ=1/η, η is the resistivity). Conductivity is usually calculated using the cross-sectional area (S) of current (I) flowing through a fixed distance (d) at constant voltage (U). Conductivity formula (σ=d·I/S·U) is derived from the resistance formulas (R=U/I and R=d/σ·S). The main factors that affect the conductivity are temperature, crystal doping degree, and crystal anisotropy. (1) Generally, the conductivity of metals is positively correlated with temperature, and the conductivity of semiconductors is negatively correlated with temperature. Liu et al. tested the ionic conductivity of electrolyte composites from 25°C to 70°C, and the results showed that the conductivity did not change much in this range, which showed that the composite material has a strong practicality. (2) The lattice of the composite material synthesized by Liu et al. is Li6PS5Cl without doping effect. (3) The electrolyte composites synthesized by Liu et al. are polycrystalline powders without anisotropy. Generally, conductivity is divided into ionic conductivity and electronic conductivity. To obtain a practical high-performance solid-state electrolyte, in addition to good ionic conductivity at room temperature, it also needs to have low electronic conductivity, which can avoid the battery self-discharge effect due to the microshort circuit. The electrolyte composites synthesized by Liu et al. have very low electronic conductivity.


## 6.1. The Effect of Crystal Structure on Electrolyte Materials

In inorganic solid-state electrolytes, the crystal structure is also a factor that affects the ionic conductivity of the material. In the face-centered cubic (FCC) lattice, the migration path of lithium ions is from one tetrahedron (T) through the middle octahedron (O) to another tetrahedron (T), which is called the T-O-T migration path. The migration barrier is 0.39 eV. In a body-centered cubic (BCC) lattice, lithium ions migrate directly from one tetrahedron (T1) to the next tetrahedron (T2), which is a T1-T2 pathway with a lower migration barrier (0.19 eV) [24]. In the hexagonal close-packed (HCP) lattice, the lithium-ion migration paths have both a T1-T2 path from one tetrahedron to another tetrahedron and a T-O-T path from one tetrahedron to another tetrahedron via an octahedron path. The two paths alternate and are extremely unstable [25]. In summary, body-centered cubic (BCC) anionic frameworks generally have the best ionic conductivity due to the lowest lithium ion migration barrier. Point defects (Schottky and Frenkel defects) play a key role in ion transport in crystals. Aliovalent doping of lattice materials can result in point defects and structural disorder, the degree of defects can be reflected by nuclear magnetic resonance (NMR). In NMR, broader peaks indicate more disordered structures [14]. Suitable defect and disorder can make diffusion easier. The NMR data of the samples of Liu et al. exhibited suitable peak widths, indicating that the material has relatively good point defects and easy ion diffusion. In addition, more advanced and efficient characterization technology plays a crucial role in promoting the exploration of catalyst physical properties and defects. Typical advanced technologies include electron paramagnetic resonance (EPR) [26], X-ray absorption fine structures (XAFS) [27], and positron annihilation lifetime spectroscopy (PALS) [28], which will more accurately analyze defects and help explore the essential properties of nanomaterials, thereby helping to improve the electrochemical performance of catalysts.The composite electrolyte materials synthesized by Liu et al. have good chemical stability and interfacial compatibility. In FT-IR spectroscopy, the pure P(VDF-TrFE) sample has a polarβ phase due to the presence of TrFE groups. The polar β-phase peaks of the composite electrolyte material are at the similar position, indicating that the polymer structure has not changed in the electrolyte composite. Raman spectroscopy revealed that the Raman peaks associated with PS43-groups in the composite electrolyte material exhibited a broadening effect, which indicated that sulfides can form chemical bonds with P(VDF-TrFE). In addition, a strong peak (85 ppm) corresponding to PS43- was also detected in the P NMR spectra of both samples, further confirming that the sulfide and polymer are bound together. In addition, the authors further confirmed the composite interaction by the density functional theory calculations to simulate the molecular dynamics of organic-inorganic composite interfaces.


## 6.2. The Effects of Electrode/Solid-State Electrolyte Interface

The electrode/solid-state electrolyte interface problem is an important research point [29]. When sulfide materials are paired with cathode materials such as layered LiCoO2, side reactions are prone to occur [30]. For example, PS43- groups in sulfides react with some cathodes (such as layered LiCoO2) to form PO43- groups and metal sulfides [2]. Liu et al. added an organic thin film between the cathode and the sulfide, which effectively alleviated this problem. In addition, the space charge layer is the main cause of the large impedance at the interface between the sulfide and the cathode [31]. Liu et al. employed physically isolating the interface of the electrode and electrolyte to improve interfacial stability, which can effectively suppress the generation of the space charge layer as a buffer layer.


## 6.3. The Effects of Generation and Expansion of Microcracks

In solid-state electrolytes, the generation and expansion of microcracks can accelerate the formation of lithium dendrites, resulting in battery short circuit [24]. Typically, a thicker solid-state electrolyte layer (~0.5-1.2 mm) is required to cope with the generation and expansion of microcracks during the pressing process [15]. This strategy not only increases the cost but also reduces the overall energy density of the battery. To obtain thin sulfide SSE films, Liu et al. adopted a strategy of compounding with polymers, effectively reducing the thickness of the solid-state electrolyte. In addition, coupled with the relative flexibility of sulfide, the P(VDF-TrFE)/Li6PS5Cl composite electrolyte material synthesized by Liu et al. possesses good flexibility and bendability, which can be applied in flexible devices [13].


## 6.4. The Effect of Electrical Conductivity on Material Performance

Conductivity is an important parameter in battery research systems. It is a measure of ease of charge transfer within a substance. Conductivity (σ) is the reciprocal of resistivity (σ=1/η, η is the resistivity). Conductivity is usually calculated using the cross-sectional area (S) of current (I) flowing through a fixed distance (d) at constant voltage (U). Conductivity formula (σ=d·I/S·U) is derived from the resistance formulas (R=U/I and R=d/σ·S). The main factors that affect the conductivity are temperature, crystal doping degree, and crystal anisotropy. (1) Generally, the conductivity of metals is positively correlated with temperature, and the conductivity of semiconductors is negatively correlated with temperature. Liu et al. tested the ionic conductivity of electrolyte composites from 25°C to 70°C, and the results showed that the conductivity did not change much in this range, which showed that the composite material has a strong practicality. (2) The lattice of the composite material synthesized by Liu et al. is Li6PS5Cl without doping effect. (3) The electrolyte composites synthesized by Liu et al. are polycrystalline powders without anisotropy. Generally, conductivity is divided into ionic conductivity and electronic conductivity. To obtain a practical high-performance solid-state electrolyte, in addition to good ionic conductivity at room temperature, it also needs to have low electronic conductivity, which can avoid the battery self-discharge effect due to the microshort circuit. The electrolyte composites synthesized by Liu et al. have very low electronic conductivity.


## 7. Practical Advantages of Sulfide-Based Organic/Inorganic Composite Solid-State Electrolytes

### 7.1. Safety of Sulfide-Based Organic/Inorganic Composite Solid-State Electrolytes

Solid-state electrolyte materials are materials developed to improve the safety of lithium-ion batteries. Therefore, safety problem is a key consideration for solid-state electrolyte materials. Solid-state electrolytes generally have stronger thermal stability than liquid electrolytes and are less prone to electrolyte decomposition at high temperatures. Therefore, the all-solid-state battery is not prone to high temperature explosion. The solid electrolyte material synthesized by Liu et al. can work normally at higher temperature, indicating that it has good safety performance. At the same time, the organic thin film layer of the electrolyte composite synthesized by Liu et al. effectively separates the electrolyte and the electrode material, which effectively avoids the decomposition reaction of the electrode material, thereby enhancing the stability of the all-solid-state battery, thereby ensuring the battery safety.


### 7.2. Industrial Electrochemical Performance of Sulfide-Based Organic/Inorganic Composite Solid-State Electrolytes

The composite electrolyte materials synthesized by Liu et al. obtained excellent electrochemical performance in ASSBs. The LiNi0.8Co0.1Mn0.1O2@LiNbO3- (NCM@LNO-) based ASSBs achieves excellent rate performance (189 mAh g-1 at 0.16°C, 114 mAh g-1 at 1.6°C) and outstanding cycling performance (92% capacity retention at 1000 cycles and 71% capacity retention at 20,000 cycles). In addition, the electrolyte material still maintains high capacity (123.1 mAh g-1) and high cycle stability (79% capacity retention at 500 cycles) under high cathode loading (24.78 mg cm-2). The applied pouch battery performance of the composite electrolyte material is also very good, showing good practicability.Electrochemical practicality research is an important aspect of battery materials research. The study of battery performance under different electrode active material loadings is an important part of industrial production. Liu et al. tested the electrochemical performance under electrode active material loadings and obtained good performance results, which showed that the electrolyte composite material had excellent production practicability. The high rate and high-cycle performance of batteries are also important indicators of industrial production. The high-rate capability enables the high-power capability of the battery, which is especially important for fast charging and extreme acceleration in electric vehicles. The electrolyte composites synthesized by Liu et al. achieved good rate performance. At the same time, its cycle performance is extremely excellent, which is the cycle performance of the best all-solid-state battery at present. Generally, the types of batteries produced in industry are divided into 18650-type cylindrical batteries, usually being used in electric vehicles, and pouch batteries, usually being used in mobile electronic devices. The pouch all-solid-state battery prepared by Liu et al. also showed a high capacity and charge/discharge plateau similar to that of the coin cell at 0.1 mA cm-2 and had a high-capacity retention rate of 92% after 100 cycles. Furthermore, a high-capacity retention rate of 81% is still achieved after 200 cycles at 1.0 mA cm-2. Alternatively, the pouch all-solid-state battery can light up a large light bulb, which shows that its application in soft pack batteries is also quite good. At present, research on flexible wearable electronic devices is gradually emerging. The organic/inorganic composite electrolyte material synthesized by Liu et al., with its good bendability, could apply to the flexibility wearable electronic devices. The problem of production cost is also a problem that industrial production has to consider. Generally, the cost of oxide-type solid electrolytes is lower than that of sulfide solid-state electrolytes in terms of raw-material costs, production-equipment costs, and process-complexity costs. The performance of sulfide-based solid electrolytes is significantly better than that of oxide solid-state electrolytes in all aspects of battery performance. Therefore, the industrial production of sulfide-based solid electrolyte materials is more practical. On this basis, Liu et al. achieved cost reduction by reducing the thickness of sulfide-based solid electrolytes without affecting the performance of the raw materials.The NCM@LNOCSELi-In ASSBs have excellent rate performance and ultralong-cycling performance, which is the best long-cycle performance among all the ASSBs operating at room temperature reported so far. It is worth mentioning that this stable cycle performance is much better than the corresponding lithium-ion batteries with liquid electrolyte, and the results of long-cycle performance further verify the conjecture of many scholars that all-solid-state batteries with solid-solid contact will be more stable than liquid batteries.


## 7.1. Safety of Sulfide-Based Organic/Inorganic Composite Solid-State Electrolytes

Solid-state electrolyte materials are materials developed to improve the safety of lithium-ion batteries. Therefore, safety problem is a key consideration for solid-state electrolyte materials. Solid-state electrolytes generally have stronger thermal stability than liquid electrolytes and are less prone to electrolyte decomposition at high temperatures. Therefore, the all-solid-state battery is not prone to high temperature explosion. The solid electrolyte material synthesized by Liu et al. can work normally at higher temperature, indicating that it has good safety performance. At the same time, the organic thin film layer of the electrolyte composite synthesized by Liu et al. effectively separates the electrolyte and the electrode material, which effectively avoids the decomposition reaction of the electrode material, thereby enhancing the stability of the all-solid-state battery, thereby ensuring the battery safety.


## 7.2. Industrial Electrochemical Performance of Sulfide-Based Organic/Inorganic Composite Solid-State Electrolytes

The composite electrolyte materials synthesized by Liu et al. obtained excellent electrochemical performance in ASSBs. The LiNi0.8Co0.1Mn0.1O2@LiNbO3- (NCM@LNO-) based ASSBs achieves excellent rate performance (189 mAh g-1 at 0.16°C, 114 mAh g-1 at 1.6°C) and outstanding cycling performance (92% capacity retention at 1000 cycles and 71% capacity retention at 20,000 cycles). In addition, the electrolyte material still maintains high capacity (123.1 mAh g-1) and high cycle stability (79% capacity retention at 500 cycles) under high cathode loading (24.78 mg cm-2). The applied pouch battery performance of the composite electrolyte material is also very good, showing good practicability.Electrochemical practicality research is an important aspect of battery materials research. The study of battery performance under different electrode active material loadings is an important part of industrial production. Liu et al. tested the electrochemical performance under electrode active material loadings and obtained good performance results, which showed that the electrolyte composite material had excellent production practicability. The high rate and high-cycle performance of batteries are also important indicators of industrial production. The high-rate capability enables the high-power capability of the battery, which is especially important for fast charging and extreme acceleration in electric vehicles. The electrolyte composites synthesized by Liu et al. achieved good rate performance. At the same time, its cycle performance is extremely excellent, which is the cycle performance of the best all-solid-state battery at present. Generally, the types of batteries produced in industry are divided into 18650-type cylindrical batteries, usually being used in electric vehicles, and pouch batteries, usually being used in mobile electronic devices. The pouch all-solid-state battery prepared by Liu et al. also showed a high capacity and charge/discharge plateau similar to that of the coin cell at 0.1 mA cm-2 and had a high-capacity retention rate of 92% after 100 cycles. Furthermore, a high-capacity retention rate of 81% is still achieved after 200 cycles at 1.0 mA cm-2. Alternatively, the pouch all-solid-state battery can light up a large light bulb, which shows that its application in soft pack batteries is also quite good. At present, research on flexible wearable electronic devices is gradually emerging. The organic/inorganic composite electrolyte material synthesized by Liu et al., with its good bendability, could apply to the flexibility wearable electronic devices. The problem of production cost is also a problem that industrial production has to consider. Generally, the cost of oxide-type solid electrolytes is lower than that of sulfide solid-state electrolytes in terms of raw-material costs, production-equipment costs, and process-complexity costs. The performance of sulfide-based solid electrolytes is significantly better than that of oxide solid-state electrolytes in all aspects of battery performance. Therefore, the industrial production of sulfide-based solid electrolyte materials is more practical. On this basis, Liu et al. achieved cost reduction by reducing the thickness of sulfide-based solid electrolytes without affecting the performance of the raw materials.The NCM@LNOCSELi-In ASSBs have excellent rate performance and ultralong-cycling performance, which is the best long-cycle performance among all the ASSBs operating at room temperature reported so far. It is worth mentioning that this stable cycle performance is much better than the corresponding lithium-ion batteries with liquid electrolyte, and the results of long-cycle performance further verify the conjecture of many scholars that all-solid-state batteries with solid-solid contact will be more stable than liquid batteries.


## 8. Conclusion and Outlook

This paper systematically introduces how sulfide-based organic/inorganic composite solid electrolyte materials can achieve the performance modification effect and introduces the relative superiority of the material. The sulfide-based organic/inorganic composite solid electrolyte material can effectively improve the chemical stability of the interface and enhance the mechanical stability of the material without reducing the electrical conductivity of the material, thereby improving the safety of the material and the stability of the battery. This measure can greatly improve the cycle life of the battery. At the same time, the flexible matrix solid electrolyte can also be applied to flexible electronic devices. This work will inspire the preparation of thin solid electrolytes with excellent electrochemical performance and guide the direction for realizing practical application of sulfide-based all-solid-state batteries.



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*Source: 2601098-2023-02-06.xml*