Glass–ceramic Li2S–P2S5 electrolytes prepared by a single step ball billing process and their application for all-solid-state lithium–ion batteries

We report that glass–ceramic Li₂S–P₂S₅ electrolytes can be prepared by a single step ball milling (SSBM) process. Mechanical ball milling of the xLi₂S·(100 − x)P₂S₅ system at 55 °C produced crystalline glass–ceramic materials exhibiting high Li-ion conductivity over 10⁻³ S cm⁻¹ at room temperature with a wide electrochemical stability window of 5 V. Silicon nanoparticles were evaluated as anode material in a solid-state Li battery employing the glass–ceramic electrolyte produced by the SSBM process and showed outstanding cycling stability.     

Halide/sulfide composite solid-state electrolyte for Li-anode based all-solid-state batteries

Li₂ZrCl₆ (LZC) solid-state electrolytes (SSEs) have been recognized as a candidate halide SSEs for all-solid-state Li batteries (ASSLBs) with high energy density and safety due to its great compatibility with 4 V-class cathodes and low bill-of-material (BOM) cost. However, despite the benefits, the poor chemical/electrochemical stability of LZC against Li metal causes the deterioration of Li/LZC interface, which has a detrimental inhibition on Li⁺ transport in ASSLBs. Herein, we report a composite SSE combining by LZC and argyrodite buffer layer (Li₆PS₅Cl, LPSC) that prevent the unfavorable interaction between LZC and Li metal. The Li/LPSC-LZC-LPSC/Li symmetric cell stably cycles for over 1000 h at 0.3 mA/cm² (0.15 mAh/cm²) and has a high critical current density (CCD) value of 2.1 mA/cm² at 25 °C. Under high temperature (60 °C) which promotes the reaction between Li and LZC, symmetric cell fabricated with composite SSE also display stable cycling performance over 1200 h at 0.3 mAh/cm². Especially, the Li/NCM ASSLBs fabricated with composite SSE exhibit a high initial coulombic efficiency, as well as superior cycling and rate performance. This simple and efficient strategy will be instrumental in the development of halide-based high-performance ASSLBs.     

Li2S-P2S5体系电解质及其在全固态锂离子电池中的应用研究进展

全固态锂离子电池具有安全性能好、能量密度高、工作温区广等优点,被广泛应用于便携式电子设备。固态电解质是全固态锂离子电池的关键材料之一,其中的硫化物电解质具有离子电导率高、电化学窗口宽、晶界电阻低和易成膜等特点,被认为最有希望应用于全固态锂离子电池。本文综述了Li_2S-P_2S_5体系电解质的发展状况,包括固态电解质的制备、改性、表征以及电极/固态电解质之间的固-固界面的稳定兼容问题。本文还涉及了以Li_2S-P_2S_5为电解质的全固态锂离子电池性能的研究进展。     

Preparation and ionic conductivity of (100−x)(0.8Li2S·0.2P2S5)·xLiI glass–ceramic electrolytes

The glass–ceramic electrolytes of (100?x)(0.8Li₂S·0.2P₂S₅)·xLiI (in mole percent; x?=?0, 2, 5, 10, 15, 20, and 30) were prepared by mechanical milling and subsequent heat treatment. Crystalline phases analogous to the thio-LISICON region II or III in the Li₂S–GeS₂–P₂S₅ system were precipitated. The thio-LISICON III analog phase was mainly precipitated at the composition x?=?0, and the thio-LISICON II analog phase was precipitated in the composition range from x?=?2 to 15. The X-ray diffraction peaks of the thio-LISICON II analog phase shifted to the lower diffraction angle side with increasing the LiI content. High conductivities above 2?×?10^?3?S?cm^?1 at room temperature were observed in the glass–ceramics at the wide composition range from x?=?2 to 15. The glass–ceramic electrolyte at x?=?5 with the highest conductivity of 2.7?×?10^?3?S?cm^?1 showed a wide electrochemical window of about 10 V. The addition of LiI to the 80Li₂S·20P₂S₅ (in mole percent) glass was effective in crystallizing the thio-LISICON II analog phase with high conductivity from the glass.     

All-solid-state batteries with Li2O-Li2S-P2S5 glass electrolytes synthesized by two-step mechanical milling

Sulfide solid electrolytes, which show high ion conductivity, are anticipated for use as electrolyte materials for all-solid-state batteries. One drawback of sulfide solid electrolytes is their low chemical stability in air. They are hydrolyzed by moisture and generate H₂S gas. Substituting oxygen atoms for sulfur atoms in sulfide solid electrolytes is effective for suppression of H₂S gas generation in air. Especially, the xLi₂O·(75-x)Li₂S·25P₂S₅ (mol%) glasses hardly generated H₂S gas in air. However, substituting oxygen atoms for sulfur atoms caused a decrease in conductivity. The x?=?7 glass showed high chemical stability in air and maintained high conductivity of 2.5?×?10^?4 S cm^?1 at room temperature. Performance of cells using the 7Li₂O·68Li₂S·25P₂S₅ and the 75Li₂S·25P₂S₅ glasses as solid electrolytes were compared. All-solid-state C/LiCoO₂ cell using the 7Li₂O·68Li₂S·25P₂S₅ glass produced performance as good as that obtained using the 75Li₂S·25P₂S₅ glass. Capacity retention and change of interfacial resistance of the former cell were superior to those of the latter cell after storage at 4.0 V and 60 °C. The diffusion of oxygen element into the 7Li₂O·68Li₂S·25P₂S₅ glass was less than that into the 75Li₂S·25P₂S₅ glass after storage at the voltage of 4.0 V at 60 °C. Improvement of the stability of sulfide solid electrolytes to moisture was related to cell performance as well as an increase in conductivity.     

Development of sulfide glass-ceramic electrolytes for all-solid-state lithium rechargeable batteries

Development of Li₂S–P₂S₅-based glass-ceramic electrolytes is reviewed. Superionic crystals of Li₇P₃S₁₁ and Li_3.25P_0.95S₄ were precipitated from the Li₂S–P₂S₅ glasses at the selected compositions. These high temperature or metastable phases enhanced conductivity of glass ceramics up to over 10⁻³ S cm⁻¹ at room temperature. The original (or mother) glass electrolytes itself showed somewhat lower conductivity of 10⁻⁴ S cm⁻¹ and have important role as a precursor for obtaining the superionic crystals, which were not synthesized by a conventional solid-state reaction. The substitution of P₂O₅ for P₂S₅ at the composition 70Li₂S·30P₂S₅ (mol%) improved both conductivity and electrochemical stability of glass-ceramic electrolytes. The all-solid-state In/LiCoO₂ cell using the 70Li₂S·27P₂S₅·3P₂O₅ (mol%) glass-ceramic electrolyte showed initial capacity of 105 mAh g⁻¹ (gram of LiCoO₂) at the current density of 0.13 mA cm⁻² and exhibited higher electrochemical performance than that using the 70Li₂S·30P₂S₅ glass-ceramic electrolyte.     

Li7P3S11电解质的合成、传导及应用

固态电解质是固态电池中的关键材料,开发具有高离子电导率、高化学/电化学稳定性、电极兼容性良好的固态电解质正成为研究热点。硫化物固态电解质相较其它固态电解质具有更高的离子电导率和良好的机械加工性能等优势,是最有前景实现实用化的固态电解质之一。在众多硫化物固态电解质中,Li₇P₃S₁₁因其高的离子电导率和较低的原料成本而极具研究意义。本文首先介绍了Li₇P₃S₁₁电解质的结构、Li+传导机理及合成路径;其次,针对该电解质的电导率提高、空气/水稳定性提升、固固界面稳定性及电解质自身稳定性改善等问题,综述了目前常用的改性策略研究;再次,总结了基于Li₇P₃S₁₁电解质的全固态锂离子电池和全固态锂硫电池的构筑;最后,本文分析了Li₇P₃S₁₁电解质的研究和应用面临的挑战,并指出该电解质未来发展的趋势。     

All-solid-state rechargeable lithium batteries using SnX-P2X5 (X = S and O) amorphous negative electrodes

SnS-P₂S₅ and SnO-P₂O₅ amorphous materials were prepared by a mechanical milling technique. The SnO-P₂O₅ milled materials worked as a reversible electrode with higher capacity than SnO crystal in rechargeable lithium cells with conventional liquid electrolytes. All-solid-state cells with a SnX-P₂X₅ (X = S and O) amorphous electrode and the Li₂S-P₂S₅ glass-ceramic electrolyte were charged and discharged at room temperature. The sulfide electrodes exhibited better charge-discharge performance than the oxide electrodes, suggesting that SnS-P₂S₅ electrodes are more compatible with Li₂S-P₂S₅ sulfide solid electrolytes. All-solid state batteries 80SnS·20P₂S₅/LiCoO₂ showed a charge-discharge plateau of about 3.4 V and high reversible capacity of over 400 mAh/g, even after 50 cycles. The SnX (X = S and O)-based amorphous materials are promising negative electrode materials with high capacity for rechargeable lithium batteries using not only liquid electrolytes but solid electrolytes.     

Grain Boundary Electronic Insulation for High-Performance All-Solid-State Lithium Batteries

Sulfide electrolytes with high ionic conductivities are one of the most highly sought for all-solid-state lithium batteries (ASSLBs). However, the non-negligible electronic conductivities of sulfide electrolytes (≈10⁻⁸ S cm⁻¹) lead to electron smooth transport through the sulfide electrolyte pellets, resulting in Li dendrite directly depositing at the grain boundaries (GBs) and serious self-discharge. Here, a grain-boundary electronic insulation (GBEI) strategy is proposed to block electron transport across the GBs, enabling Li−Li symmetric cells with 30 times longer cycling life and Li−LiCoO₂ full cells with three times lower self-discharging rate than pristine sulfide electrolytes. The Li−LiCoO₂ ASSLBs deliver high capacity retention of 80 % at 650 cycles and stable cycling performance for over 2600 cycles at 0.5 mA cm⁻². The innovation of the GBEI strategy provides a new direction to pursue high-performance ASSLBs via tailoring the electronic conductivity.     

Synthesis of New Lithium Ionic Conductor Thio-LISICON—Lithium Silicon Sulfides System

The new lithium ionic conductors, thio-LISICON (LIthium SuperIonic CONductor), were found in the ternary Li₂S-SiS₂-Al₂S₃ and Li₂S-SiS₂-P₂S₅ systems. Their structures of new materials, Li_4+xSi_1−xAl_xS₄ and Li_4−xSi_1−xP_xS₄ were determined by X-ray Rietveld analysis, and the electric and electrochemical properties were studied by electronic conductivity, ac conductivity and cyclic voltammogram measurements. The structure of the host material, Li₄SiS₄ is related to the γ-Li₃PO₄-type structure, and when the Li⁺ interstitials or Li⁺ vacancies were created by the partial substitutions of Al³⁺ or P⁵⁺ for Si⁴⁺, large increases in conductivity occur. The solid solution member x=0.6 in Li_4−xSi_1−xP_xS₄ showed high conductivity of 6.4×10^-4 S cm⁻¹ at 27°C with negligible electronic conductivity. The new solid solution, Li_4−xSi_1−xP_xS₄, also has high electrochemical stability up to ∼5 V vs Li at room temperature. All-solid-state lithium cells were investigated using the Li_3.4Si_0.4P_0.6S₄ electrolyte, LiCoO₂ cathode and In anode.     

Conducting properties of nanocomposite polymer electrolytes based on polyethylene glycol diacrylate and SiO<Subscript>2</Subscript> nanoparticles at the interface with a lithium electrode

Nanocomposite polymer electrolytes based on polyethylene glycol diacrylate and 1 M LiBF₄ solution in γ-butyrolactone with addition of SiO₂ nanoparticles were synthesized and studied. Resistance measurement at the Li/electrolyte and Li/nanocomposite electrolyte interface by the time-resolved electrochemical impedance showed its significant decrease in the presence of SiO₂ nanoparticles. Charge-discharge cycling of prototypes of Li/LiFePO₄ batteries for 50 cycles also showed the advantage of using nanocomposite polymer electrolytes over electrolytes without SiO₂ additives.     

Recent progress of composite solid polymer electrolytes for all-solid-state lithium metal batteries

In comparison with lithium-ion batteries (LIBs) with liquid electrolytes, all-solid-state lithium batteries (ASSLBs) have been considered as promising systems for future energy storage due to their safety and high energy density. As the pivotal component used in ASSLBs, composite solid polymer electrolytes (CSPEs), derived from the incorporation of inorganic fillers into solid polymer electrolytes (SPEs), exhibit higher ionic conductivity, better mechanical strength, and superior thermal/electrochemical stability compared to the single-component SPEs, which can significantly promote the electrochemical performance of ASSLBs. Herein, the recent advances of CSPEs applied in ASSLBs are presented. The effects of the category, morphology and concentration of inorganic fillers on the ionic conductivity, mechanical strength, electrochemical window, interfacial stability and possible Li⁺ transfer mechanism of CSPEs will be systematically discussed. Finally, the challenges and perspectives are proposed for the future development of high-performance CSPEs and ASSLBs.     

All-solid-state Li/S batteries with highly conductive glass–ceramic electrolytes

All-solid-state cells using sulfur-based cathode materials and Li₂S–P₂S₅ glass–ceramic electrolytes were successfully prepared and exhibited excellent cycling performance at room temperature. The cathode materials consisting of sulfur and CuS were synthesized by mechanical milling using sulfur and copper crystals as starting materials. The cell performance was influenced by the milling time for the cathode materials and the cell with cathode materials obtained by milling for 15 min retained large capacities over 650 mA h g⁻¹ for 20 cycles. Sulfur as well as CuS in cathode materials proved to be utilized as active materials on charge–discharge processes in the all-solid-state Li/S cells.     

Ultraviolet-Cured Semi-Interpenetrating Network Polymer Electrolytes for High-Performance Quasi-Solid-State Lithium Metal Batteries

Solid polymer electrolytes with relatively low ionic conductivity at room temperature and poor mechanical strength greatly restrict their practical applications. Herein, we design semi-interpenetrating network polymer (SNP) electrolyte composed of an ultraviolet-crosslinked polymer network (ethoxylated trimethylolpropane triacrylate), linear polymer chains (polyvinylidene fluoride-co-hexafluoropropylene) and lithium salt solution to satisfy the demand of high ionic conductivity, good mechanical flexibility, and electrochemical stability for lithium metal batteries. The semi-interpenetrating network has a pivotal effect in improving chain relaxation, facilitating the local segmental motion of polymer chains and reducing the polymer crystallinity. Thanks to these advantages, the SNP electrolyte shows a high ionic conductivity (1.12 mS cm⁻¹ at 30 °C), wide electrochemical stability window (4.6 V vs. Li⁺/Li), good bendability and shape versatility. The promoted ion transport combined with suppressed impedance growth during cycling contribute to good cell performance. The assembled quasi-solid-state lithium metal batteries (LiFePO₄/SNP/Li) exhibit good cycling stability and rate capability at room temperature.     

Novel technique to form electrode–electrolyte nanointerface in all-solid-state rechargeable lithium batteries

The electrode–electrolyte nanocomposites, where the nano-sized NiS electrode with large capacity was embedded in the 80Li₂S · 20P₂S₅ electrolyte with high Li⁺ conductivity, were successfully prepared by the mechanochemical method. Contact area of solid–solid interface between the electrode and the electrolyte was remarkably increased in the nanocomposites. All-solid-state cell using the nanocomposites as a working electrode exhibited larger capacity and better cycling performance than the cell using the electrode obtained by conventional hand-mixing of powders. The mechanochemical technique sheds light on a new formation process of electrode–electrolyte interfaces endowing solid-state batteries with high power density and high energy density.     

Effect of concentration and temperature factors on operation stability of Li–S<Subscript> <Emphasis Type="Italic">n</Emphasis> </Subscript>–LiN(CF<Subscript>3</Subscript>SO<Subscript>2</Subscript>)<Subscript>2</Subscript> electrochemical system

The results of the electrochemical study of the Li–S_n system in the electrolytes consisted of LiN(CF₃SO₂)₂ and tetraethylene glycol dimethyl ether in relation to the LiN(CF₃SO₂)₂ concentration, temperature, and storage conditions are presented. The optimal concentrations of the salt component in salt-solvates were determined. These concentrations make it possible to obtain high stable values of the specific capacity in cycling and charge storage at room and elevated temperatures. It was shown that the operation stability of the electrochemical system Li–S_n–LiN(CF₃SO₂)₂ in salt-solvate solutions depends on solubility of the formed lithium disulfide, ratio composition of electrolyte and temperature.     

Full Dissolution of the Whole Lithium Sulfide Family (Li2S8 to Li2S) in a Safe Eutectic Solvent for Rechargeable Lithium–Sulfur Batteries

The lithium–sulfur battery is an attractive option for next‐generation energy storage owing to its much higher theoretical energy density than state‐of‐the‐art lithium‐ion batteries. However, the massive volume changes of the sulfur cathode and the uncontrollable deposition of Li₂S₂/Li₂S significantly deteriorate cycling life and increase voltage polarization. To address these challenges, we develop an ?‐caprolactam/acetamide based eutectic‐solvent electrolyte, which can dissolve all lithium polysulfides and lithium sulfide (Li₂S₈–Li₂S). With this new electrolyte, high specific capacity (1360 mAh g^?1) and reasonable cycling stability are achieved. Moreover, in contrast to conventional ether electrolyte with a low flash point (ca. 2 °C), such low‐cost eutectic‐solvent‐based electrolyte is difficult to ignite, and thus can dramatically enhance battery safety. This research provides a new approach to improving lithium–sulfur batteries in aspects of both safety and performance.     

Lithium garnet based free-standing solid polymer composite membrane for rechargeable lithium battery

Electrolytes with high lithium-ion conductivity, better mechanical strength and large electrochemical window are essential for the realization of high-energy density lithium batteries. Polymer electrolytes are gaining interest due to their inherent flexibility and nonflammability over conventional liquid electrolytes. In this work, lithium garnet composite polymer electrolyte membrane (GCPEM) consisting of large molecular weight (W_avg ~?5?×?10⁶) polyethylene oxide (PEO) complexed with lithium perchlorate (LiClO₄) and lithium garnet oxide Li_6.28Al_0.24La₃Zr₂O₁₂ (Al-LLZO) is prepared by solution-casting method. Significant improvement in Li⁺ conductivity for Al-LLZO containing GCPEM is observed compared with the Al-LLZO free polymer membrane. Maximized room temperature (30 °C) Li⁺ conductivity of 4.40?×?10^?4 S cm^?1 and wide electrochemical window (4.5 V) is observed for PEO₈/LiClO₄?+?20 wt% Al-LLZO (GCPEM-20) membrane. The fabricated cell with LiCoO₂ as cathode, metallic lithium as anode and GCPEM-20 as electrolyte membrane delivers an initial charge/discharge capacity of 146 mAh g^?1/142 mAh g^?1 at 25 °C with 0.06 C-rate.     

Ion trapping and its effect on the conductivity of LISICON and other solid electrolytes

Conductivity data for the lithium ion conducting solid electrolyte, LISICON, Li_2+2xZn_1?xGeO₄ over a particularly wide composition range, 0.15 < x < 0.85, and over the temperature range ～25 to 150°C show that both the activation energy and preexponential factor pass through maxima around x ～ 0.4 to 0.5, at which the preexponential factor exhibits anomalously high values, ～10¹³ ohm^?1 cm^?1 K. An explanation is offered which involves the trapping of mobile Li⁺ ions by the immobile sublattice at lower temperatures. This model also accounts for ageing effects observed at lower temperatures in which the conductivity decreases slowly with time. In the isostructural Li⁺ electrolytes, Li_3+xSi_xY_1?xO₄ (Y = P, As, V), the compositional dependence of both the preexponential factor and activation energy is less marked and no evidence for ion trapping effects is observed.     

Defect Engineering and Anisotropic Modulation of Ionic Transport in Perovskite Solid Electrolyte LixLa(1−x)/3NbO3

Solid electrolytes, such as perovskite Li_3xLa_2/1−xTiO₃, Li_xLa_(1−x)/3NbO₃ and garnet Li₇La₃Zr₂O₁₂ ceramic oxides, have attracted extensive attention in lithium-ion battery research due to their good chemical stability and the improvability of their ionic conductivity with great potential in solid electrolyte battery applications. These solid oxides eliminate safety issues and cycling instability, which are common challenges in the current commercial lithium-ion batteries based on organic liquid electrolytes. However, in practical applications, structural disorders such as point defects and grain boundaries play a dominating role in the ionic transport of these solid electrolytes, where defect engineering to tailor or improve the ionic conductive property is still seldom reported. Here, we demonstrate a defect engineering approach to alter the ionic conductive channels in Li_xLa_(1−x)/3NbO₃ (x = 0.1~0.13) electrolytes based on the rearrangements of La sites through a quenching process. The changes in the occupancy and interstitial defects of La ions lead to anisotropic modulation of ionic conductivity with the increase in quenching temperatures. Our trial in this work on the defect engineering of quenched electrolytes will offer opportunities to optimize ionic conductivity and benefit the solid electrolyte battery applications.