Garnet-type electrolyte have received a lot of attention due to its high ionic conductivity, wide electro-chemical window, excellent thermal stability and lithium metal stability, which can match high-voltage cathode and lithium metal anode to promote the safety and energy density of the batteries. The preparation of solid electrolytes frequently necessitates high-temperature solid-state reaction method. However, this method would cause volatile lithium compounds, restricting the practical preparation and application of electrolytes. Herein, the impact of Li2CuO2 (LCO) as a sintering additive on the sintering behavior of Ta-doped garnet-type electrolyte (Li6.5La3Zr1.5Ta0.5O12, LLZT) is investigated. LCO plays an auxiliary sintering role to reduce the sintering temperature, and the internal Li2O atmosphere that is provided by LCO helps densification of LLZT. The relative density of LLZT-0.5 LCO is 96.07 %, and its Li-ion conductivity is 3.6 x 10-4 S cm-1. Li symmetric and full batteries show excellent cycling performance. This facile and effective strategy of utilizing sintering additive for low temperature sintering could offer useful ideas for the low-cost fab-rication of LLZT. (c) 2022 Elsevier B.V. All rights reserved.

Solid-state lithium metal batteries (SSLMBs) have caught research interest for their desirable safety and energy density. However, low density, poor uniformity of the solid-state electrolytes (SSEs), and dendrite penetration through the SSEs are the major problems that hinder the progress in SSLMB's development. Herein, a co-doping strategy is proposed for garnet-type electrolyte by utilizing a well-designed lithium rich additive Li2WO4 (LWO) doping into Li6.5La3Zr1.5Ta0.5O12 (LLZT). LWO addition yields a denser and more uniform material by acting as a sintering aid and providing an inner Li2O atmosphere. W substitutes the Zr element and forms Ta and W-doped LLZO, and second phase, which broadens the sintering temperature range of LLZT and avoids abnormal grain growth (AGG). With 2 wt% LWO, LLZT-2LWO has an ionic conductivity of 0.6 mS/cm and a relative density of 98.67%. Moreover, the critical current density (CCD) of LLZT-2LWO reaches 1.0 mA cm2. LLZT-2LWO achieves long cycling stability for 300 h at 0.5 mA cm-2 , showing an excellent dendrite-suppression capability. The full cell matched with LiNi0.6Co0.2Mn0.2O2 and sulfur cathode displays high discharge capacity and cycling stability. This modification strategy has high efficiency and is conducive to large-scale production, which opens a new opportunity for SSLMBs.(c) 2022 Elsevier Ltd. All rights reserved.

Solid‐state lithium metal batteries (SSLMBs) are attracting increasing attentions as one of the promising next‐generation technologies due to their high‐safety and high‐energy density. Their practical application, however, is hindered by lithium dendrite growth and propagation in solid‐state electrolytes (SSEs). Herein, an in situ grain boundary modification strategy relying on the reaction between Li 2 TiO 3 (LTO) and Ta‐substituted garnet‐type electrolyte (LLZT) is developed, which forms LaTiO 3 along with lesser amounts of LTO/Li 2 ZrO 3 at the grain boundaries (GBs). The second phases of LTO/Li 2 ZrO 3 inhibit abnormal grain growth. The presence of LaTiO 3 at the GBs reduces electronic conductivity and improves mechanical strength, which can hinder dendrite formation and block lithium dendrite penetration through the LLZT. Moreover, the adjacent grains by LaTiO 3 build a continuous Li + transport path, providing a homogeneous Li + flux throughout the whole LLZT‐4LTO. As a result, symmetric cells of Li | LLZT‐4LTO | Li shows a high critical current density of 1.8 mA cm −2 and a long cycling stability up to 2000 h at 0.3 mA cm −2 . Moreover, the high‐voltage full cells demonstrate remarkable cycling stability and rate performance. It is believed that this novel grain boundary modification strategy can shed light on the constructing of high‐performance SSEs for practical SSLMBs.

Solid‐state batteries (SSBs) promise high energy density and strong safety due to using nonflammable solid‐state electrolytes (SSEs) and high‐capacity Li metal anode. Ta‐substituted Li7La3Zr2O12 (LLZT) SSE possesses superior ionic conductivity and stability with Li metal, yet the interfacial compatibility and lithium dendrite hazards still hinder its applications. Herein, an interfacial engineering is demonstrated by facile acid‐salt (AS) treatment on LLZT, constructing a 3D cross‐linking LiF‐LiCl (CF) network. Such structure facilitates Li wetting via capillary permeation. Notably, CF as electronically insulting phases block the electrons through the interface and ulteriorly suppress the dendrite formation. The assembled Li symmetric cell exhibited a low interfacial impedance (11.6 Ω cm2) and high critical current densities (CCDs) in the time‐constant mode, 1.8 mA cm−2 at 25 °C and 3.6 mA cm−2 at 60 °C, respectively. Meanwhile, by exploring the capacity‐constant mode of CCD measurement, the concept of critical areal capacity (CAC) is first proposed, obtaining its values of ≈0.5 mAh cm−2 at 25 °C and 1.2 mAh cm−2 at 60 °C. Moreover, the safety‐enhanced hybrid SSBs matched with LiFePO4 and LiNi0.6Co0.2Mn0.2O2 deliver a remarkable rate and cycling performances, validating the feasibility of this interfacial engineering in various SSB systems.

Garnet-type Li7La3Zr2O12 (LLZO) Li+ ion solid electrolyte is a promising candidate for next generation high-safety solid-state batteries. Ga-doped LLZO exhibits excellent Li+ ion conductivity, higher than 1 x 10(-3) S cm(-1). In this research, the doping amount of Ga, the calcination temperature of Ga-LLZO primary powders, the sintering conditions and the evolution of grains are explored to demonstrate the optimum parameters to obtain a highly conductive ceramics reproducibly via conventional solid-state reaction methods under ambient air sintering atmosphere. Cubic LLZO phase is obtained for Li6.4Ga0.2La3Zr2O12 powder calcined at low temperature 850 degrees C. In addition, ceramic pellets sintered at 1100 degrees C for 320 min using this powder have relative densities higher than 94% and conductivities higher than 1.2 x 10(-3) S cm(-1) at 25 degrees C.

Solid-state batteries (SSBs) have attracted many attentions due to its higher energy density and improved safety. As one of the most promising solid electrolytes, garnet Li7La3Zr2O12 (LLZO) has achieved significant advances in its cell performance, however, its application in Li-metal batteries is still hindered by lithium dendrite growth at voids or grain boundaries inside the solid electrolyte. Herein, a novel grain-boundary enhancement strategy was demonstrated by introducing Li6Zr2O7 (LZO), which can be decomposed into Li2O in situ, into Ta-doped LLZO (LLZT). The Li2O provides a sufficient inner Li2O atmosphere, achieving none mother powder sintering. The Li2ZrO3 stays at garnet grain boundaries or fills up the pores, which have been shown to effectively suppress the lithium dendrite growth. More importantly, the critical current density (CCD) of the Li | LLZT-LZO | Li symmetric cell achieved as high as 1.4 mA cm(-2) at 25 degrees C and 2.0 mA cm(-2) at 60 degrees C, and the long-term lithium cycling remained stable over 2000 h at 0.3 mA cm(-2). Moreover, the Li-S battery maintained high discharge capacity of 816 mAh g(-1) after 200 cycles at 0.5C. Therefore, our work provides a facile and effective strategy to prepare a safety-enhanced electrolyte for future applications of SSBs.

Li-garnet Li7La3Zr2O12 (LLZO) is a promising solid electrolyte for lithium metal batteries owing to its excellent stability and high ionic conductivity. However, there exists serious lithium dendrite problem in LLZO electrolyte under elevated current density, easily leading to internal short-circuit and poor cycling performance. In this work, we demonstrated that Ta-doped LLZO with 4 wt% MgO additive delivered superior endurance to lithium dendrite due to its improved mechanical properties and lower electronic conductivity. The critical current density (CCD) of LLZTO-MgO composite electrolyte reached as high as 1.95 mA.cm(-2) at room temperature (RT). It also realized stable lithium plating/stripping performance for 1000h under 0.5 mA.cm(-2). Moreover, the full cell paired with LiNi0.6Co0.2Mn0.2O2 cathode exhibited better cycling stability especially at a high rate. Our work provided an alternative strategy for dendrite-suppression in solid electrolyte besides interfacial modification. (C) 2020 Elsevier B.V. All rights reserved.

Li7La3Zr2O12 (LLZO) solid electrolyte is a promising candidate for next generation batteries. In the LLZO family with various doping elements, Ga-doped LLZO (Ga-LLZO) delivers the highest Li-ion conductivity of higher than 1 x 10(-3) S cm(-1). However, Ga-LLZO ceramics always contain lots of overgrown huge grains after sintering, resulting in short-circuiting as applied with Li anode in batteries. Hence a simple two-step sintering strategy is developed to prepare fine-grained Ga-LLZO ceramics with good electrochemical properties. Pellets with the composition of Li6.4Ga0.2La3Zr2O12 deliver pure garnet phase, uniform fine grains, high relative density of 97.3% and conductivity of 1.24 x 10(-3) S cm(-1) at 27 degrees C after sintering at 1150 degrees C for 1 min and 1000 degrees C for 3 h. In addition, those fine-grained Ga-LLZO exhibit improved stability against molten Li. The Li/Ga-LLZO/Li symmetric cells show a critical current density of 0.7 mA cm(-2), and a stable cycling of over 600 hat 0.4 mA cm(-2) at 27 degrees C. The Li/Ga-LLZO/LiFePO4 full cells deliver reversible capacity of 150 mAh g(-1), showing negligible decay after 50 cycles. These results bring the Ga-LLZO electrolytes one step closer to practical application in solid-state batteries.

Garnet-type solid-state electrolytes (SSEs) show a promising application in solid-state Li batteries. Poor interfacial contact with lithium causing large interfacial impedance and dendrite penetration is a problem. Inspired by unique H+/Li+ exchange of garnet electrolyte, we used an AgNO3 aqueous solution induced strategy to construct a lithiophilic layer in situ on the garnet surface without any specific apparatus. Experimental analysis reveals the uniform distribution of Ag nanoparticles and significantly enhanced affinity between the solid state electrolyte (SSE) and Li anode for the Li-Ag alloying. As expected, the interfacial area specific resistance (ASR) is greatly reduced to similar to 4.5 Omega cm(-2), accompanying with long-cycling stability for similar to 3500 h at 0.2 mA cm(-2) and high critical current density of 0.75 mA cm(-2). With modified SSEs, quasi-solid-state batteries with a LiFePO4 or LiNi0.5Co0.2Mn0.3O2 cathode operate well at room temperature and an all-solid-state LiFePO4 /garnet/Li battery displays good cycling stability for over 200 cycles at 60 degrees C.

Poly(vinylidene fluoride‐ co ‐hexafluoropropylene) (PVDF‐HFP) based gel polymer electrolyte is regarded as a promising candidate to settle the safety issues of liquid electrolytes. However, the currently reported gel polymer electrolytes are still not safe enough owing to high amount of flammable liquid solvents contained in them. Herein, a fireproof PVDF‐HFP based gel polymer electrolyte is designed and synthesized through an in situ crosslinking method, with Li 6.4 Ga 0.2 La 3 Zr 2 O 12 as initiator and ion‐conductive filler. The obtained gel polymer electrolyte demonstrates superior fire resisting properties. The optimized gel polymer electrolyte exhibits an ionic conductivity as high as 1.84 × 10 −3 S cm −1 at 20 °C with an electrochemical window up to 4.75 V at room temperature. Moreover, the obtained gel polymer electrolyte shows excellent compatibility with lithium anodes. Therefore, the lithium anode is well protected. Lithium batteries assembled with the gel polymer electrolyte possess superb safety properties in cutting and burning tests. Furthermore, the batteries also show a discharge retention rate as high as 94.08% (in comparison with the initial discharge capacity) after cycling at 0.5 C for 360 cycles with an average columbic efficiency higher than 98%. The purpose of this report is to show the great potential of applying fire‐retardant gel polymer electrolyte to achieve high safety lithium batteries.

Solid-state lithium batteries (SSBs) promise high energy and power densities, as well as enhanced safety, owing to the use of Li metal and nonflammable solid-state electrolytes.