More importantly, the high mechanical strength is expected to block the lithium dendrite penetration. [5] The unit transference number of Li-ions in SSEs should prevent concentration gradient-induced Li dendrite growth in SSEs. [6] However, extensive investigations demonstrated that Li dendrites still easily grow in inorganic SSEs, including Li 3 PS 4 (LPS), [7] and Li 7 La 3 Zr 2 O 12 (LLZO), [8] whatever they are in single crystal, [9] amorphous or multicrystal structures. The SSEs with much higher mechanical strength show even lower dendrite suppression capability than that in conventional organic electrolytes. [10] Both intergranularly [11] and intragranularly Li dendrite growth are found in SSEs. [12] However, the mechanism for Li dendrite growth in SSEs is not fully understood. Hypotheses, such as poor interfacial contact, electronic conductivity of bulk electrolytes, and the presence of the grain boundaries (GBs), are proposed to illustrate the counterintuitive dendrite growth in SSEs. [13] The high interfacial resistance and non-uniformity at Li/SSE interface, introducing by GBs, voids, and cracks, are often blamed to be responsible for the Li dendrite growth in SSEs. [13] However, reduction of the non-uniformity by densifying SSE, [14] amorphous SSE, and single crystal SSE [15] cannot block the Li dendrite growth. In addition, to reduce the interfacial resistance, lithiophilic Au, [16] Al 2 O 3 , [17] ZnO, [18] Ge, [19] and Li 3 N, [20] which bridges the energy gap between Li and SSE, were coated on SSEs and lithiophobic Li 2 CO 3 was removed from LLZO surface by polishing and heating. [21] However, Li dendrites still grow in SSEs even though the interface resistance is reduced. [22,23] In sharp contrast to lithiophilic coating and enhancement of the uniformity of SSEs, herein, we design a lithiophobic porous SSE that has a high interface energy against Li, a high ionic conductivity and low electronic conductivity to enhance the dendrite suppression capability. Based on the total energy analyses, we established dendrite suppression criterion: the electrolytes or formed interphases should: 1) be electrochemically stable with Li; 2) have a high ionic conductivity and a low electronic conductivity; and 3) have a high interface energy against Li to suppress Li nucleation and growth inside electrolytes. Li 3 N has a high ion conductivity and is stable with Li metal. However, All-solid-state Li metal batteries have attracted extensive attention due to their high safety and high energy density. However, Li dendrite growth in solid-state electrolytes (SSEs) still hinders their application. Current efforts mainly aim to reduce the interfacial resistance, neglecting the intrinsic dendrite-suppression capability of SSEs. Herein, the mechanism for the formation of Li dendrites is investigated, and Li-dendrite-free SSE criteria are reported. To achieve a high dendrite-suppression capability, SSEs should be thermodynamically stable with a high interface energy against Li, and they should have a low electronic conducti...

Tin and its compounds hold promise for the development of high-capacity anode materials that could replace graphitic carbon used in current lithium-ion batteries. However, the introduced porosity in current electrode designs to buffer the volume changes of active materials during cycling does not afford high volumetric performance. Here, we show a strategy leveraging a sulfur sacrificial agent for controlled utility of void space in a tin oxide/graphene composite anode. In a typical synthesis using the capillary drying of graphene hydrogels, sulfur is employed with hard tin oxide nanoparticles inside the contraction hydrogels. The resultant graphene-caged tin oxide delivers an ultrahigh volumetric capacity of 2123 mAh cm–3 together with good cycling stability. Our results suggest not only a conversion-type composite anode that allows for good electrochemical characteristics, but also a general synthetic means to engineering the packing density of graphene nanosheets for high energy storage capabilities in small volumes.

The capacity of transition metal oxide cathode for Li-ion batteries can be further enhanced by increasing the charging potential. However, these high voltage cathodes suffer from fast capacity decay because the large volume change of cathode breaks the active materials and cathode-electrolyte interphase (CEI), resulting in electrolyte penetration into broken active materials and continuous side reactions between cathode and electrolytes. Herein, a robust LiF-rich CEI was formed by potentiostatic reduction of fluorinated electrolyte at a low potential of 1.7 V. By taking LiCoO 2 as a model cathode, we demonstrate that the LiF-rich CEI maintains the structural integrity and suppresses electrolyte penetration at a high cut-off potential of 4.6 V. The LiCoO 2 with LiF-rich CEI exhibited a capacity of 198 mAh g À 1 at 0.5C and an enhanced capacity retention of 63.5 % over 400 cycles as compared to the LiF-free LiCoO 2 with only 17.4 % of capacity retention.

Li 10 GeP 2 S 12 (LGPS) has a high ionic conductivity and compatibility with sulfur cathodes; however, the instability of LGPS against Li and Li dendrite growth still remains unsolved. Here, we solved these two challenges by forming a lithiophilic−lithiophobic gradient interlayer interphase layer between Li and LGPS through the sequential reduction of salts and solvent in Mg(TFSI) 2 -LiTFSI-DME liquid electrolyte at the LGPS/Li interface (TFSI = bis(trifluoromethanesulfonyl)imide; DME = dimethoxyethane). Mg(TFSI) 2 -LiTFSI is first reduced, forming a lithiophilic Li x Mg alloy-rich layer on the lithium surface and a lithiophobic LiF-rich layer on top of Li x Mg due to the lithiophobicity difference. The later reduced DME solvent forms a flexible organic polymer between the LiF-rich layer and LGPS. After evaporation of DME solvent, the Li/LGPS/Ni-Li 2 S-LiTiS 2 all-solid-state battery shows a reversible capacity of 699.7 mAh g −1 (1.07 mAh cm −2 ) based on the mass of Ni-Li 2 S-LiTiS 2 at 100 mA g −1 (0.26 mA cm −2 ). The rational design of a solid electrolyte interface between a Li anode and LGPS electrolyte opens a new opportunity to develop high-performance all-solid-state lithium batteries.