Active Interphase Enables Stable Performance for an All‐Phosphate‐Based Composite Cathode in an All‐Solid‐State Battery

Abstract

High interfacial resistance and unstable interphase between cathode active materials (CAMs) and solid‐state electrolytes (SSEs) in the composite cathode are two of the main challenges in current all‐solid‐state batteries (ASSBs). In this work, the all‐phosphate‐based LiFePO4 (LFP) and Li1.3Al0.3Ti1.7(PO4)3 (LATP) composite cathode is obtained by a co‐firing technique. Benefiting from the densified structure and the formed redox‐active Li3–xFe2–x–yTixAly(PO4)3 (LFTAP) interphase, the mixed ion‐ and electron‐conductive LFP/LATP composite cathode facilitates the stable operation of bulk‐type ASSBs in different voltage ranges with almost no capacity degradation upon cycling. Particularly, both the LFTAP interphase and LATP electrolyte can be activated. The cell cycled between 4.1 and 2.2 V achieves a high reversible capacity of 2.8 mAh cm–2 (36 µA cm–2, 60 °C). Furthermore, it is demonstrated that the asymmetric charge/discharge behaviors of the cells are attributed to the existence of the electrochemically active LFTAP interphase, which results in more sluggish Li+ kinetics and more expansive LFTAP plateaus during discharge compared with that of charge. This work demonstrates a simple but effective strategy to stabilize the CAM/SSE interface in high mass loading ASSBs.

All‐Solid‐State Garnet‐Based Lithium Batteries at Work–In Operando TEM Investigations of Delithiation/Lithiation Process and Capacity Degradation Mechanism

“…Nevertheless, the high elastic property of LLZO and LATP may allow these types of SSLBs to cycle without applying external pressure, which offers the possibility of achieving higher energy density and safety than using lower elastic modulus ones. [21,47] LLZO has many unique properties than other SSEs such as a relatively high elastic modulus, wide electrochemical window, and high Li-ion conductivity (≈1 mS cm −1 at 25 °C). [48] Depending on the substitutions, LLZO also provides excellent electrochemical stability toward metallic Li that offers the potential for achieving higher energy density.…”

“…[57][58][59][60][61][62][63][64][65] On the positive electrode side, the rigid nature of both LLZO and AC materials requires a high-temperature sintering process to establish Li-ion and electronic conductive paths, thereby reducing the interfacial resistance and promoting the electrochemical performance of the battery. [18,21,47,66,67] Since the Li-ion conductivity of AC is usually very low, composited positive electrode (CPE) is proposed to build up a 3D percolation network for ionic and electronic transportation, where LLZO provides Li-ion conductive paths and AC offers electronic and partially Li-ion pathways. The 3D structure of CPE also increases the contact area between LLZO and AC for faster ionic diffusion pathways that allow the battery for achieving higher power density.…”

“…Nevertheless, the high elastic property of LLZO and LATP may allow these types of SSLBs to cycle without applying external pressure, which offers the possibility of achieving higher energy density and safety than using lower elastic modulus ones. [ 21 , 47 ]…”

“…[ 13 , 14 ] Furthermore, the replacement of the organic liquid electrolyte with a solid one for making all‐solid‐state Li batteries (SSLBs) is a promising technique owing to the intrinsic safety of solid‐state electrolytes (SSEs) while the use of metallic Li as the anode can promote their energy densities. [ 15 , 16 ] Several common SSEs are used in SSLB research including garnet‐type Li 7 La 3 Zr 2 O 12 (LLZO), [ 17 , 18 , 19 ] sodium superionic conductor (NASICON)‐type Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP), [ 20 , 21 , 22 ] phosphosulfide‐type Li 10 GeP 2 S 12 (LGPS), [ 23 , 24 ] Li 3 PS 4 , [ 25 , 26 ] halide‐type Li 3 MCl x (M = In, Sc, Y, Zr) ( x = 4, 6), [ 27 , 28 , 29 , 30 ] and argyrodite‐type Li 6 PS 5 X (X = Cl, Br, I). [ 27 , 31 ] Among these SSEs, phosphosulfide‐type, [ 32 , 33 , 34 ] halide‐type, [ 35 ] and argyrodite‐type [ 36 ] solid electrolytes have relatively low elastic modulus than that for garnet‐type [ 37 ] and NASICON‐type.…”

“…On the other hand, the higher elastic properties of LLZO [ 37 ] and LATP [ 38 ] usually need high sintering temperatures to establish proper Li‐ion and electronic conductive paths within the battery cell. [ 18 , 21 ] A good combination of materials and interfacial engineering for avoiding material decomposition reactions or elemental interdiffusion between the solid electrolyte and the active cathode (AC) material at the high sintering temperature becomes a challenge. [ 43 , 44 , 45 , 46 ] The disadvantage of high‐temperature sintering then dramatically impedes the development of SSLBs using LLZO and LATP as their solid electrolytes.…”