HEVs (PHEVs), besides the traditional applications in portable devices. To build the next generation LIBs with higher performances, high energy density materials are urgently pursued worldwide. [1][2][3] Lithium-rich (Li-rich) materials, with the specific capacity over 260 mAh g −1 and energy density up to ≈1000 Wh kg −1 , [4] have attracted great interest in the past decades. It is reported that Li-rich materials are composed of two phases of Li 2 MnO 3 (C 2/m ) and LiMO 2 (R m 3 ) (M = Ni, Co, Mn, etc.). [5][6][7][8][9] Despite the above advantages, several concerns including structural instability and the resulted voltage degradation, as well as the poor diffusion kinetics at the interface have become the bottlenecks of Li-rich materials. [9][10][11][12][13] In this regard, multifarious modification approaches, such as doping and surface coating, have been intensively investigated. [14][15][16] Particularly, Li + diffusion at the cathode-electrolyte interphase (CEI) is widely regarded as the rate determining step in LIBs. [17][18][19] From this viewpoint, metal fluorides (FeF 3 , [20] MOF, [21,22] AlF 3 , [23,24] etc.), metal oxides (MgO, [25] Al 2 O 3 , [26,27] etc.), metal phosphates (AlPO 4 , [28] LaPO 4 , [29] Li 3 PO 4 , [30] FePO 4 /Li 3 PO 4 , [31] Li-Mn-PO 4 , [32] etc.), and those with similar structure of Li-rich Li 2 MnO 3 (Li 2 SiO 3 [33,34] and Li 2 SnO 3 , [35] ) have been widely applied to modify the surface of bulk Li-rich materials. Recently, fast lithium-ion conductors (LiVO 3 , [36] Li 2 ZrO 3 , [37] Li-La-Ti-O, [38,39] LiPON, [40] etc.) have also been proposed to decorate the surface of Li-rich cathodes to enhance the apparent diffusion coefficients. All the aforesaid surface modification materials, unexceptionally, have been proved to be effective in both stabilizing the structure and facilitating the Li + kinetics. Nevertheless, in general, the decoration layers themselves seem rather "passive" in promoting Li + diffusion. Assuming they are Li + conductive (e.g., solid electrolyte materials), fast Li + diffusion channels will be provided besides the general separation effect (in suppressing side reactions and inevitable TM dissolution). As for Li + insulators (e.g., metal fluorides), only the benefit of physical barriers could be exploited. Therefore, a more "initiative" function interface is imperative to be built to more effectively promote the Li + transport at the electrode-electrolyte interphase.It is noteworthy that piezoelectric material, as an important category in the energy-conversion community, works on the As one of the most promising cathodes for next-generation lithium ion batteries (LIBs), Li-rich materials have been extensively investigated for their high energy densities. However, the practical application of Li-rich cathodes is extremely retarded by the sluggish electrode-electrolyte interface kinetics and structure instability. In this context, piezoelectric LiTaO 3 is employed to functionalize the surface of Li 1.2 Ni 0.17 Mn 0.56 Co 0.07 O 2 (LNMCO), aiming to boost t...

Dynamic structural and chemical evolution at solid-liquid electrolyte interface is always a mystery for a rechargeable battery due to the challenge to directly probe a solid-liquid interface under reaction conditions. We describe the creation and usage of in situ liquid secondary ion mass spectroscopy (SIMS) for the first time to directly observe the molecular structural evolution at the solid-liquid electrolyte interface for a lithium (Li)-ion battery under dynamic operating conditions. We have discovered that the deposition of Li metal on copper electrode leads to the condensation of solvent molecules around the electrode. Chemically, this layer of solvent condensate tends to be depleted of the salt anions and with reduced concentration of Li(+) ions, essentially leading to the formation of a lean electrolyte layer adjacent to the electrode and therefore contributing to the overpotential of the cell. This observation provides unprecedented molecular level dynamic information on the initial formation of the solid electrolyte interphase (SEI) layer. The present work also ultimately opens new avenues for implanting the in situ liquid SIMS concept to probe the chemical reaction process that intimately involves solid-liquid interface, such as electrocatalysis, electrodeposition, biofuel conversion, biofilm, and biomineralization.

As one of the most promising cathode materials for next generation energy storage applications, spinel LiNi0.5Mn1.5O4 (LNMO) has been highlighted due to many advantages. However, it is still hindered by poor electrochemical stability derived from the bulk/interface structure degradation and side-reactions under high working voltage. In this work, fast ion conductor Li3V2(PO4)3 (LVPO) is adopted to modify the surface of spinel LNMO by a one-step facile method to harvest the maximum benefit of interface properties. It is found that 1 wt.% LVPO-LNMO exhibits the most excellent cycling performances, retaining a great capacity retention of 87.8 % after 500 cycles at room temperature and 82.4 % for 150 cycles at 55 o C. Moreover, the rate performance is also significantly improved (90.4 mAh g-1 under 20 C). It is revealed that the LVPO-involved layer could effectively suppress the surface side-reactions under high working voltage, which mainly contribute an improved interface with desirable structure stability and excellent kinetics behaviour without sacrificing the surface electrochemical activity in electrochemical environment. Thus, the dissolution of transition metal ions is effectively mitigated with avoiding further structure degradation of bulk material. Especially, it is also established that the vanadium (V) ions in LVPO could be to a certain extent migrated into the surface lattice of LNMO to generate a V-involved transition layer (Li-Ni-Mn-V-O surface solid solution), which greatly co-contributes to the enhanced electrochemical performances owning to the prominently depressed charge transfer resistance.

A well-formed solid electrolyte interface (SEI) is critical for achieving long-term cycling stability in lithium-ion batteries (LIBs). However, the SEI remains the poorly understood component in LIBs especially under dynamic conditions. Here, scanning electrochemical microscopy (SECM) was applied to study the spontaneous reaction on a graphite electrode, SEI formation in the first cycle, SEI evolution during 10 cycles, and the stability of the as-formed SEI in the electrolyte. The conversion, dissolution, stabilization, and growth behaviors of the SEI were determined. Moreover, the SECM results were analyzed in combination with ex situ material characterization to understand the SEI on the graphite electrode comprehensively.