Bi Works as a Li Reservoir for Promoting the Fast‐Charging Performance of Phosphorus Anode for Li‐Ion Batteries

Abstract

considered as a promising alternative to graphite anode, the energy density of Li 4 Ti 5 O 12 is severely limited by its low theoretical specific capacity (175 mAh g -1 ) and high lithiation potential (1.5 V vs Li + / Li) [4][5][6][7] . Low lithiation potential (0.2 V vs Li + /Li) of silicon anode with the highest specific capacity (3579 mAh g -1 ) could inevitably result in serious lithium dendrites in fast charging process. [8][9][10][11] Phosphorus with a high theoretical specific capacity (2596 mAh g -1 ) and suitable lithiation potential (0.7 V vs Li + /Li) is an ideal anode material with high-energy density and fast-charging capability [1][2][3] (Figure 1a). However, the high-rate capability of P anode is hindered by its low electronic (≈10 −12 S m -1 ) and sluggish lithiation reaction kinetics that are two important influencing factors for fast-charging electrode. In addition, the unstable solidelectrolyte interphase (SEI) is due to the side reactions at the interface of electrode and electrolyte as well as the large volume expansion (≈300%) of P upon lithiation, what is worse, the dissolution behavior of intermediates (lithium polyphosphides, Li x Ps) results in low Coulombic efficiency and continual capacity fading, impairing the long-cycling stability. [12,13] To solve these problems, various carbon carriers and conductive polymer coating layers are usually introduced into P anode. [1][2][3][14][15][16][17][18] However, high Li diffusion barriers in carbon-based frameworks (0.34 eV) [19] and the heterogeneous interface, respectively, hinder the superior fastcharging performance of P-based composites. In addition, the problem of uneven local reaction in P particles has not been solved yet.Herein, to enhance the fast-charging performance, we introduced electrochemically active bismuth, a 2D layered material with a layer spacing of 0.396 nm, [20,21] into P/graphite (P/C) composite as a functional filler by the ball-milling method. Bi works as an anode with a similar electrochemical-reaction potential range as P anode, but the starting lithiation/delithiation potential is a little bit higher/lower than the latter, respectively. Besides, Bi anode offers excellent Li-ion diffusion and electron transport capability, combined with the strong interaction at interface of Bi and P, which can promote both Li ion and electron transport at the interface between Bi and P anode. Thus, Bi can work as a small Li reservoir for trapping Li in lithiation process and emitting Li in delithiation process prior to P Phosphorus anodes are a promising for fast-charging high-energy lithium-ion batteries because of their high specific capacity (2596 mAh g -1 ) and suitable lithiation potential (0.7 V vs Li + /Li). To solve the large volumetric change and inherent poor electrical conductivity, various carbon-based materials have been studied for loading P. However, the local aggregation of Li ions and electrons in P particles especially in the fast-charging process induces an uneven lithiation reaction and the great transient stress...

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