Suppressing Manganese Dissolution from Lithium Manganese Oxide Spinel Cathodes with Single‐Layer Graphene

Abstract

Spinel-structured LiMn 2 O 4 (LMO) is a desirable cathode material for Li-ion batteries due to its low cost, abundance, and high power capability. However, LMO suffers from limited cycle life that is triggered by manganese dissolution into the electrolyte during electrochemical cycling. Here, it is shown that single-layer graphene coatings suppress manganese dissolution, thus enhancing the performance and lifetime of LMO cathodes. Relative to lithium cells with uncoated LMO cathodes, cells with graphene-coated LMO cathodes provide improved capacity retention with enhanced cycling stability. X-ray photoelectron spectroscopy reveals that graphene coatings inhibit manganese depletion from the LMO surface. Additionally, transmission electron microscopy demonstrates that a stable solid electrolyte interphase is formed on graphene, which screens the LMO from direct contact with the electrolyte. Density functional theory calculations provide two mechanisms for the role of graphene in the suppression of manganese dissolution. First, common defects in single-layer graphene are found to allow the transport of lithium while concurrently acting as barriers for manganese diffusion. Second, graphene can chemically interact with Mn 3+ at the LMO electrode surface, promoting an oxidation state change to Mn 4+ , which suppresses dissolution. 1500646(2 of 10) wileyonlinelibrary.com power applications. Furthermore, LMO offers improved thermal stability relative to LiCoO 2 , especially in a highly delithiated state, resulting in safer batteries. [ 6 ] However, a major disadvantage of LMO spinel cathodes is that they lose capacity following long term cycling due to Mn 2+ dissolution from the surface of the cathode into the electrolyte during charge/discharge as a result of the disproportionation reaction: 2Mn 3+ → Mn 4+ + Mn 2+ . [ 7,8 ] Approaches that have shown promise in combating manganese dissolution include modifi cation of the composition of the parent LMO electrode by cation substitution (e.g., LiM x Mn 2x O 4 , M = Li, Co, Ni, Zn) [9][10][11][12][13][14] to reduce the amount of Mn 3+ in the structure, thereby increasing the average oxidation state on the manganese ions in the electrode above 3.5+. In addition, a variety of protective surface oxide coatings have been employed such as Al 2 O 3 , [ 15 ] ZrO 2 , [ 16 ] Y 2 O 3 , [ 17 ] and TiO 2 . [ 7 ] However, the realization of a thin and uniform surface fi lm that does not compromise surface conductivity remains an outstanding challenge.Here, we explore single-layer graphene coatings as an alternative strategy for suppressing manganese dissolution form spinel LMO cathodes. Graphene is a promising candidate for this application since it is an effective diffusion barrier for atomic-scale species [ 18,19 ] and can withstand numerous lithiation charge/discharge cycles. [ 20 ] In addition, graphene is an excellent conductor, which facilitates electron transfer and cycling rate. [ 21 ] Graphene is also known to yield a well-defi ned and stable solid electrolyte interphase (SEI) l...

High-throughput computational design of cathode coatings for Li-ion batteries

“…Among the coatings that have been widely tested experimentally, and often found to yield sufficient protection122225262728293031323337, MgO, ZrO 2 , and Ta 2 O 5 are in the top 30 HF-scavenger lists in Fig. 5.…”

“…While alternative strategies such as doping171819, tailoring the particle morphology2021 or core–shell structures222324 have been suggested, a common approach to suppressing cathode degradation has been applying protective coatings on cathode particles1222252627282930313233. Stable binary oxides, such as Al 2 O 3 , MgO, ZnO, ZrO 2 , SiO 2 and TiO 2 may reduce the HF-content in the electrolyte123435, but their performance in suppressing the transition metal-loss from the cathode or the capacity fade can vary significantly2736.…”

Precise Surface Engineering of Cathode Materials for Improved Stability of Lithium‐Ion Batteries

“…To stabilize the cathode–electrolyte interface, surface coating of cathode materials by using electrochemically inert species has been widely practiced . Metal oxides and metal phosphates have been tested thoroughly as coating species in light of their extraordinary stability at high voltage as far as both their chemical and electrochemical stability are concerned.…”

Surface stability of spinel MgNi0.5Mn1.5O4 and MgMn2O4 as cathode materials for magnesium ion batteries

“…In order to solve this problem, surface modification of the cathode electrode is an effective way to reduce the side reactions. It was reported that the single-layer graphene can suppress Mn dissolutions of LMO cathode [53] by blocking Mn diffusion and the oxidation state of surface Mn. Mn dissolution is a possible problem for the usage of MMO and MNMO as cathode for MIBs.…”