Discovery of an Unexpected Metal Dissolution of Thin‐Coated Cathode Particles and Its Theoretical Explanation

Abstract

The degree of metal dissolution of cathode materials is a critical parameter in determining the performance of lithium-ion batteries (LIBs). Ultra-thin coated cathode particles, fabricated via atomic layer deposition (ALD), exhibit superior battery performance over that of bare particles. Therefore, it is generally believed that a coating layer protects the particles from metal dissolution of active materials, which is a critical cathode degradation mechanism. However, it is observed that ultra-thin CeO 2 coating intensified the Mn dissolution of LiMn 2 O 4 (LMO) during cycling of LIBs, whereas ultra-thin Al 2 O 3 coating tended to inhibit Mn dissolution. A detailed density functional theory (DFT) study is carried out to explain these experimental observations by analyzing interaction of Mn atoms with neighboring electrode atoms in terms of energetic and structural aspect. All atomic and electronic analyses are consistent with the experimental observations. Several common materials are investigated as possible ALD coatings for LIBs to provide general insight, and it is found that Mn dissolution can be suppressed or accelerated depending on the material selection. This is the first report finding that depending on the coating material, metal dissolution can be accelerated, providing new insights into the impact of ALD coating materials on metal dissolution in cathode materials. potential, superior capacity, a long life cycle, and a sufficiently broad range of working temperatures. Although metal oxide cathodes satisfy the criteria, they suffer from an inevitable metal dissolution degradation process. In the dissolution degradation process, transition metal ions dissolve from cathode active materials and can deposit onto the anode, causing severe cell aging and irreversible side reactions that reduce performance. [1,2] For high performance cathode materials such as LiNi x Mn y Co z O 2 (NMC, x + y + z = 1), LiNi 0.5 Mn 1.5 O 4 (LNMO), and LiMn 2 O 4 (LMO), metal dissolution (Ni, Co, Mn, etc.) is severe, and, furthermore, it was found that in such cathode materials, which are composed of two or more transition metals, there is no preferential dissolution among the constituent metals. [3] To study the metal dissolution phenomena, manganese is an excellent candidate for intensive study of the fundamental interfacial processes and side reactions at cathode surfaces because of its low toxicity, low cost, and the high natural abundance of Mn, [4][5][6][7][8][9][10][11][12] which allows it to be used in several promising cathode materials, such as NMC, LNMO, and LMO. It has been published that Mn dissolution accounts for 23% and 34% of overall capacity degradation at room temperature and at 55°C [13] in LMO, respectively. The major reason for LMO degradation, [14][15][16][17][18] as well as for other metal oxide cathode materials, [3,[19][20][21] has been identified as structural changes in the material due to phase transformations, alternation of intrinsic properties (such as electronic and ionic conductivity), dissoluti...

Regulation of Dendrite-Free Li Plating via Lithiophilic Sites on Lithium-Alloy Surface

“…To guarantee the accuracy of the surface energy calculation for Li 22 Sn 5 , the slab sizes of Li 22 Sn 5 (100), (110), and (111) are 19.73 Å × 19.73 Å, 19.73 Å × 27.90 Å, 27.90 Å × 27.90 Å, respectively. The surface energy σ defines the energy difference between a newly generated surface and that of the bulk structure where E slab is the total energy of the slab structure, E bulk is the total energy of the bulk structure, and A is the area surface.…”

“…Several reduction sites for Li on the Li metal and Li x /LiSn 5/22 are considered, and the reduction site with the lowest energy is selected for Li reduction energy calculation. The Li reduction energy E reduction can be expressed as follows , where E slab is the total energy of the Li metal or Li x /LiSn 5/22 structure, E with Li + vacancy is the total energy of the Li metal or Li x –1 /LiSn 5/22 structure with one Li + vacancy and one extra electron, and is the total energy of one Li + .…”

Powder Coatings via Atomic Layer Deposition for Batteries: A Review

“…(c) Mn concentration of uncoated (U-LMO), Al 2 O 3 coated (A-LMO), and CeO 2 coated (C-LMO) LiMnO 2 cathode particles after soaking in electrolyte for 1 week. Reprinted with permission from ref . Copyright 2020 Wiley-VCH GmbH.…”

“…Most recently, Liang's group discovered that a PC LMO cathode ALD coated with CeO 2 (even up to 3 nm thickness) can unexpectedly promote the metal dissolution during cycling. 204 Using inductively coupled plasma−optical emission spectroscopy (ICP-OES), the amount of dissolved Mn in the electrolyte was found to be even more than that of the UC cathode both at room and elevated temperatures, whereas Al 2 O 3 coating retarded the dissolution as depicted in Figure 8c.…”

Recent Advances in Theoretical Development of Thermal Atomic Layer Deposition: A Review

“…Table 2 summarizes the theoretical-study-only ALD articles found in the Web of Science and covered in this review. It is worth mentioning that this review mostly focuses on the theoretical-study-only ALD articles and does not cover the combined experimental and theoretical ones, which are cited here [ 75 , 76 , 130 , 131 , 132 , 133 , 134 , 135 , 136 , 137 , 138 , 139 , 140 , 141 , 142 , 143 , 144 , 145 , 146 , 147 , 148 , 149 , 150 , 151 , 152 , 153 , 154 , 155 , 156 ]. Figure 5 displays the publications, summarized in Table 2 , that are covered in this study.…”