Ni/Li Disordering in Layered Transition Metal Oxide: Electrochemical Impact, Origin, and Control

Abstract

CONSPECTUS: Lithium ion batteries (LIBs) not only power most of today's hybrid electric vehicles (HEV) and electric vehicles (EV) but also are considered as a promising system for grid-level storage. Large-scale applications for LIBs require substantial improvement in energy density, cost, and lifetime. Layered lithium transition metal (TM) oxides, in particular, Li(Ni x Mn y Co z )O 2 (NMC, x + y + z = 1) are the most promising candidates as cathode materials with the potential to increase energy densities and lifetime, reduce costs, and improve safety. In order to further boost Li storage capacity, a great deal of attention has been directed toward developing Ni-rich layered TM oxides. However, structural disorder as a result of Ni/Li exchange in octahedral sites becomes a critical issue when Ni content increases to high values, as it leads to a detrimental effect on Li diffusivity, cycling stability, first-cycle efficiency, and overall electrode performance. Increasing effort has been dedicated to improving the electrochemical performance of layered TM oxides via reduction of cationic mixing. Therefore, it is important to summarize this research field and provide in-depth insight into the impact of Ni/Li disordering on electrochemical characteristics in layered TM oxides and its origin to accelerate the future development of layered TM oxides with high performance. In this Account, we start by introducing the Ni/Li disordering in LiNiO 2 , the experimental characterization of Ni/Li disordering, and analyzing the impact of Ni/Li disordering on electrochemical characteristics of layered TM oxides. The antisite Ni in the Li layer can limit the rate performance by impeding the Li ion transport. It will also degrade the cycling stability by inducing anisotropic stress in the bulk structure. Nevertheless, the antisite Ni ions do not always bring drawbacks to the electrochemical performance; some studies including our works found that it can improve the thermal stability and the cycling structure stability of Ni-rich NMC materials. We next discuss the driving forces and the kinetic advantages accounting for the Ni/Li exchange and conclude that the steric effect of cation size and the magnetic interactions between TM cations are the two main driving forces to promote the Ni/Li exchange during synthesis and the electrochemical cycling, and the low energy barrier of Ni 2+ migration from the 3a site in the TM layer to the 3b site in the Li layer further provides a kinetic advantage. Based on this understanding, we then review the progress made to control the Ni/Li disordering through three main ways: (i) suppressing the driving force from the steric effect by ion exchange; (ii) tuning the magnetic interaction by cationic substitution; (iii) kinetically controlling Ni migration. Finally, our brief outlook on the future development of layered TM oxides with controlled Ni/Li disordering is provided. It is believed that this Account will provide significant understanding and inspirations toward developing high-performance la...

Correlation between manganese dissolution and dynamic phase stability in spinel-based lithium-ion battery

“…Performance improvement of cathode materials represent one of the most critical technological challenges for lithium ion batteries (LIBs) 1–5 , as existing cathode materials exhibit underachieved cycling stability and severe capacity loss 6–10 . Cathode material stability is predominately attributable to two factors: bulk structural stability and surface chemical stability 11–14 .…”

Preintercalation Strategy in Manganese Oxides for Electrochemical Energy Storage: Review and Prospects

“…Nowadays, the renewable energy sources, such as solar, wind, etc., have become worldwide hotspots, which call for the research and development of high‐efficiency energy storage/ conversion devices. [ 1–4 ] Up to now, the rechargeable batteries and supercapacitors have been considered as the most promising candidates for energy storage/conversion in electronic vehicles, portable devices, as well as large‐scale energy storage devices, [ 5–8 ] which convert the chemical energy into electronic energy via shuttling ions between the cathodes and the anodes. Due to the low‐cost, high‐capacity, and environmentally friendliness, MnO 2 ‐based materials have long been investigated as cathode materials in different kinds of batteries, including alkaline Zn/MnO 2 batteries, [ 9 ] Li‐ion, [ 10,11 ] Na‐ion, [ 12 ] Mg‐ion, [ 13,14 ] and Zn‐ion batteries.…”

Cooling Induced Surface Reconstruction during Synthesis of High‐Ni Layered Oxides

“…Significant efforts in developing high‐Ni NMC cathodes have been put on studying electrochemical impact, origin of the Li/Ni disordering, and on improving Li/Ni ordering through optimizing synthesis conditions . It is until very recently that people started to pay close attention to the surface instability, particularly surface reconstruction, including formation of NiO‐type rock salt, Li 2 CO 3 species, and nickel carbonate (NiCO 3 ·2Ni(OH) 2 ·2H 2 O) .…”

“…Despite much research into candidate cathodes for LIBs, transition metal (TM) layered oxides with a hexagonal structure (space group R3m) have remained dominant over the past three decades. [9,11,16,17] It is until very recently that people started to pay close attention to the surface instability, particularly surface reconstruction, including formation of NiO-type rock salt, [11,18,19] Li 2 CO 3 species, [10,14,[20][21][22] and nickel carbonate (NiCO 3 ·2Ni(OH) 2 ·2H 2 O). The high Ni loading, on the other hand, raises the critical issues of surface instability and poor rate performance.…”