Li-Rich Mn-Based Cathode Materials for Precise Control of Initial Coulombic Efficiency

1. Author Information and A Summary of the Article

In 2021, Xiamen university professor Peng Dongliang and Xie Qingshui researcher led the team developed a simple oleic acid (OA) auxiliary interface engineering strategy to build Yin and Yang ion double defects and in situ surface reconstruction layer of Li-Rich Mn-Based Cathode Materials, the strategy can accurately control I CE and improve the lithium cathode capacity and rate performance, and universality of other types of Li-Rich Mn-Based Cathode Materials ICE.Professor Peng Dongliang and Xie Qingshui of School of Materials of Xiamen University are the corresponding author. Guo Weibin, the doctoral student of School of Materials of Xiamen University, is the first author of this article.

2. Sample Preparation and Testing

• Raw Li-Rich Mn-Based Cathode Materials was prepared by PLRM.
• Sample preparation of PLRM after oleic acid (OA) treatment for different times: OAT-1, OAT-3, and OAT-5.
• Test items: component analysis, crystal structure analysis, crystal morphology analysis, powder conductivity & compaction density analysis, electrochemical performance analysis, etc.

3. Analysis of Results

Synthesizing the results of compositional, structural and morphological analyses of PLRM and OAT-3, the authors found that OA can provide abundant hydrogen ions to exchange with lithium ions in PLRM to construct lithium defects and form a homogeneous organic coating (OCL) on the surface of PLRM through self-polymerization reactions. During subsequent calcination, TM ions occupy lithium sites, leading to the formation of TM defects (Mn vacancies and TM doping), and OCL gradually carbonizes in air and introduces oxygen vacancies and in situ constructed surface reconstruction layers (spinel/lamellar heterostructures and carbon-covered layers) on the PLRM surface.

Figure 1. Schematic diagram of oleic acid control engineering and characterization curve of morphology, composition and structure of oleic acid control engineering.

By comparing the compaction density and conductivity performance of the powder before and after the regulation, the compaction density was almost unchanged, but the conductivity of the OAT-3 samples was significantly greater than the PLRM, and the electrochemical impedance spectral test of the buckle also found that the electronic resistance and charge transfer resistance of the regulated O AT-3 were significantly reduced, which shows that the introduction of oxygen vacancy and in situ surface reconstruction layer can improve the conductivity of the material.

Figure 2. Regulation of powder compaction density & conductivity comparison and EIS impedance test results.

The electrochemical performance test results show (Figure 3) that the first charging specific capacity gradually decreases with the prolongation of the OA treatment time, and the first discharge specific capacity first increases and then decreases, and the ICE gradually increases from 84.1% to 100.7%, i.e., the precise control of the ICE can be realized by simply adjusting the time of the oleic acid treatment. In addition, OAT-3 exhibits better rate performance than PLRM, with discharge specific capacities of 301, 285, 274, 262, 255, and 245 mAh g-1 at 0.2, 0.5, 1, 2, 3, and 5 C, respectively, and the discharge specific capacity still reaches 285 mAh g-1 when recovered to 0.2 C after cycling at a high rate of 5 C. This indicates that OAT-3 possesses This indicates that OAT-3 has good electrochemical reaction kinetics and excellent structural stability. At a multiplication rate of 0.1 C, OAT-3 exhibited a high specific capacity of 330 mAh g-1 and a high energy density of 1143 Wh kg-1. In addition, the discharge specific capacity and capacity retention of OAT-3 after 200 cycles at 1 C and 5 C are higher than those of PLRM, indicating that OAT-3 has better cycling stability. Meanwhile, the average voltage difference between PLRM and OAT-3 during cycling at 1 C is very small, which implies that mild OA-assisted interfacial engineering will not sacrifice the voltage stability of the materials.

Figure 3. Electrical performance test results of PLRM and OAT samples with different treatment times

4. Summary

In summary, through a simple universal OA-assisted interface engineering, the anionic double defects and in-situ surface reconstruction layer are introduced into the Li-rich Mn-based cathode materials(LRMs), which realizes the precise regulation of ICE from 84.1% to 100.7% and effectively improves the reversible capacity and rate performance of the Li-rich Mn-based cathodes. The introduced anionic and cationic double defects can lower the diffusion barrier of Li-ions and thus increase the diffusion rate of Li-ions; the induced in situ surface reconstruction layer can increase the conductivity and excite the ISE to stabilize the surface lattice oxygen. As a result, OAT-3 is able to exert a high specific capacity of 330 mAh g-1 and a high energy density of 1143 Wh kg-1 when cycled at 0.1 C rate.

5. References

Weibin Guo, Chenying Zhang, Yinggan Zhang, Liang Lin, Wei He, Qingshui Xie,* Baisheng Sa, Laisen Wang, Dong-Liang Peng,* A Universal Strategy toward the Precise Regulation of Initial Coulombic Efficiency of Li-Rich Mn-Based Cathode Materials, Adv.Mater., 2021, DOI:10.1002/adma.202103173.

6. IEST Related Test Equipment Recommended

Powder Resistivity & Compaction Density Measurement System（PRCD Series）

Realize compaction density and resistance synchronous test of all lithium powder pressure / discharge states, supporting two probe and four probe test methods, mainly including the following three test modes. a.Single-point pressure synchronization test;b .Multi-point pressure synchronization test;c .Backash test of pressure and discharge state.