Literature Appreciation: A Universal Strategy toward the Precise Regulation of Initial Coulombic Efficiency of Li-Rich Mn-Based Cathode Materials

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 multiplier performance, and universality of other types of Li-Rich Mn-Based Cathode Materials I CE.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 P LRM.
• Sample preparation of P LRM 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. Interpretation of Result

Combining the results of the composition, structure and morphology of P LRM and O AT-3, the authors found that OA can provide abundant H-ion exchange with lithium lithium defects in PLRM and form a uniform organic coating (OCL) on the PLRM surface through self-polymerization reaction.During subsequent calcination, the TM ions will occupy the lithium position, resulting in the formation of TM defects (Mn vacancy and TM doping), the OCL gradually carbonizes in the air and introduces oxygen vacancy and in situ construction surface reconstruction layer (spinel/laminar heterostructure and carbon coating 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 O AT-3 samples was significantly greater than the P LRM, 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 with the extension of the OA treatment time, the first charging ratio capacity gradually decreased, the first discharge ratio capacity increased first and then decreased, and the ICE gradually increased from 84.1% to 100.7%, that is, the precise control of ICE can be achieved by simply adjusting the oleic acid treatment time.In addition, OAT-3 showed better fold performance than PLRM, with discharge ratio capacities at 0.2,0.5,1,2,285,274,262,255 and 245 mAh g-1 and 5 C, respectively, and 285 mAh g-1 after cycling back to 0.2 C, indicating that OAT-3 has good electrochemical reaction kinetics and excellent structural stability.At a 0.1 C-fold ratio, OAT-3 exerts a high specific capacity of 330 mAh g-1 and a high energy density of 1,143 W h k g-1.Furthermore, OAT-3 discharged higher specific capacity and PLRM after 200 cycles at 1 C and 5 C than P L R M, indicating better cycling stability for OAT-3.Meanwhile, the average voltage difference between PLRM and OAT-3 when cycling at 1 C is very small, meaning that mild OA auxiliary interface engineering does not sacrifice the voltage stability of the material.

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

4. Summary

In conclusion, a simple universal OA ion double defects and in-situ surface reconstruction layer in LRM through auxiliary interface engineering, achieves precise regulation of ICE from 84.1% to 100.7% and effectively improves the reversible capacity and doubling performance of lithium-rich cathode.The introduced Yin-Yang ion double defect can reduce the diffusion barrier of Li ions, thus increase the diffusion rate of Li ions; the induced in situ surface reconstruction layer can improve the conductivity and stimulate the ISE to stabilize the surface lattice oxygen.Thus, when cycling at a 0.1 C-fold rate, OAT-3 is able to exert a high specific capacity of 330 mAh g-1 and a high energy density of 1,143 W h k g-1.

5. Reference Documentation

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.

IEST Related Test Equipment Recommended

PRCD series powder compaction density & resistance Tester (IEST): 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.