Self-Assembled LiNi1/3Co1/3Mn1/3O2 Nanosheet Cathode with High Electrochemical Performance

Demystifying the Lattice Oxygen Redox in Layered Oxide Cathode Materials of Lithium-Ion Batteries

The practical application of lithium-ion batteries suffers from low energy density and the struggle to satisfy the ever-growing requirements of the energy-storage Internet. Therefore, developing next-generation electrode materials with high energy density is of the utmost significance. There are high expectations with respect to the development of lattice oxygen redox (LOR)-a promising strategy for developing cathode materials as it renders nearly a doubling of the specific capacity. However, challenges have been put forward toward the deep-seated origins of the LOR reaction and if its whole potential could be effectively realized in practical application. In the following Review, the intrinsic science that induces the LOR activity and crystal structure evolution are extensively discussed. Moreover, a variety of characterization techniques for investigating these behaviors are presented. Furthermore, we have highlighted the practical restrictions and outlined the probable approaches of Li-based layered oxide cathodes for improving such materials to meet the practical applications.

High-Rate Layered Cathode of Lithium-Ion Batteries through Regulating Three-Dimensional Agglomerated Structure

LiNixCoyMnzO2 (LNCM)-layered materials are considered the most promising cathode for high-energy lithium ion batteries, but suffer from poor rate capability and short lifecycle. In addition, the LiNi1/3Co1/3Mn1/3O2 (NCM 111) is considered one of the most widely used LNCM cathodes because of its high energy density and good safety. Herein, a kind of NCM 111 with semi-closed structure was designed by controlling the amount of urea, which possesses high rate capability and long lifespan, exhibiting 140.9 mAh·g−1 at 0.85 A·g−1 and 114.3 mAh·g−1 at 1.70 A·g−1, respectively. The semi-closed structure is conducive to the infiltration of electrolytes and fast lithium ion-transfer inside the electrode material, thus improving the rate performance of the battery. Our work may provide an effective strategy for designing layered-cathode materials with high rate capability.

Enhanced Electrochemical Performance of Fast Ionic Conductor LiTi2(PO4)3-Coated LiNi1/3Co1/3Mn1/3O2 Cathode Material

Layered LiNi_1/3Co_1/3Mn_1/3O₂ (NCM333) is successfully coated by fast ionic conductor LiTi₂(PO₄)₃ (LTP) via a wet chemical method. The effects of LTP on the physicochemical properties and electrochemical performance are studied. The results reveal that a highly layered structure of NCM333 can be well maintained with less cation mixing after LTP coating. LTP of about 5 nm thickness is coated on the surface of NCM333. Such an LTP coating layer can effectively suppress the side reactions between NCM333 and electrolyte but will not hinder the lithium ion transmission. As a result, LTP-coated NCM333 owns an improved capability and cyclic performance, for example, NCM333/LTP delivers an initial capacity as high as 121.0 mA h g^-1 with a capacity retention ratio of 82.3% after 200 cycles at 10 C, whereas NCM333 only has an initial capacity of 120.4 mA h g^-1 with a very low capacity retention ratio of 66.4%. This method of using a fast ionic conductor like LTP as a coating material may provide a simple and effective strategy to modify those electrode materials with poor cyclic performance.

Exposing the {010} Planes by Oriented Self-Assembly with Nanosheets To Improve the Electrochemical Performances of Ni-Rich Li[Ni0.8Co0.1Mn0.1]O2 Microspheres

A modified Ni-rich Li[Ni_0.8Co_0.1Mn_0.1]O₂ cathode material with exposed {010} planes is successfully synthesized for lithium-ion batteries. The scanning electron microscopy images have demonstrated that by tuning the ammonia concentration during the synthesis of precursors, the primary nanosheets could be successfully stacked along the [001] crystal axis predominantly, self-assembling like multilayers. According to the high-resolution transmission electron microscopy results, such a morphology benefits the growth of the {010} active planes of final layered cathodes during calcination treatment, resulting in the increased area of the exposed {010} active planes, a well-ordered layer structure, and a lower cation mixing disorder. The Li-ion diffusion coefficient has also been improved after the modification based on the results of potentiostatic intermittent titration technique. As a consequence, the modified Li[Ni_0.8Co_0.1Mn_0.1]O₂ material exhibits superior initial discharges of 201.6 mA h g^-1 at 0.2 C and 185.7 mA h g^-1 at 1 C within 2.8-4.3 V (vs Li⁺/Li), and their capacity retentions after 100 cycles reach 90 and 90.6%, respectively. The capacity at 10 C also increases from 98.3 to 146.5 mA h g^-1 after the modification. Our work proposes a novel approach for exposing high-energy {010} active planes of the layered cathode material and again confirms its validity in improving electrochemical properties.