Chen Jun research group of Nankai University: a new cathode material for lithium-ion batteries

Lead lithium ion is widely used in portable electronic equipment, and has some demonstration applications in electric vehicles and other fields One of the main bottlenecks limiting the further development of lithium-ion batteries is the limited specific capacity of cathode materials (generally no more than 200 MAH / g) Therefore, in order to solve this problem, it is very important to develop the cathode materials with higher capacity for the further development and large-scale application of lithium-ion batteries In recent years, the cathode materials of lithium rich manganese based oxides have been widely concerned by researchers It has been found that there is oxidation-reduction of lattice oxygen in the process of charging and discharging Although it shows good capacity, due to the different synthesis methods, the structural characteristics of the materials have changed, and the oxidation-reduction mechanism of oxygen anion in this kind of layered oxides is still controversial These materials have serious problems of voltage attenuation and cation dissolution, which restrict the commercialization of these materials Recently, academician Chen Jun's research group of Nankai University has carried out cross cooperation research with Professor Yu Shulei of Wollongong University, Australia, researcher Gulin of Institute of physics of Chinese Academy of Sciences, Professor Wang Heng of Zhengzhou Light Industry University, Professor Hirofumi Yoshikawa of Kansai University, Japan and other research groups New progress has been made in this research field: cation arrangement in lithium rich manganese basic oxide has been found It has an important influence on the redox mechanism of oxygen anion When the lattice oxygen after charging (oxidation) does not form a bridge bond, the problem of voltage attenuation and cation dissolution can be improved obviously, and the discharge specific capacity of the improved material can reach 289 MAH / g at 0.05 C ratio The results were published in adv mater (DOI: 10.1002/adma.201901808) Academician Chen Jun, inorganic chemist, obtained bachelor's degree and master's degree in Nankai University in 1989 and 1992, stayed in school in 1992, obtained doctor's degree in Wollongong University in Australia in 1999, and served as researcher in Osaka Institute of industrial technology, Japan Institute of industrial technology from 1999 to 2002 Currently, he is vice president of Nankai University and director of the Key Laboratory of the Ministry of education of advanced energy materials chemistry Chen Jun is mainly engaged in the chemical research of new energy materials, has published more than 400 academic papers, cited more than 30000 times, and compiled 16 works (chapters) such as energy chemistry It has been granted 35 invention patents, some of which have been applied He has won the second prize of National Natural Science, the first prize of Tianjin Natural Science, the national "May 1st" labor medal and other awards At the same time, he is also the executive director of China Chemical Society, director of China electrochemical special committee, member of Royal chemical society, etc at present, he is also the deputy editor in chief or editorial board member of various journals such as inorg Chem Front., adv funct Mater., Journal of chemistry, electrochemistry, etc Cutting edge scientific research achievements: new cathode materials for lithium-ion batteries - redox chemistry of oxygen anions by changing the cation arrangement to control the lithium-ion rich manganese base oxide The lithium-ion rich manganese base oxide is considered to be the most likely cathode material to achieve the 400 WH / kg specific energy target of lithium-ion batteries, which has attracted great attention of research institutions and enterprises However, the problems of lattice oxygen escape and voltage decay restrict the development of research and industrialization At present, most of the literature is to improve the long cycle stability and crystal structure stability of lithium rich manganese based oxide by element replacement and surface modification However, due to the complexity of its intrinsic structure and oxidation products of oxygen anions, little attention has been paid to the influence of the intrinsic cation arrangement of lithium rich manganese based oxides on the redox chemistry of oxygen anions In view of this, the author systematically studied the influence of the intrinsic cation arrangement of lithium rich manganese base oxide on the redox chemistry of oxygen anion, characterized the oxidation products of materials with different cation arrangement after charging in detail, and found that whether the lattice oxygen formed bridge bond after being oxidized has a great influence on the electrochemical performance Fig 1 synthesis and characterization of lithium rich manganese base oxide (source: adv mater.) the author first prepared a series of lithium rich manganese base oxide Li 1.19 Ni 0.26 Mn 0.55 O 2 (1 × 3, 2 × 3 × 3, 4 × 4, 5 × 5) with different cation arrangement by solid-phase sintering using the method of secondary nickel feeding and controlling lithium content Through the characterization and analysis of the material structure (see Table 1 for the structural characteristics of each sample), the author selected a representative sample of 1 × 3 × 3 × 4 × for research Among them, 1 × is the contrast sample, 3 × is the common Li + / Ni2 + cation mixed layout, and 4 × is the Li + / Ni2 + cation mixed layout with lithium defects It is found that the structure of the pre calcined product of the precursor is directly related to the mixed cation arrangement of the final material In addition, lithium defects also have an important influence on the cation arrangement Fig 2 Structure Characterization of lithium rich manganese base oxide (source: adv mater.) table 1 structure characteristics of lithium rich manganese base oxide (source: adv mater.) the author has carried out X-ray near edge absorption (XANES) and Raman tests on 1 × 3 × 4 × samples in different voltage states The results show that the oxidation products of 1 × 3 and 3 × 4 samples are O-O dimers, while the oxidation products of 4 × 4 samples have no oxygen bridge bond In addition, the author found that more O-O dimers could be produced in 3 × 3 samples with mixed cation row Transmission electron microscopy (TEM), selected area electron diffraction (SAED) and EDS line scan results show that the formation of O-O dimer can promote the transformation of material structure from lamellar to spinel phase The author speculates that the reason for this phenomenon is that the transformation of lattice oxygen to O-O dimer increases the change of material structure, which makes the structure stability worse, and the chemical instability of O-O dimer leads to the occurrence of electrode side reactions Fig 3 redox chemistry of lattice oxygen in lithium rich manganese base oxide (source: adv mater.) by in-situ XRD and in-situ UV Vis test, the author found that the sample without O-O dimer had less structural change and less cation dissolution during charging This result verifies the above conjecture Fig 4 Structure Evolution and cation dissolution test of lattice oxygen in lithium rich manganese basic oxide (source: adv mater.) finally, the author tested the electrochemical performance of various samples, and the results showed that the performance of 3 × is the worst, and that of 4 × is the best 4 The sample shows high average voltage and low voltage attenuation: at 1C, the average voltage is 3.58 V, and after 150 cycles, the voltage attenuation rate is only 1.6% In addition, the specific discharge capacity can reach 289 MAH / g at 0.05c Figure 5 electrochemical performance of lithium rich manganese base oxide (source: adv mater.) this research work provides a new idea for preparation and modification of lithium rich manganese base oxide This achievement was recently published in advanced materials (adv mater 2019, DOI: 10.1002/adma.201901808) The corresponding author of the paper is academician Chen Jun, and the first author is Dr Zhang Jicheng This work has been funded by the Ministry of science and technology of the people's Republic of China (2016yfa0202503 and 2017yfa0206700), the National Natural Science Foundation of China (2142001), the Ministry of education of the people's Republic of China (b12015), the special fund for basic scientific research of central universities, the China Postdoctoral Science Foundation (2017m621054) and the large synchrotron radiation light source SPring-8 (No 2018a3634) of Japan ）Of the company Nowadays, people and scientific research have been paid more and more attention in the economic life China has ushered in the "node of science and technology explosion" Behind the progress of science and technology is the work of countless scientists In the field of chemistry, in the context of the pursuit of innovation driven, international cooperation has been strengthened, the influence of Returned Scholars in the field of R & D has become increasingly prominent, and many excellent research groups have emerged in China For this reason, CBG information adopts the 1 + X reporting mechanism CBG information website, chembeangoapp, chembeango official micro blog, CBG information wechat subscription number and other platforms jointly launch the column of "people and scientific research", approach the representative research groups in China, pay attention to their research, listen to their stories, record their demeanor, and explore their scientific research spirit