Battery technology plays an important role in the development of sustainable clean energy in society. Compared with traditional nickel-metal hydride batteries and lead-acid batteries, lithium-ion batteries have high energy density, no memory effect, and low environmental pollution. They are widely used in the field of energy storage and conversion. Nowadays, lithium-ion batteries have been used as power batteries in electric vehicles such as Tesla and BYD, and have a huge market share. It is expected that the global lithium-ion battery market will reach 450 billion yuan in 2020.

The lithium-ion battery was first developed by Japanese Sony Corporation in 1990. The traditional lithium ion battery‘s positive electrode material is lithium cobalt oxide (LiCoO2), the negative electrode material is graphite (C), and the rechargeable battery uses esters as electrolyte. The electrode reaction formula of the battery is as follows:

Positive reaction: Lithium ions are intercalated during discharge, and lithium ions are deintercalated during charging.

Charging: of LiCoO 2 → of Li . 1-X of CoO 2 + xLi ⁺ + XE ^-

Discharge: of Li . 1-X of CoO 2 + xLi ⁺ + XE ^- → of LiCoO ²

Negative electrode reaction: Lithium ions are deintercalated during discharge, and lithium ions are intercalated during charging.

Charging: xLi ⁺ + XE ^- + C . 6 → of Li X C . 6

Discharge: of Li X C . 6 → xLi ⁺ + XE ^- + C6

However, the actual specific capacity of lithium cobaltate materials is only about 150 mAh / g, and the lower capacity limits the increase in the energy density of single lithium ion batteries, which is only about 150 Wh / kg. The use of a lower energy density lithium ion battery as the power battery of the car prevents the electric vehicle from having the expected mileage. For example, Tesla‘s latest electric car Model X, its battery pack is composed of more than 7000 18650 lithium ion batteries, weighing about one ton. The heavy battery pack increases the weight of the car and reduces the mileage of the car. The mileage after a full charge is about 400 kilometers. Therefore, the development of lithium ion batteries with high energy density is particularly important.

At present, the research of high energy density lithium ion batteries has shifted from the initial stage to substantial development. The research field is mainly focused on the anode material and anode material of the battery. In the field of positive electrodes, lithium-rich positive electrode materials, high nickel positive electrode materials and sulfur positive electrode materials are mainly studied. The research on the negative electrode mainly focuses on the tin negative electrode, silicon negative electrode and lithium metal negative electrode. At present, there are also many teams devoted to the research of solid electrolytes, mainly to solve the hidden safety problems caused by the flammability of liquid electrolytes. In addition, in the study of lithium metal anodes, the introduction and use of solid electrolytes can suppress the growth of lithium dendrites. This article briefly introduces some of the world‘s top lithium battery research teams and explains the hot research directions of the industry.

John B. Goodenough

Professor Goodenough obtained his doctorate degree from the University of Chicago in 1952. He is currently a professor in the Department of Mechanical Engineering at the University of Texas at Austin. Professor Goodenough is a well-known solid physicist, member of the National Academy of Sciences, member of the Academy of Engineering, and foreign member of the Royal Society of Chemistry. He is also the inventor of lithium ion battery cathode materials such as lithium cobalt oxide, lithium manganate, and lithium iron phosphate. He is also one of the founders of the scientific basis of lithium ion batteries, and is known by the industry as the "father of lithium batteries." Professor Goodenough has published more than 700 papers in journals, and cited more than 46,500 times in published papers.

In recent years, Professor Goodenough has continued to conduct in-depth research in the field of lithium-ion batteries and sodium-ion batteries that he loves. At the same time, it also expands its research field to the solid-state electrolyte research of lithium-ion batteries. Recently, Professor Goodenough also published a research paper on solid electrolytes in the Journal of American Chemistry Society (10.1021 / jacs.8b03106). Professor Goodenough believes that garnet-type solid electrolytes have high electrical conductivity at room temperature and are ideal materials for solid-state electrolytes used in lithium metal batteries. This study used a new strategy to improve the interface of garnet LLTO (Li 7 La 3 Zr 2 O 12 ), which significantly reduced the impedance of the interface between lithium metal and garnet and inhibited the formation of dendrites. Therefore, the overpotential of the assembled Li / Garnet / LiFePO4 and Li-S all-solid-state batteries is reduced, the Coulomb efficiency and cycle stability are improved, and it has a broad application prospect. Through the use of solid electrolytes, the dendrite problem of lithium metal batteries and lithium sulfur batteries will be solved. The use of high specific capacity lithium metal as the anode will have considerable development and application in the future.

Figure 1. Schematic diagram of garnet-type LLZT and LLZT-C all-solid electrolyte lithium metal batteries. (10.1021 / jacs.8b03106)

Peter G. Bruce

Professor Bruce is a professor in the Department of Materials, Oxford University, a member of the Royal Academy of Sciences, a member of the Academy of Engineering, and a foreign member of the Royal Society of Chemistry. He has published more than 400 papers in the journal, with more than 55,100 citations and an H factor of 97.

The research directions of Professor Bruce‘s team mainly focus on lithium-air batteries, lithium-ion batteries, and sodium-ion batteries. In the field of cathode materials for lithium-ion batteries, Professor Bruce‘s research areas mainly involve the development of high-capacity cathode materials such as LINi x Mn 1-x O 2 , xLi 2 MnO 3 • (1-x) LiMO 2 and Li 2 FeSiO 4 and The study of its reaction mechanism.

Recently, Professor Bruce has made a huge breakthrough in the research of cathode materials for sodium ion batteries and published it in the Nature sub-journal. (Nature Chem., 2018, 10, 288–295) The article reports a P2 type Na 2/3 [Mg 0.28 Mn 0.72 ] O 2 layered sodium ion battery cathode material with a high ratio of nearly 170 mAh / g Capacity and discharge voltage of nearly 2.75V. And this high capacity comes from the stable structure of the material and the redox of elemental oxygen. When sodium ions are removed, the low content of sodium promotes the formation of an oxide layer with an O 2 structure. In addition, oxygen has a redox reaction in the process of charging and discharging, which additionally contributes to the capacity. At the same time , the introduction of Mg ²⁺ inhibits the loss of oxygen. This work provides a further understanding of the phenomenon of the additional capacity provided by the redox of oxygen in lithium and sodium battery cathode materials. In addition, it also provides materials designed from the structure and composition to achieve high capacity by inhibiting the loss of oxygen. New path of positive materials.

Figure 2. Schematic diagram of P2 type Na 2/3 [Mg 0.28 Mn 0.72 ] O 2 material. (Nature Chem., 2018, 10, 288–295)

Clare P. Grey

Clare P. Grey received his Ph.D. from Oxford University in 1991. He is currently a professor in the Department of Chemistry at Cambridge University, a member of the Royal Society, and an adjunct professor at the State University of New York at Stony Brook. Clare P. Grey has published more than 300 journal papers in world-class journals, with a total of 23,600 citations for published papers and an H factor of 78. At present, Professor Grey is the editorial board of internationally renowned journals such as the Journal of American Chemical Society, Joule, Accounts of Chemical Research, etc.

The main research work of Professor Grey‘s team is focused on the following directions: lithium-ion battery technology, sodium-ion battery technology, new-type lithium-air battery, magnesium-ion battery and solid-state electrolyte. In recent years, Professor Grey has conducted many researches on the characterization and simulation of materials in combination with the advantages of his own and advanced characterization technology in the cathode material of lithium ion batteries.

Figure 3 shows Professor Grey‘s latest achievements in studying spinel-structured lithium transition metal oxides (Chem. Mater. 2018, 30, 817−829). In the study of LiTi x Mn 2-x O 4 (0.2≤x≤1.5) materials, using NMR and other characterization techniques, combined with DFT theoretical calculations, the effect of different Ti doping on the structure of LTMO was studied. Through research, it is found that the presence of Ti doping makes the structure of the material change with the change of Ti content. At X = 0.2, Ti ⁴⁺ and Mn ^{3 + / 4 +} in LTMO are randomly distributed; at X = 0.4, they have an uneven lattice rich in Ti ⁴⁺ and Mn ⁴⁺ ; at x = 0.6 and At 0.8, a single-phase solid solution is formed; at x = 1, a combination of Li-Mn ²⁺ tetrahedron and Li-Mn ^{3 + / 4 +} -Ti octahedral configuration is presented. This work also provides a reference for studying the structural changes of other battery electrode materials.

Figure 3. The spatial distribution pattern of Al, Li, Ni, Co, O ions of LiNi 0.8 Co 0.15 Al 0.05 O 2 (Chem. Mater. 2018, 30, 817−829).

Cui Yi

Professor Cui Yi received his Ph.D. from Harvard University in 2002 and is currently a professor in the Department of Materials Science and Engineering at Stanford University. Professor Cui Yi has published more than 700 papers in world-class journals, and a total of 88 articles in the international top journal Nature and Science and their sub-journals. A total of 116,300 papers have been cited and the H factor is 160. He is currently the associate editor of the internationally renowned journal Nano letter and the editorial board of ACS applied energy material and other magazines.

The research of Professor Cui Yi‘s team is mainly focused on the silicon anode of lithium-ion batteries, and has achieved many outstanding results in the field of silicon anodes. At the same time, in recent years, many excellent results have been achieved in lithium metal anodes and lithium-sulfur batteries. Especially in the past three years, breakthrough progress has been made in the research of lithium metal anodes, and many articles have been published in science, Nature Nanotechnology, Nature Energy and other international top magazines.

Figure 4 shows the large-size silicon-lithium alloy-graphene flexible electrode recently studied by Professor Cui Yi (Nature Nanotech., 2017, 12, 993–999). The electrode is composed of active lithium-silicon alloy nanoparticles and is composed of large-size graphite The vinyl layer is evenly coated and has good air stability. This structure effectively suppresses the volume expansion effect caused by silicon alloying and inhibits the growth of lithium dendrites, making the electrode exhibit excellent cycle stability and an energy density of up to 500 Wh kg ^-1 . The developed lithium-silicon alloy negative electrode is expected to be paired with the sulfur positive electrode to form a high-energy density sulfur-silicon lithium alloy battery and be widely used.

Figure 4. Electrochemical properties of silicon-silicon alloy-graphene flexible electrodes. (Nature Nanotech., 2017, 12, 993–999)

Linda F. Nazar

Professor Linda Nazar obtained a doctorate degree from the University of Toronto in 1984. He is currently a professor in the Department of Chemistry, University of Waterloo, Canada, the country‘s chief scientist, and a member of the Royal Canadian Academy of Sciences. Professor Nazar has published more than 300 papers in well-known international magazines, and has cited more than 34,600 times in published papers, with an H factor of 89. He is currently the editorial board of internationally renowned journals Energy & Environment Science, ACS Central Science and other magazines.

Professor Nazar‘s research direction specializes in the field of lithium-sulfur batteries and lithium-air batteries. She is respected as "the queen of lithium-sulfur batteries." In recent years, the research direction of the team has simultaneously expanded to lithium anode protection and inorganic solid electrolytes and made breakthroughs. Figure 5 shows Professor Nazar‘s new strategy for lithium metal anode protection recently. (Joule, 2017, 1, 871-886) This work uses P 2 S 5 added to the electrolyte to generate a micron-level, high ionic conductivity and good stability of the solid electrolyte interface (SEI) in situ of lithium metal ). The SEI formed by this method closely adheres to the surface of the lithium metal, and remains stable during the reciprocating deposition and extraction of the lithium metal, thereby achieving a lithium metal anode with a long cycle life. In addition, the generated SEI is in close contact with the electrode and inhibits further reaction of the lithium metal with the electrolyte, while suppressing the formation of dendrites. When paired with Li 4 Ti 5 O 12 positive electrode material, the full battery achieved a cycle stability of more than four hundred cycles at a high current of 5C.

Figure 5. SEI formation process diagram, ion / electron transfer process diagram, and ion concentration, electric field strength, and potential change curve. (Joule, 2017, 1, 871-886)

summary

Combined with the current international research trends, the research of traditional lithium-ion battery materials has been basically perfected and industrialized. The hot research of silicon anodes, tin anodes and other cathode materials has also shifted from the initial stage to the application stage. The current research papers also pay more attention to the material load, cycle life and practicality. The current international research focus on lithium-ion batteries is mainly focused on the research and development of lithium metal anodes and all-solid electrolytes. The application of lithium metal anodes through the development of suitable lithium metal protection methods and the use of all-solid electrolytes to solve other battery problems (such as battery safety issues, the dissolution of polysulfides in lithium-sulfur batteries, etc.) will be future research And development direction. Commercial lithium-ion batteries have also transformed from traditional lithium cobalt oxide cathodes and graphite anodes to ternary cathodes and silicon-carbon anodes, with an expected energy density of 300 Wh / kg. Later, with the development of silicon anodes, batteries with high nickel anodes and silicon anodes will gradually appear and can achieve an energy density of 400 Wh / kg. It is expected that by 2030, with the rapid development of lithium metal protection and solid electrolyte technology, long-cycle lithium-sulfur batteries will be put into the lithium battery market and reach an energy density of 500 Wh / kg. The development of high energy density lithium ion batteries will significantly change the current energy storage system and greatly improve the storage capacity of electrochemical energy storage devices.

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