If divided according to the cathode material system, lithium batteries can be divided into lithium cobalt oxide, lithium manganate, lithium iron phosphate, ternary materials, LRMO (lithium-rich manganese-based oxides) cathode material and other technical routes. As the safety of batteries becomes the focus of public attention, lithium battery cathode materials, driven by safety concerns, are going through the fourth stage, namely medium-nickel or low-nickel cobalt-free materials. Such materials are mainly represented by high-performance lithium iron phosphate and high specific capacity LRMO cathode material. As a new development trend, new LRMO cathode material may continue to break through.
1. LRMO cathode material industry overview
At present, the energy density of commercial power lithium batteries is generally around 150Wh/kg. In order to double the cruising range of new energy vehicles corresponding to car battery voltage and meet the needs of the market and consumers, the energy density of power lithium-ion batteries must be doubled to 300-400Wh/kg. From a technical point of view, the use of cathode (anode) materials with higher specific capacity is the most direct and effective way to improve the energy density of batteries.
Among the known cathode materials, the discharge specific capacity of LRMO cathode material is as high as 300mAh/g, which is about twice the discharge specific capacity of the currently commercialized cathode materials such as lithium iron phosphate and ternary materials. From the perspective of materials, due to the use of a large amount of manganese in the material, the use of precious metals such as cobalt and nickel is reduced. Therefore, compared with ternary materials, LRMO cathode material also has the advantages of lower price, better safety, and environmental friendliness.
Therefore, LRMO cathode material is considered by academia and business circles to be the most promising and competitive cathode material for next-generation high-energy-density power lithium batteries. The commercial application of LRMO cathode material still needs to solve several key technical problems:
- One is to reduce the first irreversible capacity loss;
- The second is to improve the rate performance and cycle life;
- The third is to suppress the voltage decay during the cycle.
Therefore, the LRMO cathode material has not yet reached the stage of industrial application. In order to promote the industrial application process of LRMO cathode material, the academic community has made improvements from the following aspects:
- Optimize and modify the LRMO cathode material, such as surface coating, element doping, surface delithiation treatment, crystal structure regulation, etc.;
- Cooperate with upstream and downstream enterprises to develop matching high-voltage electrolytes, binders and stable silicon-carbon composite anodes and other materials, and at the same time strengthen market cultivation.
2. Development status of LRMO cathode material industry
Internationally, the R&D priorities and applications of several research institutes and enterprises that have laid out earlier in LRMO cathode material are as follows: South Korea LG in lithium battery companies in the world has a relatively balanced layout in each technical branch of LRMO cathode material. The R&D focus is mainly on doping modification and application in lithium-ion batteries, and there is also a small amount of coverage in material preparation and coating modification. South Korea's Samsung started late in the patent layout of various technical branches of LRMO cathode material, and its research and development focused on doping modification and application in lithium-ion batteries.
China's LRMO cathode material technology research began at the beginning of this century. In recent years, it has been strengthened, mainly focusing on material preparation and modification of cathodes. There is no layout of the whole industry chain. At present, there are many universities in China involved in LRMO material research and production.
Although there are currently many teams and companies in China whose LRMO cathode material has a specific capacity of 300mAh/g, the vacancy method is often used, and the vacancy will migrate during the reaction, and its reversible performance is not stable. In the past ten years, the expert team has been devoted to the research and development of LRMO cathode material, and has carried out research on key scientific issues such as reducing the first irreversible capacity of LRMO cathode material, voltage decay and oxygen evolution during cycling, and obtained a series of research results.
3. Future development trend of LRMO cathode material industry
Combining multiple advantages such as high voltage, high specific capacity, low cost, and strong safety, LRMO cathode material is considered to be one of the important technical routes in the mid-term development of lithium batteries. However, due to the structural defects of the material itself and the slow development of upstream supporting materials, the LRMO cathode material has been in the laboratory state for a long time. In the future, for LRMO cathode material to truly realize industrial application, it is still necessary to continue in-depth research in the following aspects:
● The structure, electrochemical reaction mechanism and failure mechanism of lithium-rich materials are not yet fully understood. Advanced characterization methods are needed to reveal the structural evolution of materials during synthesis and cycling. The structure-activity relationship between the microstructure and electrochemical performance of the material needs to be further and systematically studied.
● At present, there are many studies on LRMO cathode material in half cells, that is, by simulating the battery principle, examining factors such as electrode material, specific capacity, impedance, etc., and obtaining objective reference values, most of which belong to the laboratory stage. The factors that need to be considered when applying materials to a full battery are more comprehensive, including the ratio of cathode and anode materials, the thickness of the pole pieces, and other factors that may affect the capacity and performance of the battery.
Finally, it is necessary to continuously improve according to the feedback problems in actual use. Therefore, it is still necessary to strengthen the research and application of LRMO cathode material in full cells, and at the same time, it is also necessary to develop low-cost and high-efficiency modification preparation technology to achieve large-scale commercial preparation of materials.
● LRMO cathode material is sensitive to temperature. Especially at ultra-low temperature, the discharge specific capacity of the material decreases seriously. Therefore, it is still necessary to focus on the charge-discharge mechanism and performance improvement of lithium-rich manganese-based materials at low temperature.
● In order to promote the application of LRMO cathode material, it is necessary to coordinate the development of new high-voltage electrolytes, binders and stable silicon-carbon composite anode materials. The research and development of this material also plays a key role in the successful application of LRMO cathode material.
● High-capacity lithium-rich material technology under low voltage conditions is the direction of technological development. This material can achieve low charging voltage and high discharging voltage, thereby reducing the requirements for electrolyte, thereby increasing the number of cycles of the battery. Correspondingly, the energy density of lithium-rich manganese-based batteries can reach 400kWh/kg, and the corresponding volume energy density can compete with lithium cobalt oxide (the material system with the best volume energy density at present).
4. Market competition analysis of LRMO cathode material industry
In the relevant policies for the development of the power battery industry, it is proposed that by 2020, the specific energy of the new lithium-ion power battery will exceed 300Wh/kg, and the cost should be reduced to less than 1 RMB/Wh. By 2025, the specific energy of the new system power battery cell will reach 500Wh/kg.
Industry insiders generally believe that in the short term, the use of high-nickel ternary cathodes and silicon carbon anodes for power batteries to achieve a specific energy of 300Wh/kg has become an industry consensus, and substantial progress has been made. In the medium term, in order to achieve a specific energy of more than 300Wh/kg, LRMO cathode material with high-capacity silicon carbon anode is also one of the key directions for future exploration.
5. LRMO cathode material industry technical analysis
① Process route and material preparation
There are many synthesis methods for LRMO cathode material. At present, the common ones are co-precipitation method, sol-gel method, high temperature solid phase method and so on. In view of the practicality of the method and the stability of the properties of the synthesized materials, the co-precipitation method is usually adopted.
② Current status of technical route
Although LRMO cathode material has many advantages such as low price, good safety, and environmental friendliness, the material failure mechanism determined by its structure and electrochemical properties has also formed an important technical factor restricting the industrialization of lithium-rich manganese-based materials. The failure mechanisms widely recognized by researchers mainly include the following three types:
- Precipitation of lattice oxygen: lead to irreversible capacity loss of the electrode, deterioration of charge-discharge rate and cycle performance
- Migration of transition metal ions: leading to capacity/voltage decay of Li-rich manganese-based electrodes
- Interfacial side reactions: lead to the deterioration of the cycling and rate performance of the cathode
Faced with the challenges of the above failure mechanisms, researchers have developed a variety of modification and preparation methods to overcome the failure mechanism obstacles to a certain extent. Common treatment methods of modified materials include surface coating, ion doping, crystal structure adjustment, etc., which effectively improve the comprehensive electrochemical performance of materials. Based on the more complex and active crystal structure of LRMO cathode material, there is still a long way to go to realize industrial production and application only by the traditional material modification process, and more breakthroughs in new technologies and processes are urgently needed.
In recent years, the lithium-rich manganese-based oxides cathode material, which has received high attention from the academic and commercial circles, as a new type of cathode material with significant advantages such as high working voltage, high specific capacity, and low cost, has been upgraded through preparation and application technology. In the future, it is expected to help the lithium battery industry reach the energy density target planned by China, and promote the overall entry of China's power battery industry into the era of high energy density. Therefore, LRMO cathode material is regarded as one of the most potential and promising lithium ion battery cathode materials in the new generation, and it is worthy of in-depth research and discussion.