I. Introduction to Ternary Cathode Materials
Currently, LiNi1/3Co1/3Mn1/3O2 ternary composite cathode materials with equal molar ratios of manganese, cobalt, and nickel have attracted widespread attention.
Because LiNi1/3Co1/3Mn1/3O2 has high specific capacity, good cycle performance, and good thermal stability, and because manganese and nickel are cheaper than cobalt, it can significantly reduce material costs, making it an ideal cathode material for lithium-ion batteries. The term "nickel-cobalt-manganese ternary material" is somewhat related to lithium nickel oxide, lithium cobalt oxide, and lithium manganese oxide; strictly speaking, this understanding is incorrect, but considering the performance of ternary materials, it is not entirely unreasonable.
1. Compared with lithium nickelate, ternary materials have a lower energy density, but their stability is greatly improved.
2. Compared with lithium cobalt oxide, ternary materials have a slightly lower platform and a lower level of material maturity, but they have higher safety and cycle life, especially the feasibility of high charging voltage.
3. Compared with lithium manganese oxide, ternary lithium oxide has a lower safety profile, but it has significant advantages in high-temperature performance and energy density.
Currently, ternary lithium batteries in China are generally used to partially replace lithium cobalt oxide in various applications. They are used in combination with lithium manganese oxide or lithium cobalt oxide in low- to mid-range consumer electronics, and in combination with lithium manganese oxide in the low- to mid-range power vehicle market.
II. Technological Development Direction of Ternary Cathode Materials
Ternary materials are materials with superior overall performance, and only a performance-oriented market can truly realize their advantages as a novel cathode material. In electronic products, in addition to their inherent cost advantages, the energy density of ternary materials can be continuously improved by increasing the nickel content, raising the upper limit of charging voltage, and increasing the compaction density.
1. Ternary materials with increased nickel content have very similar properties to nickel-cobalt-aluminum materials, and their development could follow the same model. However, due to limitations in process control in China, nickel-cobalt-aluminum materials have not been developed well. Against this backdrop, high-nickel ternary materials also face difficulties in achieving significant development.
2. Increasing charging voltage is an important development path for ternary materials, and many forward-thinking domestic companies are currently developing this technology. Frankly speaking, compared to lithium cobalt oxide, ternary materials have significant advantages at high voltages. From the material's perspective, even at a charging voltage of 4.5V in a full cell, the material can maintain good stability without modification. Moreover, under these conditions, the specific capacity of ternary materials can exceed 190 kcal/v, making its prospects very promising. However, due to the significant gap in maturity between ternary battery systems and lithium cobalt oxide, the advantages of ternary materials over lithium cobalt oxide are not obvious in the development of high-voltage systems at 4.3V or 4.35V, especially compared to doped lithium cobalt oxide. Consequently, some manufacturers have only scratched the surface, while those who truly understand the advantages of ternary materials have never stopped pursuing this approach.
3. Improve compaction density. The specific capacity of conventional ternary materials is about 105% of that of lithium cobalt oxide, while that of lithium cobalt oxide is about 115%. However, the compaction density is only about 80% of that of lithium cobalt oxide. In general, the field of high-performance lithium cobalt oxide focuses on high energy density with stability as a prerequisite. Although the stability of ternary materials is better than that of lithium cobalt oxide, there is a significant gap in their energy density. From this, we can see the importance of improving the compaction density of ternary materials.
III. Common Preparation Methods of Ternary Materials
The main preparation methods for ternary materials can be broadly categorized into solid-state methods and solution methods. Solid-state methods include high-temperature solid-state methods and acetate combustion methods. Solution methods mainly include sol-gel methods, co-precipitation methods, and spray pyrolysis methods. Different synthesis methods have a significant impact on the properties of the prepared ternary materials. Below is a brief introduction to several common preparation methods:
Sol-gel method
The sol-gel method is an advanced soft chemical approach for synthesizing ultrafine particles. It is widely used in the synthesis of various ceramic powders, coatings, films, fibers, and other products. This method involves uniformly mixing low-viscosity precursors to form a homogeneous sol, which is then gelled. After gelation or during the gelation process, the mixture is shaped, dried, and then sintered or calcined.
Compared with traditional high-temperature solid-state reaction methods, materials synthesized by the sol-gel method have the following advantages:
1. The raw materials can achieve atomic-level homogeneous mixing, resulting in good chemical homogeneity, high purity, and precise control of stoichiometry. 2. Heat treatment temperature and time can be significantly reduced, making it suitable for synthesizing thin and nanoparticle films. 3. By controlling the sol-gel process parameters, it is possible to precisely tailor the material structure. 4. Furthermore, the sol-gel technology requires simple processes and is easy to control. However, the synthesis cycle is relatively long, making industrial-scale production challenging.
coprecipitation method
The coprecipitation method generally involves mixing chemical raw materials in a solution state and adding an appropriate precipitant to the solution, so that the components that have been mixed evenly in the solution are coprecipitated in stoichiometric proportions. Alternatively, an intermediate product may be precipitated in the solution first, and then calcined and decomposed to prepare a fine powder product.
Traditional solid-phase synthesis techniques make it difficult to achieve stoichiometric mixing of materials at the molecular or atomic level. However, co-precipitation methods can often solve this problem, thereby achieving the goal of preparing high-quality materials at a lower production cost.
Liquid-phase coprecipitation has the following four characteristics:
1. The process equipment is simple, and synthesis and refinement can be completed in one step during precipitation, which is conducive to industrial production; 2. The content of each component can be controlled more precisely, so that different components can achieve uniform mixing at the molecular/atomic level; 3. During the precipitation process, the purity, particle size, dispersibility and phase composition of the obtained powder can be controlled by controlling the precipitation conditions and the degree of calcination of the precipitate in the next step; 4. Compared with the high temperature solid phase method, its sample calcination temperature is lower, the performance is stable and the reproducibility is good.
High-temperature solid-state method
High-temperature solid-state reaction, where reactants undergo only a solid-state reaction, is a commonly used method for synthesizing powder materials and is also a relatively common method for preparing cathode materials. To ensure the synthesized material has ideal electrochemical performance and meets the stability requirements of the Li+ intercalation/deintercalation structure, it is essential to guarantee good crystallinity. Therefore, high-temperature solid-state reaction is a commonly used method for synthesizing powder materials and is also a relatively common method for preparing cathode materials.
hydrothermal method
Hydrothermal synthesis is a method of chemical synthesis carried out in a supersaturated aqueous solution under high temperature and pressure. It belongs to the category of wet chemical synthesis. Powders synthesized using hydrothermal methods generally have high crystallinity, and by optimizing the synthesis conditions, they can be made completely free of water of crystallization. Moreover, the size, uniformity, shape, and composition of the powder can be strictly controlled. Hydrothermal synthesis eliminates the calcination step, and thus also eliminates the grinding step, resulting in high powder purity and a reduced density of crystal defects.
summary
Combining the advantages of LiCoO2, LiNiO2, and LiMnO2, ternary cathode materials outperform any single-component cathode material, exhibiting a significant synergistic effect and are considered the most promising new cathode materials. Currently, research on nickel-cobalt-manganese ternary cathode materials mainly focuses on their synthesis and the relationship between electrochemical performance and structure.
In practical batteries, the physical properties of cathode material particles, such as morphology, particle size distribution, specific surface area, and tap density, have a significant impact on the processing performance of the material and the overall electrical performance of the battery. In order to broaden the application range of lithium-ion batteries, especially the application of ternary materials in power batteries with stringent requirements for safety, cycle performance, and rate capability, the preparation of high-density, uniformly distributed spherical ternary materials has become a research hotspot. The key to the large-scale application of ternary materials is to improve their tap density while ensuring their electrochemical performance.
