Lithium-ion ternary cathode materials: The key force in the era of new energy

In the context of the global efforts to promote the green energy transition, lithium-ion batteries, as an efficient and convenient energy storage device, are widely applied in various fields such as electric vehicles, portable electronic devices, and energy storage systems. Among the numerous components of lithium-ion batteries, the cathode material plays a decisive role in the energy density, cycle life, and safety performance of the battery. Lithium-ion ternary cathode materials, with their unique advantages, have become the mainstream choice for the cathode materials of high-energy-density lithium-ion batteries at present.

I. Overview of Tri-Component Cathode Materials

Tri-component cathode materials typically refer to lithium nickel cobalt manganese oxide (LiNixCoyMnzO2, NCM) or lithium nickel cobalt aluminum oxide (LiNiCoAlO2, NCA), in which the three transition metal elements - nickel (Ni), cobalt (Co), manganese (Mn), or aluminum (Al) - form the core part of the material. By ingeniously adjusting the proportions of these three elements, the performance of the material can be optimized to meet the requirements of different application scenarios.

The nickel element plays a crucial role in enhancing the energy density of the tri-component material. As the nickel content increases, the specific capacity of the battery is significantly improved, thereby providing longer driving ranges for electric vehicles. For example, in the high-nickel tri-component material system, such as NCM811 (with a nickel cobalt manganese ratio of 8:1:1), the higher nickel content enables the battery to store more energy, effectively improving the practicality of electric vehicles.

The cobalt element is mainly used to stabilize the layered structure of the material and can significantly improve the cycle performance and rate performance of the material. This means that the battery can be more stable during charging and discharging, and can achieve faster charging speed and longer service life. However, cobalt is a rare and expensive metal, and its high cost limits the large-scale application of tri-component materials to a certain extent. Moreover, an excessively high cobalt content may lead to a decrease in actual capacity.

Manganese or aluminum elements in tri-component materials mainly play the role of improving the safety and structural stability of the battery, while also reducing the cost of the material. Taking manganese as an example, it has good electrochemical inertness and can keep the material in a stable structure during charging and discharging, thereby enhancing the safety of the battery.

II. Development History Review

In 1970, M.S. Whittingham of Exxon Corporation produced the first lithium battery, marking the beginning of the development of lithium-ion batteries. In 1992, Sony successfully developed commercial lithium-ion batteries, and since then, battery technology has continued to evolve. Between 1997 and 2000, lithium-ion batteries with ternary materials such as nickel-cobalt-manganese and nickel-cobalt-aluminum were successively introduced, but initially, their market share was far less than that of lithium iron phosphate batteries.

Initially, the mainstream route of Chinese power batteries was lithium iron phosphate, with less application of manganese oxide lithium and ternary materials. In 2007, BYD released lithium iron phosphate batteries and entered the field of new energy vehicles, dominating the Chinese new energy vehicle market in the following years. However, with the rapid expansion of the new energy vehicle market, especially as electric vehicles expanded from the high-safety-demand and low-range-demand commercial vehicle sector to the passenger vehicle sector, the drawback of low energy density of lithium iron phosphate batteries gradually became apparent.

In 2013, Tesla achieved profitability in the first quarter, and the ternary lithium-ion batteries it adopted demonstrated significant advantages, highlighting the strengths of ternary materials in terms of energy density. At the Beijing Auto Show in 2014, many automakers announced the use of ternary materials in new models. In 2016, China included battery system energy density in the subsidy standards for new energy vehicles, and high energy density and long range became key assessment items for automakers to obtain subsidies, which further promoted the development of ternary lithium-ion batteries. In 2018, the overall installed capacity of ternary lithium-ion batteries surpassed that of lithium iron phosphate batteries for the first time, and CATL, with its ternary lithium-ion batteries, occupied an important position in the power battery field.

III. Performance Characteristics Analysis

(1) High Energy Density

Compared with lithium iron phosphate materials, ternary materials have higher discharge specific capacity and average voltage, which makes the specific energy of ternary batteries significantly higher. For example, Compaction density of the electrode sheet of lithium iron phosphate material is approximately 2.3 - 2.4 g/cm³， while that of the ternary electrode sheet can reach 3.3 - 3.5 g/cm³. Therefore， the volume specific energy of ternary materials and batteries is much higher than that of lithium iron phosphate. Higher energy density means that in the same weight or volume， ternary lithium batteries can store more energy， providing longer running support for equipment. This directly translates to longer driving range for electric vehicles， effectively alleviating users' range anxiety.

(2) Good Power Performance

The activation energy of Li⁺ in lithium iron phosphate materials is relatively high， resulting in a Li⁺ diffusion coefficient in the range of 10-15 - 10-12cm2/s. The extremely low electronic conductivity and lithium ion diffusion coefficient make the power performance of lithium iron phosphate materials poor. However， the Li⁺ diffusion coefficient of ternary materials is approximately 10-15 - 10-12cm2/s， and the electronic conductivity is high， so ternary batteries can achieve faster current transmission during charging and discharging， and have better power performance. This means that ternary lithium batteries can provide a larger current in a short time， meeting the high-power demand scenarios of equipment during startup and acceleration， providing more powerful performance for electric vehicles.

(3) Higher Temperature Compatibility

Due to the lower electronic conductivity and ionic conductivity of lithium iron phosphate materials， the low-temperature performance of lithium iron phosphate batteries is poor. When discharging at -20℃， its capacity retention rate is only about 60% of that at normal temperature， while the corresponding ternary battery can reach over 70%. Ternary lithium batteries can still maintain a relatively high capacity output in low-temperature environments， which gives them a significant advantage in cold regions. Whether it is the starting performance of electric vehicles in winter or the normal operation of other electronic devices in low-temperature environments， ternary lithium batteries can provide more reliable power support.

(4) Safety Challenges

However， ternary lithium batteries are not perfect either. From the perspective of safety， the PO₄ bond energy in the main structure of lithium iron phosphate materials is much higher than the M - O bond energy of the MO₆ octahedron in ternary materials. The thermal decomposition temperature of fully charged lithium iron phosphate materials can reach about 700℃， while the corresponding thermal decomposition temperature of ternary materials is only 200 - 300℃. This makes lithium iron phosphate materials have a more advantageous high-temperature stability. At the battery level， lithium iron phosphate batteries can pass all safety tests， while ternary batteries face challenges in puncture and overcharge tests， requiring improvements in structural components and battery design to enhance their safety.

(5) Cost and Environmental Factors

Ternary materials contain scarce metals such as nickel and cobalt， making their cost relatively higher. With the continuous progress of materials and battery technologies， the costs of both ternary and lithium iron phosphate batteries have decreased. However， currently， the market price of ternary batteries is approximately 1.1 yuan / Wh， while lithium iron phosphate batteries are relatively cheaper， about 0.9 yuan / Wh. Additionally， the nickel and cobalt elements in ternary materials and batteries have a greater environmental impact. In contrast， lithium iron phosphate batteries contain iron and phosphorus elements， which have a smaller environmental impact. In today's era of increasingly strict environmental requirements， ternary lithium batteries face greater pressure in recycling and reducing environmental impact.

Ⅳ.Research Progress and Future Prospects

Currently, the research on ternary cathode materials mainly focuses on enhancing their safety, stability, and reducing costs. Researchers are optimizing the material properties through various means, such as using advanced synthesis processes, such as sol-gel method and co-precipitation method, to improve the purity and consistency of the materials; by applying surface coating and ion doping technologies, to improve the surface properties and structural stability of the materials, thereby enhancing the safety and cycle life of the batteries.

In terms of improving safety, researchers are dedicated to developing new electrolyte additives and separator materials to enhance the thermal stability of the battery and prevent short circuits. At the same time, by optimizing the battery management system, real-time monitoring of the battery's state, and timely measures to avoid unsafe situations such as overcharging and overdischarging, the safety and cycle life of the battery are improved.