The key raw materials required for the production of lithium-ion batteries include cathode active materials, anode active materials, electrolytes, etc. Among these, the cost of the cathode active materials accounts for about 35% of the total cost, making it an extremely important component of lithium-ion batteries.
The most commonly used preparation process for lithium-ion battery cathode active materials is the high-temperature solid-state reaction.
The high-temperature solid-state reaction refers to the process in which solid reactants undergo a chemical reaction in the solid phase at a certain high temperature, ultimately forming structurally stable compounds. In solid-state reactions, the interaction forces between the reactants are very strong, resulting in a relatively slow reaction rate. However, this method can produce products with high purity and excellent crystal quality.
Even when using other preparation methods, a high-temperature solid-state reaction is still required. This is because the working principle of lithium batteries demands that the electrode materials be capable of repeatedly intercalating and deintercalating Li+, which requires the active materials to have high crystallinity and a well-ordered crystal structure. Achieving this under low-temperature conditions is very difficult. Therefore, the cathode active materials for lithium batteries are generally obtained through high-temperature solid-state reactions.
Various Cathode Active Materials & Production Processes
Mainstream lithium-ion battery cathode materials include ternary materials, lithium iron phosphate (LiFePO4), lithium cobalt oxide (LiCoO2), and lithium manganese oxide (LiMn2O4). Ternary materials and lithium iron phosphate outperform lithium cobalt oxide and lithium manganese oxide in terms of performance, lifespan, and safety. Ternary materials account for approximately 40% of usage, while lithium iron phosphate accounts for around 41%.
Lithium Iron Phosphate (LiFePO4)
Lithium iron phosphate (LiFePO4) is relatively inexpensive, environmentally friendly, and offers high safety performance and long cycle life. Its excellent high-temperature performance has led to widespread market adoption. However, its energy density is relatively low, and its performance at low temperatures is suboptimal.
Preparation Process: High-temperature Solid-state Reaction
The preparation of lithium iron phosphate (LiFePO4) can significantly affect its performance as a cathode material. Currently, the equipment investment for a lithium iron phosphate production line is approximately $137.4 per ton, though this amount may vary between manufacturers.
Advantages:
The solid-state reaction is a well-established preparation method. It features simple operation and process design, easy control of process parameters, stable material performance, and the capability for large-scale production.
Disadvantages:
The raw materials require long periods of grinding and mixing, and the mixing uniformity is limited. Consequently, the final product can exhibit significant variations in composition, structure, and particle size distribution.
Ternary Materials
Ternary materials refer to ternary polymers containing three metal elements: nickel, cobalt, and manganese (or aluminum). Nickel cobalt manganese ternary materials are abbreviated as NCM, while nickel cobalt aluminum ternary materials are abbreviated as NCA. The advantages of ternary materials include high energy density and excellent low-temperature performance. However, they are relatively costly and have a shorter cycle life. Among the mass-produced cathode active materials, ternary materials have the greatest potential.
The development trend for NCM ternary materials is towards higher nickel content. The energy density of ternary cathode materials can be continuously improved by increasing the nickel content, the upper limit of the charging voltage, and the compaction density. Ternary materials are produced using nickel cobalt manganese hydroxide, lithium carbonate, and other elements as raw materials. The production process includes batching, mixing, sintering, crushing, screening, and iron removal.
The equipment investment for a ternary materials production line is approximately $206 to $275 per ton, with higher investment required for high-nickel ternary materials.
High-nickel NCM Ternary Materials Production Process Vs. Conventional NCM Ternary Materials Production Process
Process Flow: The preparation of high-nickel ternary materials includes an additional washing step.
Raw Materials: Conventional ternary materials generally use lithium carbonate as the lithium source. High-nickel ternary materials, which require higher energy density and better charge-discharge performance, commonly use lithium hydroxide as the lithium source.
Production Environment: High-nickel ternary materials have higher humidity requirements and generally require dehumidification and ventilation equipment. In terms of magnetic control, high-nickel ternary materials also have stricter requirements, often necessitating specific modifications to factory facilities.
Key Equipment For Cathode Active Material Production
Metering & Dosing System
In processes such as raw material conveying, storage, batching, mixing, crushing, grinding, dust removal, and packaging, weighing and metering are used as detection and control methods.
Currently, the cathode material production line uses gravity-type loading weighers for the silo weighing system, mixer weighing system, batching scales, and automatic dosing scales. These systems include feeding devices, weighing and metering devices, display devices, and control devices, all featuring production capacity statistics and communication functions. The central control system integrates these components into a closed-loop automatic control system.
Mixing Equipment
To improve the rate of high-temperature solid-phase reactions and the uniformity of material structures, uniform mixing of materials is a necessary condition. Material mixing can be categorized into wet mixing and dry mixing. Wet mixing primarily requires equipment such as attritor ball mills and sand mills. Dry Mixing primarily requires equipment such as high-speed mixers and high-efficiency circulating mixers.
Drying Equipment
When wet mixing is used in the production of lithium battery cathode materials, drying issues are often encountered. The drying process and equipment used vary depending on the solvent used for wet mixing. The main solvents for wet mixing are non-aqueous solvents such as ethanol and acetone, and aqueous solvents. The main drying equipment required for the production line includes vacuum rotary dryers, vacuum rake dryers, spray dryers, and vacuum belt dryers.
Sintering Kiln
The core equipment in the production line of lithium battery cathode materials is the sintering kiln. After raw materials are uniformly mixed and dried, they are loaded into the kiln for sintering. The temperature, temperature uniformity, atmosphere, atmosphere uniformity, production capacity, energy consumption, and automation level of the kiln directly affect the production quality. Currently, the main sintering equipment used for cathode material production includes pusher kilns, roller hearth kilns, and rotary kilns.
Roller Hearth Kiln: It is a type of medium-sized tunnel kiln that allows for continuous heating. Depending on the atmosphere inside the kiln, it can be classified as an air kiln or an atmosphere kiln.
Pusher Kiln: It is a type of large sintering kiln capable of continuous heating. It offers stable processes, high output, and good cost-effectiveness, but it has poor temperature and atmosphere distribution uniformity and high pushing resistance. It can be classified as an air kiln or an atmosphere kiln.
Rotary Kiln: A cathode material rotary kiln is a large sintering kiln capable of continuous heating. It offers high output, advanced technology, uniform temperature and atmosphere distribution, energy efficiency, and reduced consumption, making it the preferred equipment choice currently.
Air Kiln: It is mainly used for sintering materials like lithium manganese oxide, lithium cobalt oxide, ternary materials, and other materials that require an oxidizing atmosphere.
Atmosphere Kiln: It is primarily used for sintering materials such as NCA ternary materials, lithium iron phosphate (LFP) materials, graphite anode materials, and other materials that require a specific atmosphere (such as N2 or O2 gas protection).
Crushing & Grading Equipment
Semi-finished products after high-temperature sintering generally need to undergo crushing and grading processes to meet product standards. Different cathode active materials require different sintering temperatures, necessitating various levels of crushing. The main equipment involved includes jaw crushers, roller crushers, rotary mills, high-speed impact crushers, and air jet mills.
Batching Equipment
In the production process of lithium battery cathode materials, to ensure consistent product quality, it is necessary to batch different batches of products to achieve uniform mixing. Common large-scale mixing equipment includes double screw cone mixers and horizontal ribbon mixers.
Magnetic Separation Equipment
Due to the highly uneven and random distribution of trace elemental iron in cathode materials, it is essential to include an iron removal process before the final packaging step to ensure product quality.
Packaging Equipment
To prevent contamination from external sources, finished products should be bagged and sealed promptly after production. They are usually packed in barrels or boxes with proper labeling. Common equipment includes automatic bagging machines, heat sealers, labeling machines, automatic palletizers, and automatic wrapping machines.
