Upstream of positive electrode materials for lithium batteries: lithium extraction process



Upstream of positive electrode materials for lithium batteries: lithium extraction process


Classification of positive electrode materials for lithium batteries

Lithium batteries are classified according to the positive electrode material system, generally including lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium iron phosphate (LFP), as well as ternary materials represented by nickel cobalt manganese oxide (NCM) and nickel cobalt aluminum oxide (NCA).

Lithium cobalt oxide has high working voltage, high compaction density, and good electrochemical performance, and is mainly used in the 3C field. However, the global reserves of raw material cobalt are very limited, and the high price of cobalt leads to high battery costs; Lithium manganese oxide has a low energy density and short cycle life, and is mainly used in the fields of small power and new energy special vehicles. Lithium iron phosphate and ternary materials are currently the mainstream positive electrode materials used in power batteries. Among them, ternary batteries have higher specific capacity than lithium iron phosphate batteries, but their safety and stability are not as good as lithium iron phosphate batteries.


Sources of Lithium Carbonate - Comparison of Three Major Processes

The research on the positive electrode industry of lithium batteries naturally relies on the core material lithium carbonate. From upstream lithium mines to the lithium carbonate used in batteries, there are generally three mainstream processes: spodumene lithium extraction, lithium mica lithium extraction, and brine lithium extraction. Each of these three methods has its own advantages and disadvantages, as shown in the table below. According to statistics, the total production of lithium carbonate in China in 2022 was 350100 tons, including 170000 tons of battery grade lithium carbonate, accounting for 49%, and 180000 tons of industrial grade lithium carbonate, accounting for 51%. From the perspective of raw materials, the salt lake produces 70100 tons of lithium carbonate, accounting for 20.02%; Spodumene produces 128000 tons of lithium carbonate, accounting for 36.56%; Lithium mica produces 103100 tons of lithium carbonate, accounting for 29.43%; 48400 tons of lithium carbonate were recovered from waste, accounting for 13.82%.


The main processes for extracting lithium from salt lakes

The magnesium lithium ratio in domestic salt lakes is generally high, and various lithium extraction technologies are developed according to local conditions; The low magnesium lithium ratio precipitation method is mainly used in South American salt lakes; One lake, one strategy, different lake areas choose different routes based on different situations.

In addition to Zabuye Salt Lake in Xizang, the ratio of magnesium to lithium in salt lakes is generally high in China, and selective extraction methods such as ion exchange adsorption and membrane separation are needed to better realize the separation of magnesium and lithium and the enrichment of lithium ions.

At present, lithium extraction from salt lakes in China mainly adopts several technical routes, including ion exchange adsorption, solvent extraction, membrane separation, calcination leaching, solar cell method, and electrochemical method.

The ion exchange adsorption method and membrane separation method have lower environmental protection costs, and the use of adsorbents, nanofiltration membranes, or electrodialysis membranes can selectively enrich lithium ions, which is superior. However, there are also bottlenecks in improving the performance of adsorbents and nanofiltration membranes, high energy consumption of electrodialysis membranes, and high maintenance costs for dismantling and washing membranes. The future development direction is mainly the research and development of high-performance adsorption and separation materials and the simplification of process flows. The inherent advantage of low magnesium lithium ratio in South American salt lakes determines that the process flow mainly relies on precipitation method.

The principle of precipitation method is to use solar energy and wind energy to naturally evaporate and concentrate salt lake brine. After removing impurities such as boron, calcium, and magnesium, a mixed precipitant or salt precipitation agent is added to the mother liquor to separate lithium in the form of precipitate. The process involves adding compounds multiple times for chemical reactions, and then filtering to obtain lithium products.

According to the different reagents added, precipitation methods can be divided into carbonate precipitation method, aluminate precipitation method, boron magnesium and boron lithium co precipitation method, etc. Among them, the mature commercial method is mainly carbonate precipitation method, and its key reagents are lime (calcium hydroxide) and pure alkali (sodium carbonate). The former can separate magnesium ions, while the latter can precipitate lithium ions in the form of lithium carbonate.

The advantages of this process are simple matching, low resource consumption, and low cost. The disadvantage is that the required brine has excellent quality, with good sunlight and wind, otherwise it is difficult to achieve the expected quality. In addition, there are also disadvantages such as long production cycles (taking 12-18 months), poor production capacity elasticity, and difficulty in extracting lithium at once. The majority of eligible salt lakes are located in the South American Triangle. Xizang Mining is the main enterprise of domestic precipitation of lithium in France, and its lithium resource endowment of Zabuye Salt Lake is not inferior to that of the South American Triangle.

The adsorption method uses porous solid adsorbents with strong adsorption capacity to selectively adsorb lithium on the solid surface, thereby achieving the separation of different components in the liquid mixture. Then, the lithium ions are washed off with an eluent to form a lithium ion solution, which is then precipitated to form lithium carbonate after adding sodium carbonate.