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What is the role of the lithium hydroxide and lithium carbonate, and which one is better for our battery-powered future?

The cathode materials commonly used in LIBs (e.g., LiFePO4 called LFP, or LiNiMnCoO2 – called NMC) are produced from lithium salt and other metal salt precursors using chemical processes. The lower energy density materials (or LFP) typically use lithium carbonate (Li2CO3) as one of their precursor chemicals. NMC materials, on the other hand, have higher energy density and are the preferred materials in many sectors such as the automotive industry. The lithium precursor for these materials is generally lithium hydroxide (LiOH). For this reason, demand for lithium hydroxide is now rapidly growing worldwide. In summary, efficient, low cost, and sustainable supplies of lithium hydroxide ensure cost effective and improved batteries for a global market.

Lithium hydroxide monohydrate is a highly corrosive white crystalline powder. Traditionally used in lithium-based lubricating greases, glass ceramics, and petrochemicals, its primary application areas have expanded to battery materials driven by the increasing global demand for high-nickel batteries. Its low melting point and other characteristics make lithium hydroxide an optimal choice for sintering positive electrode materials, resulting in superior electrochemical performance. It is also a necessary choice for NCM materials above series 8 and NCA materials that require low-temperature sintering.

Battery-grade lithium hydroxide is the inevitable choice for high-nickel ternary materials. Lithium hydroxide monohydrate has a lithium content lower than lithium carbonate (1 kg of lithium hydroxide monohydrate is equivalent to only about 0.88 kg of lithium carbonate). Nevertheless, lithium hydroxide remains the inevitable choice for high-nickel ternary materials such as NCM 811 and NCA, mainly for the following reasons.

On one hand, high-nickel ternary materials require sintering temperatures not to be too high, as it affects rate capability. Preparing high-nickel ternary materials requires moderate sintering temperatures, with NCM 811 requiring sintering temperatures to be controlled below 800°C and NCM 90505 requiring temperatures around 740°C. An increase in sintering temperature leads to higher material crystallinity, larger grain size, and smaller specific surface area, which are unfavorable for lithium ion intercalation and deintercalation during charge and discharge processes. Additionally, excessively high temperatures can lead to lithium-nickel co-segregation, making it difficult to sinter high-nickel layered materials with the required stoichiometry, resulting in decreased lithium ion diffusion capability and specific capacity. Moreover, if the temperature is too high, Ni3+ will revert back to Ni2+, thereby impairing cycling performance.

On the other hand, lithium hydroxide has a significantly lower melting point compared to lithium carbonate, which can reduce sintering temperature and optimize electrochemical performance. The melting point of lithium carbonate is 720°C, whereas that of lithium hydroxide monohydrate is only 471°C. During the sintering process, molten lithium hydroxide can mix more uniformly and thoroughly with ternary precursors, thereby reducing residual lithium on the surface and improving discharge specific capacity of the material. The use of lithium hydroxide and lower sintering temperatures can also reduce cation mixing, enhancing cycling stability. In contrast, lithium carbonate often requires sintering temperatures of over 900°C to obtain stable material performance, making it unsuitable as a lithium source for high-nickel ternary materials.

Unlike high-nickel ternary materials, middle and low nickel ternary materials such as NCM 523 and NCM 333 have higher sintering temperatures. To reduce raw material costs, battery-grade lithium carbonate is mainly used as the lithium source. NCM 622 can use either lithium carbonate or lithium hydroxide, but lithium hydroxide can bring about more ideal electrochemical performance, hence being the preferred choice for overseas cathode material manufacturers.

Producing high-quality lithium hydroxide requires not only high-quality and stable upstream resources but also expertise in lithium chemical processes. In the future, there will be higher demands for automation in production lines.

Ore can be directly used to produce battery-grade lithium hydroxide, while mature processes in salt lakes typically involve producing lithium carbonate first, followed by hydroxide production through causticization. Direct production of lithium hydroxide through brine electrolysis is still awaiting commercial validation. Microfine lithium hydroxide is preferred by downstream high-nickel customers.

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