Which one is better for NMC, NCA and LFP battery, lithium carbonate or lithium hydroxide?
| Jerry Huang
As global EV, HEV, PHEV markets & energy storage markets continue to grow, the lithium ion battery industry is driven to boom as well, which consume big volume of lithium carbonate and lithium hydroxide today. But which one is better for NMC/NCA ternary lithium battery and LFP battery, lithium carbonate or lithium hydroxide? Let's take a look at some comparisons between these two lithium salts and their performance in battery production process.
Comparison on Stability- The Nickel Manganese Cobalt (NMC) cathode material prepared with lithium carbonate has a specific discharge capacity of 165mAh/g, with a capacity retention rate of 86% at 400th cycle, while battery materials prepared with lithium hydroxide has a specific discharge capacity of 171mAh/g, with a capacity retention rate of 91% high at 400th cycle. As the cycle life increases, the full life-circle curve is smoother, and the charge and discharge performance is stabler with the material processed from lithium hydroxide than those processed from lithium carbonate. In addition, the latter one has a rapid capacity fade after about 350 cycles. Producers of Lithium Nickel Cobalt Aluminium oxides (NCA) battery, such as Panasonic, Tesla and LG Chem, have long been using lithium hydroxide as their lithium source.
Comparison on Sintering temperature- Sintering is a very important step in the preparation of NMC/NCA cathode materials. The sintering temperature has a significant impact on capacity, efficiency and cycle performance of the material, and it also has certain impact on lithium salt residue and the pH level of the material. Research has shown that when lithium hydroxide is used as the lithium source, a low sintering temperature is enough to obtain materials with excellent electrochemical performance; while if lithium carbonate is used, the sintering temperature has to be 900+℃ to obtain materials with stable electrochemical performance.
It looks like that lithium hydroxide is better than lithium carbonate as the lithium source. While actually, lithium carbonate is also often used in the production of NMC cathode materials (NMC111, NMC442, NMC532, NMC622) and LFP battery. Why? The lithium purity of lithium hydroxide fluctuates more than lithium carbonate, and lithium hydroxide is more corrosive than lithium carbonate. Therefore a lot of manufacturers tend to use lithium carbonate for production of NMC cathode materials and LFP battery.
Ordinary NMC cathode materials and LFP battery tend to use lithium carbonate, while Ni-rich NMC811 and NCA cathode materials are in favor of lithium hydroxide. The reasons rest exactly on the following:
The ternary Ni-rich NMC811/NCA material requires a low sintering temperature, otherwise it will cause low tap density and low rate of charge & discharge performance on battery. For example, NCM811 needs it to be controlled a little lower than 800℃, and NCM90505 needs it to be at about 740℃. It is much lower than 900℃.
When we check the melting point of these two lithium salts, we will find lithium carbonate being 720℃, while lithium hydroxide monohydrate being only 471℃. Another factor is that, during the synthesis process, the molten lithium hydroxide can be evenly and fully mixed with the NMC/NCA precursor, thereby reducing lithium residue on surfaces, avoiding generation of carbon monoxide and improving the specific discharge capacity of the material. Using lithium hydroxide also reduces cation mixing and improve cycle stability. Thus lithium hydroxide is a must-choice for production of NCA cathode materials. The well-known Panasonic 18650 Lithium ion battery uses lithium hydroxide, as an example.
Despite the above reasons, by raising the nickel content in lithium ion batteries, the energy density of these ternay batteries increases accordingly, with less cobalt involved and it brings an important result of cost reduction at the same time.
It is quite clear today, from lithium-ion battery researchers and manufacturers, that lithium carbonate is a good choice for ordinary NMC cathode material and LFP battery; while lithium hydroxide monohydrate battery grade is preferable for Ni-rich NMC811, NCA cathode materials and even some LFP material.
Generally, every 1GWH Ni-rich NMC/NCA batteries consume about 780 tons of lithium hydroxide. With increasing demand of these NMC/NCA batteries, the demand for lithium hydroxide is expected to rise substantially in the coming five years.
Source 1: http://news.cnpowder.com.cn/55202.html
Source 2: http://www.juda.cn/news/149069.html