Why can't ternary lithium battery completely replace lithium cobaltate?

Lithium cobaltate is the originator of cathode materials for lithium-ion batteries. Since 1980, it has never stopped exploring its performance. So far, lithium cobalt oxide still accounts for about 90% of the market for lithium-ion batteries in electronic products. Lithium cobaltate can be used today, not because it has no defects. After five years of development, lithium cobalt oxide has reached its limit. These will be explained in detail later in the analysis. I think the cobalt biggest advantage of lithium acid is that it really finds the right field for itself. It is also as saying, suitable is the best.

In fact, there are many unsatisfactory places for lithium cobalt oxide. For example, his safety and overcharge resistance are not good. The dependence on scarce cobalt resources, the cycle performance is relatively poor, etc. These defects are also destined cobalt. Lithium acid is unlikely to have a place in terms of power, which also avoids competition with other manganese-based materials and phosphoric acid system materials in the fierce power market. It is dedicated to the 3C market and, more importantly, its many defects. In the 3C field, it has been well covered. The high-capacity small 3C lithium battery has no harsh requirements for safety and overcharge resistance, and the cycle of more than 500 weeks can basically meet the demand, although the price of cobalt is very high. However, due to the simple synthesis process and the lucrative profit return of 3C products, the most important thing is that in the current cathode materials, lithium cobalt oxide has almost the highest energy density, despite the energy of lithium nickelate and NCA and high nickel. Density has different advantages than lithium cobaltate, but a series of reasons such as immaturity of the process, the mainstream status of lithium cobalt oxide has been unable to shake.

However, recently, due to the unprecedented demand for energy density of 3C products, in the high-density new materials, the defects of energy density are unprecedentedly exposed:

First, in terms of gram capacity, lithium cobaltate has a theoretical value of 275mAh/g, but because of the top phase of the band, Li1-xCoO2 leads to a large number of holes in the O2- and 2P bands when deep discharge occurs. When the amount x>0.5, the oxygen in the crystal lattice is desorbed, and the crystal structure is unstable, so the actual reversible specific capacity of the lithium cobaltate is generally about 140, and there is no further improvement under the conventional voltage.

In terms of compaction density, lithium cobalt oxide is the best positive electrode material for electrode processing, and its morphology control has become perfect. At present, its compaction density has reached its own limit, and it is almost impossible to improve again.

From the high voltage direction, another fatal defect of lithium cobaltate is sensitivity to high voltage. Of course, ordinary lithium cobaltate combined with high-pressure electrolyte, at 4.35V, can still barely meet the requirements in terms of cycle, and By doping with Mg element or the like, it has the potential at a higher voltage. However, ordinary lithium cobaltate is already the limit at 4.35 V, and the lithium cobaltate doped by doping can withstand higher voltage. However, element doping increases the processing cost of lithium cobaltate. Most importantly, ternary materials have highlighted the energy density advantage over lithium cobaltate at high voltages, and based on their potential for higher voltages, the threat to lithium cobalt oxide is increasing.

The practical application of ternary materials began with the rise of the hydroxide coprecipitation method in 2001. The materials prepared by this method have a complete layered structure, excellent electrochemical performance, almost no defects in the laboratory, and even many people believe that ternary materials will soon replace lithium cobalt oxide due to their cost advantages and relative environmental friendliness. However, ten years later, ternary materials have not replaced lithium cobalt oxide, and people have seen ternary the huge advantage of materials, however, see more of the bumps from the laboratory to the industrialization.

A good industrialization process, in addition to being simple and feasible, also needs to pay attention to all aspects of material properties, hydroxide coprecipitation method, and prepared ternary materials, which are difficult to use alone because of secondary agglomeration of small particles. Body, it is easy to break in the rolling, even if the agglomerate is dense and smooth, it is difficult to ensure the shape of the material under high pressure. Korean experts have simulated the ternary materials under different pressures at a meeting. In the case of particle breakage, it was found that even if the pressure is not very high, more than 15% of the small balls will be broken. Of course, with the continuous improvement of the synthetic process, the current ternary can already have a compaction density of 3.3-3.5. In this interval, there can be better electrochemical performance. What needs to be explained here is that the current ternary material is not incapable of compaction, but under high pressure, the secondary particles are broken, which inevitably leads to active materials and the contact of the binder conductive agent is not tight, which causes polarization and deteriorates the performance of the electrode. At present, the main solution is to mix with lithium cobaltate, and the primary particles of lithium cobaltate are three. The metamaterial provides support to ensure good electrode processing performance. In addition, some manufacturers mix and sinter lithium cobaltate and ternary to produce a material with a gram capacity higher than lithium cobaltate and a compact density of 3.95, which improves electrode processing. Performance, and relatively improved material stability, but the cost of this material is relatively high, and the energy density cannot exceed the current level of lithium cobalt oxide. This also poses new challenges to the process of ternary materials.

In fact, the true density of lithium cobaltate is about 5.1, and the ternary material (111 is an example) is about 4.8, but the ultimate compaction under the current process is very different (lithium cobaltate 4.2, ternary 3.6), in addition, due to 4.35V electrolyte has been delayed in industrialization in China, which has led to the use of ternary materials in low-end electronic products and certain power fields despite cost advantages.

Therefore, at this stage, from the material point of view, how to improve the ternary compaction density is one of the most realistic problems, to ensure that the ternary material layer structure is stable, so that it has the theoretical gram capacity to play, if By increasing the compaction density by 10%, the energy density of the ternary material can reach the level of high-grade lithium cobaltate. Based on its cost advantage, higher safety and good high voltage potential, the ternary material will replace lithium cobalt oxide. It is just a foresight of a laboratory.

In this respect, according to the idea of lithium cobaltate, we make the ternary material into a primary spherical particle of lithium cobalt oxide (it seems easy to say, but the growth environment of the ternary primary particle needs strict control, in order to ensure the control of the appearance and the consistency of the product are self-prepared from the precursor. It is very close to the lithium cobalt oxide in terms of morphology. Considering that the ternary material rate performance is not as good as that of lithium cobaltate, we have also designed the corresponding particle size distribution. Try to balance the rate, stability and energy density. The previous LNCM-35 can already achieve 3.7-3.9 compaction. The compaction of new materials after the improvement process is expected to be further improved. In addition, for the current in the mainstream 532 market, our new batch of 532 products LNCM-50 will soon be available. While guaranteeing 3.6 or more compaction, it is our current theme to improve its stability.

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