Briefly describe the characteristics of the three lithium batteries

Ternary material

The ternary polymer lithium battery refers to a lithium battery using a lithium nickel cobalt manganese ternary positive electrode material for the positive electrode material. There are many kinds of positive electrode materials for the lithium ion battery, mainly lithium cobaltate, lithium manganate, lithium nickelate, ternary materials, lithium iron phosphate and the like. The ternary material combines the advantages of lithium cobaltate, lithium nickelate and lithium manganate. It has excellent characteristics such as high capacity, low cost and good safety. It gradually takes a certain market share in small lithium batteries, and the field of power lithium has good development prospects.

For lithium batteries, cobalt metal is an indispensable material. However, on the one hand, metallic cobalt is expensive, and on the one hand, it is toxic. Regardless of the leading Japanese and Korean companies or domestic battery manufacturers, the battery has been “less cobaltized” in recent years. Under this trend, nickel-cobalt-manganese ternary materials prepared by using nickel salts, cobalt salts and manganese salts as raw materials are gradually being favored. From the chemical point of view, the ternary material belongs to excessive metal oxides, and the energy density of the battery is high.

Although the role of cobalt is still indispensable in ternary materials, the mass fraction is usually controlled at around 20%, and the cost is significantly reduced. Moreover, it has the advantages of both lithium cobaltate and lithium nickelate. With the increasing production of domestic and foreign manufacturers in recent years, the trend of replacing commercial lithium cobalt oxide with lithium batteries with ternary materials as cathode materials has become very obvious.

From electric cars to smart phones, wearables and charging pads, this new technology is perfectly suited. Tesla [microblogging] first applied the ternary battery to the electric vehicle. The ModelS has a cruising range of 486 kilometers and a battery capacity of 85kWh. It uses 8142 3.4AH Panasonic 18650 batteries. The engineers distributed the batteries one by one in the form of bricks and sheets to form an entire battery pack, which is located on the underbody.

From a global perspective, the R&D and production of ternary materials are constantly advancing. In this process, the material performance has been greatly improved, and the application field has been expanded. Japanese and Korean companies are the leader in the development of ternary material batteries. The production of domestic ternary materials started from around 2005, and more than a dozen large-scale enterprises have emerged.

Lithium iron phosphate

Lithium iron phosphate as a lithium battery material has only appeared in recent years. The domestic development of large-capacity lithium iron phosphate batteries was in 2005. Its safety performance and cycle life are incomparable to other materials, which are the most important technical indicators of power batteries. 1C charge and discharge cycle life of 2000 times. Single cell battery overcharge voltage 30V does not burn, puncture does not explode. Lithium iron phosphate cathode materials make large-capacity lithium-ion batteries easier to use in series to meet the needs of electric vehicles for frequent charging and discharging.

Lithium iron phosphate has the advantages of non-toxicity, no pollution, good safety performance, wide range of raw materials, low price and long service life. It is an ideal cathode material for a new generation of lithium ion batteries. Lithium iron phosphate batteries also have their disadvantages. For example, the lithium iron phosphate cathode material has a small tap density, and the volumetric lithium iron phosphate battery has a larger volume than a lithium ion battery such as lithium cobalt oxide, and thus has no advantage in terms of a micro battery.

Due to the inherent characteristics of lithium iron phosphate materials, the low temperature performance is determined to be inferior to other positive electrode materials such as lithium manganate. In general, for a single cell (note that it is a single cell instead of a battery pack, the measured low temperature performance may be slightly higher for the battery pack, which is related to the heat dissipation conditions), its capacity retention at 0 °C The rate is about 60 to 70%, 40 to 55% at -10 ° C, and 20 to 40% at -20 ° C. Such low temperature performance obviously cannot meet the requirements of the power source. At present, some manufacturers have improved the low temperature performance of lithium iron phosphate by improving the electrolyte system, improving the positive electrode formulation, improving the material properties and improving the design of the cell structure.

The battery has a consistency issue. The life of a single lithium iron phosphate battery is currently more than 2,000 times, but the life of the battery pack will be greatly reduced, possibly 500 times. Because the battery pack is made up of a large number of single cells, it works like a group of people tied up with ropes. Even if everyone is a sprinter, if everyone's movements are not consistent, the team will not run fast. The speed is even slower than the slowest individual player. The same is true for the battery pack. Only when the battery performance is highly consistent, the life can be close to the level of the single battery.

Lithium manganese oxide

Lithium manganate is one of the promising lithium ion cathode materials. Compared with traditional cathode materials such as lithium cobalt oxide, lithium manganate has the advantages of abundant resources, low cost, no pollution, good safety and good rate performance. The power battery cathode material, but its poor cycle performance and electrochemical stability have greatly limited its industrialization. Lithium manganate mainly includes spinel-type lithium manganate and layered lithium manganate. Among them, spinel-type lithium manganate has a stable structure and is easy to realize industrial production. Spinel-type lithium manganate belongs to cubic crystal system, Fd3m space group, theoretical specific capacity is 148mAh / g, due to the three-dimensional tunnel structure, lithium ions can be reversibly deintercalated from the spinel lattice, will not cause structural It collapses and thus has excellent rate performance and stability.

Nowadays, the traditional belief that lithium manganese oxide has low energy density and poor cycle performance has been greatly improved (typical value of Wanli New Energy: 123mAh/g, 400 times, typical value of high cycle type 107mAh/g, 2000 times). Surface modification and doping can effectively modify its electrochemical properties, and surface modification can effectively inhibit the dissolution of manganese and electrolyte decomposition. Doping can effectively suppress the Jahn-Teller effect during charge and discharge. The combination of surface modification and doping can undoubtedly further improve the electrochemical performance of the material, which is believed to be one of the future research directions for the modification of spinel lithium manganate.

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