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Detailed analysis of electrode material selection for ternary lithium ion batteries

Detailed analysis of electrode material selection for ternary lithium ion batteries

Release date:2018-12-01 author: clicks:

The ternary lithium ion battery can be recharged during use. It belongs to a secondary rechargeable battery. The main working principle is the repeated movement of lithium iron phosphate lithium ion battery between the positive and negative electrodes, regardless of the shape of the battery. How the main components are electrolyte, positive electrode, negative electrode and separator. At present, the international production of lithium iron phosphate lithium ion batteries is mainly concentrated in China, Japan and South Korea, and the main lithium ion application market is mobile phones and computers. With the continuous development of lithium-ion batteries, the application field is gradually expanding. It has changed from singularization to diversification in the use of cathode materials, including: olivine-type lithium iron phosphate, layered cobalt acid. Lithium, spinel-type lithium manganate, etc., to achieve the coexistence of a variety of materials.


It can be seen from the technical development that more new cathode materials will be produced in the future development. For the positive electrode material of the power battery, it has strict requirements in terms of cost, safety performance, cycle capacity and energy density. In the field of applied materials, since lithium cobalt oxide has high cost and low safety, it is generally suitable for general consumer batteries in specific use, and it is difficult to meet the requirements of power batteries. The other materials listed above have been fully utilized in current power batteries. In lithium ion battery materials, the anode material is an important component and can have a large impact on the performance of the overall battery. At present, the anode materials are mainly divided into two categories, one is a carbon material for commercial application, such as natural graphite, soft carbon, etc., and the other is a non-carbon anode material that is in a state of research and development, but has a good market prospect. For example, silicon-based materials, alloy materials, tin-gold materials, and the like.


1 carbon anode material: This type of material, whether it is energy density, cycle capacity, or cost input, lithium manganese oxide lithium battery is in the performance of a balanced anode material, but also the main material to promote the birth of lithium-ion batteries, carbon Materials can be divided into two broad categories, graphitized carbon materials and hard carbon. Among them, the former mainly includes artificial graphite and natural graphite. The formation process of artificial graphite is: after the graphitization of soft carbon material at a temperature above 2500 ° C, MCMB is a commonly used one of artificial graphite, its structure is spherical, the surface texture is smooth, and the diameter is about 5-40 μm. Due to the smoothness of the surface, the probability of reaction between the electrode surface and the electrolyte is lowered, thereby reducing the irreversible capacity. At the same time, the spherical structure can facilitate the insertion and extraction of lithium ions in any direction, which has a great promotion effect on the stability of the structure. Natural graphite also has many advantages. It has high crystallinity, more embeddable positions, and lower price. It is an ideal lithium manganese oxide lithium ion battery material. However, it also has certain drawbacks. For example, when the ternary lithium ion battery reacts with the electrolyte, the compatibility is poor, and there are many defects on the surface during the pulverization, which will greatly affect the performance of charging or discharging. The adverse effects.


In addition, the formation process of hard carbon is: at 2500 ° C, it is difficult to carry out graphitized carbon material, which is mainly pyrolytic carbon of a polymer compound, which can be seen by a high power microscope, which is piled up by many nanospheres. It is made into a cluster of flowers, as shown in Figure 1. An amorphous region having a large number of nanopores on its surface far exceeds the standard capacity of graphite in terms of capacity, which in turn has a large adverse effect on the cycle capacity.


2 Silicon anode material: Since the lithium iron phosphate lithium ion battery has a relatively abundant storage capacity and a relatively low price, it is ideally applied as a new anode material to a lithium ion battery. However, since silicon is a semiconductor, the conductivity is poor, and in the process of embedding, the volume will expand to several times in the past, and the maximum expansion can reach 370%, which will cause the active silicon to be powdered and detached, which is difficult to interact with. Make sufficient contact to make the capacity shrink quickly. In order to make silicon be used in lithium ion battery materials, it can effectively control its volume during charging or discharging, so that its capacity and cycle capacity can be greatly guaranteed. Several ways to achieve this, first, use nano-sized silicon. Second, silicon is combined with an inactive matrix, an active matrix, and a binder. Third, the use of silicon thin films has been regarded as the most suitable commercial negative electrode material for the next generation.


3 lithium ion battery cathode material


Lithium cobaltate has been used as a positive electrode material for the first time, and it is still the mainstream cathode material in consumer electronics products until now. Compared with other cathode materials, lithium cobalt oxide can be seen that the voltage during operation is relatively high, and the voltage operation is relatively stable during charging or discharging, which can meet the requirements of large current, has strong cycle performance, and has high conductivity efficiency. And the battery and other processes are relatively stable. However, it also has many shortcomings, such as a shortage of resources and a relatively high price. Cobalt is toxic, has certain dangers in use, and has an adverse effect on the environment. In particular, its security cannot be guaranteed, which will become an important factor restricting its extensive development. In the research conducted on it, metal cations such as Al3+, Mg2+, and Ni2+ are most widely used. With the advancement of scientific research, the metal cation doping forms such as Al3+ and Mg2+ have been put into use. In the preparation of lithium cobaltate, two methods mainly include solid phase synthesis and liquid phase synthesis. Commonly used in the industry is a high-temperature solid phase synthesis method, which mainly utilizes a lithium salt such as Li2CO3 or LiOH, and a cobalt salt such as CoCO3, etc., is fused at a ratio of 1:1, and is heated at a temperature of 600 ° C to 900 ° C. It is formed by calcination in the state. At present, the application of lithium cobalt oxide materials in the market is mainly in the secondary battery market, and also becomes the best choice for small high-density lithium ion battery materials.


The ternary cathode material has a remarkable ternary synergistic effect. Compared with lithium cobalt oxide, it can be seen that it has great advantages in thermal stability and low production cost, and can be the best substitute material for lithium cobalt oxide. . However, its density is low and the cycle performance needs to be improved. In this regard, adjustment can be made using an improved synthesis process, ion doping, and the like. The ternary materials are mainly used in cylindrical lithium ion batteries such as steel shells and aluminum shells, but their application in the soft pack batteries is greatly limited due to the influence of expansion factors. In the future application, its development direction mainly has two aspects: First, toward the high manganese direction, mainly in the development of small portable devices such as Bluetooth and mobile phones. Secondly, in the direction of high nickel, it is mainly applied in fields where electric energy bicycles, electric vehicles and the like have high demand for energy density.


Lithium iron phosphate has good cycle performance and thermal stability in terms of charging and discharging, and has strong safety guarantee during use, and the material is environmentally friendly, does not cause serious damage to the environment, and is relatively inexpensive. It is considered by China's battery industry to be the best material for large-scale battery module production. The current main application areas are: electric vehicles, portable mobile charging power supplies, etc., in the future development will be in the direction of energy storage power supply, portable power supply.


Lithium manganate has strong safety and anti-overcharge in application. Due to the abundant manganese resources in China, the price is relatively low, the pollution to the environment is small, non-toxic and harmless, and the industrial preparation operation is relatively simple. However, during the charging or discharging process, due to the unstable structure of the spinel, the Jahn-Teller effect is easily generated, and the dissolution of manganese at a high temperature state is easy to reduce the battery capacity, so its application is also greatly limited. At present, the application range of lithium manganate is mainly small batteries, such as mobile phones, digital products, etc., and lithium iron phosphate can replace each other in the power battery, so there is a strong competition, and its development direction will be toward high energy and high. The trend of density and low cost has developed.


Lithium-ion battery products are showing a booming trend. With the development of science and technology, smart phones, computers and other products are widely used, which will increase the demand for lithium-ion batteries and bring them greater development opportunities. . At the same time, on-board lithium ions and energy storage power sources have gradually developed, providing a new growth point for lithium-ion batteries. It can be seen that in the future development, research efforts in this area will be strengthened, and the role of lithium-ion batteries will be exerted even greater, which will also drive the replacement of battery materials.

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