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A Brief Analysis Of The Frontiers Of Several Lithium Ion Batteries
- Aug 07, 2018 -

1. All solid state lithium ion batteries


The commercialized lithium ion battery electrolyte is liquid, so it is also called liquid lithium-ion battery. In simple terms, all solid state lithium ion batteries means that all components in the battery structure exist in the form of solid state. The liquid electrolyte and diaphragm of the traditional lithium ion batteries are replaced by solid electrolytes.

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Compared with liquid lithium ion batteries, all solid state electrolytes have the following advantages: high safety / thermal stability and long normal working conditions at 60-120 centigrade; wide electrochemical window, which can reach more than 5V, match high voltage materials, only conduct lithium ion conduction electrons; the cooling system is simple and the energy density is high; It can be used in the field of ultra thin flexible batteries. But the disadvantages are obvious: the ionic conductivity per unit area is low, the specific power at room temperature is poor; the cost is extremely expensive; industrialized production of large-capacity batteries is difficult.


The performance of the electrolyte materials to a large extent determines the power density, cycle stability, safety performance, high and low temperature performance and service life of all solid state lithium ion batteries. Solid electrolytes can be divided into polymer electrolytes (usually based on the mixture of PEO and lithium salt LiTFSI as electrolyte substrates) and inorganic electrolyte (such as oxides and sulfides) of two major categories. All solid state battery technology is recognized as the next generation of key development of innovative battery technology. It is believed that in the near future technology is becoming more and more mature, and these problems can be solved.


Two, three yuan material battery with high energy density


With the pursuit of battery energy density, three yuan cathode materials have attracted more and more attention. Ternary cathode materials have the advantages of high specific capacity, good cycling performance and low cost, generally referring to the layered structure of lithium nickel cobalt manganate materials. By increasing the battery voltage and the content of nickel in the material, the energy density of three cathode material can be effectively improved.


Theoretically, three yuan material itself has the advantage of high voltage: the standard test voltage of half battery for three yuan positive material is 4.35V. Under this voltage, the ordinary three yuan material can show good cycle performance; the charge voltage is raised to 4.5V, the capacity of the symmetric material (333 and 442) can reach 190, and the recycling is also available. Yes, 532 cycle is worse; charging to 4.6V, three yuan material circulation began to decline, the phenomenon of flatulence is more serious. At present, the factors restricting the practicability of high voltage three electrode cathode materials are difficult to find the high voltage electrolyte matched with them.


Another way to increase the energy density of three yuan material is to improve the content of nickel in the material. Generally, the three yuan cathode material of high nickel means that the mole fraction of nickel in the material is greater than 0.6, and the three yuan material has the characteristics of high specific capacity and low cost, but its capacity is low and the thermal stability is poor. The improvement of the preparation process can effectively improve the properties of the material. Micro nano size and morphology have great influence on the properties of high nickel three element cathode materials, so most of the preparation methods currently used are concentrated in uniform dispersion, and small size and large surface area of spherical particles are obtained.


In many preparation methods, the combination of coprecipitation and high temperature solid-state method is the mainstream method. First, a co precipitation method is used to get the precursor with homogeneous mixture and homogeneous particle size, and then through high temperature calcination, three yuan materials with surface morphology and easy control are obtained. This is the main method used in industrial production at present. Compared with Coprecipitation method, spray drying method has the advantages of simpler process and faster preparation speed, and the morphology of the obtained materials is no less than that of coprecipitation method, which has the potential for further research. The disadvantages of high nickel ternary cathode materials, such as cation mixing and phase change during charge and discharge, can be effectively improved by doping and coating modification. It is still a hot topic to improve the conductivity, cycle performance, ratio performance, storage performance and high temperature and high pressure performance, while restraining the side reaction and stabilizing the structure.


Three, high capacity silicon carbon negative electrode


As an important part of lithium-ion batteries, anode materials directly affect the battery energy density, cycle life and safety performance and other key indicators. Silicon is the highest negative material of lithium ion battery with the highest known specific capacity (4200mAh/g), but because of its more than 300% volume effect, the silicon electrode material will be pulverized in the process of charge and discharge and exfoliate from the collection fluid, making the active material lose electrical contact with the active material, the active substance and the fluid gathering, and at the same time it forms a new one. Solid electrolyte layer SEI eventually leads to deterioration of electrochemical performance. In order to solve this problem, researchers have made a lot of explorations and attempts. Among them, silicon-carbon composites are promising materials.


Carbon materials, as anode materials for lithium ion batteries, have small changes in volume during charge discharge, and have good cyclic stability and excellent conductivity, so they are often used to compound silicon. In the carbon silicon composite negative material, it can be divided into two types according to the types of carbon materials: silicon and traditional carbon materials and silicon and new carbon materials. The traditional carbon materials mainly include graphite, mesophase microspheres, carbon black and amorphous carbon, and the new carbon materials mainly include carbon nanotubes, carbon nanowires, carbonaceous gels and graphite. Alkenes and so on. Using the silicon carbon composite, the volume expansion of the silicon active center is restrained and buffered by the porous effect of carbon materials, preventing the agglomeration of the particles, preventing the electrolyte from penetrating into the center, and maintaining the stability of the interface and the SEI film.

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