Introduction of anode and cathode materials for lithium-ion batteries

It is normal to see the terms of lithium iron phosphate, ternary lithium battery, which are divided by the type of anode materials of lithium-ion battery. Relatively speaking, the anode and cathode materials of lithium-ion battery have more influence on the properties of battery. But what are the common anode materials in current market? What are their strengths and weaknesses to make lithium-ion battery?

1. Anode material

First of all, let's take a look at the anode materials, the anode materials choice, mainly based on the following factors:

1) With high REDOX potential, make the lithium ion battery to achieve high output voltage;

2) Lithium content high, the material bulk density is high, the lithium ion battery has high energy density;

3) Chemical reaction in the process of structural stability is better, make the lithium ion battery has long cycle life;

4) Higher conductivity, making lithium ion battery has a good performance of charging and discharging rate;

5) Better chemical stability and thermal stability, not easy to decompose and fever, makes the safety of the lithium ion battery has good;

6) Cheap, making the cost of the lithium ion battery low enough;

7) Manufacturing process is relatively simple, easy to mass production.

8) Low pollution to the environment, easy recycling.

Currently, the energy density, charging and discharging rate, some key indicators, such as security of lithium-ion battery mainly subjects to the anode material.

Based on these factors to consider, after the marketization of engineering research and test, the market at present common anode materials shown in the table below:

The commercial application of cobalt acid lithium go first, the first generation of commercial application of lithium ion battery is SONY in 1990 into the market of cobalt acid lithium ion battery, then get large-scale application in consumer products. With the massive popularity of the mobile phone, notebook, tablet, cobalt acid lithium was once a lithium ion battery cathode material in the sales of the largest material. But the quality of its inherent drawback is given () is not the same as energy density is low, the theory of limit is 274 mAh/g, for the sake of the positive structure stability, can only achieve the theoretical value of 50% in real terms, namely 137 mah/g. At the same time, because of cobalt element on earth reserves is lower, also lead to higher cost of cobalt acid lithium, in hard Power battery field large-scale popularization, so cobalt acid lithium anode materials will be replaced by other materials gradually.

Due to the stability, security, materials synthesis difficult aspects of shortcomings, commercial application of nickel acid lithium is less, rarely seen on the market, do not discuss here.

The commercial application of manganese acid lithium, mainly in the field of power battery, is a more important branch of lithium-ion batteries. Such as Nissan's leaf electric car USES the AESC Japanese company manganese acid lithium ion battery, early Chevrolet Volt also by South Korea's LG chemical manganese acid lithium ion batteries. Manganese acid lithium prominent advantage is low cost, good low temperature performance, the disadvantage is that specific capacity is low, the limit in 148 mAh/g, and high temperature performance is poor, low cycle life. So the development of lithium manganese acid had obvious bottleneck, in recent years, the research direction is mainly modified lithium manganese acid, through the doped with other elements, change its shortcomings.

lithium iron phosphate material in China for a while, on the one hand, by the scientific research institutions and enterprises in the technical part of the drive, on the other hand, industrialization driven by BYD at home, before a few years of lithium ion battery domestic enterprises in the field of power battery basically is given priority to with lithium iron phosphate material. But as the global demand for lithium-ion battery energy density is higher and higher, and the specific capacity of the lithium iron phosphate theoretical limit is 170 mAh/g, and actually can only be reached around 120 mAh/g, has been unable to meet the current and future market demand. In addition, the ratio of the lithium iron phosphate performance, low temperature characteristics such as faults, also limits the application of lithium iron phosphate. BYD recently come up with a modified lithium iron phosphate material, the energy density increased a lot, also did not give specific technical details, do not know with what material inside. In terms of product application fields, power should be the iron phosphate lithium ion battery energy storage market, an important market, by contrast, the market is not particularly sensitive to the energy density, and of long life, low cost, high security the urgent demand of batteries, lithium iron phosphate material advantage.

In recent years, Japan and South Korea enterprise vigorously to promote the application of ternary material, nickel cobalt manganese ternary material gradually become the mainstream of the market, domestic enterprises also take following strategy, gradually turned to the ternary material. High specific capacity of the ternary material, products on the market at present already can reach 170 ~ 180 mAh/g, and be able to increase the energy density of battery monomer to nearly 200 wh/kg, satisfies the requirement of long range of electric cars. In addition, by changing the ratio of the ternary material (x, y), also can achieve a good ratio of performance, so as to meet the PHEV and HEV vehicles demand for large ratio small capacity lithium ion battery, which is the cause of the ternary material is popular. Can be seen from the chemical formula, nickel cobalt manganese ternary material combines (LiCoO2) and cobalt acid lithium manganese acid lithium (LiMn2O4) some of the advantages, at the same time as the nickel element, can improve the energy density and performance ratio.

Aluminum nickel and cobalt ternary material, strictly speaking, is actually a modification of the lithium nickel acid (LiNiO2) materials, among them with a certain proportion of cobalt and aluminum (less).Commercial application is mainly Japan, Panasonic company doing other lithium ion battery company little research on this material. For comparison, because the famous Tesla, is to use Panasonic 18650 aluminum nickel and cobalt ternary batteries for electric vehicle power battery system, and made it close to the range of 500 kilometers, illustrates the positive pole material, still has its unique value.

Above is just a common lithium ion battery cathode material, does not represent all technical route. In fact, both universities and research institutes, and companies, are trying to study a new type of lithium ion battery cathode material, hope to promote key metrics such as energy density and life to a higher level. And, of course, if you want to reach 250 in 2020 Wh/kg, even 300 Wh/kg energy density index, commercial application of the anode materials are now unable to realize, so the anode material of technological change, must be more such as change of layered structure for the spinel structure of solid materials, and the positive electrode materials for organic compounds, are currently popular research direction.

2. The cathode material

, in contrast, studies on anode materials for lithium ion batteries, not as much as the anode material, but the improvement of the performance of the anode materials for lithium ion battery still plays a vital role, lithium ion battery anode materials selection should consider the following conditions:

1) It should be layered or tunnel structure, to facilitate and take off of lithium ion embedded;

2) It is in lithium ion when embedded without the change of the structure, has good charge and discharge reversible and cycle life;

3) Lithium ion in the embedding and out should be as much as possible, so that the electrode has the high irreversible capacity;

4) The potential of REDOX reaction is lower, and the anode material to cooperate, make the battery has the high output voltage;

5) For the first time the irreversible discharge specific capacity is small;

6) It has good compatibility with electrolyte solvent;

7) Rich in resources, low price;

8) Security;

9) Environment friendly.

There are many types of lithium ion battery anode materials, according to the chemical composition can be divided into metal anode materials (including alloy), inorganic non-metallic anode materials and metal oxide anode materials.

(1) metal anode materials: this kind of material with ultra-high intercalated-li more capacity. The earliest research is anode materials for lithium metal. Due to the poor battery safety and cycle performance, metallic lithium as negative material has not been widely used. In recent years, the alloy anode materials class got more extensive research, such as tin base alloy, aluminum alloy, magnesium alloy, antimony, etc., is a new direction.

(2) Inorganic nonmetal anode materials, used in lithium ion battery cathode material of inorganic non-metallic materials mainly carbon, silicon and other non-metallic composite material.

(3) Transition metal oxide material: this kind of material is generally has the structure stability, long cycle life, such as lithium transition oxide (lithium titanate, etc.), tin base composite oxides.

In terms of the current market, large-scale commercial applications, anode materials still is given priority to with carbon materials, graphite and the graphite carbon materials are used. In the field of automobile and electric tools, lithium titanate as the cathode material also has a certain application, mainly has very excellent cycle life, security, and performance ratio, but will reduce the energy density of battery, so not mainstream. Other types of anode materials, in addition to SONY in tin alloy products, most still is given priority to with scientific research and engineering development, less market application.

In terms of the development trend of the future, if can effectively solve the circulation performance, silicon-based materials could replace carbon materials as the next generation of lithium ion battery anode materials. Tin alloy, silicon alloy anode materials of a class, is also a very popular direction, will be toward industrialization. In addition, the safety and high energy density of iron oxides, might replace lithium titanate (LTO), long service life and security requirement in some higher areas, is widely used.

The following content, we will discuss the lithium ion battery energy related two key indicators: the energy density and charge and discharge rate, a brief discussion.

Energy density, which is what can be stored energy per unit volume or weight, the index is the higher the better, of course, is all concentrated essence. Charge and discharge rate, the speed of the energy storage and release, had better be seconds speed, instantaneous is full or release, your way.

Of course, these are the ideal condition. In fact, affected by various realistic factors, it is difficult to get unlimited energy. Neither can realize the instant transfer of energy. It is our responsibility to find out the answer of how to continuously break through these limitations, and achieve a higher level research.

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