The introduction of anode and cathode material of lithium ion battery

Nov 10, 2018   Pageview:529

The term of lithium iron phosphate, ternary lithium battery, etc. are named by anode material of the lithium ion battery. Relatively speaking, the effects of anode and cathode materials play an important role on battery performance. What are the usual anode and cathode materials in recent market? What are the advantages and disadvantages of them to lithium ion battery?


Anode material


Firstly, think more about the following factors of the anode materials:


Have higher redox reaction potential, so as to help the lithium ion battery to reach higher output voltage of lithium ion battery.


High content of Li ion, high material packing density, so as to help the lithium ion battery has higher energy density.


Have good structural stability during chemical reaction, so as to help the lithium ion battery has longer cycle life.


Have high conductivity, so as to help the lithium ion battery has good charging and discharging rate.


Have good chemical stability and thermal stability, not easy to decompose and heat, so as to help the lithium ion battery has good safety performance.


Have lower price, so as to lessen the cost of the lithium ion battery.


Have relatively simple processing, so as to lead in mass production.


Be environmentally friendly, and be easy to recycle.


Some key indicators, including energy density, charging and discharging rate, safety performance, etc., are mainly limited by the anode materials.


Based on these factors, recent anode materials in market are as follow after engineering research and market inspection:


anode materials

chemical component

structure

Energy density

Cycle life

cost

Safety performance

lithium iron phosphate

LiPO4

olivine

medium

high

low

high

lithium nickelate

LiNiO2

stratiform

high

low

high

low

lithium manganate

LiMn2O4

spinel

low

medium

low

medium

lithium cobalt oxides

LiCoO2

stratiform

medium

low

high

low

NCA

LiNixCoyAl(1-x-y)O2

stratiform

high

medium

medium

low

NCM

LiNixCoyMn(1-x-y)O2

stratiform

high

high

medium

low


Lithium cobalt oxide is the earliest for commercialization. The first generation lithium ion battery is lithium cobalt oxide battery released by SONY in 1990. It was widely used in consumer products later. As the mass adoption of mobile phone, laptop and tablet PC, lithium cobalt oxide has been the popular material in sales volume of lithium ion battery anode material. However, it has a disadvantage of low ratio of quality to volume (not equal to energy density). The theoretical limitation is 274mAh/g. Considered about the stability structure of anode, it can only reach 50% of the theoretical limitation (137mAh/g). Besides, there is not so much cobalt on earth, so the lithium cobalt oxide cannot widely used in power battery area because of the high cost, and is gradually replaced by other materials.


having shortcomings on stability, safety performance and material synthesis, lithium nickelate has less commercial application. You can hardly find this material on market.


The commercialization of lithium manganite is mainly on power battery area, one of the important branches of lithium ion battery. For example, the electronic car of Japan Leaf has applied lithium manganese battery of Japan AESC. Even earlier Volt has also employed lithium manganese battery of Korea LG. The great advantages of lithium manganite are low cost and good low-temperature performance, while the disadvantages are low specific capacity (limited value is 148mAh/g), poor high-temperature performance, low cycle life. Therefore, lithium manganite has obvious bottleneck in its development. Recently, the research direction is modification of lithium manganite by doping other elements to cover its shortcomings.


Lithium iron phosphate has been popular in China for a while. On one hand, it has the technology support from American scientific research institution and enterprises. On the other hand, affected by the industrialization of BYD in China, the material of the lithium ion battery domestic enterprises mainly is lithium iron phosphate in recent years. However, the requirements of energy density of lithium ion battery from all over the world are more and more strict. The theoretical specific capacity of lithium iron phosphate is 170mAh/g, while the actual value is around 120mAh/g, which has limited its application. Besides, it doesn’t have attractive rate capability or low-temperature performance. Recently, BYD released a modified lithium iron phosphate materials and upgraded the energy density apparently. Nobody knows what they have added into the materials without technique revealing. As for production application areas, power storage market may be the important market of lithium iron phosphate battery. In contrast, this market is not sensitive on energy density, but long cycle life, low cost and high safety performance, which are exactly the advantages of lithium iron phosphate materials.


Japanese and South Korean counterparts have strongly promoted the application of ternary materials in recent years. Since NCM gradually becomes the mainstream of the market, domestic enterprises also follow the trend and gradually replace the material by NCM. The specific capacity of ternary materials is high, so the products in recent market have already up to 170~180mAh/g, and then improve the energy density of single cell to nearly 200Wh/kg, so as to meet the requirement of long driving mileage of electrical car. Besides, changing the composition of ternary materials (value of X, Y) can make good rate capability to meet the requirement of high rate but small capacity Li ion battery of PHEV AND HEV. This is the reason why ternary materials are so popular. We can see from the chemical formula that NCM has integrated the advantages of lithium cobalt oxides (LiCoO2) and lithium manganite (LiMn2O4), and it can upgrade the energy density and rate capability with Ni element.


NCA is can be a modified lithium nickelate materials, containing a certain percentage of cobalt and aluminium element (small percentage). It is Japan Panasonic that is on commercialized application, other battery companies hardly research on this material. The reason for comparison is that popular Tesla has applied the 18650 NCA ternary battery from Panasonic in electrical car power battery system, and it realized a endurance mileage of nearly 500km, which proves that this anode material has its specific value.


All these above are the common anode materials of lithium ion battery, but not the representative of all technique directions. Actually, not only university and scientific research institutions, but also enterprises, has tried hard to research new type of anode material lithium ion battery, in order to upgrade the key index of energy density, cycle life, etc. to higher level. Nowadays, the anode materials of commercialized application cannot realize to reach 250Wh/kg, or even 300Wh/kg on energy density in 2020, so the anode materials need to have technology innovation, such as modify stratified structure to spinel structure of solid solution materials and organic compound materials are also one of the popular research directions.


Cathode materials


Comparatively speaking, the research on cathode material of lithium ion battery is less than anode material, but cathode material plays essential role on battery performance upgrading. When choose a cathode material of lithium ion battery, you need to consider the following factors:


It needs to be stratified or tunnel structure, which is in favor of dis-embedding of Li ion.


It has no changes on structure during the dis-embedding of Li ion, and has great charging and discharging reversibility and cycle life.


Li ion tries to embed and dis-embed as many as possible, so as to make sure the higher reversible capacity of electrode.


Have low electric potential in redox reaction, coordinating with anode material, so as to have higher output voltage.


Small irreversible discharging specific capacity at the first time


Have good consistency with electrolytic solvent


Be rich in resources and have low price


Good safety performance


Environmentally friendly


There are different kinds of cathode materials of lithium ion battery. They can be divided into metal cathode materials (including alloy), inorganic nonmetal cathode material, and metal oxide cathode materials by their chemical composition.


Metal cathode materials: these materials have wonderful capacity of lithium insertion. The earliest cathode material in research is lithium. Due to the safety issue and poor cycle performance of the battery, lithium is not widely applied as cathode material. In recent years, people tend to research on alloy cathode materials, such as Tin-based alloy, Al-base alloy, magnesium base alloy, Sb-base alloy, etc., which is a new research direction.


Inorganic nonmetal cathode material: it mainly is carbon material, silicon material and other nonmetal composite.


Transition metal oxide material: it has advantages of stable structure, long cycle life, etc. These materials include lithium oxide (lithium titanate), Tin-based composite oxide, etc.


At recent market, the cathode materials give priority to carbon materials, including graphite and non-graphite carbon materials. In car and power tool area, lithium titanate has applied as cathode material for its wonderful cycle life, safety performance and rate capability, but it will lessen the energy density, which makes it cannot become the mainstream on market. Except the tin alloy having products carried out by SONY, other cathode materials are mainly still at research and developing phase, but seldom on marketization application.


As for the development tendency, silica-based material may replace carbon material and be the next major cathode material of lithium ion battery, if the cycle issue has been perfectly solved. Cathode materials of anode including Tin alloy, silicon alloy, etc. are another popular trend and will approach to product and market. Besides, iron oxide with high safety performance and energy density may replace lithium titanate (LTO), and is widely used in the area with requirements of long cycle life and safety performance.


Here are more details about two key indexes related to lithium ion battery and energy: energy density and charging & discharging rate.


Energy density is what capacity storage in unit volume or weight. The higher, the better it is. Charging and discharging rate is the speed of energy storage and release. It has better to speed per second, charging and discharging in a moment.


Actually, we cannot have infinite energy, or realize energy shift in a moment. This is why we need to make process continuously.

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