[[TitleIndustry]]

Analysis of Advantages, Disadvantages and Technical Parameters of Lithium Manganate Battery

Date:Oct 15, 2019

The advantage of lithium manganate is that the rate performance is good, the preparation is relatively easy, and the cost is low. The disadvantage is that the high temperature performance and cycle performance are poor due to the dissolution of manganese. By doping with aluminum and sintering granulation, the high temperature performance and the cycle introduction are greatly improved, and basically can satisfy the practical use. In general, lithium manganate batteries have low cost, high stability and low temperature, poor high temperature performance and slightly faster attenuation.

Low-cost, safe and low-temperature cathode materials, but the material itself is not stable, easy to decompose and generate gas, so it is often used in combination with other materials to reduce the cost of the battery, but its cycle life decays faster. It is prone to bulging, low temperature performance and relatively short life. It is mainly used for large and medium-sized batteries and power batteries. Its nominal voltage is 3.7V.

There are three kinds of lithium manganate:

1. layer of lithium manganate LiMnO2, the theoretical capacity is 285 mA·h/g, and the voltage platform is 4V. The layered structure is difficult to synthesize, unstable, and easily forms Li2Mn2O4 spinel structure, resulting in a drop in voltage platform, poor stability, and irreversible capacity decay.

2. high-pressure spinel lithium manganate LiMn2O4, theoretical capacity 148mA·h / g, voltage platform 4.15. The high temperature performance is poor, and the capacity attenuation above 55 °C is severe. It is also easy to generate a spinel structure of Li2Mn2O4, which leads to a drop in voltage platform, poor stability, and irreversible attenuation of capacity. Industrial lithium manganate is currently used in this way.

3. spinel lithium manganate Li2Mn2O4, low voltage (3V), low capacity, poor cycle, are studying how to avoid this kind of thing.

Ternary: In order to solve the defects of layered lithium manganate, Ni, Co(Al) substituted manganese ternary material LiNiCoMnO2 (LiNiCoAlO2) was invented by doping metal elements, taking into account the high capacity and high voltage of lithium nickelate. Lithium manganate has high pressure and high safety, and good circulation of lithium cobaltate. At the same time, it overcomes the shortcomings of difficult and unstable synthesis of lithium manganate lithium nickelate and high cost of lithium cobaltate, and has become the mainstream cathode material. The theoretical capacity is 280 mA·h/g, and the voltage is 2.7 to 4.2. The actual capacity is now around 160 mA·h/g.

In the next few years, the current ternary will be basically eliminated in three years, with high nickel and NCA taking the lead. After 10 years, it is estimated that the entire ternary will be eliminated, and there will be a new battery system to replace the ternary.

Lithium manganate is mainly spinel-type lithium manganate spinel lithium manganate LiMn2O4 is a cathode material with three-dimensional lithium ion channel first produced by Hunter in 1981. It has been the electrode of many scholars and researchers at home and abroad. Great concern, as an electrode material, it has the advantages of low price, high potential, environmental friendliness, high safety performance, etc. It is the most promising substitute for lithium cobalt oxide LiCoO2 as a cathode material for a new generation of lithium ion batteries.

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: 123 mAh/g, 400 times, typical value of high cycle type 107 mAh/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.

LiMn2O4 is a typical ionic crystal with both positive and negative configurations. XRD analysis shows that the normal spinel LiMn2O4 is a cubic crystal with Fd3m symmetry, the unit cell constant a=0.8245nm, and the unit cell volume V=0.5609nm3. Oxygen ions are face-centered cubic close-packed (ABCABC.., adjacent oxygen octahedrons adopt co-edge association), and lithium occupies 1/8 oxygen tetrahedral gap (V4) position (Li is ordered in Li0.5Mn2O4 structure: Lithium ordered to occupy 1/16 oxygen tetrahedral gap), and manganese occupied the oxygen 1/2 octahedral gap (V8) position. The unit cell contains 56 atoms: 8 lithium atoms, 16 manganese atoms, 32 oxygen atoms, of which Mn3+ and Mn4+ each account for 50%. Since the cell length of the spinel structure is twice that of the normal face-centered cubic structure (fcc), each unit cell actually consists of 8 cubic cells. These eight cubic units can be divided into two types, A and B. Each two coplanar cubic units belong to different types of structures, and each two co-edge cubic units belong to the same type of structure. Each small cubic unit has four oxygen ions, which are located at the center of the diagonal of the body to the center of the apex, ie, 1/4 and 3/4 of the body diagonal. Its structure can be simply described as 8 tetrahedrons 8a occupied by lithium ions, 16 octahedral positions (16d) occupied by manganese ions, 16d manganese is Mn3+ and Mn4+ occupied by 1:1 ratio, octahedron 16c position All vacancies, oxygen ions occupy the octahedral 32e position. In this structure, the MnO6 oxygen octahedron adopts co-edge association to form a continuous three-dimensional cubic arrangement, that is, the [M2]O4 spinel structure network provides a tetrahedral lattice 8a, 48f and eight for the diffusion of lithium ions. The three-dimensional air channel formed by the facet lattice 16c is coplanar. When lithium ions diffuse in the structure, the path is linearly diffused in the order of 8a-16c-8a (the energy barrier at the position of the tetrahedron 8a is lower than the energy barrier at the position of the oxygen octahedron 16c or 16d), and the angle of the diffusion path is 107°. This is the theoretical basis for use as a positive electrode material for secondary lithium ion batteries.

Production of lithium manganate

There are many methods for synthesizing spinel lithium manganate, mainly high temperature solid phase method, melt impregnation method, microwave synthesis method, sol gel method, emulsification drying method, coprecipitation method, Pechini method and hydrothermal synthesis method.

The main lithium manganate on the market today has two types of AB. Class A refers to materials used in power batteries, and its characteristics are mainly considering safety and circulation. Class B refers to a replacement for mobile phone batteries, which is characterized by high capacity.

The production of lithium manganate is mainly produced by using EMD and lithium carbonate as raw materials, and corresponding additives, after mixing, firing, post-treatment and the like. Considering the characteristics of raw materials and production processes, the production itself is non-toxic and environmentally friendly. No waste water is produced, and the powder in production can be recycled. Therefore, it has no impact on the environment.

The main indicators of Class A materials today are: reversible capacity between 100 and 115, and circulation can reach more than 500 times and still maintain 80% capacity. (1C charge and discharge); Class B materials have higher capacity, generally required to be around 120, but the relative requirements for cycleability are relatively low, ranging from 300 to 500 times, and the capacity retention rate can reach more than 60%. Of course, there is still a certain distance between the price of category A and the price of category B.

Lithium manganate battery refers to a battery using a lithium manganate material for the positive electrode. The lithium manganese oxide battery has a nominal voltage of 2.5 to 4.2 v. The lithium manganate battery is widely used because of its low cost and good safety.

Output voltage range: 2.5~4.2v Nominal capacity: 7500mAh

Standard continuous discharge current: 0.2C

Maximum continuous discharge current: 1C

Working temperature: Charging: 0~45°C

Discharge: -20~60°C

Lead type: national standard line UL3302/26#, line length 50mm white line is 10K NTC

Protection board parameters: (each parameter can be set according to customer's product)

Overcharge protection voltage / 4.28 ± 0.025V per string

Over-discharge protection voltage 2.4±0.1V

Overcurrent value: 2~4A

Low-cost, safe and low-temperature cathode materials, but the material itself is not stable, easy to decompose and generate gas, so it is often used in combination with other materials to reduce the cost of the battery, but its cycle life decays faster. It is prone to bulging, low temperature performance and relatively short life. It is mainly used for large and medium-sized batteries and power batteries. Its nominal voltage is 3.7V.

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