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The Basic knowledge of Lithium Battery

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The Basic knowledge of Lithium Battery
Latest company news about The Basic knowledge of Lithium Battery

 

 

This article is Herculesi original article, if you need to copy, please contact: david@herculesi.com, or by phone: +86-13632987139.

Do not copy without permition,Unauthorized duplication is a violation of applicable laws.

 

The Basic knowledge of Lithium Battery?

1. What is the relatively recognized development route for lithium batteries in the industry?

After the unremitting efforts of R&D personnel and engineers, from lead-acid batteries, nickel-hydrogen batteries, nickel-cadmium batteries, to lithium iron phosphate batteries, and now to the mainstream ternary batteries, every upgrade is a generation of efforts, Based on the safety, energy density and rate performance of lithium batteries, combined with the current state of battery research and development, a development route for lithium batteries in the future is summarized.

 

In 2020, it is a multi-cation electrode, mainly composed of NCM and NCA composite cathode materials, and the negative electrode is mainly composed of C and a part of silicon-carbon composite, and the energy density is about 300-350 wh/kg.

 

From 2020 to 2025, it is based on all-solid-state lithium-ion batteries, metal lithium anodes or silicon-carbon anodes. Energy density 400 wh / kg, while developing sodium ion batteries, sodium is cheaper than lithium, but larger than lithium ions, and there is liquid memory.

 

After 2025, mainly lithium-sulfur batteries --> lithium metal batteries --> lithium air battery development, such batteries, energy density is higher, the material is more convenient, but there are more The problem still needs to be continued. The lithium-sulfur battery is a lithium battery with a sulfur element as the positive electrode and lithium metal as the negative electrode. Elemental sulfur is abundant in the earth and has the characteristics of low price and environmental friendliness. The lithium-sulfur battery using sulfur as the positive electrode material has higher theoretical theoretical specific capacity and battery theoretical energy, reaching 1675 mAh/g and 2600 Wh/kg, respectively, which is much higher than the ternary battery widely used in commercial applications.

 

And sulfur is an environmentally friendly element, which has no pollution to the environment. It is a very promising lithium battery. Lithium metal batteries use lithium metal foil instead of graphite. It can hold more ions, but usually lithium. Metal foil and electrolyte can cause adverse reactions, which can lead to overheating of the electrolyte and even cause burning. This technology can reduce the current lithium battery volume by half. In theory, if the battery volume is constant, in the case of lithium metal battery The cruising range of electric vehicles will be doubled; lithium-air batteries are batteries that use lithium as the anode and oxygen in the air as the cathode reactant. Lithium-air batteries have a higher energy density than lithium-ion batteries because their cathodes (mainly porous carbon) are very light, and oxygen is taken from the environment without being stored in the battery. In theory, oxygen is not used as a cathode reactant. Restricted, the capacity of the battery depends only on the lithium electrode, and its specific energy is 5.21 kWh/kg (including oxygen mass), or 11.4 kWh/kg (excluding oxygen).

 

2. What are the basic requirements for energy carriers?
(1) The relative mass of the atom is small;
(2) Strong ability to gain and lose electrons;
(3) The proportion of electronic transfer should be high.
 

3. What are the main indicators of the battery?

(1) capacity;

(2) energy density;

(3) charge and discharge rate;

(4) voltage;

(5) life expectancy;

(6) internal resistance;

(7) self-discharge;

(8) Operating temperature range.

 

4. What are the characteristics of cathode materials (LFP, NCM, LiCo, etc.)?

(1) higher redox reaction potential, high output voltage;

(2) High lithium content and high energy density;

(3) structural stability in chemical reactions;

(4) High conductivity;

(5) Good chemical stability and thermal stability, not easy to decompose and react;

(6) the price is cheap;

(7) The production process is relatively simple and suitable for large-scale production;

(8) It is environmentally friendly and has low pollution.

 

5. What are the characteristics of the anode material (Li, C, AL, lithium titanate, etc.)?

(1) Layered structure or tunnel structure, which facilitates deintercalation;

(2) stable structure, good charge and discharge reversibility and cycle performance;

(3) Insertion and deintercalation of lithium ions as much as possible;

(4) low redox potential;

(5) The first irreversible discharge capacity is low;

(6) Good compatibility with electrolyte solvent;

(7) The price is low and the materials are easy to obtain;

(8) Good security;

(9) Environmentally friendly.

 

6. What are the usual ways to increase battery energy density?

(1) increasing the proportion of positive and negative active materials;

(2) increasing the specific capacity (gram capacity) of the positive and negative materials;

(3) Weight loss and weight loss.

 

7. how to improve the charge and discharge rate of lithium-ion batteries?

(1) improving the lithium ion diffusion ability of the positive and negative electrodes;

(2) increasing the ionic conductivity of the electrolyte;

(3) Reduce the internal resistance of the battery (ohm internal resistance and polarization internal resistance).

 

8. What factors affect the cycle life of lithium-ion batteries?

(1) deposition of negative metal lithium;

(2) decomposition of the positive electrode material;

(3) Formation and re-consumption of SEI;

(4) The influence of electrolytes is mainly manifested in: the total amount is reduced, impurities are present, and water is infiltrated;

(5) The diaphragm is blocked or destroyed;

(6) The positive and negative materials are detached;

(7) External use factors.

 

9, lithium ion battery internal material reaction decomposition temperature?

(1) SEI membrane decomposition, electrolyte exothermic reaction, 130 ° C;

(2) decomposition of electrolytes, heat production, 130 ° C -250 ° C;

(3) decomposition of the cathode material to produce a large amount of gas and oxygen, 180 ° C -500 ° C;

(4) Reaction of a binder and a negative electrode active material, 240 ° C - 290 ° C.

Generally, due to overcharging, large rate discharge, internal short circuit, external short circuit, vibration, collision, drop, impact, etc., short circuit occurs, resulting in a large number of

A process of heat and gas.

 

10, the most potential lithium battery materials in the future

(1) Silicon-carbon composite anode material with high energy density and industrialization above 400 wh/kg, but the volume expansion is serious and the cycle is poor;

(2) Lithium titanate, circulation more than 10,000 times, volume change <1%, no dendrite formation, excellent stability, fast charging, but high price, low energy density, about 170 wh / kg;

(3) Graphene, which can be used for anode materials and positive electrode additives, has excellent conductivity, fast ion transmission, poor first effect, about 65%, poor cycle and high price;

(4) Lithium-rich manganese-based battery, energy density is about 900 wh / kg, raw materials are rich, but the first effect is low, safety and cycle are poor, and the rate performance is low;

(5) NCM ternary material, generally 250 wh / kg, coupled with a silicon carbon negative electrode, about 350 wh / kg;

(6) CNTs, carbon nanotubes, excellent electrical conductivity, excellent thermal conductivity;

(7) coating the diaphragm, base film + PVDF + boehmite, improving the shrinkage resistance of the diaphragm, low heat conduction, preventing all thermal runaway;

(8) High-voltage electrolyte, this needless to say, with the energy density of the energy material, the voltage is also increased accordingly;

(9) Aqueous binders for environmental protection and health.

 

11. What is pre-lithiation?

Pre-lithiation, before I talk about this, let me talk about the first-effect problem of the half-cell (positive electrode is the positive electrode material, the negative electrode is the metal lithium plate) and the whole battery.

This is the first effect of lithium cobalt oxide half-cell. It doesn't matter if you don't understand the whole battery and the half-cell. You understand that this is the first effect of the positive electrode material.

latest company news about The Basic knowledge of Lithium Battery  0

From the above figure, we can see that the first charge capacity of the half-cell is slightly higher than the first discharge capacity, that is, the lithium ion deintercalated from the positive electrode during charging does not return to the positive electrode when it is discharged. The first discharge capacity / first charge capacity is the first efficiency of this half-cell.

 

The first effect of lithium iron phosphate positive half battery.

latest company news about The Basic knowledge of Lithium Battery  1

 

NCM positive half-cell first effect.

latest company news about The Basic knowledge of Lithium Battery  2

As can be seen from the above figures, the first efficiency of ternary is the lowest, generally 85~88%; lithium cobaltate is the second, generally 94~96%; lithium iron phosphate is slightly higher than lithium cobaltate, 95%~97%. The first effect of the positive electrode material is mainly due to the change of the structure of the positive electrode material after deintercalation occurs. There is not enough lithium insertion position, and lithium ions cannot be returned all at the first discharge.

 

Graphite anode half-cell first effect.

latest company news about The Basic knowledge of Lithium Battery  3

 

The graphite battery half-cell and the positive electrode are different. The graphite is used as the positive electrode and the lithium metal plate is used as the negative electrode. Therefore, the first discharge of the graphite is significantly lower than that of the positive electrode material. The main reason is that the lithium ion passes through the electrolyte and will be in the The surface of the graphite forms an SEI film, which consumes a large amount of lithium ions. Lithium ions dedicated to the SEI film cannot be returned to the negative electrode.

 

The first battery efficiency, after the battery is injected, it needs to be processed (charge only) and divided into (charge and discharge). Generally speaking, the first step of the formation and volume separation is the charging process. And, that is, the full battery is charged for the first time; the second step of the distributing step is generally discharging from the fully charged state to the empty power, so the capacity of this step is the discharge capacity of the full battery. Combining the two, we get the algorithm for the first battery efficiency:

 

First battery efficiency = volume capacity second step discharge capacity / (chemical filling capacity + volume first filling capacity)

 

In order to reduce the deviation in daily life, the second full discharge capacity is taken as the battery capacity.

 

In summary, we can draw a conclusion. If the positive electrode of the battery uses a ternary material with a first efficiency of 88%, and the negative electrode uses a graphite material with a first efficiency of 92%. For this full battery, the first efficiency is 88%, that is, when the positive first effect is 88% and the negative first effect is 92%, the first effect of the full battery is 88%, which is equal to the lower positive electrode.

 

Of course, in addition to the influence of the battery material on the first effect, the specific surface area of ​​the electrode material is also an important factor. The larger the specific surface area of ​​graphite, the larger the SEI film formed, the more lithium ions need to be consumed, and the lower the first effect. In addition, it is also related to the battery charging system. Filling in the appropriate SOC will also affect the battery's first effect to some extent.

 

latest company news about The Basic knowledge of Lithium Battery  4

For a full battery, the SEI film formed at the interface of the negative electrode during the formation consumes lithium ions deintercalated from the positive electrode and reduces the capacity of the battery. If we can find a lithium source from the outside of the positive electrode material, the formation of the SEI film consumes the lithium ion of the external lithium source, so that the lithium ion of the positive electrode deintercalation is not wasted in the formation process, and finally the full battery can be improved. capacity. This process of providing an external lithium source is pre-lithiation.

 

Below I will borrow an article to tell you about the main pre-lithiation method, and I have only seen one, that is, the negative electrode sprayed lithium powder

method.

 

1, the negative electrode advancement method.

We can separate the negative electrode into a single layer, and then form the SEI film and then assemble it with the positive electrode. This can avoid the loss of the positive electrode lithium ion and greatly improve the first cell efficiency and capacity of the whole battery, as shown in the figure:

latest company news about The Basic knowledge of Lithium Battery  5

In the above figure, the negative electrode sheet and the lithium sheet are immersed in the electrolyte and charged by an external circuit. This ensures that the lithium ions consumed in the formation are derived from the lithium metal sheet rather than the positive electrode. After the formation of the negative electrode sheet is completed, the positive electrode sheet is assembled, and the battery core does not need to be further formed, so that the lithium ion of the positive electrode is not lost due to the formation of the SEI film by the negative electrode, and the capacity is also remarkably improved.

 
The advantage of this pre-lithiation method is that it can simulate the normalization process to the maximum extent, while ensuring that the formation of the SEI film is similar to that of the whole battery. However, the two steps of the advancement of the negative electrode sheet and the assembly of the positive and negative electrode sheets are too difficult to operate.
 

2, the negative electrode sprayed lithium powder method.

Since the use of the negative electrode sheet alone to form lithium is difficult to handle, a lithium-removing method for directly spraying lithium powder on the negative electrode sheet is conceivable. First, a stable metal lithium powder particle is prepared. The inner layer of the particle is metallic lithium, and the outer layer is a protective layer having good lithium ion conductivity and electron conductivity. In the pre-lithiation process, the lithium powder is first dispersed in an organic solvent, and then the dispersion is sprayed on the negative electrode sheet, and then the residual organic solvent on the negative electrode sheet is dried, thereby obtaining a pre-lithiated negative electrode sheet. Subsequent assembly work is consistent with normal processes.
 
When formed, the lithium powder sprayed on the negative electrode is consumed by the formation of the SEI film, thereby maximally retaining lithium ions deintercalated from the positive electrode and increasing the capacity of the entire battery.
The following figure shows the efficiency comparison of the negative silicon alloy and the positive lithium cobalt oxide battery. It can be seen that after the pre-lithiation of the negative electrode, the first efficiency is obviously improved:
latest company news about The Basic knowledge of Lithium Battery  6

The disadvantage of using this pre-lithiation method is that the safety is difficult to guarantee, and the cost of material and equipment modification is high.

 

3, negative electrode three-layer electrode method.

Due to the limitations of equipment and processes, the simple cost-effective transformation for pre-lithiation is not a priority for battery manufacturers. If pre-lithiation can be done in a familiar way with battery manufacturers, the promotion is greatly enhanced. The three-layer electrode method described below makes the operation of the battery factory simpler.

Compared with the normal copper foil, the copper foil of the three-layer electrode method is coated with the metal lithium powder required for later formation, in order to protect the lithium powder from reacting with air, a protective layer is applied; the negative electrode is directly coated on the copper foil. Protective layer

 

When the cell is filled, the protective layer is dissolved in the electrolyte, so that the metal lithium is in contact with the negative electrode, and the lithium ions consumed in forming the SEI film during the formation are replenished by the lithium metal powder. The electrode after charging is shown as follows: This method has no strict requirements on the processing conditions of the battery factory, but the stability of the protective layer in the position of the pole piece rewinding, rolling, cutting and the like is a great challenge to the development of the electrode material. It is also difficult to guarantee the adhesion of the negative electrode material after the metal lithium powder is formed into a disappearance.

 

4, positive lithium rich material method.

The small partners who work in the enterprise must have deeply realized that even if the things that can be successful under the laboratory conditions are moved to the large-scale production of the enterprise, it is likely to be difficult. The cost of equipment transformation, the cost of material input, and the cost of controlling the processing environment may become fatal injuries that cannot be promoted by new technologies. For the industry where lithium-ion technology and equipment are basically mature, the pre-lithiation scheme preferred by enterprises will definitely be a method that can be directly promoted without too many on-site changes or even taking over. And the cathode is rich in lithium

The material method just meets the needs of this aspect of the battery factory.

 

The so-called positive lithium-rich method can be simply understood as that there is such a material, when the chemical is formed, the number of lithium ions released by her positive electrode is several times the number of lithium ions that can be released by the materials currently used. . When the first effect of the negative electrode is lower than the positive electrode, too much lithium ion is lost to the negative electrode during the formation, which causes the effective space of the positive electrode to be underfilled by the lithium ion after the discharge, thereby forming a waste of the lithium-inserted space of the positive electrode. If a small amount of high-capacity lithium-rich material is added to the positive electrode, this can provide more lithium ions for the formation of the SEI film during the formation.

Don't worry about the lithium-rich material not being able to re-insert lithium during discharge (because all the lithium ions supplied by the lithium-rich material have been consumed during the formation)

 

The various pre-lithiation methods described above are directed to a full battery in which the negative electrode is lower than the positive electrode. After the pre-lithiation of the whole battery, the first efficiency is the highest, and the level of the positive electrode material half-cell can only be reached. For the battery with lower initial effect, the above method is basically powerless, because the first effect of the whole battery is limited by the fact that there is no longer enough lithium intercalation space after the positive charge, even if the external lithium is added, Embedded in the positive electrode, thus no effect.

 

This article is Herculesi original article, if you need to copy, please contact: david@herculesi.com, or by phone: +86-13632987139.

Do not copy without permition,Unauthorized duplication is a violation of applicable laws.

Pub Time : 2019-04-10 14:40:16 >> News list
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