A lithium ion battery is a secondary battery (rechargeable battery) that mainly relies on lithium ions moving between a positive electrode and a negative electrode to operate. During charge and discharge, Li+ is intercalated and deintercalated between the two electrodes: when charging, Li+ is deintercalated from the positive electrode, and the electrolyte is embedded in the negative electrode, and the negative electrode is in a lithium-rich state; The battery is generally made of a material containing lithium as an electrode, and is a representative of modern high-performance batteries. Lithium batteries are classified into lithium batteries and lithium ion batteries. Both mobile phones and laptops use lithium-ion batteries, which are commonly referred to as lithium batteries. True lithium batteries are rarely used in everyday electronics because of their high risk.
Lithium Ion Battery (Li-ion, Lithium Ion Battery): Lithium-ion batteries are widely used because of their light weight, large capacity, and no memory effect. Many digital devices now use lithium-ion batteries as power sources. Although its price is relatively expensive. Lithium-ion batteries have a high energy density, and their capacity is 1.5 to 2 times that of nickel-hydrogen batteries of the same weight, and has a very low self-discharge rate. In addition, the lithium-ion battery has almost no "memory effect" and does not contain toxic substances, which is also an important reason for its wide application.
The main types of lithium-ion batteries:
Since the introduction of lithium-ion batteries in the market in the early 1990s, due to its high energy density, high voltage, long cycle life, etc., it has developed rapidly, so the variety has increased rapidly. Lithium-ion batteries can be classified from different angles. Lithium-ion batteries are classified into liquid lithium-ion batteries (Liquified Lithium-Ion Battery, LIB for short) and polymer lithium-ion batteries (Polymer Lithium). -Ion Battery, referred to as PLB).
1. According to the type of electrolyte:
Liquid lithium ion battery:
The advantage is:
(1) Lithium ion conductivity is high? Conductivity in a wide temperature range is 3 & TImes; 10-3? 2 & TImes; 10-2 / cm;
(2) The chemical properties are stable, and the positive electrode, the negative electrode, the separator, and the current collector electrolyte solution do not substantially undergo a chemical reaction;
(3) The process of manufacturing the battery is relatively simple and the cost is low.
It is easy to leak and has poor safety performance. Liquid organic solvent electrolytes are prone to fire and explosion accidents.
Liquid lithium-ion batteries can also be divided into cylindrical and square batteries according to the shape of the battery.
The polymer battery can further be further classified into an all-solid electrolyte battery and a gel-type polymer electrolyte battery. At present, it is a gel-type polymer battery that has been put to practical use and put into mass production. The characteristics of this battery are:
(1) The electrolyte is in a gel state? It is safe and leak-proof;
(2) The ionic conductivity is close to that of a liquid lithium ion battery;
(3) the positive electrode, the separator and the negative electrode are bonded together;
(4) Using flexible packaging materials to reduce the weight of the battery;
(5) Thickness reduction and volume reduction? Any shape can be produced.
Polymer batteries are an important development direction for lithium-ion batteries, not only for small batteries, but also for large power batteries.
2. Classified according to the purpose and capacity of the battery:
According to the purpose and capacity, lithium-ion batteries can be divided into: portable electrical appliances, portable telephones, notebook computers, etc. Small lithium-ion batteries? The capacity of such batteries is generally less than 2Ah.
Large-capacity lithium-ion batteries are mainly used in electric tools, electric vehicles, Electricvehicle, EV? and Hybrid elecreic vehicles (HEV). As international oil prices continue to rise, the demand for lithium batteries for EVs and HEVs will increase rapidly. The power battery is used in electric vehicles. It requires a long distance for charging the electric vehicle. Therefore, the capacity of the battery is large, and the capacity of each battery is up to one hundred Ah. The HEV battery requires high power, and the capacity of the battery is about 10 Ah.
Rechargeable lithium-ion batteries are currently the most widely used batteries in modern digital products such as mobile phones and notebook computers, but they are more "squeaky" and cannot be overcharged or over-discharged during use (which can damage the battery or cause it to be scrapped). Therefore, there are protective components or protection circuits on the battery to prevent expensive battery damage. Lithium-ion battery charging requirements are very high, to ensure that the termination voltage accuracy is within ±1%, major semiconductor device manufacturers have developed a variety of lithium-ion battery charging IC to ensure safe, reliable and fast charging.
Mobile phones basically use lithium-ion batteries. Proper use of lithium-ion batteries is important to extend battery life. It can be made into flat rectangular, cylindrical, rectangular and button type according to the requirements of different electronic products, and has a battery pack composed of several batteries connected in series and connected in parallel. The rated voltage of a lithium ion battery is generally 3.7V due to a change in material, and 3.2V is a lithium iron phosphate (hereinafter referred to as a ferrophosphorus) positive electrode. The termination charging voltage when fully charged is generally 4.2V and the phosphorus iron is 3.65V. The termination discharge voltage of the lithium ion battery is 2.75V to 3.0V (the battery factory gives the working voltage range or gives the termination discharge voltage, and the parameters are slightly different, generally 3.0V, and the phosphorus iron is 2.5V). Continued discharge below 2.5V (phosphorus iron 2.0V) is called overdischarge, and overdischarge will damage the battery.
A lithium ion battery in which the lithium cobaltate type material is a positive electrode is not suitable for use as a large current discharge, and an excessive current discharge reduces the discharge time (a high temperature is generated internally to lose energy), and may be dangerous; but lithium iron phosphate The cathode material lithium battery can be charged and discharged with a large current of 20C or more (C is the capacity of the battery, such as C=800mAh, 1C charging rate, ie, charging current is 800mA), and is particularly suitable for electric vehicles. Therefore, the battery production plant gives the maximum discharge current, which should be less than the maximum discharge current in use. Lithium-ion batteries have certain requirements on temperature. The factory gives the charging temperature range, discharge temperature range and storage temperature range. Over-voltage charging will cause permanent damage to the lithium-ion battery. Lithium-ion battery charging current should be based on the recommendations of the battery manufacturer and require a limited current circuit to avoid overcurrent (overheating). The commonly used charging ratio is 0.25C to 1C. It is often necessary to detect the battery temperature during high current charging to prevent overheating from damaging the battery or exploding.
Lithium-ion battery charging is divided into two phases: first constant current charging, and changing to constant voltage charging when it is close to the termination voltage. For example, a battery of 800 mAh capacity has a termination charging voltage of 4.2V. The battery is charged at a constant current of 800 mA (charging rate 1C). At the beginning, the battery voltage is boosted with a large slope. When the battery voltage is close to 4.2V, it is changed to 4.2V constant voltage charging, the current gradually decreases, and the voltage does not change much. When the charging current drops to 1/10-50C (the setting value of each factory is different, it does not affect the use), it is considered to be close to full, and the charging can be terminated (some chargers start the timer after 1/10C, after a certain time) End charging).
Lithium-ion battery manufacturing process:
The positive electrode material of lithium battery is lithium cobalt oxide LiCoO2, ternary material Ni+Mn+Co, lithium manganate Li2MnO4 plus conductive agent and binder, coated on aluminum foil to form positive electrode, negative electrode is layered graphite plus conductive agent and bonding The agent is coated on a copper foil base tape, and nanoporous carbon has been used for the relatively advanced negative-layered graphite particles.
1. Pulping: Mixing with a powdery positive and negative active material with a special solvent and a binder, and mixing them to form a slurry of positive and negative materials.
2. Coating film: The positive and negative electrodes are uniformly coated on the surface of the metal foil by an automatic coating machine, and automatically cut into positive and negative pole pieces after being automatically dried.
3. Assembling: According to the process of positive electrode sheet-separator-negative electrode sheet-separator from the top to bottom, the electrolyte is injected into the electrolyte, sealed, and the positive and negative electrodes are welded, that is, the assembly process of the battery is completed, and the finished battery is fabricated.
Chemicalization: Place the finished battery in the test cabinet for charging and discharging test, and screen out the qualified finished battery, waiting for delivery.
Chemical analysis of lithium ion batteries:
Like all chemical batteries, lithium-ion batteries are also made up of three parts: the positive electrode, the negative electrode, and the electrolyte. The electrode materials are all lithium ions that can be intercalated (inserted)/deintercalated (deintercalated).
Cathode material: As mentioned above, there are many alternative cathode materials, and currently the mainstream products use lithium iron phosphate. Different cathode material comparisons:
Positive electrode reaction: Lithium ions are embedded during discharge, and lithium ions are deintercalated during charging. When charging: LiFePO4→ Li1-xFePO4 + xLi + xe Discharge: Li1-xFePO4+ xLi + xe →LiFePO4
Anode material: Graphite is mostly used. New research has found that titanate may be a better material. Negative reaction: Lithium ion is deintercalated during discharge, and lithium ions are inserted during charging. When charging: xLi + xe + 6C → LixC6 When discharging: LixC6 → xLi + xe + 6C
Generally divided into the following categories:
The first type is a carbon negative electrode material: the negative electrode materials currently used in lithium ion batteries are basically carbon materials, such as artificial graphite, natural graphite, mesophase carbon microspheres, petroleum coke, carbon fiber, pyrolysis resin carbon, etc. .
The second type is tin-based anode material: tin-based anode material can be divided into tin oxide and tin-based composite oxide. Oxide refers to an oxide of various valence metal tins. There are currently no commercial products.
The third type is a lithium-containing transition metal nitride anode material, and there are currently no commercial products.
The fourth type is an alloy-based anode material: including tin-based alloys, silicon-based alloys, bismuth-based alloys, aluminum-based alloys, bismuth-based alloys, magnesium-based alloys, and other alloys, and there are currently no commercial products.
The fifth type is a nano-scale anode material: carbon nanotubes, nano-alloy materials.
The sixth nanomaterial is nano-oxide material: At present, Hefei Xiangzheng Chemical Technology Co., Ltd. based on the latest development of the market development of lithium battery new energy industry in 2009, many companies have begun to use nano titanium oxide and nano silicon oxide to add to the traditional Graphite, tin oxide, and carbon nanotubes greatly increase the amount of charge and discharge and the number of charge and discharge cycles of lithium batteries.
1. Solute: Lithium salts such as lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF?) are often used.
2. Solvent: Since the working voltage of the battery is much higher than the decomposition voltage of water, lithium ion batteries often use organic solvents such as diethyl ether, ethylene carbonate, propylene carbonate, diethyl carbonate, and the like. Organic solvents often destroy the structure of graphite during charging, causing it to exfoliate, and forming a solid electrolyte interphase (SEI) on its surface to cause electrode passivation. Organic solvents also pose safety issues such as flammability and explosives.