The principle of lithium battery - lithium battery working principle analysis and precautions

A, the principle of lithium batteries

1, a brief description of lithium batteries and the working principle of lithium-ion batteries since its introduction in 1990, because of its excellent performance has been rapid development, and widely used in society. Lithium-ion batteries to other batteries are incomparable advantages quickly occupied many areas, such as familiar cell phones, laptops, small cameras and so on. At present, the basic principle of lithium batteries is recognized as the so-called "rocking chair theory. The charge and discharge of lithium battery is not through the traditional way to achieve the transfer of electrons, but through the lithium ion in the layer of strong material in and out of the crystal, the energy change. Under normal charging and discharging conditions, the entry and exit of lithium ions generally only cause changes in the layer spacing, but not the destruction of the crystal structure, so from the charge and discharge reflection, lithium-ion batteries are an ideal reversible battery. In the charge and discharge of lithium ions in the battery positive and negative back and forth, is like a rocking chair in the positive and negative electrode swing around, so some people will lithium-ion battery image called rocking chair battery. We often say that the superiority of lithium-ion batteries is for the traditional nickel-cadmium batteries (Ni/Cd) and nickel-metal hydride batteries (Ni/MH) to speak. It has the advantages of high working voltage, high specific energy, long cycle life, low self-discharge rate, no memory effect, etc.

1. Lithium-ion battery lithium-ion battery contains two electrodes blocked by electrolyte. Electrolyte is an ion conductor and electron insulator. During the discharge process, the battery converts chemical energy into electrical energy. The battery pack can contain several or individual cells connected in parallel series. Lithium-ion batteries are known as rocking chair or swing batteries because the charge medium travels through the electrolyte during charging and discharging and is embedded in or migrated out of the electrode material.

2. Battery voltage In a sense, the battery can be seen as a "charge" pump. The pressure difference between the positive and negative terminals is referred to as the voltage or electric potential. The free energy of electron transfer through the external circuit and the chemical voltage between the two electrodes of the lithium ion between the two ends are related. The higher the potential of the electrodes, the more difficult it is for the Li in the material to migrate out. During discharge, Li is able to migrate from a higher energy state in the anode to a lower energy state in the cathode. The cell relies on its electrochemically active material to store chemical energy. This energy can be converted to electrical energy through redox reactions as required.

3. The composition of a lithium-ion battery generally contains three main components: anode, cathode, and electrolyte. Anode: During discharge, electrons are transferred away through an external circuit and the electrode material is oxidized. Most commercial batteries use a carbon/graphite based electrode material; however, metals or alloys can also be used as anode materials. Cathode: During discharge, electrons are received through an external circuit; usually transition metal oxides or phosphides are used as the cathode material. Electrolyte: The electrolyte is an ionic conductor, a poor conductor of electrons. The electrolyte blocks the cathode and anode of the battery and provides a medium for electron transfer. Electrolytes generally use some non-aqueous organic solvents in which some Li+ containing salts are dissolved. For example, LiPF6 is dissolved in propylene carbonate. Note: The introduction of diaphragm and shell is omitted here.

4. Charging and discharging process of lithium-ion battery

A. Charging process electrons are generally assembled in the discharged state. During the charging process, the cathode material (e.g., LiCoO2) is oxidized and the lithium ions are removed from the layered intercalation material, passed through the electrolyte and then intercalated into the graphite layer.

B. Discharge process During the discharge process, the negative electrode is oxidized and the lithium ions are removed from the anode and reinserted into the cathode through the electrolyte. Correspondingly, a corresponding number of electrons cross the external circuit to balance the charge. At the same time, the cathode material receives electrons from the external circuit and Li+ ions from the solution, resulting in a reduction reaction. The exchange of electron and ion currents occurs at the electrode and electrolyte interfaces. Battery based on intercalation mechanism - reversible insertion of a foreign ion into the solid structure without damaging the structure of the host material

2, lithium batteries in the process of daily use of common sense

(1), the misconception: "battery activation, the first three charging more than 12 hours" for the lithium battery "activation" problem, many say: charging time must be more than 12 hours, repeatedly do three times in order to activate the battery. This "the first three charges must be charged more than 12 hours" statement, obviously from the nickel batteries (such as NiCd and NiMH) continued down the statement. Therefore, it can be said that this statement is a misinformation from the beginning. After a sample survey, it can be seen that a significant number of people confuse the two battery charging methods. The charge and discharge characteristics of lithium and nickel batteries are very different, and all the serious official technical information consulted emphasizes that overcharging and overdischarging can cause great harm to lithium batteries, especially liquid lithium-ion batteries. Therefore, it is best to charge according to the standard time and standard method, especially do not carry out more than 12 hours of ultra-long charging. Usually, the charging method introduced on the phone manual is the standard charging method for the phone.

(2), do not benefit from a long time charging, the battery is completely used up and then charged lithium battery phones or chargers will automatically stop charging after the battery is full, and there is no nickel charger so-called "trickle" charging that lasts more than 10 hours. If the lithium battery in full, put on the charger is also no longer charged. Overtime charging and completely empty power will cause overcharging and overdischarging, which will cause permanent damage to the positive and negative electrodes of lithium-ion batteries, from the molecular level, overdischarging will lead to excessive release of lithium ions from the negative carbon and make the collapse of its sheet structure, overcharging will be too much lithium ions hard into the negative carbon structure, and make some of the lithium ions can no longer be released.

(3), battery life on the lithium-ion battery charge and discharge cycle of the experimental table, the cycle life data are listed below (DOD is the abbreviation for depth of discharge): cycle life (10% DOD): > 1000 cycle life (100% DOD): > 200 times from the above data can be seen, the number of rechargeable and depth of discharge, 10% DOD cycle life than 100 The cycle life at 10% DOD is much longer than that of 100% DOD. Of course, if converted to the actual charge of the relative total capacity of 10% * 1000 = 100, 100% * 200 = 200, the latter is still better than the complete charge and discharge. But the life of lithium batteries is mainly reflected in the charge and discharge cycle, the cycle is an absolute concept, the last time you use 30% of the power, fully charged, and the next time you use 70% of the power, and fully charged, this is just a charging cycle. So still follow the lithium battery inventor's slogan "use that charge, that charge that use" method of using lithium batteries.

(4), regular deep charging and discharging lithium-ion batteries generally come with a management chip and charge control chip. Among them, the management chip has a series of registers, there are capacity, temperature, ID, charging status, discharge times and other values. These values will gradually change in use. Instructions for use of "use about a month should be fully charged and discharged once" practice should be the main role of the correction of these registers inappropriate values.