the lithium battery charging process

 

Lithium-ion batteries generally use lithium alloy metal oxide as the positive electrode material, graphite as the negative electrode material, and the non-aqueous electrolyte. Almost all mobile phones we use are lithium batteries. At present, most of the popular electric vehicles on the market are powered bylithium iron phosphate batteries. How do the lithium batteries charge and discharge?

First, let’s take a look at the structure of lithium batteries. Lithium batteries are generally composed of a positive electrode, negative electrode, electrolyte, and separator. Our common mobile phone lithium batteries are square in daily life. The batteries in electric vehicle battery packs are generally round. There are laminated and winding types. In addition to the positive and negative electrodes of the four contacts on a common mobile phone battery, the remaining contacts are simply used to detect (or monitor) various information of the mobile phone battery.

The positive electrode of lithium battery is generally lithium manganese oxide or lithium cobalt oxide, and lithium nickel cobalt manganese oxide materials. Electric bicycles generally use lithium nickel cobalt manganese oxide (commonly known as ternary) or ternary + a small amount of lithium manganate; the negative electrode is generally active The material is graphite or carbon with a similar graphite structure. The separator between the positive electrode and the negative electrode is a specially formed polymer film with a pore size that satisfies good ion permeability and also has electronic insulation, which allows lithium ions to pass freely. And electrons cannot pass. The electrolyte plays a role in transporting charges between the positive and negative electrodes. Generally, it is a carbonate-based solvent in which lithium hexafluorophosphate is dissolved, and a gel electrolyte is used for polymers.

When alithium batteryis charged, the positive electrode releases lithium ions, and the lithium ions pass through the diaphragm through the electrolyte, move to the negative electrode, and combine with the electrons of the abdominal muscles. At this time, the chemical reaction of the positive electrode is LiCoO2=Li(1-x)CoO2 +xLi++xe- (electron), the chemical reaction on the negative electrode is 6C+xLi++xe- = LixC6. When a lithium battery is discharged, the movement of lithium ions is exactly the opposite. Lithium ions enter the electrolyte from the negative electrode, pass through the diaphragm and finally reach the positive electrode, while the electrons travel from the negative electrode to the positive electrode by the external circuit (the direction of electron movement is opposite to the current direction), and the positive electrode This process can make the lithium battery output electric energy.

The charging process of lithium batteries is generally divided into three stages: trickle charging, constant current charging, and constant voltage charging. Take a mobile phone battery as an example. When charging starts, the internal charging management chip first detects the voltage of the battery to be charged. If the voltage is lower than 3V, pre-charge is required. The charging current is 1/10 of the set current and the voltage rises to 3V. , Into the standard charging process. The standard charging process is constant current charging with the set current, when the battery voltage rises to 4.20V, change to constant voltage charging, and keep the charging voltage at 4.20V. At this time, the charging current gradually decreases, and when the current drops to 1/10 of the set charging current, charging ends. Generally, the output voltage of a mobile phone charger is 5V, and the charging management chip inside the mobile phone is responsible for reducing the voltage to 3.7V suitable for the mobile phone battery.

Lithium batteries have relatively high energy. It has a high storage energy density, reaching 460-600Wh/kg, which is about 6-7 times that of lead-acid batteries; long service life, generally up to six years; high power endurance; low self-discharge rate. The applications in daily life are becoming wider and wider.

High-voltage Lithium Batteries Development

 

A high-voltage battery refers to a battery whose battery voltage is relatively higher than the ordinary battery that we use. With the development of global diversification, our lives are constantly changing, including the various electronic products we come into know. Then you must not know some of the components of these products, such as high-voltage lithium-ion batteries.

With the continuous improvement of the requirements for the capacity of lithium-ion batteries by electrical equipment, people have higher and higher expectations for the improvement of the energy density of lithium-ion batteries. In particular, various portable devices such as smart-phones, tablet computers, and notebook computers have put forward higher requirements for lithium-ion batteries with small size and long standby time. Also in other electrical equipment, such as energy storage equipment, power tools, electric vehicles, etc., are constantly developing lithium-ion batteries with lighter weight, smaller size, higher output voltage, and power density, so the development of high energy density Lithium-ion batteries are an important research and development direction in the lithium battery industry.

A high-voltage battery refers to a battery whose battery voltage is relatively higher than the ordinary battery. According to battery cells and battery packs, it can be divided into two types. The high-voltage battery is defined from the voltage of the battery cell. This aspect is mainly for lithium batteries. At present, the types of lithium battery cells mainly include high-voltage lithium battery cells and low-voltage lithium battery cells.

At present, lithium cobalt oxide has been widely studied and applied as a high-voltage anode material. The structure is non-nafeo2 type, which is more suitable for lithium-ion insertion and ejection. The theoretical energy density of lithium cobalt oxide is 274mAh/g, the production process is simple, the electrochemical performance is stable, and the market occupancy is high. In practical applications, only part of lithium ions can be reversibly inserted and ejected. The actual energy density is about 167mAh/g (working voltage is 4.35v). Increasing the working voltage can significantly increase the energy density. For example, increasing the operating voltage from 4.2v to 4.35v can increase the energy density by about 16%.

High-voltage lithium battery cells have higher energy density and lower safety performance than low-voltage batteries, but their discharge platform is relatively high. Under the same capacity, high-voltage batteries are lighter than low-voltage batteries in terms of volume and weight.

With the increase in voltage, high-voltage lithium-ion batteries will reduce certain safety performance during use, so they have not been used in batches in power vehicles. At present, the battery cathode materials used in power vehicles are mainly ternary materials and lithium iron phosphate. To increase the energy density to meet the demand, generally choose 811NCM and NCA and other high nickel cathode materials, high capacity silicon-carbon anode or improve battery space utilization and other methods to improve its energy density and endurance.

High current and high voltage make lithium cobalt oxide materials used in high-energy-density batteries, such as high-end mobile phone battery manufacturers’ increasingly high battery performance requirements, which are mainly reflected in the demand for higher energy density, such as carbon requirements for 4.35V battery cathodes The energy density is about 660wh/L, and the 4.4V battery has reached about 740wh/L. This requires the anode material to have a higher compaction density, a higher empty volume, and the structure of the material under high pressure and high pressure has a better stability. However, lithium cobalt oxide electrode materials have shortcomings such as scarcity of cobalt resources, high prices, and certain toxicity of cobalt ions, which limit its wide application in power lithium batteries.

In terms of discharge rate of high-voltage and low-voltage batteries, high-voltage lithium batteries have a higher discharge rate and stronger power than low-voltage lithium batteries. Therefore, in theory, a high-voltage battery should be more suitable for use in products and equipment that require high-rate discharge. , In order to better exert its advantages.

In the process of research and design, there must be problems of one kind or another. This requires our scientific research workers to constantly sum up the experience in the design process in order to promote continuous product innovation.

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