Deep Interpretation of the Origin and Development Prospects of Lithium-ion Battery

Lithium batteries are new high-energy batteries developed in the 20th century. They can be understood as batteries containing lithium elements (including metallic lithium, lithium alloys, lithium ions, and lithium polymers). Can be divided into lithium metal batteries (very little production and use) and lithium ion batteries (now used in large quantities). Because of its advantages such as high energy, high battery voltage, wide operating temperature range, and long storage life, it has been widely used in military and civilian small appliances such as mobile phones, portable computers, cameras, and cameras, and has partially replaced traditional batteries.

Origin and Development of Lithium-ion Battery

In the 1970s, Exxon's M.S. Whittingham used titanium sulfide as a positive material and metallic lithium as a negative material to make the first lithium battery.

In 1980, J. Goodenough discovered that lithium cobalt can be used as a cathode material for lithium ion batteries.

R.Agarwal and J.R. Selman of the Illinois Institute of Technology in 982 found that lithium ions have the characteristics of embedded graphite. This process is fast and reversible. At the same time, lithium batteries made of metallic lithium have received much attention for their safety hazards. Therefore, people try to use the characteristics of lithium ion embedded in graphite to make rechargeable batteries. The first available lithium-ion graphite electrode was successfully trial-produced by Bell Labs.

In 1983, M. Thackeray, J. Goodenough and others discovered that manganese spinel is an excellent positive material with low price, stability, and excellent conductive and lithium conductivity. Its decomposition temperature is high, and its oxidization is much lower than that of lithium cobalt. Even if there is a short circuit and overcharging, it can avoid the danger of combustion and explosion.

In 1989, A. Manthiram and J. Goodenough found that the positive electrode using polymeric anions would generate higher voltage.

In 1991 Sony released its first commercial lithium-ion battery. Subsequently, lithium-ion batteries revolutionized consumer electronics.

In 1996 Padhi and Goodenough discovered that phosphates with olivine structure, such as lithium iron phosphate (LiFePO4), are more advantageous than traditional positive materials and have therefore become the current mainstream positive materials.

Li-ion batteries are developed from lithium batteries. So before introducing Li-ion, introduce lithium batteries. For example, button batteries belong to lithium batteries. The positive electrode material of the lithium battery is manganese dioxide or thionyl chloride, and the negative electrode is lithium. After the battery is assembled, the battery has a voltage and does not need to be charged. This type of battery can also be charged, but the cycle performance is not good. During the charging and discharging cycle, lithium dendrites are easily formed, resulting in a short circuit in the battery, so the battery is generally prohibited from charging.

Later, Sony Corporation of Japan invented a lithium battery with a carbon material as a negative electrode and a lithium compound as a positive electrode. During the charging and discharging process, no metallic lithium exists, only lithium ions, which is a lithium ion battery.

In the early 1990s, Japan's Sony Energy Development Corporation and Canada's Moli Energy Company independently developed a new type of lithium-ion battery, which not only has good performance, but also has no pollution to the environment. With the rapid development of information technology, hand-held machinery and electric vehicles, the demand for high-efficiency power supplies has increased dramatically, and lithium batteries have become one of the fastest growing areas.

Structure and Principle of Lithium-ion Battery

The main composition of lithium-ion batteries:

(1) Positive-Active substances mainly refer to lithium cobalt acid, lithium manganese acid, lithium iron phosphate, lithium nickel acid, lithium nickel cobalt manganese acid, etc. The conductive set fluid generally uses aluminum foil with a thickness of 10-20 microns;

(2) Divisor-A special plastic film that allows lithium ions to pass through, but is an insulator of electrons. Currently, there are two types of PE and PP and their combinations. There is also a class of inorganic solid diaphragm, such as aluminum oxide diaphragm coating is an inorganic solid diaphragm;

(3) Negative-Active substances mainly refer to graphite, lithium titanate, or carbon materials similar to graphite structures. Conductive fluids generally use copper foil with a thickness of 7-15 microns;

(4) Electrolytes-generally organic systems, such as carbonated solvents that dissolve lithium hexafluorophosphate, and some polymer batteries using gelatinous electrolytes;

(5) Battery shell-mainly divided into hard shell (steel shell, aluminum shell, nickel-plated iron shell, etc.) and soft package (aluminum plastic film) two kinds.

When the battery is charged, lithium ions are deintercalated from the positive electrode and embedded in the negative electrode, and vice versa when discharging. This requires an electrode to be in a state of lithium insertion before assembly. Generally, a lithium intercalation transition metal oxide having a potential greater than 3 V and stable in air is selected as a positive electrode such as LiCoO2, LiNiO2, and LiMn2O4.

Materials used as negative poles select emplaced lithium compounds with potentials as close as possible to lithium potentials, such as various carbon materials including natural graphite, synthetic graphite, carbon fiber, intermediate phase pellet carbon, etc., and metal oxides. Including SnO, SnO2, tin compound oxide SnBxPyoz (x = 0.4 ~ 0.6, Y = 0.6 ~ 0.4, Z = (2 +3 X +5 Y) / 2) and so on.

The electrolyte uses a mixed solvent system with alkyl carbonates such as LiPF6 vinyl carbonate (EC), propylene carbonate(PC), and low-viscosity diethyl carbonate(DEC).

The diaphragm adopts polyene microporous membranes such as PE, PP or their composite membranes. In particular, the PP / PE / PP three-layer diaphragm not only has a low melting point, but also has a high anti-puncture strength and plays a thermal insurance role.

The shell is made of steel or aluminum, and the cover assembly has the function of explosion-proof power outage.

Basic working principles

When the battery is charged, the lithium compound containing the positive electrode is removed from the lithium ion, and the lithium ion moves through the electrolyte to the negative electrode. The negative carbon material has a layered structure. It has many micropores. The lithium ion that reaches the negative electrode is embedded in the micropores of the carbon layer. The more lithium ions are embedded, the higher the charging capacity.

When the battery is discharged (that is, when we use the battery), the lithium ion embedded in the negative carbon layer is released and it moves back to the positive pole. The more lithium ions that return to the positive pole, the higher the discharge capacity. What we usually refer to as battery capacity refers to discharge capacity.

In the process of charging and discharging a lithium-ion battery, lithium ions are in the state of motion from the positive pole → negative pole → positive pole. This is like a rocking chair. The ends of the rocking chair are the poles of the battery, and lithium ions move back and forth at the ends of the rocking chair. Therefore, lithium-ion batteries are also called rocking chair batteries.

Charging and discharge mechanism

The charging process of lithium-ion batteries is divided into two stages: constant current charging phase and constant voltage decreasing current charging phase.

Excessive charge and discharge of lithium-ion batteries can cause permanent damage to the positive and negative poles. Excessive discharge leads to the collapse of the negative carbon layer structure, and the collapse will cause lithium ions to fail to insert during the charging process; Excessive charging allows too many lithium ions to be embedded in the negative carbon structure, causing some of these lithium ions to no longer be released.

Lithium-ion batteries maintain the best charging and discharging mode for shallow filling and shallow. In general, 60 % of the DOD is 2 to 4 times the cyclic life under 100 % DOD conditions.

Main Performance Indicators of Lithium-ion Battery

Battery capacity

The capacity of the battery is divided into rated capacity and actual capacity. The rated capacity of the battery refers to the amount of electricity that the battery should provide at an ambient temperature of 20 °C ± 5 °C at a rate of 5 H to the termination voltage, expressed in C5. The actual capacity of the battery refers to the actual amount of electricity emitted by the battery under certain discharge conditions. It is mainly affected by the discharge ratio and temperature (so strictly speaking, the battery capacity should indicate the charging and discharging conditions).

Capacity units: mAh, Ah (1Ah = 1000mAh).

Internal resistance of batteries

The internal resistance of a battery is the resistance that the current flows through the inside of the battery when the battery is working. There are two parts of ohmic resistance and polarized internal resistance. The large internal resistance value of the battery will lead to a reduction in the voltage of the battery discharge and a shortening of the discharge time. Internal resistance is mainly affected by the battery materials, manufacturing processes, battery structure and other factors. Internal resistance is an important parameter to measure battery performance.

Voltage

Open circuit voltage refers to the potential difference between the positive and negative poles of the battery when there is no current flowing through the circuit in the non-operating state. Under normal circumstances, the open circuit voltage after the lithium-ion battery is full of electricity is about 4.1 to 4.2 V, and the open circuit voltage after discharge is about 3.0 V. By detecting the open circuit voltage of the battery, the state of charge of the battery can be judged.

The operating voltage, also known as the end voltage, refers to the potential difference between the positive and negative poles of the battery when the battery is in operation, that is, when there is a current flowing through the circuit. In the battery discharge operating state, when the current flows through the battery, it is not necessary to overcome the resistance caused by the internal resistance of the battery, so the operating voltage is always lower than the open circuit voltage, and the reverse is true when charging. The discharge operating voltage of lithium-ion batteries is about 3.6 V.

Discharge platform time

Discharge platform time refers to the discharge time of discharge to a certain voltage when the battery is full. For example, the discharge platform time of a certain ternary battery is measured at 3.6 V, and the voltage is fixed at 4.2 V, and the charging current stops charging when it is less than 0.02C, which is full of electricity, and then shelved for 10 minutes. The discharge time at any rate of discharge current to 3.6 V is the discharge platform time under the current.

Because some appliances using lithium-ion batteries have voltage requirements for operating voltage, if they are below the required value, they will be unable to work. Therefore, discharge platform is one of the important standards to measure battery performance.

Charge and discharge ratio

The self-discharge rate, also known as the charge retention capability, refers to the ability of the battery to maintain its capacity under certain conditions when the battery is in an open state. Mainly affected by the manufacturing process, materials, storage conditions and other factors of the battery. It is an important parameter to measure battery performance.

Self-discharge rate

The self-discharge rate, also known as the charge holding capacity, refers to the holding capacity of the battery under certain conditions under open circuit conditions. It is mainly affected by the manufacturing process, materials, storage conditions and other factors of the battery. It is an important parameter for measuring battery performance.

Efficiency

Charging efficiency is a measure of the degree to which the electrical energy consumed by the battery during charging is converted into the chemical energy that the battery can store. Mainly affected by the battery process, formula and the working environment temperature of the battery, the higher the general ambient temperature, the lower the charging efficiency.

Discharge efficiency refers to the ratio of the actual charge emitted by the discharge to the terminal voltage to the rated capacity of the battery under certain discharge conditions. It is mainly affected by factors such as discharge rate, ambient temperature, and internal resistance. Under normal circumstances, discharge rate The higher the discharge efficiency, the lower the discharge efficiency. The lower the temperature, the lower the discharge efficiency.

Cycle life

Battery cycle life refers to the number of charge and discharge times experienced by the battery under a certain charging and discharging system when the battery capacity drops to a certain specified value. Lithium-ion batteries GB stipulates that the capacity retention rate after 500 battery cycles under 1C conditions is more than 60 %.

Main Classification of Lithium-ion Batteries

(1) According to the electrolyte materials used in lithium batteries, lithium batteries can be divided into liquid lithium batteries(LIB for short) and polymer lithium batteries(polymerlithiumbattery, LIP for short).

(2) According to the charging method, it can be divided into two categories: non-rechargeable and rechargeable.

(3) Lithium battery types: Square Lithium (such as commonly used mobile phone batteries) and columnar (such as 18650, 18500);

(4) Lithium battery outsourcing materials: aluminum shell lithium battery, steel shell lithium battery, soft package battery;

(5) Lithium batteries are divided from positive and negative electrode materials(additives): lithium cobalt (LiCoO2) batteries, lithium manganese (LiMn2O4), lithium iron phosphate batteries, and disposable lithium manganese dioxide batteries.

Polymer lithium battery

The positive and negative materials used in polymer lithium batteries are the same as liquid lithium, and the principle of the battery is basically the same. Their main difference lies in the difference in electrolytes. Lithium batteries use liquid electrolytes, while polymer lithium batteries are replaced by solid polymer electrolytes. This polymer can be "dry" or "colloidal"., At present, most polymer colloidal electrolytes are used.

Polymer lithium batteries can be divided into three categories:

1, solid polymer electrolyte lithium battery. The electrolyte is a mixture of polymer and salt. The ion conductivity of this battery at room temperature is low and suitable for high temperature use.

2, gel polymer electrolyte lithium battery. That is, additives such as plasticizers are added to solid polymer electrolytes to increase ion conductivity and enable batteries to be used at room temperature.

3, polymer positive electrode material lithium battery. The use of conductive polymers as a positive electrode material has three times the energy of existing lithium batteries and is the latest generation of lithium batteries. Because solid electrolytes are used instead of liquid electrolytes, compared with liquid lithium batteries, polymer lithium batteries have the advantages of thinning, arbitrary area and arbitrary shape, and do not cause safety problems such as leakage and combustion explosions. Therefore, aluminum composite films can be used to make battery shells, which can increase the capacity of the entire battery; Polymer lithium batteries can also use macromolecules as positive polar materials, and their mass to energy ratio will increase by more than 50 % compared to current liquid lithium batteries. In addition, lithium-polymer batteries have higher working voltage and cycle life than lithium-ion batteries.

Lithium polymer battery advantages:

1, good safety performance

Polymer lithium batteries are structurally packaged with aluminum plastic, which is different from the metal shell of the liquid core. Once a safety hazard occurs, the liquid core is prone to explosion, and the polymer core is only a drum.

2, the thickness is small, can do thinner

Ordinary liquid lithium electricity adopts the method of customizing the shell first and plugging the positive and negative material later. There is a technical bottleneck below 3.6 mm in thickness, and the polymer core does not have this problem. The thickness can be below 1mm, which is in line with the current mobile phone. Demand direction.

3, light weight

Polymer battery weight is 40 % lighter than steel shell lithium with the same capacity specification and 20 % lighter than aluminum shell battery.

4, large capacity

Polymer batteries have a capacity of 10 to 15 % higher than steel shell batteries of the same size and 5 to 10 % higher than aluminum shell batteries. They have become the first choice for color screen mobile phones and MMS mobile phones. Nowadays, new color screens and MMS mobile phones are also on the market. Most use polymer cores.

5, small internal resistance

The internal resistance of the polymer core is smaller than that of the general liquid core. At present, the internal resistance of the domestic polymer core can even be below 35mΩ, which greatly reduces the battery's self-consumption and extends the standby time of the mobile phone. It can be achieved. International level. This polymer lithium, which supports large discharge currents, is an ideal choice for remote control models and is the most promising alternative to nickel-metal hydride batteries.

6, shape can be customized

Polymer batteries can increase or reduce the core thickness according to customer demand, develop new core models, cheap, short opening cycle, and some can even be tailored to the shape of the phone to make full use of battery housing space and increase battery capacity.

7, good discharge characteristics

Polymer batteries use colloidal electrolytes. Compared with liquid electrolytes, colloidal electrolytes have stable discharge characteristics and higher discharge platforms.

8, the design of the protection plate is simple

Due to the use of polymer materials, the core does not catch fire and does not explode. The core itself has sufficient safety. Therefore, the protection line design of the polymer battery can consider omitting the PTC and fuse, thereby saving battery costs. Polymer lithium batteries have great advantages in terms of safety, volume, weight, capacity, and discharge performance.

Lithium iron phosphate battery

Lithium batteries from positive and negative materials are also divided into: lithium cobalt acid (LiCoO2) batteries, lithium manganese acid (LiMn2O4), lithium iron phosphate batteries

In Sony's first lithium battery, the positive material is lithium cobalt acid and the negative material is carbon. Among them, the main positive electrode material that determines the rechargeable maximum capacity and open circuit voltage of the battery.

The lithium iron phosphate battery refers to a lithium battery using lithium iron phosphate as a positive electrode material. There are many kinds of positive electrode materials for lithium batteries, mainly lithium cobalt acid, lithium manganate, lithium nickelate, ternary materials, lithium iron phosphate and the like. Among them, lithium cobalt acid is the cathode material used in most lithium batteries, and other cathode materials are not currently produced in large quantities on the market for various reasons. Lithium iron phosphate is also one of the lithium batteries. In principle, lithium iron phosphate is also an embedding/deintercalation process, which is identical to lithium cobalt acid and lithium manganate. Lithium iron phosphate battery is used to make lithium secondary battery. Now the main direction is power battery. Compared with NI-MH, Ni-Cd battery has great advantages.

Characteristics of lithium iron phosphate batteries

1, super long life

The long-life lead-acid battery has a cycle life of about 300 times and a maximum of 500 times, while the lithium iron phosphate power cell has a cycle life of more than 2,000 times. The standard charge (5 hour rate) can be used up to 2,000 times. The lead-acid batteries of the same quality are "new half year, old half year, maintenance and maintenance for another half year", and the maximum time is 1-1 .5 years, while lithium iron phosphate batteries will be used under the same conditions and will reach 7-8 years. Taken together, the performance price will be more than four times that of lead-acid batteries.

2, use safety

Lithium ferric phosphate completely solves the security problems of lithium cobalt phosphate and lithium manganate. Lithium cobalt phosphate and lithium manganate will cause explosions under strong collision and pose a threat to the safety of consumers. Lithium iron phosphate does not explode even in the worst traffic accidents after rigorous safety tests.

Large current 2C can be quickly charged and discharged. Under a dedicated charger, 1.5 C can be charged within 40 minutes to fill the battery. The starting current can reach 2C, and lead-acid batteries now do not have this performance.

3, high temperature resistance

Lithium iron phosphate has an electric peak of 350 °C -500 °C while lithium manganese and lithium cobalt phosphate are only around 200 °C. The operating temperature range is wide (-20C -- +75C), and the thermal peak of lithium iron phosphate with high temperature resistance can reach 350 °C -500 °C, while lithium manganese and lithium cobalt acid are only around 200 °C.

4, capacity

Has a larger capacity than ordinary batteries (lead acid, etc.) . Rechargeable batteries work under conditions that are often full and undischarged. The capacity will quickly fall below the rated capacity. This phenomenon is called the memory effect. For example, nickel-metal hydride and nickel-cadmium batteries have memory properties, and lithium iron phosphate batteries do not have this phenomenon. Regardless of the state of the battery, they can be used with charge and do not need to be discharged before charging.

The volume of lithium iron phosphate batteries of the same size is 2/3 of the volume of lead-acid batteries and 1/3 of the weight of lead-acid batteries. The battery does not contain any heavy metals and rare metals (nickel-metal hydride batteries require rare metals), non-toxic (SGS certification), pollution-free, in accordance with European RoHS regulations, is an absolute green environmental protection battery certificate.

5, no memory effect

The performance of lithium-powered batteries mainly depends on positive and negative electrode materials. Lithium-iron phosphate as a lithium battery material has only appeared in recent years. The domestic development of large-capacity lithium-iron phosphate batteries was July 2005. Its safety performance and cycle life are not comparable to other materials, and these are the most important technical indicators of power cells. 1C recharging and discharging cycle life up to 2000 times. Single battery overcharge voltage 30V does not burn, puncture does not explode. Lithium-iron phosphate positive electrode materials to make large-capacity lithium batteries are easier to use in series. In order to meet the needs of frequent charging and discharging of electric vehicles. It has the advantages of non-toxic, pollution-free, good safety performance, wide source of raw materials, cheap prices, and long life. It is an ideal cathode material for a new generation of lithium batteries.

Lithium batteries have a positive extreme iron phosphate material. This new material is not the previous lithium battery positive material LiCoO2; LiMn2O4; LiNiMO2. Its safety performance and cycle life are not comparable to other materials, and these are the most important technical indicators of power cells. 1C recharging and discharging cycle life up to 2000 times. Single battery overcharge voltage 30V does not burn, does not explode. The puncture does not explode. Lithium-iron phosphate positive electrode materials make large-capacity lithium batteries easier to use in series.

Lithium iron phosphate batteries also have their disadvantages: for example, lithium iron phosphate positive electrode materials have a smaller vibration density, and lithium iron phosphate batteries of equal capacity are larger than lithium batteries such as lithium cobalt, so they do not have an advantage in miniature batteries.

In the post-industrial era, the speed of automobile popularization has greatly exceeded our imagination. While bringing efficiency and convenience, the large amount of exhaust gas emissions also adds a lot of pressure to the environment. With the soaring oil prices and the greenhouse effect of carbon dioxide emissions, it is urgent to find new energy sources that are alternative to traditional energy sources. Liquid hydrogen, fuel cells, etc. are all good choices, but there are problems such as high prices and immature technology. Ordinary lead-acid batteries have relatively low operating costs, but they have heavy weight, low energy density, short service life, and potential heavy metals. Pollution and other issues.

A new type of lithium iron phosphate battery is used as its power core for a new generation of electric vehicles. This green and environmentally friendly power has many characteristics and advantages:

1, security is quite high

To be a car power, safety is the overriding primary consideration. Although the safety of ordinary lithium batteries can be basically guaranteed, there is a possibility of fire and explosion under extreme conditions. As the second generation of lithium battery, lithium iron phosphate battery has stable physical properties, and cooperates with the built-in protection functions of overvoltage, undervoltage, overcurrent and overcharge in the battery pack. It does not explode and does not ignite. It is the only absolute safety in the world. lithium ion battery. Thanks to the use of high thermal stability materials and meticulous process design, battery safety and reliability are greatly enhanced. Compared with the explosion that may occur in the improper use of lithium batteries, lithium iron phosphate batteries will not explode even if they are thrown into the fire. High temperature stability up to 400-500 ° C, to ensure the inherent high safety of the battery; will not explode or burn due to overcharge, over temperature, short circuit, impact. After rigorous safety testing, there is no explosion even in the worst traffic accidents.

2, long life low cost

As a power battery, the service life (recycling performance) is closely related to the overall operating cost. Compared with the general recycling service life of about 500 lithium batteries, lithium iron phosphate batteries can be charged and discharged 1,500 times at room temperature, and the capacity retention rate is 95 % or more. The cycle life of 50 % capacity has reached more than 2,000 times. The battery's continuous mileage is more than 500,000 kilometers. It can be used for about five years. It is eight times that of lead-acid batteries, three times that of nickel-metal hydride batteries, and it is the lithium cobalt acid battery. About four times. In addition, its manufacturing cost is lower than that of ordinary lithium batteries, which can undoubtedly greatly reduce the use and maintenance costs of electric vehicles.

At the same time, the discharge performance of lithium iron phosphate batteries is also very good, the power curve is stable, and the anti-over-discharge ability is strong. After the ordinary lithium electric core is below 3.2 V, the discharge is over-discharge, which may lead to scrapping. However, lithium iron phosphate batteries have energy releases at 2.8 V, and there is no problem of scrapping below 2.5 V.

3, easy to use and handle

We know that nickel-metal hydride and nickel-cadmium batteries have strong memory effects. Ordinary lithium batteries also have certain memory effects. They need to be "full and full", which will cause inconvenience to the daily use of electric vehicles. Lithium iron phosphate batteries do not have this phenomenon. Self-discharge is small; No memory effect, no matter what state the battery is in, it can be used with the charge. It does not need to be discharged first and then charged. At the same time, the battery has excellent fast charging characteristics. With a special charger, it can be filled quickly for about 95 % in half an hour. After the end of the battery life, the treatment problem is also worth our attention. Lithium-iron phosphate batteries do not contain any heavy metals and rare metals, are non-toxic and non-polluting, meet the regulations, and are absolutely green and environmentally friendly batteries. There is a large amount of lead in lead-acid batteries. If it is improperly disposed of after it is abandoned, it will constitute secondary pollution to the environment, and lithium iron phosphate material will be pollution-free regardless of its production and use.

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