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Dec 20 2019

Lithium Battery and Lithium-ion Battery Chemistry

Ⅰ. Introduction

Lithium batteries are a type of batteries that use lithium metal or lithium alloy as the negative electrode material, and use a non-aqueous electrolyte solution. In 1912, lithium metal batteries were first proposed and studied by Gilbert N. Lewis. In the 1970s, M. S. Whittingham proposed and began researching lithium-ion batteries. Due to the very active chemical properties of lithium metal, the processing, storage, and use of lithium metal require very high environmental requirements. With the development of science and technology, lithium batteries have now become mainstream. 

It can be roughly divided into two categories: lithium batteries and lithium-ion batteries. Lithium-ion batteries do not contain metallic lithium and are rechargeable. Their safety, specific capacity, self-discharge rate, and performance & price are better than lithium batteries.

  • Lithium primary battery

Lithium metal is used as the negative electrode, heat treated manganese dioxide is used as the positive electrode, and PP or PE film as the the separator.

Features:

Low self-discharge rate, annual self-discharge can be ≤1%, fully sealed (metal welded, lazer seal) batteries can meet 10 years of life, semi-sealed batteries are generally 5 years.

Lithium metal is used as the negative electrode, and the positive electrode and the electrolyte are thionyl chloride (sulfoxide). Cylindrical batteries have electricity after assembly. The voltage is 3.6V, which is one of the most stable types of batteries. It is suitable for use on electronic instruments and equipment that cannot be maintained frequently, providing subtle current.

 

  • Li-ion battery

Li-ion batteries currently include liquid lithium-ion batteries (LIB) and polymer lithium-ion batteries (PLB). Among them, the liquid lithium ion battery refers to a secondary battery whose Li + is compound. The positive electrode uses lithium cobaltate and lithium manganate, and the negative electrode uses a lithium-carbon interlayer compound. Li-ion batteries have advantages of high operating voltage, small size, light weight, high energy, no memory effect, no pollution, small self-discharge, and long cycle life.

Its practicality has greatly reduced the weight and volume of portable electronic devices such as mobile phones and notebook computers, and the using time is greatly extended. Because lithium-ion batteries do not contain heavy metal cadmium, compared with nickel-cadmium batteries, the environmental pollution is greatly reduced.

Li-ion

Ⅱ. Terminology

  • Battery structure

Lithium batteries usually come in two shapes: cylindrical and square. The inside of the battery is a spiral winding structure, and a very fine and highly permeable polyethylene film separator is used to separate the positive and negative electrodes. The positive electrode contains a current collector composed of lithium cobaltate (or nickel-cobalt lithium manganate, lithium manganate, lithium ferrous phosphate, etc.) and the aluminum foil. The negative electrode consists of a current collector composed of graphitized carbon material and the copper foil. The battery is filled with an organic electrolyte solution. It is also equipped with a safety valve and a PTC element (partially cylindrical) to protect the battery from damage during abnormal conditions and output short circuits.

 

  • Positive electrode

Material: There are many choices of positive electrode materials, and lithium iron phosphate is mostly used in mainstream products.

Reaction: The lithium ion is embedded when discharge, and de-embedded in the charge.

Charge: LiFePO4 → Li1-xFePO4 + xLi+ + xe-

Discharge: Li1-xFePO4 + xLi+ + xe- → LiFePO4

 

  • Negative electrode

Material: More graphite is used, and new research has found that titanate may be a better material.

Reaction: The lithium ion is de-embedded when discharge, and embedded in the charge.

Charge: xLi+ + xe- + 6C → LixC6

Discharge: LixC6→ xLi+ + xe- + 6C

 

  • Conductive coating

The conductive coating is also called pre-coating. In industry, it usually refers to a layer of conductive coating applied to the surface of the positive electrode current collector-aluminum foil. The earliest experiments on aluminum foil in batteries can be traced back to the 1970s. With the development of new energy industry, especially the development of Li-iron phosphate batteries, it has become a hot new technology in the industry.

The conductive coating can effectively improve the adhesion of the pole pieces in the lithium battery, reduce the amount of binder used, and also significantly improve the battery's electrical performance:

1) Contact resistance decreases 40%

2) Adhesive reduces 50%

3) Battery voltage increases 20% at the same magnification.

4) Material and current collector adhesion increases 30%, and no delamination after long-term cycling.

 

  • Carbon coated aluminum foil

Carbon coated aluminum foil is made of conductive carbon-based composite paste and high-purity electronic aluminum foil, which is made by transfer coating process.

 

  • Shell characteristics

To improve safety and voltage, scientists have invented materials such as graphite and lithium cobaltate to store lithium atoms. The molecular structure of these materials forms nano-scale small storage lattices that can be used to storage. In this way, even if the battery case is broken and oxygen enters, the oxygen molecules will be too large to enter these small storage cells, so that lithium atoms will not react with the oxygen to avoid explosion.

 Li-ion battery electricity

Ⅲ. Working Principle

Lithium metal battery: it is generally a battery using manganese dioxide as the positive electrode material, metallic lithium or its alloy metal as the negative electrode material, and a non-aqueous electrolyte solution.

Discharge reaction: Li+MnO2=LiMnO2

Lithium-ion batteries: it is a type of batteries that use lithium alloy metal oxides as the positive electrode material, graphite as the negative electrode material, and non-aqueous electrolyte.

Reaction on the positive electrode:

LiCoO2=Li(1-x)CoO2+XLi++Xe-(electron)

Reaction on the negative electrode:

6C+XLi++Xe- = LixC6

Total reaction on rechargeable battery:

LiCoO2+6C = Li(1-x)CoO2+LixC6

 

Ⅳ. Battery Features

  • Advantages

1) High energy density. With high storage power density, it has reached 460-600Wh / kg, which is about 6-7 times that of lead-acid batteries.

2) Long cycle life, the service life can reach more than 6 years. For example, the battery 1C (100% DOD) with lithium ferrous phosphate as the positive electrode is charged and discharged about 10,000 times.

3) High rated voltage, a single battery working voltage is 3.7V or 3.2V, which is approximately equal to the series voltage of 3 Ni-Cad or Ni-MH rechargeable batteries, in addition, it is convenient to form a battery power pack. Whats more, lithium batteries can use a new type of voltage regulation technology to adjust the voltage to 3.0V to suit the use of small appliances.

4) High power resistance capacity. For example, phosphate lithium-ion battery for electric vehicles can reach 15-30C charge and discharge capacity, which is convenient for high-intensity startup acceleration.

5) Low self-discharge rate. It is one of the most outstanding performances of the battery, which can generally be less than 1% / month, and less than 1/20 of the nickel-hydrogen battery.

6) Light weight, about 1 / 6 to 1 / 5 of lead acid products under the same volume.

7) Good capability at high and low temperature. For example, the battery can be used in the environment of -20 ℃ ~ 60 ℃, after processing, it can be used in the environment of -45 ℃.

8) Less harm to environment. Regardless of production, use and scrap, it does not contain or produce any toxic and harmful heavy metal substances, such as lead, mercury, cadmium.

9) Production basically consumes no water

 

  • Disadvantages

1) Lithium primary batteries have poor safety and risk of explosion.

2) Li-ion batteries (lithium cobaltate) cannot be discharged at high currents, are expensive, and have poor safety.

3) Li-ion batteries need protecting circuit to prevent the battery from being overcharged and over discharged.

4) High production requirements and costs.

5) Limited use conditions, high risk of very high & low temperature use.

 

  • Li-ion battery characteristics

1) High energy density

The weight of a Li-ion battery is half that of a nickel-cadmium or nickel-hydrogen battery of the same capacity, and the volume is 20-30% of a nickel-cadmium battery and 35-50% of a nickel-hydrogen battery.

2) High voltage

The operating voltage of a lithium-ion battery cell is 3.7V (average value), which is equivalent to three nickel-cadmium or nickel-metal hydride batteries connected in series.

3) Small pollution

Li-ion batteries do not contain harmful metal substances such as cadmium, lead, and mercury.

4) No lithium metal

Li-ion batteries do not contain metallic lithium, so they are not subject to the ban imposed by airlines of carrying lithium batteries in passenger aircraft.

5) Long cycle life

Under normal conditions, the charge-discharge cycle of a lithium-ion battery can exceed 500 times, and a iron phosphate battery can reach 2000 times.

6) No memory effect

The memory effect refers to the phenomenon that the capacity of the battery decreases during the charge and discharge cycle of the nickel-cadmium battery. Lithium-ion batteries do not have this effect.

7) Quick charge

Using a constant current & voltage charger with a rated voltage of 4.2V, the lithium-ion battery can be fully charged in 1.5 ~ 2.5 hours; and the newly developed lithium iron phosphate battery can be fully charged in 35 minutes.

 Li-ion battery

Ⅴ. History

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

In 1980, J. Goodenough discovered that lithium cobaltate could be used as a cathode material for lithium-ion batteries.

In 1982, R.R.Agarwal and J.R.Selman of the Illinois Institute of Technology discovered that lithium ions can be embedded into the graphite, which is fast and reversible. At that time, lithium batteries made of metal lithium have attracted much attention because of their safety issues. Therefore, people tried to embed lithium ions to graphite to make rechargeable batteries. Finally, first available lithium-ion graphite electrode was successfully trial-produced by Bell Labs.

In 1983, M. Thackeray, J. Goodenough, and others found that manganese spinel is an excellent cathode material, which has good properties of low cost, stability, and excellent electrical and lithium conduction. Its decomposition temperature is high, and its oxidizing property is far lower than that of lithium cobaltate. Even if having a short circuit or overcharge, combustion and explosion can be avoided as far as possible.

In 1989, A. Manthiram and J. Goodenough discovered that a positive electrode using a polymeric anion would generate a higher voltage.

In 1991 Sony released the first commercial Li-ion battery. Subsequently, lithium-ion batteries revolutionized the development of consumer electronics. For example, the weight and volume of portable electronic devices such as mobile phones, notebooks, and calculators has greatly reduced.

In 1996, Padhi and Goodenough discovered that phosphates with an olivine structure, such as lithium iron phosphate (LiFePO4), are more superior than traditional cathode materials, and  become the mainstream cathode materials gradually.

Lithium batteries were first used in pacemakers. Lithium batteries have the advantages of low self-discharge rate and gentle discharge voltage, so that the pacemaker implanted in the human body can operate for a long time without recharging. Lithium batteries generally have a nominal voltage higher than 3.0V, making them more suitable as integrated circuit power supplies.

To develop a new better lithium battery, various materials have been researched and tested.


Ⅵ. Battery Explosion

The type of battery cell explosion can be summarized into three types: external short circuit, internal short circuit, and overcharge. Here, the external refers to the outside of the battery cell and includes short circuits caused by poor internal insulation design of the battery pack. When a short circuit occurs outside the battery cell and the electronic component fails to cut off the circuit loop, high heat will be generated inside the battery cell, causing some of the electrolyte to vaporize, which will expand the battery case.

When the internal temperature of the battery reaches 135 degrees Celsius, a good quality separator paper will close the pores, the electrochemical reaction will be terminated almost, the current will drop suddenly, and the temperature will decrease slowly, avoiding the explosion. However, if the pore closing rate is too poor, or the separator paper with poor quality, the battery temperature will continue to increase, causing more electrolyte vaporize, and finally the battery case will be broken, even be exploded.

The internal short circuit is mainly caused by piercing diaphragm by the burrs of copper foil and aluminum foil piercing the diaphragm, or dendritic crystals of lithium atoms.

These tiny needle-like metals can cause micro-short circuits. The copper and aluminum foil burrs are caused during the production process, and the observed phenomenon is that the battery leaks too quickly, and most of them can be detected by the cell plant or assembly plant. Moreover, because the burr is small, it is sometimes blown out, which makes the battery return to normal. Therefore, this kind of explosion is less happened. Therefore, the explosion caused by the internal short circuit is mainly caused by overcharge.

After overcharging, needle-shaped lithium metal crystals are everywhere on the pole pieces, piercing points are everywhere to make micro short circuits. Therefore, the temperature of the battery will gradually increase, and finally the electrolyte is vaporized at high temperature. In this case, whether the temperature is too high to damage electrode materials and the battery housing burns and explodes, both situations will cause an explosion.

Based on the above types of explosions, we can focus on batteries protection in three aspects: overcharge, external short circuits, and improvement of battery safety.

When designing a battery system, two electronic protections must be provided for overcharge, overdischarge, and overcurrent. Final protection method, the safety level of batteries, which can be roughly differentiated according to the ability to withstand short circuit and overcharge. In addition, before the battery explodes, if lithium atoms accumulate on the surface of the battery, the explosion power will be greater. Comparing the performance of aluminum shell cells with steel shell cells, aluminum shells have high safety advantages. Moreover, consumers use inferior chargers. Thus the ability of cells to resist overcharge is more important than the ability to withstand external short circuits.

 labels for battery systems

  • Explosion Cause

1) Large internal polarization

2) The pole piece absorbs water and reacts with the electrolyte.

3) The quality and performance of the electrolyte.

4) The amount of injection does not meet the process requirements.

5) Poor sealing performance during laser welding in assembly process.

6) Manufacturing dust is easy to cause micro short circuit.

7) The positive and negative plates are thicker according to technological requirements, and it is difficult to insert the case.

8) Sealing problem of liquid injection, for example, poor sealing of steel ball causes air drum.

9) The shell is too thick, and the deformation of the shell will affect the thickness.

10) High external ambient temperature.

 

Ⅶ. Battery Security

To avoid over-discharging or over-charging due to improper use, a triple protection mechanism is provided in the single-cell lithium-ion battery. The first is the use of switching elements. When the temperature in the battery rises, its resistance value rises, if the temperature is too high, the power supply will automatically stop. The second is to choose an appropriate separator material. When the temperature rises to a certain value, micron-sized micropores on the separator will automatically dissolve, so that lithium ions cannot pass through, and the internal reaction of the battery stops. The third is to set a safety valve (that is, the vent hole on the top of the battery). When the internal pressure of the battery rises to a certain value, the safety valve will automatically open to ensure the safety of battery.

Sometimes, although the battery itself has safety control measures, due to some reasons, for example, security control fails, or the lack of a safety valve, or the gas is too slowly to release through the safety valve, therefore, the internal pressure of the battery will rise sharply and cause an explosion.

In general, the total energy stored in a lithium-ion battery is inversely proportional to its safety. As the battery capacity increases, the battery volume also increases, its heat dissipation performance becomes poor, and the possibility of accidents will increase significantly. For Li-ion batteries for mobile phones, the basic requirement is that the probability of a safety accident is less than one in a million. For large-capacity lithium-ion batteries, especially electric vehicles, the use of forced heat dissipation is particularly important.

Choose a safer electrode material, for example lithium manganate material, to ensure that the molecular structure is fully charged, the lithium ions of the positive electrode have been completely embedded in the carbon pores of the negative electrode to avoid the generation of dendrites is fundamentally. At the same time, the stable structure of lithium manganate makes its oxidation performance much lower than that of lithium cobaltate, and the decomposition temperature exceeds 100 °C of lithium cobaltate. The danger of burning and explosion caused by the precipitation of metallic lithium is avoided when having short circuit or overcharge.

After the lithium battery cell is overcharged to a voltage higher than 4.2V, side effects will begin to occur. The higher the overcharge voltage, the higher the danger. Because the number of lithium atoms remaining in the positive electrode material is less than half, at this time, the storage cell collapses, causing the battery capacity to permanently decrease. If you continue to charge, since the storage cell of the negative electrode is already filled with lithium atoms, subsequent lithium metal will accumulate on the surface of the negative electrode material. These lithium atoms will grow dendritic crystals from the surface of the negative electrode toward the lithium ions. These lithium metal crystals will pass through the separator paper, making the positive and negative electrodes short-circuit. Sometimes the battery explodes before a short circuit occurs. During the overcharge process, materials such as the electrolyte will vaporize, which will cause the battery case or pressure valve to swell and rupture, allowing oxygen to enter and react with the lithium atoms accumulated on the negative electrode surface.

Therefore, when charging a lithium battery, the upper limit of the voltage must be set to guarantee the battery life, capacity, and safety. The optimal charging voltage limit is 4.2V. There is also a lower voltage limit when the lithium battery is discharged. When the cell voltage is lower than 2.4V, some materials will start to be destroyed. In addition, when the lithium battery is discharged from 3.0V to 2.4V, the released energy accounts for only about 3% of the battery capacity. Therefore, 3.0V is an ideal discharge cutoff voltage. When charging and discharging, the limitation of current is also necessary. If the current is too large, lithium ions have no time to enter the storage cell, and will collect on the surface of the material, which will affect the battery performance.

After these lithium ions have obtained electrons, lithium atom crystals will be generated on the surface of the material, which will cause danger, like overcharge. Therefore, the protection of lithium-ion batteries must include: the upper limit of the charging voltage, the lower limit of the discharge voltage, and the upper limit of the current. In general, except the lithium battery cell, there is a protective plate in the lithium battery pack.


Ⅸ. Matters

  • Matters need attention

Storage requirements: In the environment with a temperature of 20 ± 5℃ and a humidity of not more than 50%, the air and water vapor must be prevented from contacting the aluminum foil during transportation.

 

  • Matters of use

Keeping lithium-ion batteries regularly charged and discharged can extend battery life. Lithium-ion battery power is maintained at 10% ~ 90% is better for the battery. This means that you don't need to reach 100% when charging batteries for digital products such as mobile phones and laptops. Under normal circumstances, 50% of the power is best for lithium-ion battery storage.

When digital products equipped with lithium-ion batteries are exposed to sunlight or stored in hot cars, it is best to turn these products off because lithium-ion batteries will age faster if the operating temperature exceeds 60℃ (lithium battery charging temperature range: 0 ~ 45℃, lithium battery discharging temperature range is 0 ~ 60℃).

 Electricity sign

Ⅹ. Charging Rules

  • Charging voltage

Generally, the battery voltage of a mobile phone is 3.7V, but the voltage of a general charger is 5V, but it will not affect the use.

  • Shallow charge and discharge

This is more beneficial for lithium batteries. Only when the power module of the product is calibrated for lithium batteries, it is necessary to deepen and deep charge. Therefore, lithium-ion-powered products do not have to be constrained by the process.

  • Overcharge and overdischarge

The rated voltage of a lithium-ion battery is generally 3.7V. Depending on different materials, the positive electrode of lithium iron phosphate is 3.2V. The international standard for termination charge voltage when fully charged is 4.2V, and iron phosphate is 3.6V. Overdischarge or self-discharge reaction at low voltage will cause decomposition and destruction of lithium active material, and may not be recovered. And any kind of overcharging of lithium-ion battery will cause severe damage to the battery performance and even cause explosion. Therefore, the lithium-ion battery must avoid overcharging during the charging process.

 

Ⅺ. Application

With the development of microelectronic technology, more and more miniaturized devices have been put forward, which places high requirements on power sources. Lithium batteries have subsequently entered a large-scale practical stage.

The earliest application was lithium sub primary battery, used in pacemakers. Due to the low self-discharge rate and gentle the discharge voltage, this makes it possible to implant the pacemaker into the human body for long-term use.

Lithium manganese batteries generally have a nominal voltage higher than 3.0V, which is more suitable for integrated circuit power supplies and is widely used in computers, calculators, and watches.

Li-ion batteries are widely used in mobile phones, notebook computers, power tools, electric vehicles, street light backup power supplies, navigation lights, and small household appliances, which can be said to be the most popular type.

 

Ⅻ. Selection

Li-ion batteries are divided into liquid lithium-ion batteries and polymer lithium-ion batteries. The electrolyte of a lithium-ion battery is fluid, so it is more unstable than a lithium polymer battery, and it may explode if it is hit by an external force or if a non-compliant charger is used. And now that the popularization of portable electronic products such as smart phones, e-books, tablets, and laptops uses batteries as a power source, battery hidden troubles will break out at any time. To prevent these, we must pay attention to the following:

1) The capacity is clearly marked. Batteries without a clearly marked capacity (such as 1000mAh) are likely to be inferior or recycled.

2) Standby time. It is the continuous use time from the time the battery is loaded to the next charge.

3) Safety protection circuit board. Without it, the lithium battery is at risk of deformation, leakage, and explosion.

 

XIII. Battery Storage

  • Lithium primary battery

Primary lithium battery can be discharged continuously or intermittently. Once the power is exhausted, it can no longer be used, and it is widely used in electronic products with low power consumption such as cameras. It has a low self-discharge rate and can be stored for up to 3 years. In addition, it is good to store lithium primary batteries in low temperature to get better storage.

Note: Lithium primary batteries are different from lithium ion batteries, the former cannot be charged.

 

  • Li-ion battery

Also called secondary lithium battery. It can be stored for more than half a year at 20°C. This is due to its low self-discharge rate and most of its capacity can be recovered.

The self-discharge phenomenon e4xists in lithium batteries. If the battery is stored below 3.6V for a long time, it will cause the battery to over-discharge and damage the internal structure of the battery, reducing the battery service life. Therefore, long-term storage of lithium batteries should be recharged every 3 to 6 months, that is, keeping the battery voltage at 3.8 ~ 3.9V, and it is appropriate to maintain the discharge depth at 40% ~ 60%. The battery should be stored in a dry environment at 4 ℃ ~ 35 ℃ or in a moisture-proof packaging. In addition, Keep away from heat sources and sunlight.

 Lithium

XIV. Development Prospects

To develop more excellent batteries, various materials have been studied. For example, lithium sulfur dioxide batteries and lithium thionyl chloride batteries are very characteristic. Their positive electrode active materials are solvents for the electrolyte. This structure made only in non-aqueous electrochemical systems. Therefore, the research of lithium batteries has also promoted the development of electrochemical theory of non-aqueous systems. Except the use of various non-aqueous solvents, polymer thin film batteries has also been studied.

Lithium batteries are widely used in energy storage systems such as hydropower, thermal power, wind power and solar power, telecommunications, electric vehicles, military equipment, aerospace and other fields.

Lithium-ion batteries have been widely used in portable appliances such as laptop computers, video cameras, and mobile communications due to their unique performance advantages. With the shortage of energy and environmental protection, lithium battery is widely used in the electric vehicle industry, especially the emergence of lithium iron phosphate material batteries, which has promoted the development and application of the lithium battery industry.

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