A lithium-ion battery is a secondary battery (rechargeable battery) that
relies primarily on the movement of lithium ions between the positive and
negative electrodes to work. During the charge and discharge process, Li+
intercalates and deintercalates back and forth between the two electrodes:
during charging, Li+ is deintercalated from the positive electrode and embedded
in the negative electrode through the electrolyte, and the negative electrode is
in a lithium-rich state; during discharge, the opposite is true. Batteries
generally use materials containing lithium as electrodes and are representatives
of modern high-performance batteries. Lithium-based batteries are divided into
lithium batteries and lithium-ion batteries. Mobile phones and laptops use
lithium-ion batteries, which are commonly known as lithium batteries. However,
real lithium batteries are rarely used in daily electronic products due to their
high risk.
Lithium-ion battery (Li-ion, LithiumIonBattery): Lithium-ion battery has
the advantages of light weight, large capacity, and no memory effect, so it is
widely used. Many digital devices now use lithium-ion batteries as power
sources, although their prices are relatively high. It's relatively expensive.
The energy density of lithium-ion batteries is very high, its capacity is 1.5 to
2 times that of nickel-metal hydride batteries of the same weight, and it has a
very low self-discharge rate. In addition, lithium-ion batteries have almost no
"memory effect" and do not contain toxic substances, which are also important
reasons for their widespread use.
Main types of lithium-ion batteries:
Since lithium-ion batteries were put on the market in the early 1990s, they
have developed rapidly due to their advantages such as high energy density, high
voltage, and long cycle life, so the variety has also increased rapidly.
Lithium-ion batteries can be classified from different perspectives. According
to the different electrolyte materials used in lithium-ion batteries,
lithium-ion batteries are divided into liquid lithium-ion batteries
(LiquifiedLithium-IonBattery, referred to as LIB) and polymer lithium-ion
batteries (polymerLithium-IonBattery, Referred to as pLB).
1. According to the type of electrolyte, it is divided into:
Liquid lithium-ion battery:
The advantage is:
(1) The conductivity of lithium ions is high. The conductivity is
3&TImes;10-3?2&TImes;10-2/cm in a wide temperature range;
(2) The chemical properties are stable, and the positive electrode,
negative electrode, separator, and current collector electrolyte solution
basically do not undergo chemical reactions;
(3) The process of manufacturing batteries is relatively simple and the
cost is low.
weakness is:
It is easy to leak and has poor safety performance. The organic solvent
electrolyte in the liquid can easily cause fire and explosion accidents.
Liquid lithium-ion batteries can also be divided into cylindrical and
prismatic batteries according to the shape of the battery.
Polymer battery:
Polymer batteries can further be divided into: all-solid electrolyte
batteries and gel polymer electrolyte batteries. At present, gel-type polymer
batteries have been put into practical use and mass production. The
characteristics of this battery are:
(1) The electrolyte is in a gel state? It does not leak and is safe;
(2) The ionic conductivity is close to that of liquid lithium-ion
batteries;
(3) The positive electrode, separator and negative electrode are bonded
together;
(4) Using soft packaging materials reduces the weight of the battery;
(5) The thickness is reduced? The volume is reduced? Any shape can be
made.
Polymer batteries are an important development direction for lithium-ion
batteries. They are not only used in small batteries, but also in large power
batteries.
2. Classify the battery according to its purpose and capacity:
According to the purpose and capacity, lithium-ion batteries can be divided
into: small lithium-ion batteries used in portable appliances, mobile phones,
notebook computers, etc. The capacity of this battery is generally within
2Ah.
Large-capacity lithium-ion batteries are mainly used in power tools,
electric vehicles, EVs, and hybrid vehicles (Hybridelecvehicle, HEV). As
international oil prices continue to rise, the demand for lithium batteries for
EVs and HEVs will increase rapidly. Power batteries are used in electric
vehicles, which require the electric vehicle to travel a long distance on a
single charge, so the battery capacity is large, with the capacity of each
battery reaching hundreds of Ah; HEV batteries require high power, and the
battery capacity is around 10Ah.
Rechargeable lithium-ion batteries are currently the most widely used
batteries in modern digital products such as mobile phones and laptops. However,
they are relatively delicate and should not be overcharged or overdischarged
during use (the battery will be damaged or scrapped). Therefore, there are
protective components or protective circuits on the battery to prevent expensive
battery damage. Lithium-ion battery charging requirements are very high, and the
termination voltage accuracy must be ensured within ±1%. Major semiconductor
device manufacturers have developed a variety of lithium-ion battery charging
ICs to ensure safe, reliable, and fast charging.
Mobile phones basically use lithium-ion batteries. Proper use of
lithium-ion batteries is very 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 parallel. The rated voltage of
lithium-ion batteries, due to changes in materials, is generally 3.7V, and the
positive electrode of lithium iron phosphate (hereinafter referred to as iron
phosphate) is 3.2V. The termination charging voltage when fully charged is
generally 4.2V and 3.65V for phosphorus iron. The terminal discharge voltage of
lithium-ion batteries is 2.75V ~ 3.0V (the battery factory gives the operating
voltage range or the terminal discharge voltage, each parameter is slightly
different, generally 3.0V, phosphorus iron is 2.5V). Continuing to discharge
below 2.5V (phosphorus iron 2.0V) is called over-discharge. Over-discharge will
damage the battery.
Lithium-ion batteries with lithium cobalt oxide type material as the
positive electrode are not suitable for high-current discharge. Excessive
current discharge will reduce the discharge time (higher internal temperatures
will be generated and energy will be lost), and may be dangerous; but lithium
iron phosphate The cathode material lithium battery can be charged and
discharged with a high current of 20C or more (C is the capacity of the battery,
such as C=800mAh, the 1C charging rate means the charging current is 800mA), and
is especially suitable for electric vehicles. Therefore, the maximum discharge
current given by the battery production factory should be less than the maximum
discharge current during use. Lithium-ion batteries have certain temperature
requirements. The factory provides charging temperature ranges, discharge
temperature ranges and storage temperature ranges. Overvoltage charging will
cause permanent damage to lithium-ion batteries. Lithium-ion battery charging
current should be based on the battery manufacturer's recommendations and
requires a current-limiting circuit to avoid overcurrent (overheating). The
commonly used charging rate is 0.25C~1C. When charging with high current, it is
often necessary to detect the battery temperature to prevent overheating from
damaging the battery or causing explosion.
Lithium-ion battery charging is divided into two stages: constant current
charging first, and changing to constant voltage charging when it is close to
the end voltage. For example, a battery with a capacity of 800mAh has a charge
termination voltage of 4.2V. The battery is charged at a constant current of
800mA (charge rate 1C). At the beginning, the battery voltage increases at 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
changes little. When the charging current drops to 1/10-50C (the settings vary
from factory to manufacturer and does not affect use), it is considered to be
nearly full and charging can be terminated (some chargers start the timer after
reaching 1/10C. After a certain period of time, end charging).
Lithium-ion battery manufacturing process:
The positive electrode materials of lithium batteries include lithium
cobalt oxide LiCoO2, ternary material Ni+Mn+Co, lithium manganate Li2MnO4 plus
conductive agent and adhesive, which are coated on aluminum foil to form the
positive electrode. The negative electrode is layered graphite plus conductive
agent and adhesive. The agent is coated on the copper foil base tape. So far,
the more advanced negative electrode layered graphite particles have adopted
nanocarbon.
1. Pulping: Use special solvents and binders to mix the powdered positive
and negative active materials respectively, and stir them evenly to form
slurry-like positive and negative materials.
2. Coating film: The positive and negative electrode slurries are evenly
coated on the surface of the metal foil through an automatic coating machine,
and then automatically cut into positive and negative electrode pieces after
automatic drying.
3. Assembly: According to the order from top to bottom, the positive
electrode sheet separator and the negative electrode sheet separator are wound
and injected with electrolyte, sealed, and positive and negative tab welding,
etc., that is, the assembly process of the battery is completed and the finished
battery is made.
4. Formation: Place the finished batteries in the test cabinet for charge
and discharge testing, and select qualified finished batteries before leaving
the factory.
Chemical analysis of lithium-ion batteries:
Like all chemical batteries, lithium-ion batteries are composed 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).
positive electrode
Cathode material: As mentioned above, there are many optional cathode
materials. Currently, most mainstream products use lithium iron phosphate.
Comparison of different cathode materials:
Positive electrode reaction: lithium ions are intercalated during discharge
and lithium ions are deintercalated during charging. When charging:
LiFepO4→Li1-xFepO4+xLi+xe When discharging: Li1-xFepO4+xLi+xe→LiFepO4
negative electrode
Anode material: mostly graphite. New research finds titanate may be a
better material. Negative reaction: lithium ions are removed and inserted during
discharge, and lithium ions are inserted during charging. When charging:
xLi+xe+6C→LixC6 When discharging: LixC6→xLi+xe+6C
They are roughly divided into the following categories:
The first is carbon anode material: the anode materials that have been
actually used in lithium-ion batteries are basically carbon materials, such as
artificial graphite, natural graphite, mesophase carbon microspheres, petroleum
coke, carbon fiber, pyrolytic resin carbon, etc. .
The second type is tin-based negative electrode materials: Tin-based
negative electrode materials can be divided into two types: tin oxide and
tin-based composite oxide. Oxides refer to oxides of metal tin in various
valence states. There are currently no commercial products.
The third type is lithium-containing transition metal nitride anode
materials, which currently have no commercial products.
The fourth type is alloy anode materials: including tin-based alloys,
silicon-based alloys, germanium-based alloys, aluminum-based alloys,
antimony-based alloys, magnesium-based alloys and other alloys. There are
currently no commercial products.
The fifth type is nanoscale negative electrode materials: carbon nanotubes
and nanoalloy materials.
The sixth type of nanomaterial is nanooxide material: At present, Hefei
Xiangzheng Chemical Technology Co., Ltd. According to the latest market
development trends of the lithium battery new energy industry in 2009, many
companies have begun to use nanometer titanium oxide and nanometer silicon oxide
to add to the previous traditional Graphite, tin oxide, and carbon nanotubes
greatly improve the charge and discharge capacity and number of charge and
discharge times of lithium batteries.
a
1. Solute: Lithium salts are often used, such as lithium perchlorate
(LiClO4), lithium hexafluorophosphate (LipF6), and lithium tetrafluoroborate
(LiBF?).
2. Solvent: Since the operating voltage of the battery is much higher than
the decomposition voltage of water, lithium-ion batteries often use organic
solvents, such as ether, ethylene carbonate, propylene carbonate, diethyl
carbonate, etc. Organic solvents often destroy the structure of graphite during
charging, causing it to peel off and form a solid electrolyte interphase (SEI)
on its surface, leading to electrode passivation. Organic solvents also bring
safety issues such as flammability and explosiveness.
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