1. Mixing can also be called mixing, homogenization, pulping, ingredients,
etc. Through a certain feeding sequence, stirring process, vacuum control,
temperature control and other conditions, key components such as positive and
negative active materials, conductive agents, binders, solvents, etc. are
prepared into non-Newtonian fluids with certain viscosity requirements and
particle size requirements. (non-Newtonian liquids) process. The properties of
the slurry that need to be controlled are good fluidity, viscosity and particle
size that meet the coating requirements. 2. Coating is also called coating.
Coating is a process in which the stirred slurry is evenly coated on the current
collector and dried to form a pole piece. Coating methods include continuous
coating and intermittent coating. The main coating methods for lithium-ion
battery slurry include blade direct coating, blade roller coating, and slit
extrusion coating. The control parameters of the coated product are surface
density, adhesion, moisture content, etc. 3. Rolling (Pressing) Rolling pressing
refers to the process of passing the coated product through two steel rollers
under a certain gap and under a certain pressure to compact the pole piece to a
specified thickness. The influencing factors of rolling include feeding angle,
gap value, pressure value, rolling speed, rewinding and unwinding tension, pole
piece temperature, etc. The purpose of rolling is to further compact the loose
and porous electrodes, reduce the contact resistance between materials, and
increase the battery capacity within a certain battery volume. At the same time,
it cannot be over-pressured to ensure the infiltration effect of the electrolyte
on the electrode pieces. 4. Slitting Slitting is also called slitting. The pole
piece after coating is wide, so the pole piece needs to be cut into multiple
strips. The slit products are mainly affected by the quality of the cutter, the
angle of the cutter and the tension. 5. Tab Forming is a process in which the
pole pieces are sheared by controlling the engagement between the upper and
lower dies of the equipment so that the pole pieces form tabs according to the
design size requirements. 6. Electrode Defects: Electrode defects occur at all
stages in the production of pole pieces. During coating, thick heads, thin
tails, thick edges, exposed foil, unstable surface density, horizontal and
vertical stripes, dry materials, and pinholes are easy to occur. , white spots,
pitting, foreign matter, etc., the specific causes will be analyzed in detail.
The main defects of roller-pressed pole pieces include uneven winding, wrinkles,
thickness rebound, material falling off and sticking to the roller, particles,
and unstable thickness. Defects in pole piece slitting include wavy edges,
burrs, curling edges, material loss, etc. 7. Winding (Winding) Winding is a
composition method of battery cells, which is suitable for cylindrical
batteries, square batteries and soft pack batteries. By controlling the speed,
tension, size, deviation and other factors of the equipment, the negative
electrode pieces, positive electrode pieces and separators of matching sizes are
rolled into bare cells. The key point of winding is that the separator wraps the
positive and negative electrodes, and the negative electrode piece wraps the
positive electrode piece. This requires that the negative electrode piece cannot
expose the foil. Exposing the foil will cause local lithium precipitation on the
electrode piece and pierce the separator, causing a short circuit. 8. Lamination
(Lamination) is another composition method of laminated battery cells, suitable
for square and soft-pack lithium-ion batteries. The process of stacking the
punched negative electrode pieces, positive electrode pieces and separators into
bare cells through control equipment. It is also required that the separator
should wrap the positive and negative electrodes, and the negative electrode
piece should wrap the positive electrode piece. 9. Hot Pressing: Hot pressing is
also called shaping. The wound battery core is in a bulging state, which is not
conducive to the insertion into the case and the infiltration of the
electrolyte. It needs to be hot pressed to promote the contact between the pole
pieces and the diaphragm. At the same time Reduce the volume and prevent the
misalignment of the positive and negative electrode pieces. The influencing
factors of hot pressing include pressure, temperature, time, etc. Generally, hot
pressing at 60~80℃ is selected. 10. Vacuum Baking Vacuum baking is divided into
pole piece baking and battery core baking, both of which are to control the
moisture in the battery core. Moisture can be fatal to lithium batteries. When
moisture comes into contact with the electrolyte, the hydrofluoric acid formed
can cause huge damage to the battery, and the gas generated can also cause
battery bulging. Baking efficiency is affected by vacuum degree, drying
temperature, and time. By adjusting the baking process, try to dry efficiently
with low energy consumption. 11. Tab Welding (Tab Welding) Whether it is rolled
or laminated, welding of tabs and current collectors is required. Weld the
positive and negative electrode tabs at the current collector position to ensure
the strength of the welding and prevent the tabs from falling off. The
ultrasonic welding method is generally used for tab welding. The principle is
that under the condition of auxiliary pressure, high-frequency vibration waves
are transmitted to the two objects to be welded through the welding head and the
welding base, and the two contact surfaces to be welded rub against each other.
Molecules diffuse into each other and form molecular fusion welding together.
The strength of ultrasonic welding is affected by welding pressure, amplitude,
frequency, time, welding machine stability, welding head quality, tooling,
material hardness, etc. 12. Packaging There are two main types of packaging:
metal shell packaging and aluminum-plastic film packaging. Metal shells include
steel shells and aluminum shells, which are suitable for cylindrical batteries
and square batteries. Aluminum-plastic film packaging is suitable for soft-pack
batteries. For the 18650 cylindrical battery, the packaging step is to put the
rolled core into the steel shell and perform spot welding, rolling grooves,
liquid injection, laser welding of the cap and final mechanical sealing. For
prismatic batteries, the packaging step is to perform laser welding and sealing
after entering the shell, and then complete the final sealing after the liquid
injection hole is filled. The difference between soft pack battery packaging is
that it is packaged with aluminum-plastic film. The aluminum-plastic film is
composed of three layers, PP layer, aluminum layer and nylon layer. The key to
encapsulation is to melt the PP layers and bond them together. Heat sealing is
mainly affected by temperature, heat sealing time, and heat sealing pressure. It
is necessary to ensure that there is no heat sealing failure or failure, etc.
Special attention should be paid to the top sealing of the tabs. It is necessary
to ensure that the PP layer of the aluminum-plastic film is well bonded and
sealed with the PP layer on the outer surface of the tabs, and to ensure that
the PP layer of the aluminum-plastic film in the non-tab area is bonded
face-to-face. , well sealed. In addition, compared with metal-cased batteries,
aluminum-plastic film soft-pack batteries need to be covered with a protective
film after heat sealing to prevent scratches on the aluminum-plastic film by
external substances. 13. Air tightness test (LeakageTest) is the process of
detecting whether there is leakage in the battery through negative pressure
detection method or helium detection method. Air tightness testing is very
necessary. Poorly sealed batteries will introduce moisture, impurities, etc.,
causing side reactions between the battery and the electrolyte, causing the
battery to be scrapped. 14. Electrolyte Injection The electrolyte is a channel
for lithium ions to move inside the battery, and is mainly composed of solute
and solvent. The solute is lithium hexafluorophosphate, and the solvent is
generally used in combination with three or more solvents, such as EC/DMC/DEC,
etc. The liquid injection process is to inject electrolyte into the interior of
the battery core. The parameters controlled mainly include electrolyte volume,
injection pressure, time, etc. 15. Formation (Formation) is the first charge and
discharge of the battery after injection and sealing. There are two main
purposes of formation: after the battery is made, the electrode material is not
in the best applicable state, or the physical properties are inappropriate (such
as the particles are too large, the contact is not close, etc.), or the phase
itself is wrong (such as some Metal oxide negative electrode with alloy
mechanism) needs to be activated for the first time by charging and discharging.
Second, when a lithium battery is charged and discharged for the first time,
electrons reach the surface of the graphite anode through an external path and
react with the electrolyte solvent and lithium ions to form a solid electrolyte
membrane (SEI). SEI has an important impact on the performance of the lithium
battery. The formation process has a great impact on battery performance,
because factors such as charge and discharge current and time have a great
impact on key parameters such as high-quality SEI formation, gas production, and
resistance in the battery.
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