In the electrode manufacturing of lithium-ion batteries, the positive
electrode slurry is composed of binders, conductive agents, positive electrode
materials, etc.; the negative electrode slurry is composed of binders, graphite
carbon powder, etc. The preparation of positive and negative electrode slurries
includes a series of processes such as mutual mixing, dissolution, and
dispersion of liquids and liquids, liquids and solid materials, and this process
is accompanied by changes in temperature, viscosity, environment, etc. In the
positive and negative electrode slurries, the dispersion and uniformity of the
granular active materials directly affect the movement of lithium ions between
the two electrodes of the battery. Therefore, the mixing and dispersion of the
slurry of each electrode material is crucial in the production of lithium-ion
batteries. , The quality of slurry dispersion directly affects the quality of
subsequent lithium-ion battery production and the performance of its
products.
Ultra-fine dispersion is carried out based on traditional technology. This
is because: through traditional mixing and stirring equipment, only large powder
groups in the solution can be broken up and evenly distributed; however, the
powder form exists in the form of fine powder groups. In the solution, it only
meets the processing requirements of macroscopic dispersion. The slurry after
macroscopic stirring and dispersion can further disperse and homogenize the fine
powder or solid particle agglomerates in the solution under the strong
mechanical cutting force of the ultra-fine dispersion and homogenization
equipment to obtain sufficiently fine solids. The particles are evenly
distributed in the solution to achieve microscopic ultra-fine dispersion and
homogeneity, which can significantly improve the comprehensive performance of
the slurry.
The current traditional slurry process is:
(1) Ingredients:
1. Solution preparation:
a) Mixing ratio and weighing of PVDF (or CMC) and solvent NMP (or deionized
water);
b) Stirring time, stirring frequency and times of the solution (and
solution surface temperature);
c) After the solution is prepared, inspect the solution: viscosity (test),
degree of dissolution (visual inspection) and storage time;
d) Negative electrode: SBR+CMC solution, stirring time and frequency.
Low temperature and high energy density 18650 3350mAh-40℃ 0.5C discharge
capacity ≥60%
Charging temperature: 0~45℃ Discharge temperature: -40~+55℃ Specific
energy: 240Wh/kg -40℃ Discharge capacity retention rate: 0.5C Discharge capacity
≥ 60%
Click for details
2. Active substances:
a) Monitor whether the mixing ratio and quantity are correct when weighing
and mixing;
b) Ball milling: ball milling time of positive and negative electrodes;
ratio of agate beads to mixed material in ball mill barrel; ratio of large balls
to small balls in agate balls;
c) Baking: Setting of baking temperature and time; test the temperature
after cooling after baking is completed.
d) Mixing and stirring of active substances and solutions: stirring method,
stirring time and frequency.
e) Sieve: pass through 100 mesh (or 150 mesh) molecular sieve.
f) Testing and inspection:
Conduct the following tests on slurries and mixtures: solid content,
viscosity, mixture fineness, tap density, and slurry density.
In addition to clarifying the traditional manufacturing process, it is also
necessary to understand the basic principles of lithium battery slurry.
colloid theory
The main effect that causes the agglomeration of colloidal particles comes
from the van der Waals force between particles. If you want to increase the
stability of colloidal particles, there are two ways. One is to increase the
electrostatic repulsion between colloidal particles, and the other is to create
steric positions between powders. Block the agglomeration of powder in these two
ways.
The simplest colloidal system consists of a dispersed phase and a phase
dispersion medium, where the scale of the dispersed phase ranges from 10-9 to
10-6m. Substances in colloids must have a certain degree of dispersion ability
to exist in the system. A variety of different colloidal forms can be produced
depending on the solvent and dispersed phase. For example, mist is an aerosol in
which droplets are dispersed in gas, and toothpaste is a sol in which solid
polymer particles are dispersed in liquid.
The applications of colloids abound in life, and the physical properties of
colloids vary depending on the dispersed phase and dispersion medium. Observing
colloids from a microscopic perspective, the colloidal particles are not in a
constant state, but move randomly within the medium. This is what we call
Brownian motion. Above absolute zero, colloidal particles will undergo Brownian
motion due to thermal motion. This is the dynamic characteristic of microscopic
colloids. The collision of colloidal particles due to Brownian motion is an
opportunity for aggregation. Colloidal particles are in a thermodynamically
unstable state, so the interaction force between particles is one of the key
factors in dispersion.
electric double layer theory
The electric double layer theory can be used to explain the distribution of
charged ions in colloids and the potential problems generated on the surface of
particles. In the 19th century, Helmholtz proposed the parallel capacitor model
to describe the electric double layer structure. He simply assumed that the
particles are negatively charged and the surface is like an electrode in a
capacitor. The positively charged counterions in the solution are attracted to
the particle surface due to the attraction of different charges. However, this
theory ignores the diffusion behavior of charged ions due to thermal motion.
Therefore, in the early 20th century, Gouy and Chapman proposed the
diffusion double layer model. Counter ions in the solution will be adsorbed on
the surface of charged particles due to electrostatic interaction, and at the
same time diffuse around the particles due to the influence of thermal motion.
Therefore, the distribution concentration of counterions in the solution will
decrease as the distance from the particle surface increases. In 1924, Stern
combined the two models of parallel capacitor and diffused electric double layer
to describe the electric double layer structure. Stern believes that counterions
will form a tight adsorption layer on the surface of the particle, also known as
the Sternlayer. As the distance from the particle surface increases, the
potential of the particle will decrease linearly. At the same time, there is
also a diffusion layer outside the Sternlayer, and the particles are in the
diffusion layer. The potential decreases exponentially with distance.
The zeta potential is closely related to the dispersion stability of the
colloid. When the zeta potential is larger, the more electrostatic charges are
on the surface of the colloidal particles. When the zeta potential of the
particles in the aqueous solution reaches more than ±25~30mV, the colloid has
sufficient Electrostatic repulsion overcomes the van der Waals forces between
particles to maintain colloidal stability.
From 1940 to 1948, Deryagin, Landau, Verwey, and Overbeek established
relevant theories on energy changes when colloidal particles approach each other
and their impact on colloid stability, referred to as DLVO theory. Its theory
mainly describes the relationship between the distance between colloidal
particles and energy changes. This interaction energy is the result of the
addition of the overlapping charge repulsion energy of the colloidal double
electric layer and the van der Waals force.
The figure below is a schematic diagram of DLVO, indicating that there are
attraction and repulsion forces between colloidal particles. The magnitude of
these two forces determines the stability of the colloidal solution. The
attraction between particles is the main effect, and the particles will
agglomerate; while the repulsion force In a state where the attraction force is
greater than the attraction force, particle aggregation can be avoided and the
stability of the colloid can be maintained.
According to the DLVO curve, when the distance between particles becomes
shorter and shorter, the particles will first generate attraction. If the
particles continue to approach each other, a repulsive force will be generated
between the particles. If the particles cross the repulsive energy barrier,
there will be Quickly produces reunions. Therefore, in order to improve the
dispersion stability of particles in the colloid, the repulsive force between
particles must be increased to avoid agglomeration between particles.
Read recommendations:
6LR61
Ten advantages of lithium ion battery.9.6kwh energy storage lithium solar battery
26650 lithium battery
12v 50ah lifepo4 lithium battery pack
aaa battery
360° FACTORY VR TOUR
Whatsapp
Tel
Email
TOP