Traditional processes and basic principles of charging lithium battery electrical core slurry

Traditional processes and basic principles of charging lithium battery electrical core slurry

Lithium-ion battery cells are stirred in the entire production process of mixed dispersion processes in the entire production process of lithium ion batteries, which is the most important link in the production process.. The electrode manufacturing of the lithium-ion battery, the positive pole slurry consists of an adhesive, a conductive agent, a positive electrode material, and the like; the negative slurry is composed of a binder, graphite toner.

. Positive, the preparation of the negative slurry includes a series of processes such as mutual mixing, dissolution, and dispersion between liquids and liquids, liquids, and solid materials, and in this process, with temperature, viscosity, and environment..

In the positive, negative slurry, the dispersibility and uniformity of the particulate active substance directly ring the movement of the lithium ion in the battery, and therefore is essential in the mixing dispersion of the slurry of each pole material in lithium ion battery. , The quality of the slurry is good and the quality is directly affected to the quality of subsequent lithium-ion battery and the performance of its products..

Ultrafine dispersion is performed in conventional processes, because: only the large powder in the solution can be dispersed by a conventional mixing and stirring equipment, and evenly distributed; however, the powder form is stored in the form of a fine powder group. In the solution, only the machining requirements of macro dispersion. After macroscopic stirring and dispersed slurry, under the intensive mechanical cutting force of ultrafine dispersion homogeneous equipment, the fine powder group or solid particulate gadder in the solution can be further dispersed and homogeneous to obtain a solid sufficiently fine solid.

Particles, and evenly distributed in solution, reaching the use of micro-ultrafine dispersion homogeneous, significantly increase the overall performance of slurry. At present, traditional slurry processes are: (1) ingredients: 1. Solution: a) mixing ratio and weighing of PVDF (or CMC) and solvent NMP (or deionized water); b) The mixing time of the solution, stirring frequency and After completion of the number (and solution surface temperature); C) After the solution is prepared, the test of the solution: viscosity (test) \ solubility (visual) and shelving time; D) negative electrode: SBR + CMC solution, stirring time and frequency.

2. Active substance: a) Weighing and mixing monitoring mix ratio, the number is correct; b) ball milling: positive negative ball mill; ball grinding bucket in Argous beads and mixtures; agate ball big balls and small balls Proportion; C) Bake: baking temperature, time setting; after the baking is completed, then the test temperature. d) Mixed stirring of active substances and solution: stirring, agitation time and frequency.

e) Sieve: over 100 mesh (or 150 mesh) molecular sieves. f) Test, test: the following tests are performed on the slurry: solid content, viscosity, mixing fineness, vibration density, slurry density. In addition to clearly making traditional processes, it is necessary to understand the basic principles of lithium-ion battery slurry.

. Colloidal theory leads to an important use of colloidal particles, is from Van Dew Huawhua, which is to add colloidal particle stability, and two ways, one is the electrostatic repulsive force between the new colloidal particles, two is the powder There is a spatial resistance, in these two ways block the powder reunion. The simplest colloidal system is constructed of a dispersed phase and a phase dispersion medium, wherein the dispersed phase scale ranges from 10-9 to 10-6m.

. The substance in the colloid is present in the system to have a degree of dispersibility..

A variety of different colloidal types can occur depending on the solvent and dispersed phase, such as: the fog is a gas glue dispersed in the gas, the toothpaste, the solid polymer particles dispersed in the liquid.. The application of colloid is in life, while the physical characteristics of colloids are different from the dispersion and dispersion medium.

. Observe the colloid from the microscopic angle, the colloidal particles are not in a constant state, but in the medium in the medium, this is the BrownianMotion we call..

Above the absolute zero, the colloidal particles will occur due to thermal exercise, which is the kinetic characteristics of microscopic colloides.. The colloid particles have collisions due to Brown movements, which is an opportunity that occurs in aggregate, and colloidal particles are in unstable state in thermodynamics, and thus the interactivity of particles is a key factor in dispersing.

. Double-circuit layer Theory Duplex layer Theory can be used to explain the distribution of electric ions in colloids, and potential problems in particle surfaces. The 19th century Helmholtz proposed a parallel capacitor model to describe the two-electric layer structure, simple assumption that the particles are negatively charged, and the surface is like the electrodes in the capacitor, and the positive electrical resection is adsorbed in the surface of the particle due to the electrical charge phase.

. However, this theory ignores the diffusion behavior of the with electric ions..

Therefore, in the early 20th century, GouY and Chapman proposed a diffusion dual-layer layer model. The anti-ion in the solution will be adsorbed to the surface of the charged particles due to the electrostatic application, while the impact of the heat movement is diffused around the particles..

Therefore, the distribution concentration of the anti-ion in the solution will decrease as the distance from the surface of the particles. In 1924, Stern (Stern) combined with two models of parallel capacitors and diffusion duplexers to describe dual-electrical layer structures..

Stern believes that the anti-ion is a tight adsorption layer on the surface of the particles, also known as Sternlayer, and the potential of the particles will decrease in linear decreases as the surface distance of the particles, while SternLayer has the presence of a diffusion layer, and particles are in the diffusion layer The potential in the middle will fall as the distance increases.. The picture below shows the string two-wire model, Zeta potential (ξ, zetapotential) is an important parameter in the two-wire model.

When actually measured, the surface potential of the particles cannot be directly measured, but can be calculated from a sound wave method or an electrophoresis method. Zeta potential of particles. There is a Zeta potential on the shear plane between the Stern layer and the diffusion layer in the two-wire layer model.

. The zeta potential and the dispersion stability of the colloid have a close relationship. When the zeta potential is higher, the static charge on the surface of the colloidal particles is more, when the zeta potential of the particles reaches ± 25 to 30 mV in the aqueous solution, the colloid is sufficient.

Electrostatic repulsive force overcomes Van Dehua Li to maintain colloidal stability. Stern Two-Electronics Model DLVO Theory 1940-1948, by Dryagin, Landau, Verwey, OverBeek, Energy changes and related theories affecting colloidal stability, referred to as DLVO theory. Its theory is important to describe the relationship between colloidal particle spacing and energy changes.

This use energy is the resulting rejection of the colloid duplex layer and the result of Van Dehua Di.. The following figure shows the DLVO schematic, indicating that there is attractive and repulsive force between colloidal particles.

The size of these two uses determines the stability of the colloidal solution, the attraction between the particles is an important purpose, the particles will agglomerate; In a large state of the attraction, the particles can be prevented from aggregating and maintaining the stability of colloids.. From the DLVO curve, when the distance between the particles is increasing, the particles will first appear, and when the particles are continuously approached, the particles will cause repulsive force between the particles, and if the particles are crused, they will Quickly reunion.

Therefore, in order to improve the particle dispersion stability in the rubber, there must be increased particle repulsion force to prevent aggregation between particles.. DLVO schematic colloidal stabilization mechanism colloidal particles tend to agglomerate due to high surface energy, in order to make the gelatin system have dispersion stability, it must improve the repulsive force between particles.

The stabilization mechanism between the colloid can be divided into three: 1) Electrostatic Stability Mechanism 2) Sterichindrance 3) electrostatic stereoscopic stability (ELECTROSTERICSTABILIZATION), the stabilization mechanism As shown below: (a) static stretching force, (b) stereo barriers, (c) electrostatic stereo disorder static stabilization mechanism is a repulsive force caused by surface charge of particles, and when the particles are proximity to each other, the dual layer of colloid particles is overlapped, due to particle surface That-based charge, therefore there is a repulsive force. However, the electrostatic stabilization mechanism is susceptible to the electrolyte concentration in the solution system. When the electrolytic concentration in the solution is too high, the particle surface is double-electrically compressed, but it causes aggregation of particles.

. The steady mechanism of stereobacros is to use a polymer to adsorb to a colloidal particle surface, and there are two different effects of different effects to increase the repulsive force between particles: 1) Osmoticeffect) is when the two plasma particles are close to the polymer long The residual polymer that is attached to the surface of the particle or in the solution is between the particles, and the high molecular concentration between the particles is constantly increasing will cause the change of osmotic pressure, and the surrounding medium enters the two particles, and the distance is discharged from each other. Dispersed and stable effect.

2) Volumerestrictioneffect has a certain spatial hindrance to adsorbing the polymer adsorbed on the surface of the particles, and when the particle distance is shortened, since the polymer does not penetrate the particles, the polymer will compress, resulting in raising the elastic freedom, thus Drain the particles to achieve the effect of dispersing. Compared to static stabilization mechanism, polymer stereo disorder has many advantages. The electrostatic stabilization mechanism is extremely susceptible to the environment, which cannot be applied to high electrolyte environments or organic system solutions.

. However, high molecular stereo disorders are relatively insensitive to electrolyte concentration, and are equal to the aqueous solution or have equal efficiency in the organic solvent, and the high molecular stereo disorder does not affect the effect due to colloidal solid content..

When the polymer is adsorbed to the surface of the colloidal particles, even if the agglomeration is also a soft reunion, it can simply break the agglomeration phenomenon. Even if the colloid particles pass the drying process, it is still a solvent again. Therefore, the use of stereo disorders regarding dispersion stability is relatively high static and stable effect.

. The electrostatic stereoscopic stability is the simultaneous static stabilization mechanism and stereo barrier. The high molecules of the grafting of the particles are charged, so that the two different stabilization mechanisms can make colloid particles have good dispersion stability.

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