How do you improve the infiltration effect of electrolyte on the electrode sheet?

The electrolyte battery is negative ion conduction effect between conductors, charge and discharge process, the positive and negative electrode round-trip transport lithium ion. The electrolyte of battery charging and discharging performance of the high and low temperature) (ratio, life expectancy (circular storage), the influence of temperature has a larger scope.

Suitable solvent to its high dielectric constant, low viscosity, with alkyl carbonate in common use such as PC, EC, such as strong polarity, high dielectric constant, but the viscosity, molecular inter-atomic forces, in which lithium ions move slowly.Linear ester, such as DMC (dimethyl carbonate), DEC (diethyl carbonate) such as low viscosity, dielectric constant is low, therefore, in order to obtain high ionic conductivity of the solution, generally USES the PC + DEC, EC + DMC such as mixed solvent.

Used for lithium ion batteries electrolytes generally should meet the following basic requirements:

A. high ionic conductivity, generally should reach 1 x 10-3-2 x 10-2 s/cm;

B. high thermal stability and chemical stability, in a wide range of voltage separation does not occur;

C. a wide electrochemical window, in the wide voltage range maintain the stability of the electrochemical properties;

D. with other parts of cells such as electrode material and electrode set fluid and the diaphragm has good compatibility;

E. safe, non-toxic, no pollution.

2. The electrolyte seepage effect

When lithium battery use reached the standard of abandoned or suddenly fails, often to be disassembled to analysis, what is the objective cause attenuation or plunge in the performance of the battery.Small make up on lithium battery disassembly analysis, found the loop performance is not very good battery and infiltration of the electrolyte to often the result is bad.Electrolyte seepage effect is bad, ion transport path becomes far, hindered the lithium ion shuttle between is negative, no contact from the pole piece of battery electrolyte electrochemical reaction, the battery interface resistance increases at the same time, the influence on the performance of the lithium battery ratio, discharge capacity and service life.

So, in order to avoid the shortcomings, we need to find a way to make the electrolyte of infiltrating pole piece as much as possible.Of course the cost into consideration, we need to use the right amount of electrolyte as much as possible.

3. How to improve the invasive of electrolyte

Electrolyte infiltration of pole piece, involved the content of solid, liquid, gas three-phase contact.When injecting electrolyte into the battery shell, first to discharge the air inside the shell, electrolyte electrolyte after across the electrodes will adhere to the surface of the living quality, some electrolyte will pass the core winding between diaphragm into the positive - diaphragm - negative.As a continuation of the time, there will be a infiltration within the plate, diaphragm electrolyte electrolyte reverse infiltration phenomenon of pole piece, when quiet place to a certain degree of time, under the action of surface tension, infiltration of pole piece to a state of balance.

In this process, will involve a concept in physical chemistry "contact Angle" (wetting Angle).As shown in the figure below, the blue areas in the figure represent liquid, grey area representative solid interface.So blue and gray contact area is solid liquid interface, the location of the liquid solid interface and tangent to the cross formed an Angle theta, the smaller the contact Angle of theta that electrolyte to invasive or diaphragm, the better.

But, in the actual operation process, often unable to grasp the electrolyte seepage effect of pole piece, according to the above mentioned electrolyte seepage principle, we can from the following points to find a way to improve the effect of electrolyte infiltration of sheet:

(1) improve liquid injection process

Improve the injection fluid technology is one of the most conventional way, from the liquid injection efficiency, injection fluid conditions, the incubation time, fluid injection mode can improve the infiltrating effect of the electrolyte.

Bet fluid in vacuum condition, is not only beneficial to gas discharge in batteries, also can reduce the gas to the resistance of the electrolyte injection, help the electrolyte infiltration of pole piece.Its principle is vacuum injection can reduce the solid - gas - liquid three-phase interface the existence of gas phase resistance, make direct contact with a piece of electrolyte, reduced the infiltration time.

Let stand by extending the vacuum time, can guarantee the electrolyte fully infiltrates pole piece.After injection liquid, as stand for prolonged, electrode liquid wetting Angle decreases with pole piece, wetting radius increases gradually, finally achieve good effect.

In order to avoid the electrolyte to the phenomenon of infiltration of the diaphragm, the sheet was inadequate, can inject electrolyte in batches, facilitate the electrolyte to fully infiltrates, the operating mode in principle: increases the chances of solid-liquid contact and enlarge the contact area, on the basis of the amount of electrolyte, infiltration can shorten the time.

(2) improve core winding process

Electrolyte seepage effect with the nature of electrode material particles, the pole piece compaction density, volume core looseness, etc.Different morphology and particle size are negative active material, conductive agent, the effect of infiltration of electrolyte on the pole piece is different, the greater the particle size of raw materials, the more close to the ball, the electrolyte osmotic rate, the greater the shorter infiltration time.When excessive pole piece of the compaction density, porosity reduced in the pole piece, is not conducive to the electrolyte infiltration of pole piece, need to adjust the proper compaction density, under the condition of the battery of low impedance, satisfy the infiltration degree of electrolyte.Also, the batteries stacked or winding looseness may also affect infiltration of the electrolyte.

Winding is loose, the positive - diaphragm - negative between the porosity is larger, accumulated amount of electrolyte is more, the enrichment of parts, and the lack of some places that there is no doubt a great influence on the performance of the battery.When winding tighter, and affects the infiltration rate and efficiency of the electrolyte, is unsatisfactory.

(3) adding electrolyte infiltration agent

Usually adopted electrolyte for organic solvent, pole piece for inorganic materials, electrolyte absorption ability is weak.To join in the electrolyte additive can improve the infiltration of the electrolyte.Fang-fang Liu took a desflurane materials such as as the electrolyte additive, the experimental results showed that adding a small amount of electrolyte infiltration agent can effectively shorten the battery fluid injection time, and obviously improve the cycle performance of battery, but it is important to note when infiltrating agent content of 1%, will have a negative effect on the cycle performance.

Infiltration agent is the essence of the surfactant, such infiltration agent with high surface activity, high thermal stability, low flammability and Gao Huaxue stability etc., and after infiltration agent is added in the electrolyte can reduce the surface tension of liquid, improve the wetting ability of electrolyte on the pole piece and penetration ability, thus improve the electrochemical performance of the battery.

Through the above several kinds of method, it can effectively improve the electrolyte seepage effect of pole piece. Shortening the time of infiltration, can save the production cost, improve the effect of infiltration, can reduce the battery impedance interface, improve the utilization efficiency of living quality, raise battery capacity, improve discharge rate characteristics.

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