Lithium ion battery full resolution

China's energy storage net news:Lithium ion batteries is a secondary The battery(rechargeable batteries), it mainly rely on Li + embedded back and forth between the two electrodes and embedded off to work. Downstream industry development, such as energy car lithium-ion battery production scale is expanding.

This topic is divided into upper and lower two parts, the last focuses on the principle of lithium ion battery, formulation and technological process. The next lecture The lithium battery Production and performance, this paper this topic last.

A, work principle

1, the anode structure

LiCoO2 (PVDF) + + conductive agent, binder set fluid (aluminum foil)

2, the cathode structure

Graphite + conductive agent, thickening agent (CMC) + binder (SBR) + fluid (copper foil)

3, working principle

3.1 charging process

A power supply to recharge the battery, the positive on the electronic e running on the cathode through an external circuit is lithium ion Li + "jump" from the positive electrolyte, "climb" diaphragm winding holes, "swimming" arrived at the cathode, and would have run to come over together. At this time:

On a positive response to:

On a negative response is:

3.2 the battery discharge process

Electric discharge has permanently exile and constant resistance discharge, electricity is actually in the external circuit with a constant exile can changes over voltage variable resistance, constant resistance discharge is of the essence of the battery is negative and a resistor through electronic. Therefore, as long as the cathode electron can't run away from the cathode to the anode, the battery will not discharge. Electronic and Li + is action at the same time, in the same direction is different, but the road is discharging, electrons from the cathode through electronic conductor ran to the anode, lithium ion Li + from the cathode "jump" in the electrolyte, "climb" diaphragm winding holes, "swimming" to the anode, and would have run to come over together.

3.3 charge and discharge characteristics

Batteries anode used LiCoO2, LiNiO2, LiMn2O2, of which the LiCoO2 is a very stable crystal layer structure, but when away from LiCoO2 x Li ion, its structure may change, but whether to change depends on the size of the x.

Through the study found that when x > 0.5, Li1 - xCoO2 structure is extremely unstable, can produce crystal structure collapsed, its external performance for batteries over end. So the batteries in use process should be through the limit of the charging voltage to control the Li1 - xCoO2 x value, average charging voltage isn't as less than 0.5 x is greater than 4.2 V, then Li1 - xCoO2 crystal structure is still stable.

Negative C6 itself has its own characteristics, when the first time into the positive Li of LiCoO2 is filled to negative C6, when Li returned to the anode discharge LiCoO2, but after into there must be a part of Li at the cathode C6 center, to ensure the normal embedding of charge-discharge Li next time, otherwise the batteries over a short, in order to ensure that there is a part of Li in anode C6, generally by limiting the discharge threshold voltage to achieve: safe maximum charge voltage of 4.2 V or less, discharge threshold voltage is 2.5 V or higher.

The principle is the crystallization of memory effect, in Lithium electricity Almost won't produce this kind of reaction in the pool. However, lithium ion battery in the many falls and put the filling capacity will still be the reason for this is complex and diverse. Mainly is the change of the anode materials itself, from the molecular level, is the cathode for lithium ion hole structure will gradually collapse, congestion; From the chemical point of view, is anode materials are active passivation, appear side effects to generate stable other compounds. Physically there will be the anode material gradually spalling, etc., in short eventually reduce the battery is free to move in the process of charging and discharging lithium ion number.

Overcharge and over discharge, across the electrodes for lithium ion batteries cause permanent damage to the molecular level, can be intuitive understanding, anode carbon discharge will cause excessive release of lithium ion and its layer structure appeared to collapse, excessive charging will take too much lithium ion shoehorned into the structure of cathode carbon, and makes some of the lithium ion can no longer be released.

Unsuitable temperature will trigger a lithium ion battery internal chemical reaction to generate we don't want to see other compounds, so in many of the lithium ion battery is between the cathode is equipped with protective temperature control diaphragm or electrolyte additives. Under the condition of the battery heating up to a certain, composite membrane film hole closed or electrolyte degeneration, battery internal resistance increases until the cut-off, battery is no longer to heat up, make sure the battery temperature is normal.

Second, the formulation and technological process of lithium-ion batteries

1. Is the cathode formula

1.1 the positive formula: LiCoO2 + conductive agent, binder + set fluid (aluminum foil)

LiCoO2 (10 microns) : 96.0%

Conductive agent (Carbon ECP) 2.0%

Adhesive (PVDF761) 2.0%

NMP (increase) bonding: the weight of the solid matter than about 810, 1496

A) the positive 6000 CPS viscosity control (3) temperature 25 rotor;

B) NMP weight should be appropriate adjustment, it is advisable to meet the requirements of viscosity;

C) pay special attention to the influence of temperature and humidity on the viscosity

The positive active material:

Cobalt acid lithium: the positive active material, lithium ion source, the source for lithium battery increase. Nonpolar substances, irregular shape, particle size D50 generally for 6 to 8 microns, water content of 0.2% or less, usually in the form of alkali, pH value of around 10-11.

Lithium manganese acid: nonpolar substances, irregular shape, particle size D50 generally for 5-7 microns, water content of 0.2% or less, usually a weak alkaline, pH value of 8 or so.

Conductive agent: catenary, water content < 1%, particle size is usually 1-5 microns. Excellent conductivity superconductivity carbon black are often used, such as the carbon black Carbon ECP and ECP600JD, its role: to improve the conductivity of the anode materials, compensate for the positive active material electronic conductivity; Improve the positive plate of electrolyte fluid absorption quantity, increase the interface reaction, reduce the polarization.

PVDF binder: nonpolar substances, catenary, the molecular weight range from 300000 to 3000000;After absorbing water molecular weight drops, viscosity variation. Used to cobalt acid lithium, conductive material and aluminum foil or aluminum mesh together. The used brands such as Kynar761.

NMP: weak polar liquid to dissolve/swelling PVDF, used to dilute pulp at the same time.

Set fluid (the anode lead) : made from aluminum foil or aluminum tape.

Anode recipe: 1.2 + graphite conductive agent + thickening agent (CMC) + binder (SBR) + fluid (copper foil)

Anode materials (graphite) : 94.5%

Conductive agent (Carbon ECP) : 1.0% (jean superconductive carbon black)

Binder (SBR) : 2.25% (SBR = styrene butadiene rubber latex)

Thickener (CMC), 2.25% sodium carboxy methyl cellulose (CMC =)

Water: the weight of the solid material ratio of 1600:1417.5

A) negative viscosity control CPS, 5000-6000 (3) temperature 25 rotor

B) water weight need appropriate adjustment, it is advisable to meet the requirements of viscosity;

C) pay special attention to the temperature humidity effect on the viscosity

2, positive and negative mixed materials

Graphite: the cathode active material, form the main material of cathode reaction; Mainly divided into two categories: natural graphite and artificial graphite. Non polar substances, vulnerable to non polar substances pollution, easy to disperse in non polar substances; Has difficulty in absorbing water, not easily dispersed in water. After the contaminated graphite, dispersed in water, easy to reunite. Average particle diameter D50 about 20 microns. Particle shape diverse and more irregular, mainly such as spherical, lamellar and fibrous.

Conductive agent, its function is:

A) improve the cathode piece, the conductivity of the compensation of the cathode active material electronic conductivity.

B) improve the reaction depth and utilization.

C) prevent the formation of dendrite.

D) using liquid absorbing ability of conductive materials, improve the interface reaction, reduce the polarization.(can choose with or without according to graphite particle size distribution).

Additives: reduce the irreversible reaction, improve the adhesion strength, improve the slurry viscosity, prevent pulp precipitation.

Thickener/anti precipitation agent (CMC) : high polymer compounds, soluble in water and polar solvent.

Isopropyl alcohol: weak polar material, can reduce the polarity of the glue solution after China's entry into WTO, to improve the compatibility of graphite and adhesive solution; Have strong defoaming effect; Easy to catalytic adhesive mesh chain, improve the bonding strength.

Ethanol: weak polar material, can reduce the polarity of the glue solution after China's entry into WTO, to improve the compatibility of graphite and adhesive solution; Have strong defoaming effect; Easy catalytic adhesive linear chain, improve the bonding strength, the effect of isopropyl alcohol and ethanol in essence is the same, when mass production, can consider cost factors and then decide which one to add).

Water-based adhesives (SBR) : using graphite and conductive agent, additives and copper foil or copper mesh together. Small molecule linear chain emulsion, easily soluble in water and polar solvents.

Deionized water or distilled water, diluent, whether to add, change the size of liquidity.

The cathode lead: made from copper foil or nickel.

2.1 the anode mixture:

2.1.1 the pretreatment of the raw material

1) cobalt acid lithium: dehydration.120 ° C atmospheric is commonly used in baking 2 hours or so.

2) conductive agent: dehydration.200 ° C atmospheric is commonly used in baking 2 hours or so.

3) adhesive: dehydration.120-140 ° C is commonly used in atmospheric bake for 2 hours, baking temperature depending on the size of the molecular weight of the decision.

4) NMP: dehydration. Using molecular sieve dehydration drying or the use of special facilities, direct use.

2.1.2 material ball mill:

1) over four hours, sieving isolated ball mill;

2) the LiCoO2 and Carbon ECP pour into barrels, while adding a grinding ball grinding balls (dry: = 1:1), on the rolling cylinders and ball mill, speed control in more than 60 RMP

2.1.3 raw material with:

1) the dissolution of adhesive (according to the standard concentration) and heat treatment.

2) cobalt acid lithium and conductive material ball mill: make preliminary mixed powder, cobalt acid lithium and conductive material together, improve the function and the electrical conductivity of the reunion. Match into pulp after not separate distribution in the adhesive, ball grinding time is usually 2 hours; To avoid mixed with impurities, often use agate ball for ball mill meson.

2.1.4 powder dispersion, wet:

Principle: solid powder is placed in the air, with the passage of time, will be part of the air on the surface of the solid adsorption, liquid adhesive after joining, liquid and gas on the solid surface; If the ratio of solid and gas adsorption with liquid adsorption force strong, liquid cannot wet solid; If the solid and liquid adsorption ratio and gas adsorption force strong, solid and liquid can be soaked out gas.

When the wetting Angle 90 ° or less, solid water. When the wetting Angle > 90 °, solid not wet.

The anode material of all team members can soak glue solution, so the positive powder dispersed relatively easy.

The influence of dispersion method of dispersion:

1) incubation method (a long time, the effect is poor, but not the original structure damage material);

2) mixing method: rotation or rotation and revolution (time is short, the effect is good, but is likely to damage its structure of individual materials).

Impeller effects of dispersion speed impeller generally include serpentine, butterfly, ball, blades, gears, etc. General serpentine, butterfly, paddle type impeller is difficult to deal with scattered materials or ingredients in the initial stage; Spherical, the gear form is used to disperse the difficulty low status, the effect is better.

Stirring speed to the influence of the dispersion velocity. Generally the higher the stirring speed, the faster the scattered, but the material itself structure and the greater the damage to equipment.

The influence of concentration of dispersion rate. Normally slurry concentration is smaller, the faster the scattered, but it's too thin will cause the waste of material and pulp precipitation increase.

The influence of concentration of bond strength. Concentration, the greater the soft system, the greater the intensity, the greater the bonding strength; The lower the concentration, the smaller the bonding strength.

The influence of vacuum degree of dispersion rate. High vacuum is advantageous to the material on the surface of the gap and gas discharge, reduce the difficulty of the liquid adsorption, Material in the case of weightlessness or weaker gravity will greatly reduced the difficulty of dispersed evenly.

The influence of temperature on the dispersion rate. Good appropriate temperature, slurry flow, easy to spread. Too hot paste easy crust, too cold slurry liquidity will be discounted.

Dilution: adjust the size to the appropriate concentration, is advantageous for the coating.

2.1.5 steps

A) will combine NMP dynamic mixer (100 l) to 80 ° C, weigh and PVDF join, start; Parameter Settings: speed to 25 + 2 r/min, 115-125 minutes;

B) turn on the cooling system, will have the positive dry grinding size averaged four times, each time interval 28-32 minutes, the third time charging depending on the materials you need to add NMP, fourth NMP is joined after loading; The mixing machine parameters Settings: speed of 20 plus or minus 2 revolutions per minute

C) for the fourth time charging for high speed stirring, after 30 + 2 minutes time of 480 + 10 minutes; Dynamic mixing machine parameter Settings: revolution for 30 + 2 r/min, since to 25 + 2 r/min;

D) vacuum mixing: mix power machine connected to the vacuum, keep the vacuum degree is 0.09 MPA, mixing 30 + 2 minutes; Dynamic mixing machine parameter Settings: revolution for 10 + 2 minutes, since to 8 + 2 revolutions per minute

E) take 250-300 - ml size, viscosity meter is used to measure the viscosity; Test conditions: the rotor number 5, 12 or 30 RPM speed, temperature range is 25 ° C;

F) extracted from the anode material dynamic mixer for colloid mill, sieving, at the same time on the stainless steel bowl with logo, and plasma equipment operators after the handover can be inflow pulp operation process.

2.1.6 matters needing attention

A) complete, clean the machine equipment and working environment;

B) the operation of the machine, need to pay attention to safety, to avoid hitting the head.

2.2 the cathode mixture

2.2.1 the pretreatment of the raw material:

1) graphite:

A, mixing, making raw material homogenizing, and improve the consistency.

Atmospheric pressure baking, B, 300 ~ 400 ° C to remove surface oily substance, improve compatibility with the water-based adhesive ability, repairing circular graphite surface edges (some materials to keep the surface features, are not allowed to baking, or poor performance).

2) water-based adhesives: appropriate dilution, improve the dispersion ability.

2.2.2 admixture, wetted and dispersed:

1) graphite and adhesive solution polarity is different, not easy to spread.

2) alcohol aqueous solution can be used first graphite initial wetting, then mixed with adhesive solution.

3) should decrease the mixing concentration, improve the dispersion.

4) the dispersion process in order to reduce the polar and non polar distance, improve the potential energy or surface energy, so as the endothermic reaction, the decrease in the overall temperature at the time of mixing. If conditions permit should be appropriate mixing temperature rising and makes it easy to heat, increasing liquidity at the same time, the dispersed easier.

5) mixing process, such as add vacuum degassing process, eliminate gas, promote the solid-liquid adsorption, the effect is much better.

6) dispersion principle, dispersion method with the positive ingredients in the related content

2.2.3 dilution:

Adjust the size to the appropriate concentration, easy to coating.

2.2.4 material ball mill

1) will be negative and Ketjen black ECP to VAT at the same time add ball mill (grinding balls dry: = 1:1. 2) in the roll on bottle and ball mill, speed control in more than 60 RMP;

2) over four hours, sieving isolated ball mill;

2.2.5 steps

1) pure water heated to 80 ° C in a dynamic mixer (2 l)

2) adding CMC, stir 60 + 2 minutes; The mixing machine parameters Settings: revolution is 25 + 2 minutes, since to 15 + / - 2 r/min;

3) add SBR and deionized water and stir 60 + 2 minutes;

Dynamic mixing machine parameter Settings: revolution for 30 + 2 minutes, since to 20 plus or minus 2 r/min;

4) negative dry points, four times the average in order to join, charging at the same time in pure water, 28-32 minutes every time interval; Dynamic mixing machine parameter Settings: revolution is 20 + 2 r/min, since to 15 + / - 2 r/min;

5) fourth charging for high speed stirring, after 30 + 2 minutes time of 480 + 10 minutes;

Dynamic mixing machine parameter Settings: revolution for 30 + 2 r/min, since to 25 + 2 r/min;

6) vacuum mixing: mix power machine connected to the vacuum, keep the vacuum degree is 0.09 to 0.10 MPA, mixing 30 + 2 minutes;

Dynamic mixing machine parameter Settings: revolution for 10 + 2 minutes, since to 8 + 2 revolutions per minute

7) take 500 ml size, viscosity meter is used to measure the viscosity;

The test conditions: rotor number 5, 30 RPM speed, temperature range is 25 ° C;

8) will be the cathode materials extracted from the dynamic mixing machine for grinding and sieving, at the same time on the stainless steel bowl with logo, and plasma equipment operators after the handover can be inflow pulp operation process.

2.2.6 matters needing attention

1) complete, cleaning machinery and equipment and working environment;

2) when operating the machine, need to pay attention to safety, to avoid hitting the head.

Ingredients to note:

Avoid mixed with other impurities;

To prevent slurry spray;

The concentration of the slurry (solids) from high to low gradually adjusted, so as not to increase the trouble;

Pay attention to in the process of mixing of intermittent scraping sides and a bottom, to ensure uniform dispersion;

Size should not be shelved for a long time, in order to prevent precipitation or uniformity;

After baking materials must be sealed cooling can join, lest constituent material properties change;

The length of the stirring time is given priority to with equipment performance, the amount of material;

Impeller used in pulp dispersion change difficulty, can't change can be to adjust the speed from slow to fast, in order to avoid damage to equipment;

Before discharge to sieve size, remove larger particles to prevent coating caused by broken belt;

For ingredients personnel should strengthen training, to ensure the master professional knowledge, in order to avoid the disaster;

Is the key ingredient in dispersed evenly, grasps the center, other ways can adjust itself.

A, battery production required parameters

1, the size of the pole piece

2, plasma technology

A) set fluid size

The anode (aluminum foil), intermittent coating

The cathode (copper foil), intermittent coating

B) slurry weight requirements

After 3, the anode paste for the following process:

Cutting large cutting small piece according to piece (with) baking flaking pole ear welding negative after the pulp for the following process:

Cutting large cutting small piece according to piece (with) baking flaking ear welding

4, flaking

5, with solutions

6, sheet roasted

Note: the vacuum degree of vacuum system for - 0.095-0.10 MPA. Protection for high purity nitrogen gas, the gas pressure is greater than 0.5 MPA

7, a ear

A) the positive:

The positive pole ear in the positive plate by ultrasonic welding. Aluminum bar end with flush plate edge.

B) negative:

Nickel size: 0.10 x 3.0 x 48 mm, nickel directly with spot welding spot welding, spot welding points to article 8 point nickel right aligned with the cathode piece on the right side, end of the article nickel and flush plate edge.

8 the diaphragm size: 0.025 * 44.0 * 790 + / - 5 mm

9 needle width: 22.65 + / - 0.05 mm

After 10 pressure core: battery winding, first in the bottom of the batteries, as 24 mm width of transparent tape, reoccupy cold pressing machine two times.

Requirements before 11 batteries into the shell

Gummed paper 1:10. 0 x 38.0 + / - 1.0 mm, gummed paper distributed evenly on both sides of batteries;

Tape 2:10. 0 x 38.0 + / - 1.0 mm, nickel strip in the middle of the tape.

Gummed paper 3:24. 0 x 30.0 + / - 2.0 mm, gummed paper distributed evenly on both sides of batteries;

Nickel strip on the right side is apart from the batteries on the right side of 7.0 + / - 1.0 mm.

12 pack shell

When packing and application of both hands, slowly the batteries into the battery shell, scratch batteries is prohibited.

13 negative pole ear welding

Anode nickel strip and steel shell with spot welding machine for welding, to ensure the welding strength, virtual welding is forbidden.

14 laser welding

Laser welding fixture should be carefully, can only be carried out after the battery shell and cover with good welding, pay attention to avoid the partial welding.

Vacuum bake 15 batteries

Remark:

(1) the vacuum degree of vacuum system for 0.095 ~ 0.10 MPA;

(2) protection for high purity nitrogen gas, gas pressure > 0.5 MPA;

(3) a vacuum injection every hour nitrogen