CN100466364C - A kind of safe lithium-ion battery - Google Patents

Abstract

The invention relates to a safe lithium ion battery. The invention belongs to the technical field of lithium ion batteries. Safe lithium-ion battery, including positive electrode, negative electrode, diaphragm and non-aqueous electrolyte, positive electrode and negative electrode are composed of metal foil current collector and coating containing active material coated on its surface, which is characterized by: positive electrode coating contains layered structure The active material of nickel-cobalt-manganese-lithium oxide; the negative electrode coating contains one or two active materials of carbon fiber and spherical graphite and flake graphite, wherein the weight content of carbon fiber is 1-5%. The invention has the advantages of reducing the risk of thermal runaway, avoiding lithium electrolysis, and improving the safety performance of the lithium ion battery. It can be widely used as a power source for electronic equipment, space operation, electric vehicles and various boosters.

Description

A kind of safe lithium-ion battery

technical field

The invention belongs to the technical field of lithium ion batteries, in particular to a safe lithium ion battery.

Background technique

A lithium-ion battery consists of a negative plate, a positive plate, an electrolyte, and a separator interposed between the positive and negative plates to prevent short circuits. For example, the negative plate is a carbonaceous material that absorbs/releases lithium ions fixed on the current collector; Based oxides and composite oxides such as lithium manganese oxide with a spinel structure; the electrolyte is a solution in which LiPF ₆ and other aprotic organic solvents are dissolved.

The positive plate and the negative plate are made into thin plates or foils, and then the electrode plates and the intervening separator are stacked in sequence or spirally wound to form a battery cell. Then put this battery core into stainless steel, nickel-plated iron, or lighter aluminum metal shell, or laminated A1 soft packaging film battery container, then inject electrolyte, seal and make a battery.

Because lithium cobalt oxide and lithium nickel oxide have large capacity and relatively high real density, lithium-ion batteries using the above two materials usually have high specific energy. However, lithium ion batteries using the above two materials are inferior in safety performance such as resistance to overcharge. The discharge capacity of spinel lithium manganese oxide is low, but the safety performance of lithium-ion batteries using this material is better.

At present, there are many ways to improve the safety performance of lithium-ion batteries, such as using a PP/PE/PP three-layer separator with thermal blocking function, adding additives such as flame retardants, and coating with ceramic materials. However, the reliability and practicability of these methods cannot be guaranteed when a large rate is overcharged.

Contents of the invention

The invention provides a safe lithium ion battery for solving the technical problems existing in the existing lithium ion battery.

The object of the present invention is to provide a positive and negative electrode material and proportion of a lithium-ion battery with high safety, which can improve the safety of the lithium-ion battery, especially the overcharge resistance performance.

The feature of the present invention is that the mixed material is selected as the active material of the positive electrode, and by optimizing the ratio of the positive electrode/negative electrode active material, the high-current charging performance of the electrode is improved, so as to improve the safety performance of the lithium-ion battery including overcharge resistance.

The present invention adopts following technical scheme:

Safe lithium-ion battery, including positive pole, negative pole, diaphragm and non-aqueous electrolyte, positive pole and negative pole are all made of metal foil current collector and the coating containing active material coated on its surface, it is characterized in that: positive pole coating contains lamellar structure Nickel-cobalt-manganese-lithium oxide active material; the negative electrode coating contains one or two active materials of carbon fiber, spherical graphite and flake graphite, wherein the weight content of carbon fiber is 1-5%.

The overcharge resistance of the positive electrode and even the battery is improved. At the same time, the negative electrode uses carbon fiber with good conductivity, thereby reducing the internal resistance of the battery and avoiding lithium electrolysis on the surface of the negative electrode during high-rate overcharging, thereby reducing the thermal reaction of the negative electrode out of control.

The present invention can also adopt following technical measures:

Described a kind of safe lithium ion battery is characterized in that: positive pole coating comprises the cobalt oxide lithium of layered structure and the nickel oxide cobalt manganese lithium active material of layered structure.

The described safe lithium-ion battery is characterized in that the weight content of the active material nickel oxide cobalt manganese lithium in the positive electrode coating is not less than 20%.

The positive electrode adopting more than 20wt% of nickel oxide, cobalt, manganese and lithium mixed positive electrode active material can fully ensure that the lithium ion battery will not catch fire under abuse conditions such as overcharging without changing the electrochemical performance of the lithium ion battery. don't explode.

Described a kind of safe lithium-ion battery is characterized in that: positive electrode active material weight is 1.5-2.2 times of negative electrode active material coating weight.

Described a kind of safe lithium-ion battery is characterized in that: positive electrode active material weight is 1.75-2 times of negative electrode active material coating weight.

Described a kind of safe lithium-ion battery is characterized in that: negative electrode active material carbon fiber is nano carbon fiber.

Described a kind of safe lithium-ion battery is characterized in that: the shape of battery is cylindrical, oblong shape, square or button shape.

Although the present invention uses a mixture of cobalt lithium oxide and nickel cobalt manganese lithium oxide as the positive electrode active material, the present invention is not limited to cobalt lithium oxide, and can be used in the positive electrode active materials of the present invention LiNiO ₂ , LiCo _x Ni _1-x O _2, etc., another positive electrode active material can be _LiNix Co _y Mn _1-xy O ₂ , LiMn ₂ O ₄ , Li ₂ Mn ₂ O ₄ , LiFePO ₄ , etc. Of course, derivatives of the above-mentioned compounds doped with elements such as Al and Mg are also included.

As the lithium ion battery of the present invention, it is characterized in that the negative electrode contains 1-5 wt% of nano-carbon fibers. This is because by adding a certain amount and a certain length of carbon nanofibers, the conductivity between the active material in the electrode and the current collector can be fully guaranteed. At the same time, the comprehensive performance of the electrode can be guaranteed. If the length of the fiber exceeds 20 microns, it is possible that part of the fiber will pass through the separator and reach the counter electrode, causing a micro-short circuit between the positive and negative plates. In addition, if the added amount exceeds 5 wt%, a large amount of binder must be added at the same time to maintain the adhesion of the electrode material layer. Excessive binder is the reason for the increase of electrode internal resistance. Therefore, the addition amount of carbon nanofiber should not exceed 5wt%; if the addition amount is too small <1wt%, then the performance of negative maximum current charging cannot be improved.

The present invention exemplifies vapor-phase grown carbon nanofibers (VGCF), and also carbon black, acetylene black (AB), and stable metal nanofibers such as Ni. Fibrous conductive materials are preferred. Because the fibrous conductive material is suitable for maintaining a conductive path.

The layered nickel-based oxide of the present invention is LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , but it is not limited to this composition, and can also be other groups whose Mn content does not exceed 1/2 of the molar content of transition metal elements. ternary layered compound, but the composition of high manganese and low Ni and Co is better. Compounds with a molar content of Al, Mg or Li between 1 and 1.1 can also be doped.

Although spherical graphite and flaky graphite have been enumerated as the negative electrode material that can be used in the present invention, the negative electrode active material that can be used in the present invention is not limited to this, and carbonaceous materials such as easy graphitization carbon materials and hard carbons and the above-mentioned materials can also be used. mixture.

As the electrolytic solution of the present invention, one or more mixtures of the following organic solvents may be included. Ethyl carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), gamma-butyrolactone (GBL) , sulfolane, dimethyl sulfoxide, acetonitrile (AN), dimethylformamide, diethylformamide, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran (THF ), 2-methyltetrahydrofuran, dioxolane, methyl acetate and other polar solvents. In order to obtain good discharge performance and life of the battery, it is preferable to contain ethylene carbonate (EC) in the above-mentioned solvent.

The electrolyte salt dissolved in the electrolyte solvent may include the following single electrolyte salts and mixtures thereof. Such as LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiCF ₃ CO ₂ , LiCF ₃ (CF) ₃ , LiCF ₃ (C ₂ F ₅ ) ₃ , LiCF ₃ SO ₃ , LiN(SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂ CF ₃ ) ₂ , LiN(COCF ₃ ) ₂ , LiN(COCF ₂ CF ₃ ) ₂ , LiBOB, and LiPF ₃ (CF ₂ CF ₃ ) ₃ . It is preferable to partially contain LiPF ₆ or LiBF ₄ in the electrolyte salt, so as to form a good film on the negative electrode and obtain good discharge characteristics and life.

At the same time, in order to suppress the irreversible capacity and the transitional growth of the SEI film on the surface of the negative electrode material, it is preferable to add additives such as vinylene carbonate (VC) and its derivatives, such as 4,5-dimethyl vinylene carbonate, 4,5-diethyl 4,5-dipropyl vinylene carbonate, 4-ethyl-5-methyl vinylene carbonate, 4-ethyl-5-propyl vinylene carbonate. In addition, cyclic sulfates are also conducive to the formation of good SEI, such as ethylene glycol sulfate, 1,2-propylene glycol sulfate, 1,2-butanediol sulfate, 1,3-butanediol sulfate, 2,3 -Butanediol, phenylethylene glycol sulfate, etc.

As the separator of the present invention, woven fabrics, non-woven fabrics, microporous synthetic resin films, and the like can be used. Among the above separator layer materials, microporous synthetic resin films are particularly preferred, and polyolefin microporous films such as polyethylene and polypropylene microporous films or composite microporous films thereof are particularly preferred. The reason why these polyolefin-based microporous membranes are used is that they are superior in thickness, membrane strength, and membrane resistance characteristics.

If a colloidal electrolyte is used, it can also be used as an isolation layer. In this case, a porous polymer solid electrolyte can be used, which then contains an electrolytic solution.

The battery of the present invention can be made into a cylindrical shape, a long garden shape, a square shape, a button shape, and A1 laminated film flexible packaging and the like. The capacity can be tens of mAh to tens of Ah or even more than 100Ah. But when making large-capacity lithium-ion batteries, it is better to use cylindrical, oblong, and square shapes.

Advantage and positive effect that the present invention has:

By adopting the positive electrode of the present invention, when the battery is overcharged, the calorific value is suppressed, reducing the risk of thermal runaway, adopting the positive and negative electrode ratio of the present invention, and adopting the negative electrode with fiber conductive agent, the electronic conductivity of the negative electrode It can be improved to realize the high-current charging performance of the negative electrode of the lithium-ion battery, avoid lithium electrolysis, and improve the safety performance of the lithium-ion battery.

The lithium ion battery of the present invention can be widely used in power sources such as 3C electronic equipment, space power supplies, electric vehicles, hybrid vehicles, electric tools, and various boosters.

Description of drawings

Fig. 1. Structural schematic diagram of safe lithium-ion battery of the present invention;

Among them, 1-battery cover, 2-insulating gasket, 3-positive pole ear, 4-positive pole, 5-diaphragm, 6-battery shell, 7-safety valve, 8-negative pole ear, 9-negative pole.

Figure 2. Schematic diagram of the cross-section of the positive and negative plates of the safe lithium-ion battery in Figure 1;

Among them, 10 and 12 are positive electrode active material coatings (front and back), 11 is positive electrode current collector; 13 and 15 are negative electrode active material coatings (front and back), and 14 is negative electrode current collector.

Fig. 3. the present invention adopts the comparative schematic diagram of the charge-discharge curve of the lithium ion battery of mixed positive electrode material and comparative example cobalt oxide lithium material; 16: adopt LiCoO _the battery of positive electrode active material; 17: adopt active material containing 20% LiNi _{1/ 3} Co _1/3 Mn _1/3 O ₂ and 80% LiCoO ₂ cathode.

Fig. 4. The present invention adopts the temperature and voltage change schematic diagram of the lithium-ion battery of the mixed positive electrode material and comparative example cobalt oxide lithium material during overcharging. 18: The overcharge voltage curve of the battery using LiCoO ₂ positive electrode active material; 19: The battery using the positive electrode containing 20% LiNi _1/3 Co _1/3 Mn _1/3 O ₂ and 80% LiCoO ₂ in the active material Variation curve of overcharge voltage; 20: The temperature change when the battery adopts LiCoO ₂ positive electrode active material when overcharged; 21: The active material contains 20% LiNi _1/3 Co _1/3 Mn _1/3 O ₂ and 80% LiCoO _2. The temperature change of the positive electrode of the battery when it is overcharged.

Detailed ways

For being able to further understand content of the invention of the present invention, feature and effect, enumerate example and describe in detail as follows:

Example 1

With reference to accompanying drawing 1, Fig. 2, Fig. 3 and Fig. 4.

A safe lithium-ion battery comprises a positive pole 4, a negative pole 9, a separator 5 and a non-aqueous electrolyte, and a battery case 6, a battery cover 1, an insulating gasket 2, and a safety valve 7 are arranged on the outside, wherein the positive pole 4 is made of an aluminum foil current collector 11 and coated on Its surface consists of layered lithium cobalt oxide and layered nickel-cobalt-manganese-lithium oxide active material coatings 10 and 12; the positive current collector 11 is connected with the positive tab 3 . The negative electrode 9 is composed of a copper foil current collector 14 and active materials 13 and 15 coated on its surface containing carbon nanofibers, spherical graphite, and flake graphite. The negative electrode current collector 14 is connected to the negative electrode ear 8 .

1. Production of the positive plate:

Weigh LiCoO ₂ and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ positive electrode active materials in a weight ratio of 4:1, mechanically mix them with a powder mixer for 30 minutes, then weigh the mixture, binder and conductive agent, According to the N-methyl-2-pyrrolidone (NMP) solution of 93wt% positive electrode active material mixture, polyvinylidene fluoride (PVdF) binder and make the content of PVdF be 4.5wt%, as the 2.5wt% of conductive material VGCF, mixed to form a positive electrode mixture, NMP was added to the mixture to prepare a paste with a mixer, and then the paste was evenly coated on both sides of an aluminum foil with a thickness of 20 μm, and then dried and rolled to obtain a positive electrode plate. The coating weight was 22 mg/cm ² .

2. Preparation of negative plate:

At 20% (weight) of mesophase carbon microspheres MCMB, 70% of flake graphite, 2% (weight) of VGCF and 8% (weight) of PVdF (added in the solution mode of NMP) to make a paste, Then the paste was evenly coated on both sides of the copper foil with a thickness of 10 μm, dried and rolled to obtain a negative electrode plate. The coating weight was 11 mg/cm ² .

A microporous polyethylene film with a thickness of about 25 µm was used as the diaphragm body.

The non-aqueous electrolyte used is a mixed solvent solution of EC+DEC+DMC (volume ratio 1:1:1) that is dissolved with 1mol/lLiPF ₆ , and on this basis, 1.0wt% of vinylene carbonate (relative to the total amount of electrolyte) is added ).

3. Battery assembly:

The above-mentioned positive electrode 4, separator 5, and negative electrode 9 are stacked and wound in order to form a cell, inserted into the cylinder, welded the electrodes, and then vacuum-dried at 60°C before injecting liquid to seal. The cylindrical battery thus assembled was designated as battery A1, and the electrochemical test was carried out as follows.

4. Charge and discharge test:

First a capacity test was performed. Charging is CC-CV mode; discharging is CC mode. That is, charge to 4.2V with a constant current of 0.2C rate, and then 4.2V constant voltage for 2 hours; discharge also use a constant current of 0.2C rate to discharge to 2.75V. The discharge capacity obtained by the above method is taken as the initial capacity, and the ratio of the discharge to charge quantity is taken as the charge-discharge efficiency.

5. Safety test:

After the above-mentioned experimental battery was fully charged, overcharge, overdischarge and external short circuit experiments were carried out respectively. That is, the same as the capacity test, charge to 4.2V with CC-CV, and then overcharge different experimental batteries with the same composition and capacity at a current of 1C until the safety device works, and record the voltage change and the temperature change of the outer surface of the battery; Discharge to 0V; conduct an external short-circuit test with a resistance wire of 5 milliohms. The results of the safety experiments carried out by the above methods are summarized in Table 1. Among them, the safety performance of overcharging is measured by 5V and 2 hours.

Example 2

Except the weight ratio of LiCoO ₂ and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ : 1, everything else is the same as in Example 1 to make battery A2 of the present invention, and its measurement results are also listed in Table 1 middle.

Example 3

Except for the weight ratio of LiCoO ₂ and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ of 1:1, everything else is the same as in Example 1 to make battery A3 of the present invention, and the measurement results are also listed in Table 1 middle.

Example 4

The weight ratio of the positive electrode active material LiCoO ₂ and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is 1:1, and the coating weight of the negative electrode is 12.6 mg/cm ² , and everything else is the same as in Example 1. Battery A4 of the present invention was obtained, and its measurement results are also listed in Table 1.

Comparative example 1

Except for using LiCoO ₂ alone as the positive electrode active material, everything else was the same as in Example 1 to produce a comparative battery B1, and its measurement results are also listed in Table 1.

Comparative example 2

Except that _LiCoO2 is used alone as the positive electrode active material, no conductive agent VGCF is added to the negative electrode, and the coating weight is 10mg/ ^cm2 , everything else is the same as in Example 1 and a comparative battery B2 is produced. The measurement results are also listed in Table 1 middle.

Table 1

Battery Capacity mAh overcharge The maximum temperature of the outer wall of the battery during overcharging Overdischarge External short circuit Example A1 725 no change 65 Safety Safety Example A2 731 no change 62 Safety Safety Example A3 735 no change 60 Safety Safety Example A4 715 no change 67 Safety Safety Comparative Example B1 720 thermal runaway 85 (safety valve operating due to thermal runaway) Safety Safety Comparative Example B2 722 catch fire >120 Safety Safety

From the results of Table 1, it can be seen that: when adding LiNi _1/3 Co _1/3 Mn _1/3 O in the positive electrode When the _amount is not less than 20wt%, the overcharge of the battery A1-A4 when the positive and negative electrode weight ratio is suitable is the highest The temperature of the outer wall does not exceed 70°C, and the safety performance is guaranteed. However, when the battery of the comparative example is overcharged, thermal runaway phenomenon (B1) or even fire (B2) occurs, and the overcharge resistance performance fails to meet the requirements.

Claims (7)

1. safety lithium ion cell, comprise positive pole, negative pole, barrier film and nonaqueous electrolytic solution, anodal and negative pole constitutes by metal forming collector and the active material coating that contains that is coated in its surface, and it is characterized in that: anodal coating comprises the nickel cobaltous manganese lithium oxide active material of layer structure; The negative pole coating comprises one or both active materials of carbon fiber and spherical graphite, flaky graphite, and wherein the weight content of carbon fiber is 1-5%.

2. safety lithium ion cell according to claim 1 is characterized in that: anodal coating comprises the cobalt-lithium oxide of layer structure and the nickel cobaltous manganese lithium oxide active material of layer structure.

3. safety lithium ion cell according to claim 1 is characterized in that: the weight content of active material cobalt nickel oxide manganses lithium is not less than 20% in the anodal coating.

4. safety lithium ion cell according to claim 1 is characterized in that: positive electrode active materials weight is 1.5-2.2 times of negative active core-shell material coating weight.

5. safety lithium ion cell according to claim 4 is characterized in that: positive electrode active materials weight is 1.75-2 times of negative active core-shell material coating weight.

6. safety lithium ion cell according to claim 1 is characterized in that: the negative active core-shell material carbon fiber is a carbon nano-fiber.

7. a kind of safety lithium ion cell according to claim 1 is characterized in that: being shaped as of battery is cylindrical, Long Circle, square or button shaped.

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