CN110364681A - A triple-protected high-safety lithium-ion battery cathode - Google Patents

Abstract

A lithium ion battery positive plate with triple protection and high safety belongs to the technical field of lithium batteries. The positive plate consists of a current collector, a high-viscosity material layer, a PTC material layer and an active material layer; the two sides of the current collector are sequentially provided with a high-viscosity material layer, a PTC material layer and an active material layer from inside to outside; the high-viscosity material layer consists of an active material, at least one binder and at least one conductive agent; the PTC material layer is composed of at least one polymer material and at least one conductive agent; the active material layer is a conventional positive active material of a lithium ion battery. The positive plate can give consideration to high energy density and stable high safety, and provides triple protection for the battery; the active material capable of providing energy is combined with the positive temperature coefficient material, the high-viscosity material layer is added, the short circuit failure of the aluminum foil and the negative electrode diaphragm is avoided, the temperature rise of the battery after short circuit is controlled by utilizing the characteristics of the PTC material layer, and meanwhile, the loss of energy density is reduced as much as possible.

Description

A triple-protected high-safety lithium-ion battery cathode

technical field

The invention belongs to the technical field of lithium batteries, and in particular relates to a triple-protected high-safety lithium-ion battery positive plate.

Background technique

Lithium-ion batteries have been commercialized for 25 years. Lithium-ion batteries have gradually replaced other types of batteries with advantages such as high energy density, long cycle life, and high energy conversion efficiency, and have steadily occupied a dominant position in mobile device power supplies. Our daily life has been closely linked with lithium-ion batteries. Therefore, the safety of corresponding lithium-ion batteries has attracted more and more attention, especially the continuous fermentation of some mobile phone explosions. At present, there are still many deficiencies in the safety improvement of lithium-ion batteries. The methods to improve the safety of lithium-ion batteries are all at the cost of sacrificing the energy density of lithium-ion batteries, which greatly restricts the development of batteries. In order to improve safety performance, some methods are to apply a layer of PTC (Positive Temperature Coefficient Material) layer on the current collector to use the PTC characteristics of organic matter to improve safety performance or to apply a layer of high-viscosity active material layer to improve the adhesion of the active material layer. Improve safety; both need a certain thickness to produce effective effects, and only provide a layer of protection for battery safety; batteries that take into account safety performance and electrical performance are the foundation for the foothold and development of the lithium battery industry. It can be said that the development of higher safety batteries on the basis of maintaining electrical performance is an inevitable trend in the development of the industry.

Contents of the invention

The purpose of the present invention is to solve the problem that the existing batteries cannot take into account the safety performance and the electrical performance, and provide a lithium-ion battery positive electrode sheet with triple protection and high safety.

In order to achieve the above object, the technical scheme that the present invention takes is as follows:

A lithium-ion battery positive electrode sheet with triple protection and high safety. The positive electrode sheet is composed of a current collector, a high-viscosity material layer, a PTC material layer, and an active material layer; both sides of the current collector are sequentially arranged from the inside to the outside There are a high viscosity material layer, a PTC material layer, and an active material layer; the current collector is an aluminum foil; the high viscosity material layer is composed of an active material material, at least one binder and at least one conductive agent; the PTC material The layer is composed of at least one polymer material and at least one conductive agent; the active material layer is a conventional positive electrode active material for lithium ion batteries.

Compared with the prior art, the beneficial effects of the present invention are as follows: the positive electrode sheet of the present invention can take into account high energy density and stable high safety, and provide triple protection for the battery; the active material material that can provide energy is combined with the positive temperature coefficient material, Add a high-viscosity material layer to avoid short-circuit failure between the aluminum foil and the negative electrode diaphragm, and use the characteristics of the PTC material layer to control the temperature rise of the battery after a short circuit, while minimizing the loss of energy density.

Description of drawings

Figure 1 is a cross-sectional view of the coating effect of the positive electrode sheet, in which ①-active material layer, ②-PTC material layer, ③-high viscosity material layer, ④-current collector.

Detailed ways

The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments, but it is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit of the technical solution of the present invention should be included in the scope of the present invention. Within the protection scope of the present invention.

The present invention is mainly aimed at improving the safety of the lithium-ion battery and avoiding a large loss of energy density. The factors affecting the safety of the battery mainly come from two aspects. On the one hand, the battery is short-circuited when the external circuit is abused (such as overcharging). On the other hand, when the battery is tested by acupuncture, extrusion, etc., a short circuit occurs in the battery. Among them, 99.9% of the explosion and fire of the battery is caused by the internal short circuit. The internal short circuit of the normal battery is mainly the internal short circuit of the electrons, which leads to heat generation at the short circuit point. When the temperature of the short circuit point exceeds the temperature that triggers the reaction between the negative electrode and the electrolyte, the reduction occurs instantaneously. The reaction will lead to two results: one is the rupture of the battery case, at this time, a large amount of oxygen from the outside pours in, and the battery catches fire and explodes; The reaction also causes a lot of heat generation. Once the heat is transferred to the positive electrode, the temperature of the entire positive electrode will rise. At this time, if the positive electrode active material contains LFO/LNO, when it reaches a certain temperature, it will react with the electrolyte to generate O ₂ , and then cause the battery to catch fire and explode; so the present invention improves safety from the following points: ① avoid the internal short circuit from the direct contact between the negative electrode and the aluminum foil; When the temperature rises, the reduction reaction between the negative electrode and the electrolyte does not occur; ③ When the reduction reaction between the negative electrode and the electrolyte occurs, the temperature of the positive electrode is controlled so that the positive electrode does not participate in the reaction, so as to provide triple protection for the battery and improve battery safety.

Specific Embodiment 1: This embodiment describes a triple-protected high-safety lithium-ion battery positive electrode sheet, which is composed of a current collector, a high-viscosity material layer, a PTC material layer, and an active material layer; Both sides of the current collector are sequentially provided with a high-viscosity material layer, a PTC material layer, and an active material layer from the inside to the outside, as shown in Figure 1; the current collector is aluminum foil; the high-viscosity material layer is made of active material, at least A binder and at least one conductive agent; the PTC material layer is composed of at least one polymer material and at least one conductive agent; the active material layer is a conventional positive electrode active material for lithium ion batteries. The conventional positive electrode active material is lithium cobaltate, lithium manganate, lithium nickelate, lithium nickel cobalt manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, lithium-rich manganese-based materials, nickel One or a combination of at least two materials among lithium cobalt aluminum oxide and lithium titanate.

The preparation method of the positive electrode sheet: select the materials required for the high-viscosity material layer, mix them in a certain proportion to obtain a high-viscosity material slurry, and use a coating machine to coat it on the aluminum foil to obtain a high-viscosity material layer. Current collector; then mix the selected PTC material with a conductive agent to prepare a PTC slurry, and coat it on the high-viscosity material layer to obtain a positive electrode collector coated with a PTC material layer and a high-viscosity material layer, and then press the conventional Methods Coating conventional positive electrode active materials on it, drying at 80-110°C for 2-5 minutes to obtain positive electrode sheets, and rolling and cutting into positive electrode sheets with length×width=1000mm×65mm.

Specific embodiment two: a kind of lithium-ion battery cathode sheet with triple protection and high safety described in specific embodiment one, the coating thickness on one side of the high-viscosity material layer is 5-20 μm, and the one side of the PTC material layer is The thickness of the coating is 1.5-3 μm, the coating thickness of one side of the active material layer is 50-110 μm, and the thickness is designed according to the battery capacity.

Specific embodiment three: a kind of lithium-ion battery positive plate with triple protection and high safety described in specific embodiment one, the active material material is lithium cobaltate, lithium manganate, lithium nickelate, lithium nickel cobalt manganate , lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, lithium-rich manganese-based materials, lithium nickel cobalt aluminate and lithium titanate or a combination of at least two materials.

Embodiment 4: A lithium-ion battery cathode sheet with triple protection and high safety described in Embodiment 1, the binder is polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride Amide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene and butyl One or a combination of at least two materials in styrene rubber.

Specific embodiment five: a kind of lithium-ion battery anode sheet of the high security of triple protection described in specific embodiment one, described conductive agent is carbon black, carbon fiber, carbon nanotube, graphite, graphene, metal powder, Composite conductive material, conductive ceramic powder or a combination of at least two materials.

Embodiment 6: A lithium-ion battery cathode sheet with triple protection and high safety described in Embodiment 1, the mass ratio of the active material, binder, and conductive agent is 80% to 94%: 4 %~16%; 1.2%~4%.

Embodiment 7: A lithium-ion battery cathode sheet with triple protection and high safety described in Embodiment 1, the mass ratio of the polymer material to the conductive agent is 85% to 95%: 5% to 15% .

Embodiment 8: A lithium-ion battery cathode sheet with triple protection and high safety described in Embodiment 1, the polymer material is carboxymethyl cellulose, polyvinylidene fluoride, styrene-butadiene rubber, polytetrafluoroethylene One of vinyl fluoride and polyamide or a combination of at least two materials.

Example 1:

Mix NCM523, polyvinylidene fluoride, and carbon black according to the mass ratio of 88.5:10:1.5, dissolve in NMP, use a ball mill to stir at a high speed, and use a coating machine to coat it on a 10μm thick aluminum foil. Dry at 110°C for 2 to 5 minutes to remove NMP, and obtain pole piece 1 of high-viscosity material layer ③+aluminum foil ④+high-viscosity material layer ③ in Figure 1, wherein the thickness of one side of the high-viscosity material layer is 13 μm; then polyvinylidene fluoride and Mix carbon black according to the mass ratio of 93:7, dissolve it in NMP, use a ball mill to stir it evenly at high speed, use a coating machine to coat it on the surface of the pole piece 1 made above, and dry it at 80-110°C for 2-5 minutes Remove the NMP to obtain the pole piece 2 of the PTC material layer ②+high viscosity material layer ③+aluminum foil ④+high viscosity material layer ③+PTC material layer ② in Figure 1, wherein the thickness of one side of the PTC material layer is 2 μm, and the pole piece 2 Bake at 120°C for 3 hours in a vacuum state, and then coat the upper and lower sides of the lithium battery current collector with the PTC material layer ② and the high-viscosity material layer ③ in a conventional way with a conventional positive electrode active material, as shown in Figure 1 The active material layer ① is dried at 80-110°C for 2-5 minutes to obtain a positive electrode sheet, which is cut into positive electrode sheets with length × width = 1000 mm × 65 mm by roll pressing, and then the prepared positive electrode sheet is combined with a conventional negative electrode Sheets, diaphragms and electrolytes are made into square soft-pack batteries according to the conventional lithium battery manufacturing process, and the battery capacity is about 4100mAh.

Example 2:

The difference between this embodiment and Embodiment 1 is that the thicknesses of the PTC material layer ② and the high-viscosity material layer ③ are 2 μm and 10 μm, respectively.

Example 3:

The difference between this embodiment and Embodiment 1 is that the thicknesses of the PTC material layer ② and the high-viscosity material layer ③ are 2 μm and 7 μm, respectively.

Example 4:

The difference between this example and Example 1 is that in the high viscosity material layer, the mass ratio of NCM523, polyvinylidene fluoride, and carbon black is 88:10:2.

Example 5:

The difference between this embodiment and embodiment 4 is that the thicknesses of the PTC material layer ② and the high-viscosity material layer ③ are 2 μm and 7 μm respectively.

Embodiment 6:

The difference between this embodiment and embodiment 4 is that the thicknesses of the PTC material layer ② and the high-viscosity material layer ③ are 2 μm and 10 μm respectively.

Embodiment 7:

The difference between this embodiment and embodiment 1 is that in the high viscosity material layer, the mass ratio of NCM523, polyvinylidene fluoride, and carbon black is 87.5:10:2.5.

Embodiment 8:

The difference between this embodiment and Embodiment 1 is that the thicknesses of the PTC material layer ② and the high-viscosity material layer ③ are 1.3 μm and 12 μm respectively.

Embodiment 9:

The difference between this example and Example 1 is that the mass ratio of polyvinylidene fluoride: carbon black is 92:8.

Example 10:

The difference between this example and Example 1 is that the mass ratio of polyvinylidene fluoride: carbon black is 94:6.

Comparative example:

The difference between this comparative example and Example 1 is that the current collector of the lithium battery is an aluminum foil with a thickness of 10 μm, and there is no PTC material layer ② and high-viscosity material layer ③ on the surface.

Performance test: conduct 4.2V acupuncture and energy density test on the manufactured lithium-ion battery;

The test method is as follows:

1. Nail penetration test method:

Place the lithium-ion battery in a normal temperature environment, charge the lithium-ion battery at a constant current of 0.5C to a voltage of 4.2V, and then charge it at a constant voltage to a current of 0.025C. Transfer the lithium-ion battery to the nail penetration test equipment, keep the test environment temperature at 25°C, and use a steel nail with a diameter of 4mm to pass through the lithium-ion battery at a constant speed of 30mm/s. Keep it for 300s, and the lithium-ion battery will not catch fire or explode, and it will be recorded as a pass. Five lithium-ion batteries were tested in each case, and the passing rate of the nail penetration test was used as an index to evaluate the safety of lithium-ion batteries.

2. Volume energy density test method:

Place the lithium-ion battery at a room temperature of 25°C, charge it at a constant current of 0.5C to a voltage of 4.4V, then charge it at a constant voltage of 4.4V to a current of 0.05C, discharge at 0.5C to a voltage of 3.0V, and record the discharge energy.

Volume energy density=discharge energy×platform voltage/(length of lithium-ion battery×width×thickness); wherein, length, width and thickness all refer to the length, width and thickness of the lithium-ion battery after packaging. Acupuncture pass rate = number of cells passed by acupuncture/total number of cells subjected to acupuncture; ED loss rate/% = (Example ED-Comparative Example ED)/Comparative Example ED.

The measurement results of various embodiments and comparative examples are shown in the table below:

From Table 1, the following conclusions can be drawn by comparison: according to Comparative Examples and Examples 1, 2, 3 and Examples 4, 5, when the thickness of the high-viscosity material layer increases, the safety is better, and the loss of energy density is also small. Changes are very big; According to comparative examples and Examples 1 and 4, it can be known that the high-viscosity material layer conductive agent content is too much and will affect the safety of the battery; According to Comparative examples and Examples 1 and 8, it can be known that the thicker the thickness of the PTC material layer, the greater the safety. The better; according to the comparative examples and Examples 1, 9, and 10, it can be seen that the PTC material content of the PTC material layer is the best in safety within a certain range.

Claims (8)

1. a kind of based lithium-ion battery positive plate of the high security of triple protection, it is characterised in that: the positive plate by collector, Heavy viscous material layer, ptc layer, active material layer composition；The collector two sides are disposed with high viscous from the inside to the outside Spend material layer, ptc layer, active material layer；The collector is aluminium foil；The heavy viscous material layer is by active matter material Material, at least one binder and at least one conductive agent composition；The ptc layer is by least one polymer material and at least A kind of conductive agent composition；The active material layer is lithium ion battery conventional cathode active material.

2. a kind of based lithium-ion battery positive plate of the high security of triple protection according to claim 1, it is characterised in that: The heavy viscous material layer one-sided coatings are with a thickness of 5~20 μm, and the ptc layer one-sided coatings are with a thickness of 1.5~3 μm, institute Active material layer one-sided coatings are stated with a thickness of 50~110 μm.

3. a kind of based lithium-ion battery positive plate of the high security of triple protection according to claim 1, it is characterised in that: The active material is cobalt acid lithium, LiMn2O4, lithium nickelate, nickle cobalt lithium manganate, LiFePO4, iron manganese phosphate for lithium, vanadium phosphate The combination of one of lithium, vanadium phosphate oxygen lithium, lithium-rich manganese base material, nickel cobalt lithium aluminate and lithium titanate or at least two materials.

4. a kind of based lithium-ion battery positive plate of the high security of triple protection according to claim 1, it is characterised in that: The binder be Kynoar, the copolymer of biasfluoroethylene-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, Polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinylpyrrolidone, polyvinylether, polymethyl methacrylate, The combination of one of polytetrafluoroethylene (PTFE), polyhexafluoropropylene and butadiene-styrene rubber or at least two materials.

5. a kind of based lithium-ion battery positive plate of the high security of triple protection according to claim 1, it is characterised in that: The conductive agent is carbon black, carbon fiber, carbon nanotube, graphite, graphene, metal powder, composite conducting material, conductivity ceramics The combination of one of powder or at least two materials.

6. a kind of based lithium-ion battery positive plate of the high security of triple protection according to claim 1, it is characterised in that: The mass ratio of the active material, binder and conductive agent is 80%~94%:4%~16%；1.2%~4%.

7. a kind of based lithium-ion battery positive plate of the high security of triple protection according to claim 1, it is characterised in that: The mass ratio of the polymer material and conductive agent is 85%~95%:5%~15%.

8. a kind of based lithium-ion battery positive plate of the high security of triple protection according to claim 1, it is characterised in that: The polymer material be one of carboxymethyl cellulose, Kynoar, butadiene-styrene rubber, polytetrafluoroethylene (PTFE), polyamide or The combination of at least two materials.