CN101295802A - Safety lithium ion battery - Google Patents

Abstract

The present invention relates to a safe lithium-ion battery with anode membrane having a large resistance. The lithium-ion battery comprises an electrode group, wherein the electrode group is provided with an anode sheet and a cathode sheet, wherein the anode sheet comprises a current collector and a membrane sheet having an active material attached to the surface of the current collector, wherein the active material of the anode membrane is a graphite material, and the resistance in the membrane of the anode sheet is between 0.5Ω/ ^cm2 and 10Ω/ ^cm2 . Since the resistance of the anode sheet is relatively high, the contact resistance is relatively small when short-circuited, and the short-circuit current density is also relatively small, so that the temperature of the lithium-ion battery will not rise suddenly when short-circuited, thereby preventing the lithium-ion battery from catching fire, thereby improving the safety of the lithium-ion battery.

Description

Safe Lithium-Ion Batteries

technical field

The invention relates to the technical field of lithium-ion batteries, in particular to a safe lithium-ion battery with an anode diaphragm having relatively high resistance.

Background technique

Lithium-ion battery is a battery with high energy density and good environmental performance, which is widely used in various portable electronic devices. Lithium-ion batteries generally include mutually wound cathode sheets, separators and anode sheets, wherein the cathode sheet includes a cathode current collector and a diaphragm with a cathode active material attached thereto; the anode sheet includes an anode current collector and an anode sheet attached to it A diaphragm with an anode active material on it. The cathode current collector is generally made of aluminum foil, the anode current collector is generally made of copper foil, and the isolation diaphragm is generally made of polypropylene and polyethylene composite film. During production, the cathode sheet, separator and anode sheet are stacked and then wound to form a battery core, and the battery core is put into a battery packaging case, and then electrolyte is injected into the packaging case, and the battery is made after sealing.

However, due to the flammability of the organic electrolyte used in the existing lithium-ion batteries, and the graphite material is generally used for the anode film, the resistance is relatively small and it is easy to burn. When a short circuit occurs inside the battery, it is easy to cause the battery to burn. Combustion poses a safety hazard.

Table 1 shows the safety test results of a group of existing lithium-ion batteries. The test method is: directly contact the cathode current collector and the cathode diaphragm with the anode current collector and the anode diaphragm in the anode sheet respectively, and then record the test results respectively. .

Table I

According to the above test results, when there is a short circuit between the cathode current collector (aluminum foil) and the anode membrane in the cathode sheet, the temperature of the battery will rise rapidly, smoke will start to be emitted, and an open flame will be generated. The reason for this phenomenon is that the resistance of the anode diaphragm in ordinary lithium-ion batteries is generally between 0.1 and 0.2 Ω/cm ² , while the resistance of the cathode diaphragm is about 1.6 Ω/cm ² , and the anode material itself is also It is easy to burn. In this way, when the cathode current collector is in direct contact with the anode diaphragm, due to the small resistance, its current density is relatively large, resulting in a large amount of heat generation. At this time, a large amount of heat generated by the current is concentrated in the short circuit, plus The anode material itself is also easy to burn, so it is very easy to cause combustion, causing the battery to fail the above short-circuit test and causing hidden dangers to the safe use of the battery.

Invention content:

The object of the present invention is to provide a safe lithium-ion battery, especially a safe lithium-ion battery with an anode membrane with relatively high resistance to overcome the above-mentioned problems.

In order to achieve the purpose of the above invention, the present invention provides a safe lithium-ion battery. The anode sheet of the lithium-ion battery has a relatively high resistance, and its resistance is generally 0.5Ω/cm ² -8Ω/cm ² . In this way, if there is an unexpected situation, such as when the cathode current collector-aluminum foil contacts the anode membrane and causes an internal short circuit due to the metal particles in the battery piercing the separator, the contact resistance is relatively high during the short circuit due to the high resistance of the anode sheet. Smaller, the short-circuit current density is also relatively small, so that the temperature of the lithium-ion battery will not rise suddenly and cause fire, thereby improving the safety of the lithium-ion battery.

In order to solve the problems of the technologies described above, the present invention adopts the following specific schemes:

1. Mix one or more insulating materials in the anode sheet of the battery, such as titanium oxide (TiO ₂ ), silicon oxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ) or zinc oxide (ZnO ₂ ) and other insulating materials Material.

2. Do not add conductive carbon powder to the anode film, and increase the amount of binder at the same time.

3. Use graphite material with low conductivity, and use metal oxides such as aluminum oxide (Al2O3) or magnesium oxide (MgO2) to surface treat the graphite material to reduce its conductivity.

The above-mentioned measures can be used alone or in combination with several schemes. After the above scheme is adopted, the anode sheet of the lithium-ion battery has a relatively high resistance, and its resistance is generally 0.5Ω/cm ² to 8Ω/cm ² , preferably 1.4Ω/cm ² , so as to ensure that the battery does not catch fire when it is short-circuited. , and can basically not affect the capacity and cycle performance of the battery.

Description of drawings:

Below in conjunction with accompanying drawing, the present invention will be further described:

Fig. 1 is a schematic structural view of the lithium ion battery anode sheet in the present invention.

Detailed ways:

Implementation mode one:

Safe lithium-ion battery of the present invention, its structure and manufacturing process are basically the same as the technology that current common lithium-ion battery is made, and difference is to adopt following method when making anode sheet: see Fig. 1, anode sheet 1 in this experiment It includes an anode current collector 11 and a membrane 12 attached thereon with an anode active material. The anode current collector 11 is generally made of copper foil. Firstly, graphite powder as negative active material, AL ₂ O ₃ is mixed with hydroxy-methyl-cellulose sodium (CMC) and styrene-butadiene rubber (SBR), among which hydroxy-methyl-cellulose sodium and styrene-butadiene rubber as a binder. This mixture was dispersed in water as a solvent to obtain an anode mixed slurry. Then, the above slurry was evenly coated on the negative electrode current collector made of copper foil to prepare the anode sheet 1, and then cold pressed. Next, the anode sheet 1 is dried, and the solvent is volatilized, so that a layer of film 12 is formed on the surface of the anode sheet, and the drying temperature can be selected as required. In addition, in addition to coating, the slurry can be attached to the surface of the current collector 11 by dipping, and then cold-pressed to form a layer of membrane 12 on the surface of the current collector 11 after drying.

In order to improve the reliability of the experiment, a total of three sets of experiments are done in this embodiment.

experiment one

In this experiment, the mass percentage of the active material, binder and insulating material in the diaphragm 12 is: 94.5:4:1.5, wherein the active material is: graphite, the insulating material is AL ₂ O ₃ , the binder is: CMC and For the mixture of SBR, the mass percentages of the two in the diaphragm are respectively: 1.5% and 2.5%.

Experiment 2

The manufacturing method of Experiment 2 is the same as that of Experiment 1, except that the mass percentages of active material, binder and AL ₂ O ₃ are different. The mass percentage of the three in this experiment is: 91.5:4:4.5. Wherein, the mass percentages of CMC and SBR in the diaphragm are still 1.5% and 2.5%, respectively.

Experiment three

Active material, binder and AL ₂ O ₃ mass percentages in this experiment. The mass percentage of the three in this experiment is: 86.5:4:9.5. Wherein, the mass percentages of CMC and SBR in the diaphragm are still divided into: 1.5% and 2.5%.

comparative example

The comparison column also adopts the experimental manufacturing method, the difference is that the diaphragm does not contain AL ₂ O ₃ , and the mass percentage of the active material and the binder is: 96:4. Wherein, the mass percentages of CMC and SBR in the diaphragm are still 1.5% and 2.5%, respectively.

Table 2 shows the data of the above three groups of experiments and the experimental results of the resistance.

Table II

It can be seen from the data in the table that, compared with the current lithium ion battery, the resistance layer of the surface membrane of the anode sheet of the present invention is obviously improved. After formation, the nail penetration test can be successfully passed in the fully charged state, especially after the battery is disassembled, no smoke or fire occurs when the anode sheet is directly in contact with the cathode current collector. And there is no significant difference in other electrochemical performances, such as capacity and cycle performance, of the three groups of lithium-ion batteries after adding AL ₂ O ₃ , that is, mixing AL ₂ O ₃ in the diaphragm 12 will not affect the performance of the lithium-ion batteries.

Implementation mode two:

Embodiment 2 also made three sets of experiments and a comparative example. The experimental conditions of the three sets of experiments are basically the same as those of Embodiment 1, except that Al ₂ O ₃ is replaced by TiO ₂ , and the comparative example remains unchanged. The experimental data and experimental results are shown in Table 3.

Table three

As can be seen from the data in Table 3, the three groups of lithium-ion batteries in this embodiment can also greatly increase the anode sheet resistance after adding TiO ₂ , thereby improving the safety performance of lithium-ion batteries, and other electrochemical properties, such as capacity and cycle performance No significant difference.

Implementation Mode Three

In this embodiment, no insulating substance is added to the anode membrane, and graphite with low electrical conductivity is used as the anode material, and the content of the binder is appropriately increased. The percentage of graphite and binder is between 90-92.5:10-7.5, and at the same time ensure that the resistance of the anode film using the above-mentioned materials is between 0.5Ω/cm ² -8Ω/cm ² . After testing, the battery made of the anode membrane of the above material will not smoke or catch fire during the short-circuit test, which meets the safety requirements of the battery.

It should be pointed out that: the inventive concept of the present invention is to achieve the purpose of improving battery safety by increasing the anode body phase resistance, so it should be considered that: through various methods, especially the several methods disclosed in the present invention, whether used alone Or combined use to improve the implementation of the anode film resistance should fall within the protection scope of the present invention.

Claims (6)

1, a kind of safety lithium ion cell, this lithium ion battery comprises an electrode group, the electrode group is provided with anode strip and cathode sheets, wherein anode strip comprises collector and is attached to the diaphragm that collection liquid surface has active material, the active material of anode diaphragm adopts graphite material, and it is characterized in that: resistance is at 0.5 Ω/cm in the diaphragm of this anode strip ²～10 Ω/cm ²Between.

2, safety lithium ion cell according to claim 1, it is characterized in that: the diaphragm on this anode strip surface comprises: active material, binding agent and as the aluminium oxide of megohmite insulant, its three's mass percent is: 86.5～94.5: 4: 9.5～1.5.

3, safety lithium ion cell according to claim 1, it is characterized in that: the diaphragm on this anode strip surface comprises: active material, binding agent and as the titanium oxide or the silica of megohmite insulant, its three's mass percent exists: 86.5～94.5: between 4: 9.5～1.5.

4, safety lithium ion cell according to claim 1 is characterized in that: the graphite material surface as anode diaphragm active material is coated with one deck aluminium oxide or magnesium oxide.

5, safety lithium ion cell according to claim 4 is characterized in that: exist through coating graphite material and the two mass percent of binding agent of handling: 93～94.5: between 7～5.5.

6, safety lithium ion cell according to claim 4 is characterized in that: it is characterized in that: described binding agent is: the mixture of sodium cellulose glycolate and butadiene-styrene rubber.