CN102332603A - Lithium ion battery - Google Patents

Abstract

The invention discloses a lithium ion battery with good low-temperature electrochemical performance. The positive pole piece contains a lithium ion conductor additive, the lithium ion conductor additive is a perovskite type oxide, and the molecular formula of the additive is as follows: a. the_xB_yTiO₃Wherein x is more than 0.25 and less than 0.45, y is more than 0.4 and less than 0.7, x + y is more than 0.65 and less than 1, A is at least one of Li and Na elements, and B is at least one of La, Ce and Pr elements. The lithium ion battery provided by the invention still keeps higher discharge capacity under the low-temperature condition, has good low-temperature electrochemical performance, and can expand the working temperature range of a power battery when being used for a power battery system.

Description

A lithium ion battery

technical field

The invention relates to a lithium ion battery, more specifically, to a lithium ion battery with good low-temperature electrochemical performance. the

Background technique

In 1991, Japan's Sony (Sony) took the lead in commercializing lithium-ion batteries. Due to its advantages of high energy density, high voltage, low self-discharge rate and light weight, it has been widely used in various fields. Among them, high-tech fields such as aerospace, military, and power vehicles have increasingly demanding performance requirements for lithium-ion batteries, especially for low-temperature electrochemical performance. the

The low-temperature electrochemical performance of commercial lithium-ion batteries is one of the limiting conditions for their wide application. For the electrochemical reaction of lithium-ion batteries, that is, the delithiation-lithium intercalation process, it mainly involves positive electrode active materials, negative electrode active materials, electrolytes, etc. When the temperature decreases, the corresponding electrochemical reactions will become slow, thereby reducing its comprehensive electrochemical performance. In order to improve the low temperature, people have made a lot of research on low temperature electrolyte and made great progress. For example, M.C.Smart et al. (Journal of Power Sources, Volumes 119-121, 1 June 2003, Pages 349-358) reported a quaternary electrolyte system composed of EC, DEC, DMC, and EMC. Performance has improved significantly. the

However, the poor low-temperature electrochemical performance of lithium-ion batteries is not entirely caused by the deterioration of the electrolyte at low temperatures. For a lithium ion deintercalation reaction to occur, the following two basic conditions must be met, one is to reach the deintercalation potential of the reaction, and the other is to have both lithium ions and electrons on the reaction interface. As the temperature decreases, the polarization intensifies, and the migration of lithium ions and electrons in the electrode material is severely hindered, which has a relatively large negative impact on the deintercalation reaction of lithium ions, and the final result is a decrease in the low-temperature electrochemical performance. The current method for improving electron migration usually uses adding a conductive agent (conductive carbon powder, carbon nanotube, carbon nanowire, etc.) to the electrode active material. However, only from the aspect of improving electron migration, it is found that its low-temperature electrochemical performance still cannot meet the requirements. the

In view of this, it is indeed necessary to provide a lithium-ion battery with good low-temperature electrochemical performance that can improve lithium-ion migration. the

Contents of the invention

In order to overcome the above-mentioned problems in the prior art, adding a specific lithium ion conductor to the electrode sheet can significantly improve the low-temperature electrochemical performance of the lithium ion battery. the

Therefore, it is an object of the present invention to provide a lithium-ion battery with good low-temperature electrochemical performance. the

In order to achieve the above-mentioned purpose of the invention, the present invention provides a lithium-ion battery with good low-temperature electrochemical performance, including a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, and the positive electrode sheet contains lithium ion conductor additives. The lithium ion conductor additive is a perovskite oxide, and its molecular formula is:

A _x B _y TiO ₃

Wherein, 0.25<x<0.45, 0.4<y<0.7, 0.65<x+y<1, A is at least one of Li and Na, and B is at least one of La, Ce and Pr. the

As an improvement of the present invention, the positive electrode active material in the positive electrode sheet is Li ₄ Ti ₅ O ₁₂ or LiFePO ₄ .

As an improvement of the present invention, the ratio of the mass of the lithium ion conductor additive to the mass of the positive electrode diaphragm is 0.05% to 4%, and the mass of the positive electrode diaphragm is the substance attached to the positive electrode current collector in the positive electrode sheet the quality of. the

As an improvement of the present invention, the electrolyte contains at least one of cyclic carbonates and chain carbonates. the

As an improvement of the present invention, the cyclic carbonate is at least one of propylene carbonate (PC) and ethylene carbonate (EC). the

As an improvement of the present invention, the chain carbonate is one or more of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dimethyl carbonate (DMC). the

As an improvement of the present invention, the electrolyte contains a lithium salt, and the lithium salt is at least one of LiPF ₆ , LiBF ₄ , LiBOB, and LiBC ₂ O ₄ F ₂ .

As an improvement of the present invention, the concentration of the lithium salt is 0.6M-2M. The beneficial effects of the invention are: the lithium ion battery provided by the invention has good low-temperature electrochemical performance. This is because the lithium ion conductor additive in the positive electrode sheet can significantly improve the lithium ion transport capacity between the positive electrode active material particles, and increase the lithium ion transport rate under low temperature conditions. The lithium-ion battery provided by the invention still maintains a high discharge capacity under low temperature conditions, has good low-temperature electrochemical performance, and can expand the working temperature range of the power battery when used in a power battery system. the

Detailed ways

The lithium ion battery provided by the present invention will be described in detail below in combination with specific embodiments, which does not constitute any limitation to the present invention. the

Example 1

Preparation of positive electrode sheet: LiFePO ₄ (the content of Coating carbon is about 2.5%), lithium ion conductor additive Li _0.35 La _0.55 TiO ₃ , and polyvinylidene fluoride (PVDF) are mixed uniformly in a weight ratio of 93:0.05:6.95, and added NMP was mixed and stirred evenly to obtain a positive electrode slurry with a certain fluidity; then, the positive electrode slurry was coated on a 20um thick aluminum foil with a coating weight of 0.012g/cm ² and dried to form a positive electrode sheet with a certain degree of flexibility; Finally, the positive electrode sheet is punched into a circular diaphragm with a diameter of 14mm after cold pressing.

Preparation of the negative electrode sheet: the negative electrode is a circular metal lithium sheet with a diameter of 20 mm. the

Electrolyte: the electrolyte contains cyclic carbonate and chain carbonate, the cyclic carbonate is propylene carbonate (PC) and ethylene carbonate (EC), and the chain carbonate is methyl ethyl carbonate ester (EMC), diethyl carbonate (DEC) and dimethyl carbonate (DMC), the electrolyte in the electrolyte is lithium salt, and the lithium salt is LiPF ₆ with a concentration of 0.6M.

Preparation of lithium-ion battery: Assemble a button-type lithium-ion battery (model: CR2430). The positive electrode sheet, negative electrode sheet and separator (Tonen's F20BMU, thickness 20um) prepared by the above method are stacked together, and an appropriate amount of electrolyte is added, then sealed, and the lithium ion battery is obtained after standing. the

Example 2

Preparation of positive electrode sheet: LiFePO ₄ (the content of Coating carbon is about 2.5%), lithium ion conductor additive Li _0.25 La _0.69 TiO ₃ , and polyvinylidene fluoride (PVDF) are mixed uniformly in a weight ratio of 93:2:5, and other Parts are completely the same as the preparation of the positive electrode sheet in Example 1, and will not be described in detail.

Preparation of the negative electrode sheet: exactly the same as the preparation of the negative electrode sheet in the examples. the

Electrolyte: same as embodiment 1. the

Preparation of the lithium ion battery: exactly the same as the preparation of the lithium ion battery in the examples. the

Example 3

Preparation of positive electrode sheet: LiFePO ₄ (the content of Coating carbon is about 2.5%), lithium ion conductor additive Li _0.45 La _0.40 TiO ₃ , polyvinylidene fluoride (PVDF) are mixed uniformly in a weight ratio of 93:4:3, and other Parts are completely the same as the preparation of the positive electrode sheet in Example 1, and will not be described in detail.

Preparation of the negative electrode sheet: exactly the same as the preparation of the negative electrode sheet in the examples. the

Electrolyte: same as embodiment 1. the

Preparation of the lithium ion battery: exactly the same as the preparation of the lithium ion battery in the examples. the

Comparative example 1

Preparation of the positive pole piece: The difference from the preparation of the positive pole piece in the examples is: LiFePO ₄ (the content of Coating carbon is about 2.5%) and polyvinylidene fluoride (PVDF) are mixed uniformly in a weight ratio of 93:7 , No lithium ion conductor additives. The other parts are completely the same as the preparation of the positive electrode sheet in the embodiment, and will not be described in detail.

Preparation of the negative electrode sheet: the same as the preparation of the negative electrode sheet in Example 1. the

Electrolyte: same as embodiment 1. the

Preparation of the lithium ion battery: exactly the same as the preparation of the lithium ion battery in Example 1. the

In a specific embodiment of the present invention, the lithium-ion batteries prepared in Examples 1-3 and Comparative Example 1 are respectively subjected to discharge tests at different temperatures, and the specific test operations are as follows:

The lithium-ion batteries prepared in Examples 1-3 and the comparative example were respectively charged to the full charge state of 3.75V at room temperature with a charging current of 0.1C, and then the lithium-ion batteries were placed at room temperature, 0°C, Stand still at -20°C for 30 minutes, and then discharge the lithium-ion battery to a cut-off voltage of 2.0V with a discharge current of 0.1C. the

Table 1

Table 1 shows the data obtained from the discharge tests of the lithium-ion batteries prepared in Examples 1-3 and Comparative Example 1 at different temperatures. It can be seen from the table that when the lithium-ion battery pole piece contains the lithium-ion conductor additive Li _x La _y TiO ₃ , its low-temperature electrochemical performance is greatly improved, especially at -20 ° C, the discharge

The specific capacity is increased by 11.2%, the discharge specific energy is increased by 13.4%, and the low-temperature discharge performance of the battery is obviously improved. the

Example 4

Preparation of positive electrode sheet: Li ₄ Ti ₅ O ₁₂ , lithium ion conductor additive Li _0.35 Ce _0.55 TiO ₃ , conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed uniformly in a weight ratio of 91:0.05:2.5:6.45, and added NMP was mixed and stirred evenly to obtain a positive electrode slurry with a certain fluidity; then, the positive electrode slurry was coated on a 20um thick aluminum foil with a coating weight of 0.012g/cm ² and dried to form a positive electrode sheet with a certain degree of flexibility; Finally, the positive electrode sheet is punched into a circular diaphragm with a diameter of 14mm after cold pressing.

Preparation of the negative electrode sheet: the negative electrode is a circular metal lithium sheet with a diameter of 20 mm. the

Electrolyte: the electrolyte contains cyclic carbonate and chain carbonate, the cyclic carbonate is propylene carbonate (PC), and the chain carbonate is ethyl methyl carbonate (EMC), dicarbonate ethyl ester (DEC) and dimethyl carbonate (DMC), the electrolyte in the electrolytic solution is a lithium salt, and the lithium salt is LiBC ₂ O ₄ F ₂ at a concentration of 1M.

Preparation of lithium-ion battery: Assemble a button-type lithium-ion battery (model: CR2430). The positive electrode sheet, negative electrode sheet and separator (Tonen's F20BMU, thickness 20um) prepared by the above method are stacked together, and an appropriate amount of electrolyte is added, sealed, and the lithium ion battery is obtained after standing. the

Example 5

Preparation of positive electrode sheet: Li ₄ Ti ₅ O ₁₂ , lithium ion conductor additive Na _0.35 La _0.65 TiO ₃ , conductive carbon black, polyvinylidene fluoride (PVDF) were mixed uniformly in a weight ratio of 91:1.5:2.5:5, and other Parts are completely the same as the preparation of the positive electrode sheet in Example 4, and will not be described in detail.

Preparation of the negative electrode sheet: the same as the preparation of the negative electrode sheet in Example 4. the

Electrolyte: the electrolyte contains cyclic carbonate and chain carbonate, the cyclic carbonate is propylene carbonate (PC), and the chain carbonate is ethyl methyl carbonate (EMC), dicarbonate ethyl ester (DEC) and dimethyl carbonate (DMC), the electrolyte in the electrolytic solution is a lithium salt, and the lithium salt is LiBOB with a concentration of 1.8M. the

Preparation of the lithium-ion battery: exactly the same as the preparation of the lithium-ion battery in Example 4. the

Example 6

Preparation of positive electrode sheet: Li ₄ Ti ₅ O ₁₂ , lithium ion conductor additive Li _0.35 La _0.25 Ce _0.35 TiO ₃ , conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed uniformly in a weight ratio of 91:2.5:2.5:4 , and other parts are completely the same as the preparation of the positive electrode sheet in Example 4, and will not be described in detail.

Preparation of the negative electrode sheet: the same as the preparation of the negative electrode sheet in Example 4. the

Preparation of the lithium-ion battery: exactly the same as the preparation of the lithium-ion battery in Example 4. the

Example 7

Preparation of positive electrode sheet: Li ₄ Ti ₅ O ₁₂ , lithium ion conductor additive Li _0.35 Pr _0.50 TiO ₃ , conductive carbon black, polyvinylidene fluoride (PVDF) were mixed uniformly in a weight ratio of 91:4:2.5:2.5, and other Parts are completely the same as the preparation of the positive electrode sheet in Example 4, and will not be described in detail.

Preparation of the negative electrode sheet: the same as the preparation of the negative electrode sheet in Example 4. the

Electrolyte: the electrolyte contains cyclic carbonate and chain carbonate, the cyclic carbonate is propylene carbonate (PC), and the chain carbonate is ethyl methyl carbonate (EMC), dicarbonate Ethyl ester (DEC) and dimethyl carbonate (DMC), the electrolyte in the electrolyte is lithium salt, and the lithium salt is LiBF ₄ with a concentration of 1.8M.

Preparation of the lithium-ion battery: exactly the same as the preparation of the lithium-ion battery in Example 4. Comparative example 2

Preparation of the positive pole piece: the difference from the preparation of the positive pole piece in Example 4 is: mix Li ₄ Ti ₅ O ₁₂ , conductive carbon black, and polyvinylidene fluoride (PVDF) in a weight ratio of 91:2.5:6.5 Uniform, free of Li-ion conductor additives. The other parts are completely the same as the preparation of the positive electrode sheet in Example 4, and will not be described in detail.

Preparation of the negative electrode sheet: the same as the preparation of the negative electrode sheet in Example 4. the

Electrolyte is identical with embodiment 4. the

Preparation of the lithium-ion battery: exactly the same as the preparation of the lithium-ion battery in Example 4. the

In a specific embodiment of the present invention, the lithium-ion batteries prepared in Examples 4-7 and Comparative Example 2 are respectively subjected to discharge tests at different temperatures, and the specific test operations are as follows:

The lithium-ion batteries prepared in Examples 4-7 and Comparative Example 2 were respectively charged to the full charge state of 2.5V with a charging current of 0.1C at room temperature, and then the lithium-ion batteries were respectively placed at 0°C, - Stand at 20°C for 30 minutes, and then discharge the lithium-ion battery to a cut-off voltage of 1.0V with a discharge current of 0.1C. the

Table 2

Table 2 shows the discharge test results of the lithium-ion batteries prepared in Examples 4-7 and Comparative Example 2 at different temperatures. The results show that the battery performance, especially the low-temperature electrochemical performance, is greatly improved after adding lithium-ion conductors. Compared with Comparative Example 2, at -20°C, the discharge specific capacity of Examples 4-7 is greatly improved, and the discharge specific capacity of Example 6 is increased by 13.2%. It can thus be explained that the lithium ion battery provided by the present invention has good low-temperature electrochemical performance. the

In addition, adding Li _0.24 La _0.75 TiO ₃ and Li _0.7 La _0.29 TiO ₃ as additives to the above battery system can also significantly improve the low temperature effect. It can be understood that although the description only takes the lithium ion conductor additive Li _x La _y TiO ₃ as an example to describe the lithium ion battery with good low-temperature electrochemical performance of the present invention. According to other embodiments of the present invention, the lithium ion conductor in the positive pole piece is a type of perovskite oxide, and the structural formula of the lithium ion conductor additive is:

A _x B _y TiO ₃

Wherein, 0.25<x<0.45, 0.4<y<0.7, 0.65<x+y<1, A is at least one of Li and Na, and B is at least one of La, Ce and Pr. the

It should be noted that, according to the disclosure and elaboration of the above specification, those skilled in the art to which the present invention pertains can also make changes and modifications to the above implementation manners. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some equivalent modifications and changes to the present invention should also be within the protection scope of the claims of the present invention. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the present invention. the

Claims (8)

1. A lithium ion battery, comprising a positive pole piece, a negative pole piece, a separator and an electrolyte, characterized in that: the positive pole piece contains a lithium ion conductor additive, and the lithium ion conductor additive is a perovskite type Oxide, whose molecular formula is: A _x B _y TiO ₃ Wherein, 0.25<x<0.45, 0.4<y<0.7, 0.65<x+y<1, A is at least one of Li and Na, and B is at least one of La, Ce and Pr. 2 . The lithium ion battery according to claim 1 , wherein the positive electrode active material in the positive electrode sheet is Li ₄ Ti ₅ O ₁₂ or LiFePO ₄ . 3. The lithium ion battery according to claim 1, characterized in that: the ratio of the quality of the lithium ion conductor additive to the mass of the positive electrode diaphragm is 0.05% to 4%, and the mass of the positive electrode diaphragm is The mass of the material attached to the positive current collector in the sheet. 4. The lithium ion battery according to claim 1, characterized in that: said electrolyte contains at least one of cyclic carbonate and chain carbonate. 5. The lithium-ion battery according to claim 4, wherein the cyclic carbonate is at least one of propylene carbonate (PC) and ethylene carbonate (EC). 6. The lithium-ion battery according to claim 4, characterized in that: the chain carbonate is one of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dimethyl carbonate (DMC). species or several. 7. The lithium-ion battery according to claim 1, characterized in that: the electrolyte contains a lithium salt, and the lithium salt is at least one of LiPF ₆ , LiBF ₄ , LiBOB, and LiBC ₂ O ₄ F ₂ . 8 . The lithium ion battery according to claim 7 , wherein the concentration of the lithium salt is 0.6M˜2M.