CN101295780B - Anode active material composition of lithium ion secondary battery and battery - Google Patents

Abstract

The invention relates to a lithium ion secondary battery cathode active material composition and a lithium ion secondary battery containing the composition. The composition mainly consists of LiFe _0.5 Co _0.5 PO ₄ and LiNi _0.75 Co _0.1 Al _0.1 Mn _0.05 O ₂ . Mixing LiFe _0.5 Co _0.5 PO ₄ and LiNi _0.75 Co _0.1 Al _0.1 Mn _0.05 O ₂ as the positive electrode active material of the lithium-ion secondary battery makes the lithium-ion secondary battery of the present invention have outstanding high-temperature stability, excellent high-current cycle Capacity retention performance and excellent safety performance solve various defects caused by using LiFe _0.5 Co _0.5 PO ₄ and LiNi _0.75 Co _0.1 Al0.1Mn _0.05 O ₂ alone as positive electrode active materials to prepare lithium ion secondary batteries. The invention can be widely used in the field of preparation of lithium ion secondary batteries, especially power batteries.

Description

Lithium-ion secondary battery cathode active material composition and battery

【Technical field】

The invention relates to a positive electrode active material for a lithium ion secondary battery, in particular to a positive electrode active material composition for a lithium ion secondary battery and a battery using the positive electrode active material composition.

【Background technique】

Lithium-ion batteries are a new generation of green batteries, and are considered to be high-tech products that are of great significance to the national economy and people's lives in the 21st century. Lithium-ion batteries have many advantages such as high voltage, high energy density, good cycle performance, small self-discharge, no memory effect, and wide operating temperature range. As a high-energy chemical power source, it has been widely used in mobile phones, notebook computers, UPS, Camcorders, various portable electric tools, electronic instruments, weapons and equipment, etc. are also the preferred supporting power sources for electric vehicles and space power sources that are vigorously researched by various countries. Advanced battery materials, especially cathode materials, constitute the core technology for the current replacement of lithium-ion batteries, and are one of the key technologies for lithium-ion batteries.

The positive electrode materials used in lithium-ion secondary batteries are mainly embedded compounds. Usually, the available materials mainly include ternary positive electrode materials, layered lithium cobalt oxide, and spinel lithium manganese oxide. The cathode material that has been widely used at present is layered lithium cobalt oxide material. Although layered lithium cobaltate, ternary positive electrode materials and their various derivatives (through doping of anions and cations or coating of other substances) have high discharge specific capacity, they are thermally stable in the charged state. Poor reliability, and cobalt and nickel as raw materials are expensive, and there is a problem of resource shortage.

CN200610072027.7 Mixing the ternary positive electrode material with spinel lithium manganese oxide hopes to obtain a positive electrode material with excellent comprehensive performance and low cost. But various performances of this positive electrode material such as discharge specific capacity, 100 cycle capacity retention rate, 100 high temperature cycle capacity retention rate, thermal stability are all lower than each performance of ternary positive electrode material (see the table in CN200610072027.7 specification sheet 1), and the specific capacity of the battery containing lithium manganese oxide is low, the cycle performance is poor, especially the high temperature cycle performance, the crystal lattice is unstable during charging and discharging, and it will explode under strong collision, which poses a threat to the life safety of consumers. Threats are not conducive to the preparation of high-capacity power batteries.

Lithium iron phosphate (LiFePO ₄ ) cathode material with olivine structure has gradually become a new research hotspot at home and abroad. Preliminary research shows that this new type of cathode material combines the advantages of LiCoO ₂ , LiNiO ₂ , LiMnO ₂ and other materials: it does not contain precious elements, the raw materials are cheap, and the resources are extremely rich; the working voltage is moderate (3.40V); the platform characteristics are good, the voltage Extremely stable, comparable to a stabilized power supply: large theoretical capacity (170mAh/g); stable structure, excellent safety performance (oxygen atoms and phosphorus atoms are firmly combined with strong covalent bonds, making it difficult for materials to decompose by oxygen evolution); high temperature Good performance and cycle performance; the volume shrinks during charging, and the volume effect is good when it is combined with carbon negative electrode materials; it has good compatibility with most electrolyte systems and good storage performance; it is non-toxic and is a real green material. However, lithium iron phosphate has two obvious disadvantages. One is low conductivity, resulting in poor high-rate charge and discharge performance and low actual specific capacity; the other is low bulk density, resulting in low volume specific capacity. These two disadvantages hinder the large-scale application of this material.

【Content of invention】

The purpose of the present invention is to overcome the limitations of the ternary positive electrode material and olivine-type lithium iron phosphate as the positive electrode material of the lithium ion secondary battery respectively, and provide a kind with excellent comprehensive performance, low cost, high capacity, and good high-rate charge and discharge performance. 1. A cathode active material composition for a lithium ion secondary battery with good safety performance and a battery using the composition as an anode material.

In order to achieve the above technical purpose, the present invention adopts the following technical solutions:

A lithium-ion secondary battery cathode active material composition mainly consists of LiNi _0.75 Co _0.1 Al _0.1 Mn _0.05 O ₂ and LiFe _0.5 Co _0.5 PO ₄ .

In the anode active material composition for lithium ion secondary batteries, the weight ratio of LiFe _0.5 Co _0.5 PO ₄ to LiNi _0.75 Co _0.1 Al _0.1 Mn _0.05 O ₂ is 1-9:9-1.

In the above lithium ion secondary battery positive electrode active material composition, the weight ratio of LiNi _0.75 Co _0.1 Al _0.1 Mn _0.05 O ₂ to LiNi _0.75 Co _0.1 Al _0.1 Mn _0.05 O ₂ is preferably 4-6:6-4.

A lithium ion secondary battery, comprising a positive electrode, a negative electrode, an electrolyte and a separator, characterized in that the positive electrode active material is mainly composed of LiNi _0.75 Co _0.1 Al _0.1 Mn _0.05 O ₂ and LiFe _0.5 Co _0.5 PO ₄ .

In the above lithium ion secondary battery, the weight ratio of LiFe _0.5 Co _0.5 PO ₄ to LiNi _0.75 Co _0.1 Al _0.1 Mn _0.05 O ₂ in the positive electrode material is 1-9:9-1.

In the above lithium ion secondary battery, the weight ratio of LiFe _0.5 Co _0.5 PO ₄ to LiNi _0.75 Co _0.1 Al _0.1 Mn _0.05 O ₂ in the positive electrode material is preferably 4-6:6-4.

Adopting said technical scheme, compared with the prior art, the beneficial technical effect produced is: it overcomes the limitation when ternary positive electrode material and olivine type lithium iron phosphate are respectively used as lithium ion secondary battery positive electrode material. Ternary cathode materials have poor thermal stability and poor high-current discharge performance, while olivine-type lithium iron phosphate has the function of deintercalating lithium, which combines the advantages of LiCoO ₂ , LiNiO ₂ , LiMnO ₂ and other materials: moderate operating voltage, platform It has good characteristics and extremely low self-discharge rate. Its crystal structure determines that its volume will basically not change during the intercalation/deintercalation process of lithium ions. The intercalation and extraction of lithium ions have little effect on the crystal lattice. The reversibility, the voltage is very stable, comparable to the stabilized power supply; the oxygen atom and the phosphorus atom in the crystal structure are firmly combined with a strong covalent bond, which makes it difficult for the material to be decomposed by oxygen evolution, making its structure stable and excellent in safety performance; high temperature performance It has good cycle performance, which can reach 2000 times; the volume shrinks during charging, and the volume effect is good when it is combined with carbon negative electrode materials; it has good compatibility with most electrolyte systems and good storage performance. In the present invention, the ternary cathode material whose volume becomes larger during charging and shrinks during discharge, and LiNi _0.75 Co _0.1 Al _0.1 Mn _0.05 O ₂ obtained by doping with anions and cations or coating with other substances are added to the volume during charging. In LiFe _0.5 Co _0.5 PO ₄ that shrinks and becomes larger during discharge, on the one hand, the volume of the composition can be complemented during charge and discharge, so that the total volume remains basically unchanged; on the other hand, it is equivalent to the lithium iron phosphate coated conductive material, Electrode modification by doping increases the electronic ion conductivity of lithium iron phosphate, which overcomes the defect that it is not suitable for high current charging and discharging. The experimental results prove that the mixed use of LiFe _0.5 Co _0.5 PO ₄ and LiNi _0.75 Co _0.1 Al _0.1 Mn _0.05 O ₂ can effectively overcome their respective shortcomings, and at the same time inherit the advantages of high capacity of the two, and significantly improve the thermal stability of the material , high temperature resistance and specific capacity, prolong its cycle life and increase the retention rate of high-current cycle discharge capacity. In addition, the price of LiFe _0.5 Co _0.5 PO ₄ is relatively cheap, so it can effectively reduce the cost.

【Detailed ways】

The invention discloses a positive electrode active material composition for a lithium ion secondary battery, which is mainly composed of a ternary positive electrode material and an olivine-type lithium iron phosphate, and aims to overcome the use of the ternary positive electrode material and the olivine-type lithium iron phosphate as positive electrode materials At the same time, it inherits the respective advantages of the two, so that the battery made of the combined material has excellent comprehensive performance, low cost, high capacity, and good high-rate charge and discharge performance.

In the above lithium ion secondary battery cathode active material composition, the general chemical formula of the ternary cathode material is Li _a (Ni _b Co _c ) M _1-bc O ₂ , wherein 0.97≤a≤1.07, 0<b< 1, 0<c<1, 0.5≤b+c<1, M is aluminum (Al), manganese (Mn), iron (Fe), titanium (Ti), zinc (Zn), calcium (Ca), chromium ( at least one of Cr) and copper (Cu).

In the above-mentioned lithium ion secondary battery, the general chemical formula of the olivine-type lithium iron phosphate in the positive electrode material is LiFe _x M' _1-x PO4 (0<x≤1) wherein M' can be cobalt, manganese, magnesium or titanium.

In the above-mentioned cathode active material composition for lithium ion secondary batteries, the weight ratio of the olivine-type lithium iron phosphate to the ternary cathode material is 1-9:9-1, preferably 4-6:6-4.

The invention also discloses a lithium-ion secondary battery, which includes a positive electrode, a negative electrode, an electrolyte and a diaphragm, and is characterized in that the positive active material is basically composed of a ternary positive electrode material and olivine-type lithium iron phosphate.

In the above lithium ion secondary battery, the general chemical formula of the ternary positive electrode material in the positive electrode material is Li _a (Ni _b Co _c )M _1-bc O ₂ , where 0.97≤a≤1.07, 0<b< 1, 0<c<1, 0.5≤b+c<1, M is aluminum (Al), manganese (Mn), iron (Fe), titanium (Ti), zinc (Zn), calcium (Ca), chromium ( at least one of Cr) and copper (Cu).

In the above-mentioned lithium ion secondary battery, the general chemical formula of the olivine-type lithium iron phosphate in the positive electrode material is LiFe _x M' _1-x PO4 (0<x≤1) wherein M' can be cobalt, manganese, magnesium or titanium.

In the above lithium ion secondary battery, the weight ratio of the olivine-type lithium iron phosphate to the ternary positive electrode material in the positive electrode material is 1-9:9-1.

In the above lithium ion secondary battery, the weight ratio of the olivine-type lithium iron phosphate to the ternary positive electrode material in the positive electrode material is preferably 4-6:6-4.

By using the ternary cathode material and the olivine-type lithium iron phosphate material in combination, the respective limitations of the ternary cathode material and the olivine-type lithium iron phosphate material as the cathode material are overcome. Due to the poor thermal stability of the ternary positive electrode material, the high-current discharge performance is also poor, while the high-temperature performance of the olivine-type lithium iron phosphate is good, and the high-current discharge is stable. The mixed use of the two can effectively overcome their respective shortcomings and inherit both. The advantage of high capacity. In addition, the price of olivine-type lithium iron phosphate is relatively cheap, which can effectively reduce the cost.

According to the following examples, the technical conception and advantages of the present invention can be better understood.

Example 1

First, the ternary cathode material with the chemical formula LiNi _1/3 Mn _1/3 Co _1/3 O ₂ and the olivine-type lithium iron phosphate with the chemical formula LiFePO ₄ are taken, and the mass ratio of the two is 9:1, and the two are mixed as Positive active material. With PVDF as the binder, its mass is 4% of the mass of the positive active material, with acetylene black as the conductive agent, its mass is 2% of the mass of the positive active material, with NMP as the solvent, its mass is 50% of the mass of the positive active material %. The positive electrode active material, binder, acetylene black and NMP were mixed and stirred at a speed of 6000 rpm for 5 hours to make them uniformly dispersed. After coating, drying, tableting and other processes, the positive electrode sheet material is obtained. Among them, the three processes of mixing, coating and drying need to be carried out in a vacuum environment, and the positive electrode sheet material obtained after tableting is cut according to the specified size to obtain the positive electrode sheet.

The negative electrode is prepared by the prior art. Use carbon powder and acetylene black as the conductive agent, CMC as the binder, water as the solvent, add an appropriate amount of SBR, stir and mix evenly, coat, dry, press, and cut into a specified size to make the negative electrode sheet .

The positive electrode sheet and the negative electrode sheet prepared by the above method use LiPF6 as the electrolyte, and a mixture of ethylene carbonate, ethylene carbonate and diethyl carbonate as the solvent, and its concentration is 1.2 mol/liter, and it is composited with polyethylene and polypropylene. Separator paper, the lithium ion secondary battery of the present invention is made by conventional technology.

The lithium-ion secondary battery assembled from the above-mentioned positive electrode sheet, negative electrode sheet, electrolyte and separator has the advantages of low cost, high capacity, and good high-rate charge and discharge performance.

Example 2

In this example, a mixture of a ternary cathode material with a chemical formula of LiNi _0.1 Mn _0.1 Co _0.8 O ₂ and an olivine-type LiFe _0.2 Mn _0.8 PO ₄ was used as the positive electrode active material, and the mass ratio of the two was 1:9. The proportioning of auxiliary materials and the preparation process of positive electrode sheet, negative electrode sheet and lithium ion battery are the same as in Example 1.

Example 3

In this example, a mixture of a ternary positive electrode material with a chemical formula of LiNi _0.4 Mn _0.2 Co _0.4 O ₂ and an olivine-type LiFe _0.8 Mg _0.2 PO ₄ was used as the positive electrode active material, and the mass ratio of the two was 4:6. The proportioning of auxiliary materials and the preparation process of positive electrode sheet, negative electrode sheet and lithium ion battery are the same as in Example 1.

Example 4

In this example, a mixture of a ternary positive electrode material with a chemical formula of LiNi _0.75 Co _0.1 Al _0.1 Mn _0.05 O ₂ and LiFe _0.5 Co _0.5 PO ₄ with a crystal structure of olivine type is used as the positive electrode active material, and the mass ratio of the two is 6:4 , other auxiliary materials proportioning and the preparation process of positive electrode sheet, negative electrode sheet and lithium-ion battery are the same as in Example 1.

Example 5

In this example, a mixture of a ternary positive electrode material with a chemical formula of LiNi _0.4 Co _0.1 Mn _0.4 Al _0.05 Fe _0.05 O ₂ and LiFe _0.2 Mn _0.8 PO ₄ with a crystal structure of olivine type is used as the positive electrode active material, and the mass ratio of the two is 2 : 8, the preparation process of other auxiliary material proportioning and positive electrode sheet, negative electrode sheet and lithium-ion battery is the same as embodiment 1.

Example 6

In this example, a mixture of a ternary positive electrode material with a chemical formula of LiNi _0.7 Co _0.15 Mn _0.1 Ti _0.03 Cu _0.02 O ₂ and LiFe _0.8 Mg _0.2 PO ₄ with a crystal structure of olivine type is used as the positive electrode active material, and the mass ratio of the two is 7 : 3, the preparation process of other auxiliary material proportioning and positive electrode sheet, negative electrode sheet and lithium-ion battery is the same as embodiment 1.

Example 7

In this embodiment, a mixture of a ternary positive electrode material with a chemical formula of LiNi _0.8 Co _0.1 Mn _0.05 Al _0.02 Cr _0.02 Ti _0.01 O ₂ and an olivine-type LiFe _0.2 Mn _0.8 PO ₄ as a positive electrode active material is used. The mass ratio of the two is The ratio of other auxiliary materials and the preparation of positive electrode sheet, negative electrode sheet and lithium-ion battery are the same as in Example 1.

Example 8

In this embodiment, a ternary positive electrode material with a chemical formula of Li(Ni _1/3 Co _1/3 Mn _1/3 ) _0.95 Zn _0.02 Ca _0.01 Ti _0.02 O ₂ and a crystal structure of LiFe _0.5 Co _0.5 PO ₄ of olivine type are used. The mixture is used as the positive electrode active material, and the mass ratio of the two is 5:5. The ratio of other auxiliary materials and the preparation of the positive electrode sheet, the negative electrode sheet and the lithium ion battery are the same as in Example 1.

Example 9

In this example, a mixture of a ternary positive electrode material with a chemical formula of Li _0.97 Ni _0.51 Mn _0.25 Co _0.24 O ₂ and LiFePO ₄ with an olivine crystal structure is used as the positive electrode active material. The mass ratio of the two is 8:2, and other auxiliary materials are formulated Ratio and the preparation process of positive electrode sheet, negative electrode sheet and lithium ion battery are the same as embodiment 1.

Example 10

In this example, a mixture of a ternary positive electrode material with a chemical formula of Li _1.07 Ni _0.25 Mn _0.27 Co _0.48 O ₂ and LiFe _0.2 Mn _0.8 PO ₄ with a crystal structure of olivine type is used as the positive electrode active material, and the mass ratio of the two is 4:6 , other auxiliary materials proportioning and the preparation process of positive electrode sheet, negative electrode sheet and lithium-ion battery are the same as in Example 1.

Example 11

In this embodiment, a mixture of a ternary positive electrode material with a chemical formula of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ and an olivine-type LiFe _0.1 Ti _0.9 PO ₄ with a crystal structure as the positive electrode active material is used. The mass ratio of the two is The ratio of other auxiliary materials and the preparation process of positive electrode sheet, negative electrode sheet and lithium ion battery are the same as in Example 1.

Comparative example 1

In this comparative example, the positive electrode active material is selected as the ternary positive electrode material whose chemical formula is LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , and the preparation process of other auxiliary material proportions and positive electrode sheet, negative electrode sheet and lithium-ion battery is the same as in the embodiment 1

Comparative example 2

In this comparative example, the positive electrode active material is olivine-type lithium iron phosphate with the chemical formula LiFePO ₄ , and the ratio of other auxiliary materials and the preparation process of the positive electrode sheet, the negative electrode sheet and the lithium-ion battery are the same as in Example 1.

Comparative example 3

In this comparative example, the positive electrode active material is a ternary positive electrode material with the chemical formula LiNi _0.1 Mn _0.1 Co _0.8 O ₂ , and the ratio of other auxiliary materials and the preparation process of the positive electrode sheet, negative electrode sheet and lithium ion battery are the same as in Example 2.

Comparative example 4

In this comparative example, the positive electrode active material is a ternary positive electrode material with the chemical formula LiFe _0.2 Mn _0.8 PO ₄ , and the ratio of other auxiliary materials and the preparation process of the positive electrode sheet, the negative electrode sheet and the lithium ion battery are the same as in Example 2.

Comparative example 5

In this comparative example, the positive electrode active material is a ternary positive electrode material with the chemical formula LiNi _0.4 Mn _0.2 Co _0.4 O ₂ , and the ratio of other auxiliary materials and the preparation process of the positive electrode sheet, the negative electrode sheet and the lithium ion battery are the same as in Example 3.

Comparative example 6

In this comparative example, the positive electrode active material is a ternary positive electrode material with the chemical formula LiFe _0.8 Mg _0.2 PO ₄ , and the ratio of other auxiliary materials and the preparation process of the positive electrode sheet, negative electrode sheet and lithium ion battery are the same as in Example 3.

Comparative example 7

In this comparative example, the positive electrode active material is a ternary positive electrode material with the chemical formula LiNi _0.75 Co _0.1 Al _0.1 Mn _0.05 O ₂ , and the ratio of other auxiliary materials and the preparation process of the positive electrode sheet, negative electrode sheet and lithium ion battery are the same as in Example 4.

Comparative example 8

In this comparative example, the positive electrode active material is a ternary positive electrode material with the chemical formula LiFe _0.5 Co _0.5 PO ₄ , and the ratio of other auxiliary materials and the preparation process of the positive electrode sheet, negative electrode sheet and lithium ion battery are the same as in Example 4.

Lithium-ion secondary battery performance test

Performance tests were performed on the lithium-ion secondary batteries prepared in Examples and Comparative Examples, and the test results are shown in Table 1.

Table 1 Performance of lithium-ion secondary batteries using different cathode active materials

As can be seen from Table 1, compared with the lithium ion secondary battery prepared by using the ternary positive electrode material as the positive electrode active material, the lithium ion secondary battery prepared by each embodiment of the present invention was tested for 300 cycles of 1C high current and 5C high current After 300 cycles, the discharge capacity retention rate is relatively large, and its high temperature stability is strong. By adjusting the type and proportion of the ternary positive electrode material and olivine-type lithium iron phosphate, the discharge capacity retention rate of the lithium-ion secondary battery 5C of the present invention after 300 cycles of high current can be higher than that of the olivine-type iron phosphate The retention rate of the discharge capacity of the lithium-ion secondary battery with lithium as the positive electrode active material after 300 cycles at 5C high current. It shows that using the mixture of olivine-type lithium iron phosphate and ternary cathode material as the cathode active material of lithium-ion secondary battery can overcome the poor thermal stability of ternary cathode material in the charged state and the high-rate charge-discharge performance of olivine-type lithium iron phosphate Poor defects, realize the complementary performance of ternary cathode material and olivine-type lithium iron phosphate, so that the performance of the battery is greatly improved.

Claims (6)

1. an anode active material composition of lithium ion secondary battery is characterized in that, by LiNi _0.75Co _0.1Al _0.1Mn _0.05O ₂And LiFe _0.5Co _0.5PO ₄Form.

2. according to each described anode active material composition of lithium ion secondary battery of claim 1, it is characterized in that: described LiFe _0.5Co _0.5PO ₄With LiNi _0.75Co _0.1Al _0.1Mn _0.05O ₂Weight ratio be 1～9: 9～1.

3. anode active material composition of lithium ion secondary battery according to claim 2 is characterized in that: described LiNi _0.75Co _0.1Al _0.1Mn _0.05O ₂With LiNi _0.75Co _0.1Al _0.1Mn _0.05O ₂Weight ratio be 4～6: 6～4.

4. a lithium rechargeable battery comprises positive pole, negative pole, electrolyte and barrier film, it is characterized in that: described positive electrode active materials is by LiNi _0.75Co _0.1Al _0.1Mn _0.05O ₂And LiFe _0.5Co _0.5PO ₄Form.

5. lithium rechargeable battery according to claim 4 is characterized in that: LiFe in the described positive electrode _0.5Co _0.5PO ₄With LiNi _0.75Co _0.1Al _0.1Mn _0.05O ₂Weight ratio be 1～9: 9～1.

6. lithium rechargeable battery according to claim 5 is characterized in that: LiFe in the described positive electrode _0.5Co _0.5PO ₄With LiNi _0.75Co _0.1Al _0.1Mn _0.05O ₂Weight ratio be 4～6: 6～4.