CN114628774A - Lithium ion battery - Google Patents

Abstract

In order to overcome the existing lithium ion battery's problems that high-compression LiFePO ₄ is prone to breakage, gas generation and Fe ²⁺ dissolution under high-temperature cycle conditions, resulting in insufficient high-temperature cycle performance and high-temperature storage performance, the present invention provides a The lithium ion battery includes a positive electrode, a negative electrode and a non-aqueous electrolyte, the positive electrode includes a positive electrode material layer, the compaction density of the positive electrode material layer is 2.35-3.0 g/cc, and the positive electrode material layer includes a positive electrode active material, so The positive active material is LiFePO ₄ , and the non-aqueous electrolyte includes a solvent, an electrolyte salt, vinylene carbonate and a compound shown in structural formula 1;

Wherein, n is selected from 0 to 3, and R is selected from halogen or alkyl or haloalkyl of 1 to 3 carbon atoms. The lithium ion battery provided by the invention can effectively solve the problems existing in high compaction LiFePO ₄ and has excellent high temperature storage performance and high temperature cycle performance.

Description

A lithium-ion battery

technical field

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

Background technique

In recent years, the popularity of new energy vehicles and 3C consumer goods on a larger scale has led to higher and higher requirements for lithium-ion batteries in terms of high energy density, high rate charge and discharge, long life, and high safety. Compared with ternary battery system, lithium iron phosphate battery has obvious advantages in safety, manufacturing cost, cycle life and so on. Due to the specific capacity of the lithium iron phosphate cathode material, the current main method is to improve the compaction density of the cathode to achieve high energy density of the battery. The increase in the compaction density of the positive electrode sheet will lead to a decrease in the porosity of the electrode sheet and a slow infiltration rate of the electrolyte, which will affect the uniformity of the distribution of the electrolyte in the cell, and may even lead to lithium metal precipitation and power loss due to poor electrolyte infiltration. At the same time, by-products will be produced on the surface of the negative electrode, which will affect the cycle life and safety of the battery. At the same time, the volume change of the electrode increases during the process of lithium ion intercalation and extraction of the positive electrode material with high compaction density. Due to the low porosity of the electrode itself, it is easy to cause particle cracking of the positive electrode active material during long-term cycling. , the dissolution of Fe ²⁺ , resulting in the shedding of the positive electrode active material, the reduction of battery capacity and Coulomb efficiency, and the increase of internal resistance, which affect the cycle performance of the battery.

There are two main directions of the currently developed electrolyte suitable for high-pressure solid-state plates. One is to add a low-viscosity solvent to promote the infiltration of the electrolyte and improve the performance of the battery's cycle and rate; the other is to add a low-viscosity solvent. Impedance, cycling-promoting additives increase battery life. However, these two methods may lead to poor high-temperature performance of the electrolyte and serious gas swelling. Therefore, under the condition of ensuring the high energy density of the battery, it can not precipitate lithium and improve the high-temperature cycle and high-temperature storage performance of the battery, which is a difficult problem faced by the high-pressure lithium iron phosphate battery electrolyte.

Usually, the improvement of cell energy density and the improvement of cell safety are a pair of contradictions in the performance of battery products. How to balance the relationship between the dynamic performance, energy density, cycle life and safety of the battery is a problem that needs to be solved.

SUMMARY OF THE INVENTION

Aiming at the problems that high-compression LiFePO ₄ is prone to breakage, gas generation and Fe ²⁺ dissolution under high temperature cycle conditions in existing lithium ion batteries, resulting in insufficient high temperature cycle performance and high temperature storage performance, the present invention provides a lithium ion battery. ion battery.

The technical scheme adopted by the present invention to solve the above-mentioned technical problems is as follows:

The invention provides a lithium ion battery, comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, the positive electrode comprises a positive electrode material layer, the compaction density of the positive electrode material layer is 2.35-3.0 g/cc, and the positive electrode material layer Including a positive electrode active material, the positive electrode active material is LiFePO ₄ , and the non-aqueous electrolyte includes a solvent, an electrolyte salt, vinylene carbonate and a compound shown in structural formula 1;

Wherein, n is selected from 0 to 3, and R is selected from halogen or alkyl or haloalkyl of 1 to 3 carbon atoms.

Optionally, the compound represented by the structural formula 1 is selected from one or more of compounds 1 to 12:

Optionally, based on the total mass of the non-aqueous electrolyte solution as 100%, the addition amount of the compound represented by the structural formula 1 is 0.01-5%.

Optionally, based on the total mass of the non-aqueous electrolyte as 100%, the added amount of the vinylene carbonate is 0.1-5%.

Optionally, the lithium salt is selected from LiPF6, _LiBF4 , LiBOB, _LiDFOB , _LiDFOP , _LiPO2F2 , _LiSbF6 , LiAsF6, LiN _{( SO2CF3 )2 , LiN ( SO2C2F5} ) ₂ , one or more of LiC(SO ₂ CF ₃ ) ₃ , LiN(SO ₂ F) ₂ and LiFSI;

In the non-aqueous electrolyte, the addition amount of the lithium salt is 0.1-4 mol/L.

Optionally, the solvent is selected from ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl methyl carbonate, ethyl acetate and methyl acetate. one or more of.

Optionally, the non-aqueous electrolyte also includes an auxiliary additive selected from 1,3-propane sultone, 1,4-butane sultone, fluoroethylene carbonate, and vinyl sulfate , one of methylene methanedisulfonate, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, propylene sultone, fluorobenzene and vinyl ethylene carbonate or variety.

Optionally, based on the total mass of the non-aqueous electrolyte as 100%, the addition amount of the auxiliary additive is 0.1-3%.

Optionally, the negative electrode includes a negative electrode material layer, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes artificial graphite, natural graphite, silicon carbon, silicon oxycarbon, intermediate carbon microspheres and graphene. one or more.

According to the lithium ion battery provided by the present invention, the inventors added vinylene carbonate and the compound represented by structural formula ₁ to the electrolyte, and found that the two are effective in inhibiting the particle breakage, The gas generation and the dissolution of Fe ²⁺ have a good synergistic effect. It is speculated that the addition of the compound represented by structural formula 1 can reduce the surface tension and contact angle of the electrolyte on the surface of the LiFePO ₄ active material, thereby improving the high compaction state. _The compatibility of the LiFePO active material with the electrolyte promotes the penetration of vinylene carbonate in the electrolyte into the highly _compacted LiFePO, thereby promoting the formation of a stable SEI film _on the surface of the LiFePO active material, and at the same time, The co-addition of vinylene carbonate and the compound represented by structural formula 1 can effectively widen the electrochemical stability window of the electrolyte, make it more difficult to be oxidized during use, inhibit the side reactions on the surface of the highly compacted LiFePO ₄ , and finally make The prepared lithium-ion battery has excellent high-temperature storage performance and high-temperature cycle performance.

The inventors found through the combination screening of a large number of compounds and vinylene carbonate, in the compound shown in structural formula 1, the carbon chain length of the cycloalkyl group and the carbon chain length of the R group on the cycloalkyl group were the most important factors for the high pressure compaction of LiFePO. ₄ The performance improvement of the battery plays a decisive role. When the carbon chain length of the cycloalkyl group or the carbon chain length of the R group exceeds the scope of the present invention, the improvement effect for the high-pressure LiFePO ₄ battery is not obvious. even inhibited.

It should be noted that the electrolyte provided by the present invention has a better coordination effect with the high-compression LiFePO ₄ active material. Since the low-compression LiFePO ₄ active material itself does not have the problems of particle cracking and the electrolyte is difficult to penetrate, adding the present invention The provided electrolyte will instead lead to increased impedance, increased gas production and Fe ²⁺ dissolution problems in the battery, which is not conducive to the improvement of battery performance.

Description of drawings

1 is a scanning electron microscope image of the positive electrode active material provided in Example 1 of the present invention after being cycled at high temperature;

2 is a scanning electron microscope image of the positive electrode active material provided in Comparative Example 39 of the present invention after being cycled at high temperature.

Detailed ways

In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

An embodiment of the present invention provides a lithium ion battery, including a positive electrode, a negative electrode and a non-aqueous electrolyte, the positive electrode includes a positive electrode material layer, the compaction density of the positive electrode material layer is 2.35-3.0 g/cc, and the positive electrode material layer is 2.35-3.0 g/cc. The material layer includes a positive electrode active material, and the positive electrode active material is LiFePO ₄ , and the non-aqueous electrolyte includes a solvent, an electrolyte salt, vinylene carbonate, and a compound shown in structural formula 1;

wherein, n is selected from 0 to 6, and R is selected from H, halogen, or alkyl or haloalkyl of 1 to 10 carbon atoms.

The inventors added vinylene carbonate and the compound represented by structural formula 1 to the electrolyte, and found that both of them have the advantages of inhibiting particle breakage, gas generation and Fe ²⁺ dissolution of high-compacted LiFePO ₄ during high-temperature charge-discharge cycles. The better synergistic effect is presumed to be due to the co-addition of vinylene carbonate and the compound represented by structural formula 1, which can reduce the surface tension and contact angle of the electrolyte on the surface of the LiFePO ₄ active material, thereby improving the LiFePO ₄ under high compaction state. _The compatibility of the active material with the electrolyte promotes the penetration of vinylene carbonate in the electrolyte into the highly compacted LiFePO4, thereby promoting the formation of a stable SEI film _on the surface of the LiFePO4 active material, and at the same time, the vinylene carbonate The co-addition of the ester and the compound shown in structural formula 1 can effectively widen the electrochemical stability window of the electrolyte, make it more difficult to be oxidized during use, inhibit the side reactions on the surface of the highly compacted LiFePO ₄ , and finally make the prepared Lithium-ion batteries have excellent high-temperature storage performance and high-temperature cycling performance.

The inventors have found through the combination screening of a large number of compounds that in the compound shown in structural formula 1, the carbon chain length of the cycloalkyl group and the carbon chain length of the R group on the cycloalkyl group are important for its performance on high-pressure LiFePO ₄ batteries. It plays a decisive role. When the carbon chain length of the cycloalkyl group or the carbon chain length of the R group exceeds the scope of the present invention, the improvement effect on the high-compression LiFePO ₄ battery is not obvious, and even has an inhibitory effect. .

It should be noted that the electrolyte provided by the present invention has a better coordination effect with the high-compression LiFePO ₄ active material. Since the low-compression LiFePO ₄ active material itself does not have the problems of particle cracking and the electrolyte is difficult to penetrate, adding the present invention On the contrary, the provided electrolyte will lead to the increase of internal resistance of the battery, the increase of gas production and the dissolution of Fe ²⁺ , which is not conducive to the improvement of battery performance.

In some embodiments, the compound represented by the structural formula 1 is selected from one or more of compounds 1-12:

It should be noted that the specific substance selection of the compound represented by the above structural formula 1 is only the preferred compound of the present application, and should not be construed as a limitation of the present invention.

In some embodiments, the compound represented by the structural formula 1 is added in an amount of 0.01-5% based on 100% of the total mass of the non-aqueous electrolyte.

In a preferred embodiment, based on the total mass of the non-aqueous electrolyte solution as 100%, the addition amount of the compound represented by the structural formula 1 is 1-4%.

In the battery system and electrolyte system provided by the present invention, when the added amount of the compound represented by the structural formula 1 in the non-aqueous electrolyte is within the above range, the oxidation resistance of the non-aqueous electrolyte can be effectively improved, and the LiFePO can be significantly reduced at the same time. ₄ The internal resistance of the active material is conducive to improving the overall performance of the battery. When the amount of the compound shown in structural formula 1 is too low, it is difficult to reflect the synergistic effect with the vinylene carbonate, and the performance improvement of the battery is not obvious; when When the addition amount of the compound represented by Structural Formula 1 is too high, the side reactions inside the battery will be increased, the resistance of the battery will be increased, and the cycle performance of the battery will be degraded on the contrary.

In different embodiments, based on the total mass of the non-aqueous electrolyte as 100%, the addition amount of the compound represented by the structural formula 1 can be selected from the following values: 0.01%, 0.05%, 0.1%, 0.3% , 0.6%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2.1%, 2.5%, 2.9%, 3%, 3.4%, 3.7%, 3.9%, 4.1%, 4.4%, 4.7%, 5 %.

In some embodiments, the vinylene carbonate is added in an amount of 0.1-5% based on 100% of the total mass of the non-aqueous electrolyte.

In a preferred embodiment, based on the total mass of the non-aqueous electrolyte solution as 100%, the addition amount of the vinylene carbonate is 0.5-3%.

When the added amount of the vinylene carbonate is too low, it is difficult to manifest the synergistic effect with the compound represented by the structural formula 1, and the performance improvement of the battery is not obvious; when the added amount of the vinylene carbonate is too high, This will lead to an increase in gas production during battery cycling, and a significant capacity decay.

In different embodiments, based on the total mass of the non-aqueous electrolyte as 100%, the added amount of the vinylene carbonate can be selected from the following values: 0.5%, 0.6%, 0.8%, 1%, 1.3% %, 1.5%, 1.8%, 2.1%, 2.5%, 2.7%, 2.9%, 3%.

In some embodiments, the lithium salt is selected from LiPF6, _LiBF4 , LiBOB, _LiDFOB , _LiDFOP , _LiPO2F2 , _LiSbF6 , LiAsF6, LiN _{( SO2CF3 )2 ,} LiN _{( SO2C2} One or more of F ₅ ) ₂ , LiC(SO ₂ CF ₃ ) ₃ , LiN(SO ₂ F) ₂ and LiFSI;

In the non-aqueous electrolyte, the addition amount of the lithium salt is 0.1-4 mol/L.

In a preferred embodiment, the lithium salt is selected from one or more of LiPF ₆ , LiPO ₂ F ₂ and LiFSI;

In the non-aqueous electrolyte, the lithium salt is added in an amount of 0.1-2 mol/L.

In some embodiments, the solvent is selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl methyl carbonate, ethyl acetate, and methyl acetate one or more of the esters.

In a preferred embodiment, the solvent is selected from a mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate.

In some embodiments, the non-aqueous electrolyte further includes auxiliary additives selected from 1,3-propane sultone, 1,4-butane sultone, fluoroethylene carbonate, sulfuric acid One of vinyl ester, methylene methanedisulfonate, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, propylene sultone, fluorobenzene and vinyl ethylene carbonate one or more;

Based on the total mass of the non-aqueous electrolyte solution as 100%, the addition amount of the auxiliary additive is 0.1-3%.

In a preferred embodiment, the auxiliary additive is selected from one or more of 1,3-propane sultone, methylene methanedisulfonate, fluoroethylene carbonate and vinyl sulfate.

In some embodiments, the negative electrode includes a negative electrode material layer, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes artificial graphite, natural graphite, silicon carbon, silicon oxycarbon, intermediate carbon microspheres, and graphene one or more of.

In a preferred embodiment, the negative electrode active material is selected from one or more of artificial graphite, natural graphite and silocarb.

In some embodiments, the negative electrode material layer further includes a negative electrode conductive agent and a negative electrode binder.

In some embodiments, the negative electrode further includes a negative electrode current collector for drawing current, and the negative electrode material layer is attached to the negative electrode current collector.

The negative electrode current collector can be selected from various existing metal materials, and in a preferred embodiment, the negative electrode current collector is selected from copper foil.

In some embodiments, the positive electrode material layer further includes a positive electrode conductive agent and a positive electrode binder.

In some embodiments, the positive electrode further includes a positive electrode current collector for drawing current, and the positive electrode material layer is attached to the positive electrode current collector.

The positive electrode current collector can be selected from various existing metal materials, and in a preferred embodiment, the positive electrode current collector is selected from aluminum foil.

In some embodiments, the lithium ion battery further includes a separator, the separator is located between the positive electrode and the negative electrode, and the separator includes a polyolefin separator, a polyamide separator, a polysulfone separator, a polyphosphorus separator One or more of nitrile type diaphragm, polyethersulfone type diaphragm, polyetheretherketone type diaphragm, polyetheramide type diaphragm and polyacrylonitrile type diaphragm.

The present invention will be further illustrated by the following examples.

Example 1

This embodiment is used to illustrate the lithium ion battery disclosed in the present invention and the preparation method thereof, including the following operation steps:

1) Preparation of electrolyte: Mix ethylene carbonate (EC) and ethyl methyl carbonate (EMC) by mass ratio as EC:EMC=3:7, then add lithium hexafluorophosphate (LiPF ₆ ) to a molar concentration of 1 mol/L , and then based on the total mass of the electrolyte as 100%, the unsaturated ethylene carbonate shown in Table 1, the compound shown in structural formula 1 and other additives are added.

2) Preparation of positive electrode

The cathode active material lithium iron phosphate, conductive carbon black Super-P and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 93:4:3, and then dispersed in N-methyl-2-pyrrolidone ( NMP), the positive electrode slurry was obtained. The slurry is evenly coated on both sides of the aluminum foil, dried, calendered and vacuum-dried, and the aluminum lead wire is welded with an ultrasonic welder to obtain a positive electrode, and the thickness of the electrode plate is 120-150 μm. Table 1 shows the compaction density of the positive electrode material layer on the surface of the obtained positive electrode.

3) Preparation of negative plate

Mixed negative active material modified natural graphite, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) in a mass ratio of 94:1:2.5:2.5, and then dispersed them In deionized water, a negative electrode slurry was obtained. The slurry was coated on both sides of the copper foil, dried, rolled, and welded with a nickel lead wire with an ultrasonic welder to obtain a negative electrode.

4) Preparation of cells

A polyethylene microporous film with a thickness of 20 μm was placed between the positive plate and the negative plate as a separator, and then the sandwich structure composed of the positive plate, the negative plate and the separator was wound, and the rolled body was flattened and placed in aluminum plastic. In the film, after the lead wires of the positive and negative electrodes are drawn out respectively, the aluminum-plastic film is hot-pressed and sealed to obtain the battery core to be injected.

5) Liquid injection and formation of cells

In a glove box whose dew point is controlled below -40°C, the electrolyte prepared above is injected into the cell through the liquid injection hole, and the amount of electrolyte should ensure that the gap in the cell is filled. Then it is formed according to the following steps: 0.05C constant current charging for 180min, 0.1C constant current charging for 180min, rest for 24hrs, shape and seal, and then further charge to 3.65V with 0.2C current and constant current, after 24hrs at room temperature, charge at 0.2C Current constant current discharge to 2.0V.

Examples 2 to 26

Examples 2 to 26 are used to illustrate the non-aqueous electrolyte, lithium ion battery and preparation method thereof disclosed in the present invention, including most of the operation steps in Example 1, and the differences are:

The compaction density of the positive electrode material layer on the surface of the positive electrode is shown in Examples 2 to 26 in Table 1.

Based on the total mass of the electrolyte solution as 100%, the unsaturated ethylene carbonate shown in Examples 2 to 26 in Table 1, the compound shown in Structural Formula 1 and other additives were respectively added.

Comparative example 1～55

Comparative Examples 1 to 55 are used to illustrate the non-aqueous electrolytes, lithium ion batteries and preparation methods thereof disclosed in the present invention, including most of the operation steps in Example 1, and the differences are:

The compaction density of the positive electrode material layer on the surface of the positive electrode is shown in Comparative Examples 1 to 55 in Table 1.

Based on the total mass of the electrolyte as 100%, the unsaturated ethylene carbonate shown in Comparative Examples 1 to 55 in Table 1, the compounds shown in structural formula 1, compounds 13 to 20 and other additives were added respectively.

Performance Testing

The following performance tests were performed on the lithium ion batteries prepared in the above-mentioned Examples 1-26 and Comparative Examples 1-55:

High temperature cycle performance test

Under the condition of 45℃, charge to 3.65V with a constant current of 1C, then charge with a constant voltage until the current drops to 0.1C, and then discharge with a constant current of 1C to 2.0V, cycle for 2000 cycles, and record the discharge in the first week capacity and discharge capacity in the 2000th cycle, the capacity retention rate is calculated by the following formula:

Capacity retention rate = (discharge capacity at the 2000th cycle ÷ discharge capacity at the first cycle) × 100%

3.65V full charge 60℃ storage test:

At room temperature, charge the divided battery at 0.5C to 3.65V, and the cut-off current is 0.02C. After 5 minutes of storage, put it at 0.5C to 2.0V, record the initial capacity D1, and then charge it to 3.65V with 0.5C constant current and constant voltage. The cut-off current is 0.02C, and the thickness T1, voltage and internal resistance of the battery are tested; after the fully charged battery is stored in a 60°C incubator for 30 days, the thermal thickness of the battery is measured and recorded as T2, and the cold thickness of the battery is tested after leaving it at room temperature for 4 hours. T3, voltage and internal resistance, then press 0.5C to 2.0V to record the holding capacity D2, after 5 minutes of storage, use 0.5C constant current and constant voltage to charge to 3.65V, cut-off current 0.02C, after 5 minutes of storage, use 0.5C to put it to 2.0 V, record the recovery capacity D3.

Thermal expansion rate of battery (%)=(T2-T1)/T1*100%;

Battery capacity retention rate (%)=D2/D1*100%;

Battery capacity recovery rate (%)=D3/D1*100%

Contact angle test:

The lithium iron phosphate positive electrode sheet was used as the test substrate of the electrolyte to be tested, the prepared electrolyte was used as the electrolyte to be tested, the drop process of the electrolyte to be tested was observed and photographed by a contact angle measuring instrument, and then the half-angle method was used to measure the obtained electrolyte. The photos were analyzed to obtain the contact angles of different electrolytes on the lithium iron phosphate positive electrode sheet. The smaller the contact angle, the stronger the permeability of the electrolyte on the electrode sheet.

The obtained test results are filled in Table 1.

Table 1

From the test results of Examples 1-12 and Comparative Example 39, it can be seen that the addition of compounds 1-12 to the electrolyte containing vinylene carbonate (VC) can significantly improve the performance of high temperature cycling at 45°C and high temperature storage at 60°C and is effective. The dissolution of Fe ²⁺ is inhibited, and the improvement effect is about the same as the contact angle. That is, the addition of compounds 1-12 of the present invention can significantly improve the high-temperature cycle and storage performance of the high-density lithium iron phosphate battery.

Comparing Example 1 and Examples 13-18, it can be seen that with the increase of the content of the compound represented by Structural Formula 1 (0.1%-5%), after 2000 cycles of 1C/1C at 45°C and storage at 60°C for 30 days, the performance first improved and then changed. Difference. That is, when the compound 1 of the present invention is added in an amount of 0.5% in the electrolyte, it can effectively improve the overall performance of the battery and reduce the contact angle; when the content is greater than or less than 0.5%, the residual amount in the positive electrode sheet also increases. , excessive or too little compound represented by structural formula 1 will increase the side reaction inside the battery, increase the battery impedance, and deteriorate the performance of the battery cycle and the like.

From the test results of Examples 1-12 and Comparative Examples 37-38, it can be seen that the electrolyte does not contain vinylene carbonate (VC), and the performance deterioration of high temperature cycle at 45 ° C and high temperature storage at 60 ° C is very obvious and increases gas production and Fe ²⁺ dissolution, VC and the compound represented by structural formula 1 have a good synergistic effect, which can further reduce side reactions and improve the cycle performance and high-temperature storage performance of high-density lithium iron phosphate batteries.

From Example 1-12, Example 19-21, Comparative Example 1-36, it can be seen that adding compound 1-12 to the electrolyte containing vinylene carbonate (VC) has the effect of 2.35, 2.5, 2.8 and 3.0g/cc. The improvement effect of high temperature storage and cycle performance of lithium iron phosphate battery is obvious, while the improvement effect of high temperature storage and cycle performance of 2.2, 1.9 and 1.7g/cc low density lithium iron phosphate battery is poor. Secondly, the contact angle of the same electrolyte is the same, and the size of the compaction density is an important parameter affecting the performance of the battery. That is, the added compounds 1-12 of the present invention have a more significant effect on the high-temperature cycle and storage performance of the high-density lithium iron phosphate battery (2.35-3.0 g/cc).

It can be seen from Examples 1-12 and Comparative Examples 40-55 that the high temperature storage and cycle performance of high-pressure lithium iron phosphate batteries are improved most obviously when compound 1-12 is added to the electrolyte containing vinylene carbonate (VC). , while the addition of compounds 13-20 did not have a good improvement effect. Among them, compared with compounds 1-12, compounds 13-16 have no electron-donating groups (alkyl or halogen), which makes the surface tension and compatibility of the electrolyte with the surface of the _LiFePO active material poorer, thus showing poor electrochemical performance. performance. Compared with compounds 1-12, compounds 17-19 have larger chain lengths of electron-donating alkanes connected to the cyclic structure, which increases the viscosity of the electrolyte and increases the internal resistance of the battery, thereby deteriorating the high-temperature cycling and storage performance of the battery. . Compared with compounds 1-12, compound 20 has more carbon chains in its cyclic structure, resulting in poor synergy with VC and more side reactions in the battery, thereby deteriorating the high-temperature performance of the battery. The addition of compounds 1-12 to high-density lithium iron phosphate batteries can better improve battery performance.

Electron microscope observation

After the lithium-ion batteries obtained in the above Example 1 and Comparative Example 39 were cycled at 45°C 1C/1C for 2000 weeks, the positive active material in the battery was taken out and observed by scanning electron microscope. The obtained images are shown in Figures 1 and 2. , wherein, FIG. 1 is the positive electrode active material of Example 1, and FIG. 2 is the positive electrode active material of Comparative Example 39.

It can be seen from Figure 1 and Figure 2 that in Comparative Example 39, that is, when only 2% VC was added to the electrolyte, there was obvious particle breakage _on the LiFePO active material after 2000 cycles (Figure 2), while in Example 2 In 1, when 0.5% of compound 1 was added on the basis of ₂ % VC, the LiFePO active material after 2000 cycles of cycling had no particle breakage (Fig. 1), so the addition of the compound represented by structural formula 1 and the VC combination can suppress high pressure Fragmentation of solid LiFePO ₄ active particles.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims (10)

1. a lithium ion battery, is characterized in that, comprises positive electrode, negative electrode and non-aqueous electrolyte, described positive electrode comprises positive electrode material layer, and the compaction density of described positive electrode material layer is 2.35-3.0g/cc, described positive electrode The material layer includes a positive electrode active material, and the positive electrode active material is LiFePO ₄ , and the non-aqueous electrolyte includes a solvent, an electrolyte salt, vinylene carbonate, and a compound shown in structural formula 1;

Wherein, n is selected from 0 to 3, and R is selected from halogen or alkyl or haloalkyl of 1 to 3 carbon atoms. 2 . The lithium ion battery according to claim 1 , wherein the compound represented by the structural formula 1 is selected from one or more of compounds 1 to 12: 2 .

3 . The lithium ion battery according to claim 1 , wherein the compound represented by the structural formula 1 is added in an amount of 0.01 to 5% based on 100% of the total mass of the non-aqueous electrolyte. 4 . 4 . The lithium ion battery according to claim 1 , wherein the vinylene carbonate is added in an amount of 0.1 to 5% based on 100% of the total mass of the non-aqueous electrolyte. 5 . 5 . The lithium ion battery according to claim 1 , wherein the lithium salt is selected from LiPF ₆ , LiBF ₄ , LiBOB, LiDFOB, LiDFOP, LiPO ₂ F ₂ , LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ . One or more of CF ₃ ) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ , LiC(SO ₂ CF ₃ ) ₃ , LiN(SO ₂ F) ₂ and LiFSI. 6 . The lithium ion battery according to claim 5 , wherein, in the non-aqueous electrolyte, the addition amount of the lithium salt is 0.1-4 mol/L. 7 . 7. The lithium ion battery according to claim 1, wherein the solvent is selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, One or more of methyl propyl carbonate, ethyl acetate and methyl acetate. 8 . The lithium ion battery according to claim 1 , wherein the non-aqueous electrolyte further comprises an auxiliary additive selected from the group consisting of 1,3-propane sultone, 1,4-butane Sultone, Fluorinated Vinyl Carbonate, Vinyl Sulfate, Methylene Methylene Disulfonate, Tris(trimethylsilane) Phosphate, Tris(trimethylsilane) Borate, Propylene Sultone, One or more of fluorobenzene and vinyl ethylene carbonate. 9 . The lithium ion battery according to claim 8 , wherein, based on the total mass of the non-aqueous electrolyte solution as 100%, the addition amount of the auxiliary additive is 0.1-3%. 10 . 10. The lithium ion battery according to claim 1, wherein the negative electrode comprises a negative electrode material layer, the negative electrode material layer comprises a negative electrode active material, and the negative electrode active material comprises artificial graphite, natural graphite, silicon carbon, One or more of siloxane, mesocarbon microspheres and graphene.

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