WO2019061674A1

WO2019061674A1 - Lithium iron phosphate-containing composite negative electrode active material of lithium ion battery, composite negative electrode plate, and lithium ion battery

Info

Publication number: WO2019061674A1
Application number: PCT/CN2017/109003
Authority: WO
Inventors: 张灵志; 闫晓丹; 张聪聪; 伊娜
Original assignee: 中国科学院广州能源研究所
Priority date: 2017-09-27
Filing date: 2017-11-01
Publication date: 2019-04-04
Also published as: CN109560260A

Abstract

A lithium iron phosphate-containing composite negative electrode active material of a lithium ion battery. The active material of the composite negative electrode comprises: lithium iron phosphate and a conventional negative electrode material. The composite negative electrode has low volumetric swelling, a high specific capacity, highly stable circulation and optimal rate performance. The battery is safe, non-polluting, and uses affordable raw materials. The preparation method is simple, easily executed and well suited for large scale industrial production.

Description

Lithium ion battery composite anode active material, composite anode sheet and lithium ion battery containing lithium iron phosphate

Technical field:

The invention relates to the technical field of lithium ion batteries, in particular to a lithium ion battery composite anode active material, a composite anode sheet and a lithium ion battery containing lithium iron phosphate.

Background technique:

Since the world's first commercial lithium-ion battery was introduced to the market by Sony in Japan in 1991, the lithium-ion battery industry has been developed for more than 20 years. Today, lithium-ion batteries play a pivotal role in products such as smartphones, tablets, and electric vehicles, and continue to affect people's daily lives. With the upgrading of electronic products, people have higher and higher requirements on the capacity and service life of lithium-ion batteries, which requires continuous improvement of the performance of various components of lithium-ion batteries, especially the optimization and improvement of positive and negative materials. . The negative electrode material currently in common use is a graphite negative electrode, and its capacity utilization rate basically reaches the upper limit value (372 mAh/g). To make the role of the negative electrode in the whole battery to a greater extent, it is necessary to use a negative electrode with a higher specific capacity.

The theoretical specific capacity of the silicon anode material reaches 4200 mAh/g, which is much higher than that of the graphite anode. The silicon negative electrode has a lower delithiation potential (<0.5V), and the voltage platform of silicon is slightly higher than that of graphite. It is difficult to cause surface lithium deposition during charging, and the safety performance is higher, which is a favorable competition for the next generation lithium ion battery anode material. By. However, silicon negative electrodes have natural defects. During electrochemical cycling, lithium ion deintercalation is accompanied by huge volume expansion and shrinkage (up to 300%). Constant volume change has certain stability to battery cycle performance. The effect limits the application of pure silicon materials in the negative electrode of lithium ion batteries.

LiFePO ₄ has the advantages of low price, non-toxicity, good environmental compatibility, high specific capacity (170 mAh/g), high working voltage, long cycle life, high temperature performance and good safety performance. Positive electrode material.

Summary of the invention:

The object of the present invention is to provide a composite anode active material of a lithium ion battery containing lithium iron phosphate, comprising lithium iron phosphate and a conventional anode material, and the electrode prepared by using the composite anode active material has a low volume. Expansion, high specific capacity, high cycle stability and excellent rate performance.

The present invention is achieved by the following technical solutions:

A composite anode active material of a lithium ion battery, the composite anode active material comprising lithium iron phosphate and a conventional anode material selected from any one of a carbon-based powder, a silicon-containing powder, or a combination thereof.

The lithium iron phosphate accounts for 0 to 100% by weight of the total amount of the composite negative electrode active material, but does not include 0% by weight.

The carbon-based powder is selected from one or a combination of artificial graphite, natural graphite, mesocarbon microbeads, petroleum coke, carbon fiber, pyrolyzed carbon, and the like.

The silicon-containing powder is selected from one or a combination of one or more of amorphous silicon, polycrystalline silicon, silicon oxynitride, silicon-based alloy, and silicon-carbon composite structural powder.

Specifically, the amorphous silicon or polycrystalline silicon is in the form of nanometer or micron-sized particles; the silicon oxide oxide is in the form of micron-sized particles; the silicon-based alloy powder is a micron-sized silicon-nickel alloy; and the silicon-carbon composite structural powder The nano-silicon particle structure powder is coated with carbon.

The present invention also protects a composite negative electrode sheet of a lithium ion battery, a composite negative electrode active material comprising the above lithium ion battery, and a conductive agent and a binder.

Preferably, the conductive agent is selected from one or any of acetylene black, Super P and PEDOT-PSS mixed in any ratio, and accounts for 5 to 20% by weight of the total amount of the negative electrode.

The binder is an oily binder polyvinylidene fluoride (PVDF), or a water-based binder polyacrylic acid (PAA), sodium polyacrylate (PAANa), styrene butadiene rubber, alginic acid, sodium alginate. One or any of several kinds mixed in any ratio, or one of the thickeners carboxymethyl cellulose (CMC) or sodium carboxymethyl cellulose (CMCNa), accounting for 5 to 10% by weight of the total amount of the negative electrode.

Preferably, the active material of the composite negative electrode accounts for 70 to 90% by weight of the total amount of the negative electrode.

The invention also protects the preparation method of the composite negative electrode sheet of the above lithium ion battery, which comprises the steps of: mixing lithium iron phosphate powder with a conventional negative electrode material into a composite negative active material of a lithium ion battery; adding a conductive agent and a binder to disperse The body is subjected to grinding or high-speed mechanical stirring to prepare a uniform fluid slurry; after the obtained fluid slurry is coated, dried and rolled, a negative electrode sheet of a lithium ion battery is obtained.

The solvent used in the preparation method is high purity deionized water or N-methylpyridinone (NMP) having a purity of 99.9%.

The present invention also protects a lithium ion battery comprising a composite negative electrode sheet of the above lithium ion battery.

The beneficial effects of the invention are as follows: the composite negative electrode sheet of the invention has low volume expansion, high specific capacity, high cycle stability and excellent rate performance, safety and pollution-free, low raw material cost, simple preparation method and suitable for industrial scale. produce.

BRIEF DESCRIPTION OF THE DRAWINGS:

1 is a comparison chart of charge and discharge curves of the negative electrode half-cells prepared in Comparative Example 1, Example 1 and Example 2.

2 is a graph showing the comparison of charge and discharge efficiency of the negative electrode half-cells prepared in Comparative Example 1, Example 1, and Example 2.

3 is a comparison chart of the rate performance curves of the negative electrode half-cells prepared in Comparative Example 1 and Example 1.

4 is an SEM image of the silicon-carbon composite powder used in Example 3 and Comparative Example 2.

5 is a comparison chart of charge and discharge cycle curves of the negative electrode half-cells prepared in Example 3 and Comparative Example 2.

Fig. 6 is a graph showing the comparison of the first charge and discharge voltage-capacity curves of the negative electrode half-cells prepared in Examples 4-7 and Comparative Example 3.

7 and 8 are charge and discharge cycle curves of the negative electrode half-cell prepared in Example 8.

9 is a comparison chart of d Q/dV curves of the first charge and discharge of the negative electrode half-cells prepared in Comparative Example 1, Example 1, Example 2, and Example 8.

Figure 10 is a graph showing the comparison of the first charge and discharge curves of the negative electrode half-cells prepared in Example 9, Example 10 and Comparative Example 4.

Fig. 11 is a SEM surface top view of the negative electrode half-cell prepared in Example 11 after 100 cycles of charge and discharge cycles.

Fig. 12 is a SEM surface topography diagram after 100 cycles of charge and discharge cycles of the negative electrode half-cell prepared in Comparative Example 5.

Figure 13 is a cyclic voltammogram of the first to third revolutions of the negative half-cell prepared in Example 12.

Fig. 14 is a graph showing the charge and discharge cycle of the negative electrode half-cell prepared in Example 13.

Detailed ways:

The following is a further description of the invention and is not to be construed as limiting.

See Table 1 for the composition of the middle and negative pole pieces of all the examples and comparative examples.

Table 1

Example 1:

The nano silicon powder (polysilicon) and the LFP powder are mixed as an active material of the composite negative electrode of the lithium ion battery, acetylene black is added as a conductive agent, and is uniformly ground in an agate mortar, and then sodium carboxymethyl cellulose (CMC) is added. The aqueous dispersion was continuously ground into a uniform fluid slurry, and the slurry was coated on a copper foil by a vacuum coater, and then vacuum dried, rolled, and cut at 60 ° C to prepare a 50 Si/20 LFP composite electrode sheet. Among them, the mass ratio of nano silicon powder, LFP, acetylene black and sodium carboxymethyl cellulose (CMC) was 50/20/20/10, respectively.

Electrochemical performance test: The above-prepared pole piece and separator, lithium sheet, stainless steel gasket and shrapnel were stacked one on another, and the electrolyte was added dropwise to form a 2025 button lithium ion half-cell. The composition of the electrolyte was 1 mol LiPF. ₆ Dissolved in EC/EMC/DEC (volume ratio = 1:1:1) + 10 wt% FEC, and the diaphragm used Celgard 2400. The charge and discharge performance and rate performance of the battery were tested on the Shenzhen Xinwei battery cycle test equipment. The charge and discharge voltage was 0.01 to 1.5 V, and the charge and discharge current was 200 mA/g. The rate performance of the battery was measured by charging and discharging at 500 mA/g, 1 A/g, 2 A/, 5 A/g, 7 A/g, and 10 A/g, and finally returning to different current densities of 500 mA/g for 10 weeks. As a result, as shown in Fig. 1, the 50S/20LFP composite electrode half-cell has a first reversible discharge specific capacity of 2937 mAh/g, and the first charge-discharge efficiency is 74%. After 100 cycles, the discharge capacity was reduced to 1415 mAh/g, and the capacity retention was 48%.

In the following examples, the negative electrode sheets of the obtained lithium ion battery were made into a half-cell in the same manner as in Example 1, and the electrochemical performance of the battery was tested on the same equipment.

Example 2:

Reference Example 1 was carried out except that the mass ratio of nano silicon powder, LFP, acetylene black and sodium carboxymethyl cellulose (CMC) was 30/40/20/10, respectively, and the obtained 30Si/40LFP composite electrode sheet.

The electrochemical performance test results are shown in Fig. 1. The first reversible discharge specific capacity of the 30Si/40LFP composite electrode half-cell was 2296 mAh/g, and the discharge capacity decreased to 710 mAh/g after 100 cycles, and the capacity retention rate was 31%. As shown in Fig. 2, the first charge and discharge efficiency of the 30Si/40LFP composite electrode half-cell was 71%.

Comparative example 1:

Weigh the nano-silica powder and acetylene black powder, grind it thoroughly in an agate mortar, then add an aqueous dispersion of sodium carboxymethyl cellulose (CMC), continue grinding to a uniform fluid slurry, and use a vacuum coater. The slurry was coated on a copper foil, and then vacuum dried, rolled, and cut at 60 ° C to prepare a pure Si negative electrode tab. Among them, the mass ratio of nano silicon powder, acetylene black and sodium carboxymethyl cellulose (CMC) was 70//20/10, respectively.

Electrochemical performance test: The above-mentioned pole piece and separator, lithium sheet, stainless steel gasket and shrapnel were stacked one on another, and the electrolyte was added dropwise to form a 2025 button lithium ion half-cell. The composition of the electrolyte was 1 mol LiPF6. Dissolved in EC/EMC/DEC (volume ratio = 1:1:1) + 10 wt% FEC, and the diaphragm used Celgard 2400. Shenzhen Xinweier battery cycle The test device was tested for charge and discharge performance and rate performance of the battery. The charge and discharge voltage was 0.01 to 1.5 V, and the charge and discharge current was 200 mA/g. The rate performance of the battery was measured by charging and discharging at 500 mA/g, 1 A/g, 2 A/, 5 A/g, 7 A/g, and 10 A/g, and finally returning to different current densities of 500 mA/g for 10 weeks. The results are shown in Fig. 1. It can be seen that the first reversible discharge specific capacity of the pure silicon anode half-cell reaches 2792 mAh/g, and the first charge-discharge efficiency is 76%. The discharge capacity was reduced to 597 mAh/g after 100 cycles, and the capacity retention rate was 21%.

By comparing the electrochemical performance test results of Example 1, Example 2, and Comparative Example 1, as shown in FIG. 1 and FIG. 2, the addition of lithium iron phosphate powder greatly improved Si compared with the pure silicon powder anode of the lithium ion battery. Cyclic stability of the /LFP composite electrode. By comparing the battery rate performance results of Comparative Example 1 and Example 1, as shown in FIG. 3, the initial discharge capacity of the pure silicon powder anode at a charge/discharge current of 500 mA/g was 2043 mAh/g, and the capacity appeared at a large current density. Rapid decay, almost no capacity at 7A / g charge and discharge current. The Si/LFP composite electrode exhibits excellent rate performance, and the initial capacity reaches 3328 mAh/g at a charge/discharge current of 500 mA/g, and an initial capacity of 500 mAh/g or more at a charge/discharge current of 10 A/g.

Example 3:

The silicon carbon composite structure powder is mixed with LFP as a lithium ion battery composite negative electrode active material, acetylene black is added as a conductive agent, and is uniformly ground in an agate mortar, and then an aqueous dispersion of sodium carboxymethyl cellulose (CMC) is added. The slurry was continuously ground into a uniform fluid slurry, and the slurry was coated on a copper foil by a vacuum coater, and then vacuum dried, rolled, and cut at 60 ° C to prepare a 50 SiC/20 LFP composite electrode sheet. Among them, the mass ratio of the silicon-carbon composite powder, LFP, acetylene black and sodium carboxymethylcellulose (CMC) was 50/20/20/10, respectively.

SEM surface topography test: Figure 4 is a scanning electron micrograph of a silicon-carbon composite powder. It can be seen from the figure that carbon is uniformly coated on the surface of the silicon particles, and the diameter of the silicon-carbon composite material is about 200 nm.

Electrochemical performance test: As shown in Fig. 5, the charge and discharge current was 500 mA/g. The 50SG/20LFP composite electrode half-cell has a first reversible discharge specific capacity of 1133 mAh/g.

Comparative example 2:

The silicon-carbon composite structural powder is used as a composite material of a lithium ion battery composite negative electrode, and acetylene black is added as a conductive agent, and is uniformly ground in an agate mortar, and then an aqueous dispersion of sodium carboxymethylcellulose (CMC) is added to continue grinding. A uniform fluid slurry was applied to a copper foil by a vacuum coater, and then vacuum dried, rolled, and cut at 60 ° C to prepare a SiC electrode sheet. Among them, the mass ratio of the silicon carbon composite powder, acetylene black and sodium carboxymethyl cellulose (CMC) was 70/20/10, respectively.

Electrochemical performance test: As shown in Fig. 5, the charge and discharge current was 500 mA/g. First reversible SiC electrode half-cell The specific capacity is 774mAh/g.

By comparing the electrochemical performance test results of Example 3 and Comparative Example 2, as shown in FIG. 5, the introduction of lithium iron phosphate can increase the discharge specific capacity of the SiC electrode.

Example 4:

The natural graphite powder is mixed with LFP as a lithium ion battery composite anode active material, acetylene black is added as a conductive agent, and is uniformly ground in an agate mortar, and then a PVDF NMP dispersion is added to continue grinding into a uniform fluid slurry. The slurry was coated on a copper foil by a vacuum coater, and then dried, rolled, and cut at 110 ° C to prepare an 80 G/10 LFP composite electrode sheet. Among them, the mass ratio of graphite, LFP, acetylene black and polyvinylidene fluoride (PVDF) was 80/10/5/5, respectively.

Example 5:

The artificial graphite powder and LFP are mixed as a lithium ion battery composite negative active material, acetylene black is added as a conductive agent, and fully ground in an agate mortar, and then the PVDF NMP dispersion is added to continue grinding into a uniform fluid slurry. The slurry was coated on a copper foil by a vacuum coater, and then vacuum dried, rolled, and cut at 110 ° C to prepare a 70 G/20 LFP composite electrode sheet. Among them, the mass ratio of graphite, LFP, acetylene black and polyvinylidene fluoride (PVDF) was 70/20/5/5.

Example 6

The artificial graphite powder is mixed with LFP as a composite negative active material of a lithium ion battery, acetylene black is added as a conductive agent, and is uniformly ground in an agate mortar, and then the NMP dispersion of PVDF is added to continue grinding into a uniform fluid slurry. The slurry was coated on a copper foil by a vacuum coater, and then vacuum dried, rolled, and cut at 110 ° C to prepare a 60 G/30 LFP composite electrode sheet. Among them, the mass ratio of graphite, LFP, acetylene black and polyvinylidene fluoride (PVDF) was 60/30/5/5, respectively.

Example 7

The artificial graphite and LFP are mixed as a composite active material of lithium ion battery composite, acetylene black is added as a conductive agent, and fully ground in an agate mortar, then the NMP dispersion of PVDF is added, and the slurry is continuously ground into a uniform fluid slurry, and vacuum is used. The coater coats the slurry on a copper foil, and then vacuum-dried, rolled, and cut at 110 ° C to prepare a 50 G/40 LFP composite electrode sheet. Among them, the mass ratio of graphite, LFP, acetylene black and polyvinylidene fluoride (PVDF) was 50/40/5/5, respectively.

Comparative example 3:

The natural graphite powder is used as a composite negative electrode active material of a lithium ion battery, and acetylene black is added as a conductive agent, and is uniformly ground in an agate mortar, and then the NMP dispersion of PVDF is added, and the slurry is continuously ground into a uniform fluid slurry. The empty coater coats the slurry on a copper foil, and then vacuum-dried, rolled, and cut at 110 ° C to prepare a 90 G electrode sheet. Among them, the mass ratio of graphite, acetylene black and polyvinylidene fluoride (PVDF) is 90/5/5.

Electrochemical performance test: The charge and discharge voltages of the negative electrode half-cells prepared in Examples 4 to 7 and Comparative Example 3 were 0.01 to 3 V. The comparison diagram of the first charge and discharge voltage-capacity curve is shown in Fig. 6. The first discharge specific capacity of the pure graphite negative electrode battery was 431 mAh/g. After the addition of LFP, the first discharge specific capacity increases and increases as the proportion of LFP increases. The first discharge specific capacities of the 80G10LFP, 70G20LFP, 60G30LFP and 50G40LFP were 502, 523, 537, 570 mAh/g.

Example 8

Weigh LFP powder and acetylene black powder, fully grind it in an agate mortar, then add an aqueous dispersion of sodium carboxymethyl cellulose (CMC), continue grinding to a uniform fluid slurry, and use a vacuum coater to slurry The material was coated on a copper foil, and then vacuum dried, rolled, and cut at 60 ° C to prepare a pure LFP negative electrode tab. Among them, the mass ratio of LFP, acetylene black and sodium carboxymethylcellulose (CMC) was 70//20/10, respectively.

Electrochemical performance test: As shown in Fig. 7, the charge and discharge voltage was 0.01 to 1.5 V, the charge and discharge current was 500 mA/g, the first discharge specific capacity was 818 mAh/g, and the charge and discharge efficiency was 29%. In order to compare the charge and discharge performance under different voltages and currents, as shown in FIG. 8, the charge and discharge voltage is 0.01 to 3 V, the initial charge and discharge current is 20 mA/g, and the first discharge specific capacity is 980 mAh/g. When the charge and discharge current was increased to 200 mA/g, the discharge specific capacity was stabilized at 300 mAh/g.

Comparative Example 1, Example 1, Example 2 and Example 8 The comparison of the d Q/dV curves of the first charge and discharge of the negative half-cell was as shown in Fig. 9. The pure LFP negative electrode had an obvious reduction at about 0.5V. The peak, while the pure Si negative electrode has no reduction peak at around 0.5V. Since both the 50Si20LFP and the 30Si40LFP negative electrodes have introduced LFP, they also have reduction peaks at around 0.5V.

Example 9

The SiO2 powder is mixed with the LFP powder as a lithium ion battery composite anode active material, acetylene black is added as a conductive agent, and is uniformly ground in an agate mortar, and then an aqueous dispersion of sodium carboxymethylcellulose (CMC) is added. The slurry was continuously ground into a uniform fluid slurry, and the slurry was coated on a copper foil by a vacuum coater, and then vacuum dried, rolled, and cut at 60 ° C to prepare a 50 SiO/20 LFP composite electrode sheet. Among them, the mass ratio of SiO2, LFP, acetylene black and sodium carboxymethylcellulose (CMC) was 50/20/20/10, respectively.

Example 10:

The siloxane powder is mixed with the LFP powder as a composite anode active material of a lithium ion battery, acetylene black is added as a conductive agent, and is uniformly ground in an agate mortar, and then an aqueous dispersion of sodium carboxymethylcellulose (CMC) is added. Continue grinding to a uniform fluid slurry, apply the slurry to a copper foil with a vacuum coater, and then vacuum dry at 60 ° C. Rolling and cutting were prepared into a 30 SiO/40 LFP composite electrode sheet. Among them, the mass ratio of SiO2, LFP, acetylene black and sodium carboxymethylcellulose (CMC) was 30/40/20/10, respectively.

Comparative example 4:

The SiO2 powder and the acetylene black powder were weighed, thoroughly ground in an agate mortar, and then an aqueous dispersion of sodium carboxymethylcellulose (CMC) was added to continue grinding to a uniform fluid slurry using a vacuum coater. The slurry was coated on a copper foil, and then vacuum dried, rolled, and cut at 60 ° C to prepare a pure SiO negative electrode tab. Among them, the mass ratio of silicon oxypropylene, acetylene black and sodium carboxymethyl cellulose (CMC) was 70//20/10, respectively.

Electrochemical performance test: As shown in Fig. 10, the charge and discharge voltage was 0.01 to 3 V, and the charge and discharge current was 200 mA/g. As can be seen from Fig. 10, after the addition of LFP, the discharge specific capacity of the negative half-cell is lowered because the oxidized silicon has a higher theoretical capacity than the LFP. The first charge and discharge efficiencies of the negative electrode half-cells prepared in Comparative Example 4, Example 9 and Example 10 were 54%, 52.9% and 50%, respectively, although the first discharge specific capacity and charge-discharge efficiency were reduced after the addition of LFP, Long-term cycle performance is expected to increase.

Example 11

The nano silicon powder (amorphous silicon) and the LFP powder are mixed as an active material of the composite negative electrode of the lithium ion battery, acetylene black is added as a conductive agent, fully ground in an agate mortar, and then an aqueous dispersion of sodium alginate is added. The slurry was continuously ground into a uniform fluid slurry, and the slurry was coated on a copper foil by a vacuum coater, and then vacuum dried, rolled, and cut at 60 ° C to prepare a 50 Si/20 LFP composite electrode sheet. Among them, the mass ratio of nano silicon powder, LFP, acetylene black and sodium alginate is 50/20/20/10, respectively.

SEM topography analysis: The battery was disassembled after the charge-discharge voltage was 0.01-1.5 V, and the charge-discharge current was 200 mA/g for 100 weeks, and the morphology was analyzed. The procedure is as follows: Disassemble the battery in the glove box, as opposed to the procedure for assembling the battery. The negative electrode tab was taken out, the pole piece was rinsed off with dimethyl carbonate (DMC), and vacuum dried for testing. The topographical features were tested using a cold field emission electron scanning microscope (Hitachi S4800). As shown in Figure 11. The surface of the 50Si/20LFP composite electrode after the cycle has a relatively dense film, and no obvious cracks appear.

Comparative example 5:

The nano silicon powder (amorphous silicon) is used as an active material of the composite negative electrode of a lithium ion battery, and acetylene black is added as a conductive agent, and is uniformly ground in an agate mortar, and then an aqueous dispersion of sodium alginate is added to continue grinding to uniformity. The fluid slurry was coated on a copper foil with a vacuum coater, and then vacuum dried, rolled, and cut at 60 ° C to prepare a Si composite electrode sheet. Among them, the mass ratio of nano silicon powder, acetylene black and sodium alginate is 70/20/10 respectively.

SEM topography analysis: The morphology of the negative electrode tab after the 100-week cycle was tested in the same manner as in Example 11. Such as Figure 12 shows. There are obvious cracks on the surface of the Si pole piece after the cycle, which is caused by the volume expansion of silicon during charge and discharge. These cracks seriously affect the cycle performance of the silicon negative electrode. Comparing Fig. 11 and Fig. 12, it can be concluded that the addition of LFP effectively suppresses the volume expansion of the silicon negative electrode, and is beneficial for protecting the stability of the silicon surface film, thereby improving the electrochemical performance of the electrode.

Example 12

Mixing nano-silica powder (amorphous silicon) and LFP powder as active materials of composite negative electrode of lithium ion battery, adding super P and PEDOT-PSS as conductive agent, fully grinding in an agate mortar, and then adding polyacrylic acid (PAA) The aqueous dispersion was continuously ground into a uniform fluid slurry, and the slurry was coated on a copper foil by a vacuum coater, and then vacuum dried, rolled, and cut at 60 ° C to prepare a 20Si/70LFP composite electrode sheet. Among them, the mass ratio of nano silicon powder, LFP, super P and PEDOT-PSS to polyacrylic acid was 20/70/3/2/5, respectively.

Electrochemical performance test: The results of the first to third cycles of cyclic voltammetry of the prepared electrode are shown in FIG. The scan rate is 100 uV/s. On the first lap, two distinct oxidation peaks appeared at around 0.3V and 0.5V, respectively, and the reduction peak was at 0.2V. On the 2nd and 3rd laps, only one obvious oxidation peak was around 0.4V, and the reduction peak shifted to the left.

Example 13

The nano silicon powder (amorphous silicon) and the LFP powder are mixed as an active material of the composite negative electrode of the lithium ion battery, acetylene black is added as a conductive agent, and is uniformly ground in an agate mortar, and then styrene-butadiene rubber/carboxymethyl fiber is added. The aqueous dispersion of sodium is continuously ground into a uniform fluid slurry, and the slurry is coated on a copper foil by a vacuum coater, and then vacuum dried, rolled, and cut at 60 ° C to prepare a 60Si/10LFP composite electrode sheet. . Among them, the mass ratio of nano silicon powder, LFP, acetylene black and styrene butadiene rubber/carboxymethyl cellulose sodium is 60/10/20/10, respectively.

Electrochemical performance test: As shown in Fig. 14, the first reversible discharge specific capacity of the 60Si/10LFP composite electrode half-cell was 3456 mAh/g, and the first charge-discharge efficiency was 69.9%.

Claims

A composite anode active material for a lithium ion battery, characterized in that the active material of the composite anode contains lithium iron phosphate and a conventional anode material, and the conventional anode material is selected from any one of a carbon-based powder and a silicon-containing powder. Or a combination thereof.
The composite anode active material according to claim 1, wherein the lithium iron phosphate accounts for 0 to 100% by weight of the total amount of the composite anode active material, but does not include 0% by weight.
The composite anode active material according to claim 1, wherein the carbon-based powder is one selected from the group consisting of artificial graphite, natural graphite, mesocarbon microbeads, petroleum coke, carbon fiber, and pyrolyzed carbon powder. Or any combination of several; the silicon-containing powder is selected from any one or a combination of amorphous silicon, polycrystalline silicon, oxysulfide, silicon-based alloy, silicon-carbon composite structural powder.
The composite anode active material according to claim 3, wherein the amorphous silicon and the polycrystalline silicon are in the form of nanometer or micron-sized particles; the silicon oxide oxide is in the form of micron-sized particles; and the silicon-based alloy powder is a micron-sized silicon-nickel alloy; the silicon-carbon composite structural powder is a carbon-coated nano-silicon particle structured powder.
A composite negative electrode sheet of a lithium ion battery, characterized by comprising the composite negative electrode active material according to any one of claims 1 to 4, further comprising a conductive agent and a binder.
The composite negative electrode sheet according to claim 5, wherein the conductive agent is selected from one or any of acetylene black, Super P and PEDOT-PSS mixed in any ratio, and accounts for 5 to 5 of the total amount of the negative electrode. 20wt%; the binder is an oily binder or a water-based binder or a thickener, accounting for 5 to 10% by weight of the total amount of the anode.
The composite negative electrode sheet according to claim 5, wherein the oily binder is polyvinylidene fluoride, and the aqueous binder is selected from the group consisting of polyacrylic acid, sodium polyacrylate, styrene butadiene rubber, alginic acid, One or any of several sodium alginate is mixed in an arbitrary ratio, and the thickener is selected from one of carboxymethylcellulose or sodium carboxymethylcellulose.
The composite negative electrode sheet according to claim 5, wherein the active material of the composite negative electrode accounts for 70 to 90% by weight of the total amount of the negative electrode.
A method for preparing a composite negative electrode sheet according to claim 5, characterized in that the method comprises the steps of: mixing lithium iron phosphate powder with a conventional negative electrode material into a composite negative active material of a lithium ion battery; adding a conductive agent, sticking The mixture dispersion is prepared by grinding or high-speed mechanical stirring to prepare a uniform fluid slurry; after the obtained fluid slurry is coated, dried and rolled, a negative electrode sheet of the lithium ion battery is obtained.
A lithium ion battery comprising the composite negative electrode sheet according to any one of claims 5-7.