Negative electrode material for improving first efficiency and cycle life of lithium ion battery as well as preparation method and application of negative electrode material

Abstract

The invention relates to the field of lithium ion batteries, in particular to a negative electrode material for improving the first efficiency and the cycle life of a lithium ion battery as well as a preparation method and application thereof. According to the all-solid-state electrolyte material Li (Zr < 0.2 > Ni < 0.2 > Co < 0.2 > Mn < 0.2 > Zn < 0.2 >) O < 2 > obtained by the preparation method disclosed by the invention, a lithium element is added into a traditional high-entropy alloy, and a material with uniform texture is obtained through ball-milling pulverization, so that sintering of a target material is more facilitated; according to the method, the high-entropy alloy is introduced into a lithium battery system in a film form by utilizing a magnetron sputtering method, the high-entropy alloy amorphous film with a stable surface is obtained through magnetron sputtering, generation of an SEI film is more effectively promoted by virtue of a stable structure of the high-entropy alloy, the stability of the SEI film is improved, and the problem of low first efficiency of a lithium ion battery is improved; and meanwhile, the high-entropy alloy non-crystallized thin film effectively improves the safety of the negative electrode of the battery.

Description

Technical Field

[0001] The present invention relates to the field of lithium - ion batteries, and particularly to a negative electrode material for improving the first - cycle efficiency and cycle life of lithium - ion batteries, and a preparation method and application thereof. Background Art

[0002] In recent years, with the booming development of the consumer electronics market, new energy vehicle market, and energy storage market, higher requirements have been put forward for the energy density, volume ratio, and cycle life of batteries. Among the selection of various types of batteries, lithium - ion batteries have become the mainstream choice in the battery market due to their green and clean nature, high energy density, and excellent cycle life. However, during the first charge - discharge process of lithium - ion batteries, some Li participates in the formation of the SEI film, resulting in capacity loss and reduced first - cycle efficiency. How to further improve the first - cycle efficiency of lithium - ion batteries has become a new research direction.

[0003] Improving the first - cycle Coulombic efficiency of lithium - ion batteries requires breakthroughs in the intrinsic properties of materials. Traditional strategies focus on optimizing the structural stability of the main positive and negative electrode materials and regulating the lithium salt ratio in the electrolyte, but the improvement space has approached the theoretical limit. The design and addition of materials such as lithium - supplemented cathodes have been widely used in recent years. However, the addition of lithium - based compounds to the negative electrode is difficult to apply because it is easily oxidized to generate Li2O / LiOH, leading to safety hazards such as battery gas generation and thermal runaway. High - entropy materials are a new type of multi - component material composed of multiple elements in equimolar or near - equimolar ratios. Due to the high structural stability and unique physical and chemical properties brought about by their multi - principal - element design, they have become a popular research object for battery materials. However, the preparation of amorphous thin films of high - entropy materials still faces problems such as complex processes and insufficient degree of amorphization, resulting in limited material usage. Summary of the Invention

[0004] The purpose of the present invention is to provide, in view of the deficiencies in the prior art, a negative electrode material for improving the first - cycle efficiency and cycle life of lithium - ion batteries, and a preparation method and application thereof.

[0005] To achieve the above - mentioned purpose, the technical solution adopted by the present invention is as follows:

[0006] The first aspect of the present invention is to provide a preparation method of a negative electrode material for improving the first - cycle efficiency and cycle life of lithium - ion batteries, and the steps include:

[0007] S1. Place high - purity Zr, Ni, Co, Mn, and Zn inside the crucible of a high - vacuum non - consumable plasma arc melting furnace for multiple melting treatments to obtain a high - entropy alloy;

[0008] S2. After ingot - casting the high - entropy alloy, use the mechanical stamping method to refine and crush the ingot to obtain high - entropy alloy powder;

[0009] S3. Place the high-entropy alloy powder and lithium oxide powder in a ball mill for ball milling to obtain the negative electrode material Li(Zr 0.2 Ni 0.2 Co 0.2 Mn 0.2 Zn 0.2 )O2 high-entropy alloy.

[0010] Preferably, in step S1, the melting treatment includes: evacuating to 5×10 -3 pa, then sequentially filling with argon and oxygen, and melting for 30 s in an argon and oxygen atmosphere.

[0011] More preferably, the proportion of oxygen filled is 5%.

[0012] Preferably, in step S3, the ball milling treatment includes: using a mixed ball charge to ball mill at a speed of 250 - 500 rpm for 20 - 40 h, then evacuating and filling with the protective gas argon and the milling gas oxygen.

[0013] More preferably, the mixed ball charge includes: 4 mm large balls and 2 mm small balls with a mass ratio of (3 - 5):1.

[0014] The second aspect of the present invention is to provide a negative electrode material prepared by the above preparation method. The negative electrode material is in powder form and has a diameter of 20 - 40 μm.

[0015] The third aspect of the present invention is to provide a negative electrode for a lithium-ion battery, using the negative electrode material Li(Zr 0.2 Ni 0.2 Co 0.2 Mn 0.2 Zn 0.2 )O2 high-entropy alloy.

[0016] The fourth aspect of the present invention is to provide a preparation method for the above lithium-ion battery negative electrode. The steps include:

[0017] A1. Mix N-methylpyrrolidone, polyvinylidene fluoride, conductive carbon black, graphite, and styrene-butadiene rubber and stir evenly to obtain a negative electrode slurry; coat the negative electrode slurry on a copper foil, and sequentially perform drying treatment, compaction treatment, rolling treatment, and cutting treatment to obtain a negative electrode sheet;

[0018] A2. Perform surface activation treatment on the negative electrode material Li(Zr 0.2 Ni 0.2 Co 0.2 Mn 0.2 Zn 0.2 )O2 high-entropy alloy to obtain Li(Zr 0.2 Ni 0.2 Co 0.2Mn 0.2 Zn 0.2 )O2 high-entropy alloy target;

[0019] A3. Using clean quartz glass and the negative electrode sheet as the coating substrate, and performing coating treatment on the Li(Zr 0.2 Ni 0.2 Co 0.2 Mn 0.2 Zn 0.2 )O2 high-entropy alloy target to obtain the negative electrode of the lithium-ion battery.

[0020] Preferably, in step A1, the mass ratio of N-methylpyrrolidone, graphite, polyvinylidene fluoride, conductive carbon black, and styrene-butadiene rubber is (95-102):(60-65):(5-8):1:(2-3).

[0021] Preferably, in step A1, the drying treatment includes: drying at 100 °C for 2 h.

[0022] Preferably, in step A2, the surface activation treatment includes: heating to 800 °C at a heating rate of 8-12 °C / min and sintering under a sintering pressure of 40 MPa.

[0023] Preferably, in step A3, the vacuum degree of the coating treatment is 2.5×10 -4 Pa, the protective gas is argon, the gas flow rate is 20 sccm, the working pressure is 1 Pa, the sputtering power is 40-100 W, and the sputtering time is 2-5 min.

[0024] The present invention adopts the above technical solutions, compared with the prior art, has the following technical effects:

[0025] (1) The all-solid electrolyte material Li(Zr 0.2 Ni 0.2 Co 0.2 Mn 0.2 Zn 0.2 )O2 obtained in the present invention adds lithium element to the traditional high-entropy alloy, and through ball milling pulverization, a material with uniform texture is obtained, which is more conducive to the sintering of the target.

[0026] (2) The present invention uses magnetron sputtering method to introduce high-entropy alloy into the lithium battery system in the form of a thin film, and obtains a surface-stable high-entropy alloy amorphous thin film through magnetron sputtering. With the help of the stable structure of the high-entropy alloy, it can more effectively promote the formation of the SEI film, improve the stability of the SEI film, and improve the problem of low initial efficiency of the lithium-ion battery; at the same time, the high-entropy alloy amorphous thin film effectively improves the safety of the battery negative electrode. Description of the Drawings

[0027] Figure 1 Micrograph of the high-entropy amorphous film in Example 1 of the present invention

[0028] Figure 2 X-ray diffraction pattern of the high-entropy amorphous film in Example 1 of the present invention

[0029] Figure 3 shows the charge-discharge curve and cycling curve of the battery prepared from the negative electrode of the lithium-ion battery in Example 1 of the present invention; wherein, Figure 3A is the charge-discharge curve, Figure 3B is the cycling curve;

[0030] Figure 4 shows the charge-discharge curve and cycling curve of the battery prepared from the negative electrode of the lithium-ion battery in Comparative Example 2 of the present invention; wherein, Figure 4A is the charge-discharge curve, Figure 4B is the cycling curve;

[0031] Figure 5 Test results of cycle life-capacity retention rate in the detection example of the present invention Detailed implementation manners

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0033] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other.

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but it is not intended to limit the present invention.

[0035] Example 1

[0036] This example provides a negative electrode material for improving the first efficiency and cycle life of a lithium-ion battery and a negative electrode of a lithium-ion battery.

[0037] Take Zr, Ni, Co, Mn, and Zn elemental materials with a purity greater than 99.99 wt%. Remove the oxide scale of the original metal material by mechanical polishing. After washing the polished metal with ultrasonic alcohol before batching, vacuum dry it at 60 °C for 10 h. Weigh the materials according to the atomic percentage of the chemical composition Li(Zr 0.2 Ni 0.2 Co 0.2 Mn 0.2 Zn 0.2 )O2.

[0038] Place high-purity Zr, Ni, Co, Mn, and Zn inside the crucible of a high-vacuum non-consumable plasma arc melting furnace, and melt them under an Ar+O atmosphere to obtain alloy ingots of 30 g each. Refine and crush the ingots by mechanical stamping.

[0039] Using a double-chamber three-dimensional oscillating high-energy ball mill, add the crushed ingots and lithium oxide powder to the chamber by mechanical ball milling. Use a mixture of 4-mm large balls and 2-mm small balls, with the mass ratio of small balls to large balls being 3.5:1; the ball milling time is 40 h; the rotation speed is 450 rpm. Apply negative pressure vacuum to the ball milling container and fill it with a 5% oxygen atmosphere. Select powdery Li(Zr 0.2 Ni 0.2 Co 0.2 Mn 0.2 Zn 0.2 )O2 high-entropy alloy. Use spark plasma sintering to perform surface activation treatment on the obtained powder alloy. The sintering pressure is 40 MPa, the heating rate is 10 °C / min, and the sintering temperature is 800 °C. Finally, obtain a Li(Zr 0.2 Ni 0.2 Co 0.2 Mn 0.2 Zn 0.2 )O2 high-entropy alloy target.

[0040] Weigh 50 g of N-methylpyrrolidone (NMP), add 3 g of polyvinylidene fluoride (PVDF) while stirring, and stir evenly. Then add 0.5 g of conductive carbon black (SP), stir at high speed until it is in a uniform state, then add 31.66 g of graphite and 4 g of deionized water, stir at high speed for 10 min, and then add 1.34 g of styrene-butadiene rubber (SBR) and stir at high speed to remove bubbles to prepare the negative electrode slurry; coat the negative electrode slurry on a 9-μm-thick copper foil, dry it at 100 °C for 2 h, roll press the obtained electrode sheet according to a compaction of 1.5, and then select a die head with a diameter of Φ14 mm to cut it to obtain the negative electrode sheet.

[0041] Place the negative electrode sheet on quartz glass as the substrate material. Using a magnetron sputtering instrument, require the vacuum degree to reach 2.5×10 -4 Pa, select Ar gas as the protective gas, the gas flow rate is 20 sccm, the working pressure is 1 Pa, the sputtering power is 80 W, and the sputtering time is 2 min. Sputter the Li(Zr 0.2 Ni 0.2 Co 0.2 Mn 0.2 Zn 0.2 )O2 high-entropy alloy target onto the substrate material to obtain a high-entropy amorphous film with a thickness of 0.128 μm as shown in Figure 1 Figure.

[0042] Example 2

[0043] This embodiment provides another anode material for improving the initial efficiency and cycle life of lithium-ion batteries and a lithium-ion battery anode.

[0044] Adjust the sputtering time to 5 min, and the rest is the same as in Example 1.

[0045] Comparative Example 1

[0046] This comparative example provides a lithium-ion battery anode.

[0047] Adjust the sputtering time to 20 min, and the rest is the same as in Example 1.

[0048] Comparative Example 2

[0049] This comparative example provides another lithium-ion battery anode.

[0050] Weigh 50 g of NMP, add 3 g of PVDF while stirring, stir evenly, then add 0.5 g of SP, stir at high speed until homogeneous, then add 31.66 g of graphite and 4 g of deionized water, stir at high speed for 10 min, and then add 1.34 g of SBR and stir at high speed to defoam, obtaining the anode slurry; coat the anode slurry on a 9-μm-thick copper foil, dry at 100 °C for 2 h, roll press the obtained electrode sheet according to a compaction of 1.5, and then select a die head with a diameter of Φ14 mm to cut to obtain the anode sheet.

[0051] Detection Examples

[0052] Measure the thickness of the high-entropy amorphous films in Examples 1-2 and Comparative Example 1, and perform X-ray diffraction detection on the high-entropy amorphous film in Example 1. As Figure 2 shown, there are no sharp crystalline phase diffraction peaks in the range of 20°-80° for the high-entropy amorphous film in Example 1, indicating that it is an amorphous structure.

[0053] Assemble the lithium-ion battery anodes in Examples 1-2 and Comparative Examples 1-2 into batteries and perform constant current charge and discharge performance tests. Specifically: use a lithium metal sheet as the positive electrode in an anaerobic glove box, use the anode sheets in Examples 1-2 and Comparative Examples 1-2 as the negative electrode, and assemble a button cell with a polyethylene microporous separator, electrolyte (LBC305-01), and a negative electrode shell. Test the constant current charge and discharge performance of the assembled lithium-ion battery in the voltage range of 0-3 V; the results are shown in Table 1 and Figures 3-4;

[0054] Table 1

[0055]

[0056]

[0057] As shown in Figure 3, at a current density of 100 mA / g, the first reversible discharge specific capacity of Example 1 can reach 375.4477 mAh / g, and the first discharge efficiency can reach 98.012%. At a current density of 1000 mA / g, after 800 cycles, the discharge specific capacity is 368.562 mAh / g, and the capacity retention rate is 98.166%;

[0058] At a current density of 100 mA / g, the first reversible discharge specific capacity of Example 2 is 367.8775 mAh / g, and the first discharge efficiency can reach 97.882%. At a current density of 1000 mA / g, after 800 cycles, the discharge specific capacity is 360.189 mAh / g, and the capacity retention rate is 97.91%. It can be seen that as the sputtering time prolongs and the thickness of the high-entropy amorphous film increases, the initial efficiency of the battery is still improved.

[0059] At a current density of 100 mA / g, the first reversible discharge specific capacity of Comparative Example 1 is 352.649 mAh / g, and the first discharge efficiency is only 95.882%. At a current density of 1000 mA / g, after 1000 cycles, the discharge specific capacity is 328.933 mAh / g, and the capacity retention rate is 93.275%. It can be seen that as the thickness of the high-entropy amorphous film increases excessively, it has a greater impact on the initial efficiency and cycle life of the battery.

[0060] As shown in Figure 4, for the coin cell sample without the high-entropy film, its first reversible discharge specific capacity is 352.3662 mAh / g, and the first discharge efficiency is 94.44%. At a current density of 1000 mA / g, for the coin cell sample without the high-entropy film, after 800 cycles, the discharge specific capacity is 335.717 mAh / g, and the capacity retention rate is 95.275%. Compared with the coin cell sample with the high-entropy film, both the first charge-discharge efficiency and the capacity retention rate decrease by 1 to 4 percentage points. Especially for Example 1, the battery shows a decrease in performance.

[0061] In summary, the lithium-ion battery anode material Li(Zr 0.2 Ni 0.2 Co 0.2 Mn 0.2 Zn 0.2 )O2 high-entropy amorphous thin film obtained in the embodiments of the present invention has a high initial efficiency and excellent long-cycle stability.

[0062] The above are only the preferred embodiments of the present invention, and do not limit the implementation manners and protection scope of the present invention. For those skilled in the art, it should be realized that all equivalent substitutions and obvious changes made by using the description and illustrations of the present invention should be included in the protection scope of the present invention.

Claims

1. A preparation method of a negative electrode material for improving the first efficiency and cycle life of a lithium-ion battery, characterized in that the steps Including: S1. Place high-purity Zr, Ni, Co, Mn, and Zn inside the crucible of a high-vacuum non-consumable plasma arc melting furnace for multiple melting treatments to obtain a high-entropy alloy; S2. After casting the high-entropy alloy ingot, use the mechanical stamping method to refine and crush the ingot to obtain high-entropy alloy powder; S3. Place the high-entropy alloy powder and lithium oxide powder in a ball mill for ball milling treatment to obtain the negative electrode material Li(Zr 0.2 Ni 0.2 Co 0.2 Mn 0.2 Zn 0.2 )O2 high-entropy alloy.

2. The preparation method according to claim 1, wherein In step S1, the smelting process includes: evacuating to 5×10 -3 Pa, then sequentially filling with argon and oxygen, and smelting for 30 s under an argon and oxygen atmosphere.

3. The preparation method according to claim 1, characterized in that, In step S3, the ball milling treatment includes: ball milling with a mixed ball material at a rotation speed of 250 - 500 rpm for 20 - 40 h, then evacuating and filling with protective gas argon and milling gas oxygen.

4. The preparation method according to claim 3, characterized in that, The mixed ball material includes: 4 mm large balls and 2 mm small balls with a mass ratio of (3 - 5):

1.

5. A negative electrode material prepared by the preparation method according to any one of claims 1 to 4, characterized in that, The negative electrode material is in powder form with a diameter of 20 - 40 μm.

6. A negative electrode of a lithium-ion battery, characterized in that, The negative electrode material Li(Zr 0.2 Ni 0.2 Co 0.2 Mn 0.2 Zn 0.2 )O2 high-entropy alloy prepared by the preparation method described in any one of claims 1-4.

7. A method for preparing the negative electrode of a lithium-ion battery as described in claim 6, the steps include: A1. Mix N-methylpyrrolidone, polyvinylidene fluoride, conductive carbon black, graphite, and styrene-butadiene rubber and stir evenly to obtain a negative electrode slurry; coat the negative electrode slurry on a copper foil, and successively perform drying treatment, compaction treatment, rolling treatment, and cutting treatment to obtain a negative electrode sheet; A2. The negative electrode material Li(Zr 0.2 Ni 0.2 Co 0.2 Mn 0.2 Zn 0.2 )O2 high entropy alloy prepared by the preparation method according to any one of claims 1-4 is subjected to surface activation treatment to obtain a Li(Zr 0.2 Ni 0.2 Co 0.2 Mn 0.2 Zn 0.2 )O2 high entropy alloy target; A3. Using the clean quartz glass and the negative electrode sheet as the coating substrates, the Li(Zr 0.2 Ni 0.2 Co 0.2 Mn 0.2 Zn 0.2 )O2 high-entropy alloy target is used for coating treatment to obtain the negative electrode of the lithium-ion battery.

8. The preparation method according to claim 7, characterized in that, In step A1, the mass ratio of the N-methylpyrrolidone, the graphite, the polyvinylidene fluoride, the conductive carbon black, and the styrene-butadiene rubber is (95 - 102):(60 - 65):(5 - 8):1:(2 - 3).

9. The preparation method according to claim 7, wherein In step A2, the surface activation treatment includes: heating at a heating rate of 8 - 12 °C / min to 800 °C and performing sintering under a sintering pressure of 40 MPa.

10. The preparation method according to claim 7, characterized in that, In step A3, the vacuum degree of the coating treatment is 2.5×10 -4 Pa, the protective gas is argon, the gas flow rate is 20 sccm, the working pressure is 1 Pa, the sputtering power is 40 - 100 W, and the sputtering time is 2 - 5 min.

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