A lithium supplement additive for lithium ion battery positive electrode and its application

Abstract

The present application discloses a lithium supplement additive for the positive electrode of a lithium-ion battery and its application. The lithium supplement additive for the positive electrode of the present application is a Li2O powder doped with a conductive metal. The lithium supplement additive of the present application improves the conductivity of the Li2O powder by doping copper in the Li2O powder, enabling it to be used as a lithium supplement additive. Compared with the existing lithium supplement additives for the positive electrode, the highest theoretical specific capacity of the lithium supplement additive of the present application can be as high as 1794 mAh / g. Moreover, the lithium supplement additive of the present application is safe, environmentally friendly, and non-toxic, laying a foundation for the preparation of high-capacity lithium-ion batteries.

Description

Technical Field

[0001] The present application relates to the field of lithium-ion battery materials, and in particular to a lithium supplement additive for a lithium-ion battery positive electrode and an application thereof. Background Art

[0002] Lithium-ion batteries with high voltage, high energy density and long cycle life are currently the most widely used secondary battery system, not only occupying the portable electronic product market, but also gradually occupying the power battery market such as electric vehicles. However, whether it is used as a 3C battery, a power battery, or an energy storage battery, its cost needs to be reduced, and its energy density and power density need to be improved.

[0003] In order to improve the energy density, the current mainstream direction is to increase the battery charging voltage and adopt electrode materials with high specific capacity. In terms of the selection of high specific capacity negative electrode materials, silicon-based negative electrodes are gradually becoming the top choice for battery companies and material suppliers to improve negative electrodes due to their abundant reserves and ultra-high theoretical specific capacity. They are one of the most promising negative electrode materials for the next generation of lithium-ion batteries. However, the mismatch between the efficiency of positive and negative electrode materials caused by the low first coulomb efficiency of silicon negative electrodes has seriously limited its practical application. In fact, not only silicon negative electrodes, but most negative electrode materials have an important phenomenon: during the first charge and discharge process, the organic electrolyte will combine with the lithium ions and electrons migrated from the positive electrode on the surface of the negative electrode material, and undergo reduction and decomposition to form an electronically insulating, lithium-ion conductive passivation film, namely the solid electrolyte membrane, referred to as the SEI membrane. In the full battery system, lithium ions are all provided by the positive electrode material. The formation of the SEI membrane consumes the active lithium ions in the battery, resulting in waste of positive electrode materials and reduced battery capacity.

[0004] In response to the above problems, people have proposed to replenish lithium for lithium-ion batteries to replenish the lithium ions consumed by the formation of the negative electrode SEI film during the first charging of the battery. Currently, in the research on lithium replenishment technology, most of the lithium replenishment is carried out on the negative electrode, and lithium metal is generally used directly on the surface of the negative electrode sheet for physical lithium replenishment. For example, patent CN102779975A uses lithium powder to replenish lithium for the negative electrode, and patent CN 105489846A uses a method of compounding a rolled lithium strip with a negative electrode sheet to replenish lithium.

[0005] The advantage of using lithium metal for negative electrode replenishment is that lithium metal has a high specific capacity and a small amount of lithium replenishment. However, as a very active metal, lithium metal brings safety issues that cannot be ignored. In addition to high environmental requirements, such as humidity <1%, the negative electrode replenishment process of lithium metal is cumbersome and costly, and the uniformity of lithium replenishment is difficult to control. It is difficult to effectively replenish the negative electrode edge and internal electrode particles, resulting in poor battery consistency and difficulty in actual production and application.

[0006] Positive electrode lithium supplementation can avoid the above problems. By selecting a suitable positive electrode lithium supplementation additive and adding it directly to the positive electrode material during homogenization, there is no need to change the existing production process, which does not increase the cost and can achieve a uniform lithium supplementation effect. US Patent US 2016 / 0133933A1 reports a positive electrode lithium supplementation additive Li 2+x Mo 6-y M y S 8-z (-0.1≤x≤0.5,0≤y≤0.5,-0.1≤z≤0.5), where M is a transition metal cation. The patent points out that the positive electrode lithium supplement additive needs to have a high lithium removal capacity within the battery charging range and a low reversible capacity within the battery discharge voltage range. This irreversible lithium supplement additive removes lithium ions to participate in the reaction during the first charging process, and does not embed or rarely embeds lithium ions during the subsequent discharge process. Summary of the invention

[0007] The purpose of the present application is to provide a new formula of lithium supplement additive for lithium ion battery positive electrode and its application.

[0008] This application adopts the following technical solutions:

[0009] In one aspect, the present application discloses a lithium supplement additive for a positive electrode of a lithium ion battery, wherein the lithium supplement additive is a conductive metal-doped Li 2 O powder.

[0010] It should be noted that the lithium supplement additive of the present application overcomes the problem of Li 2 The poor conductivity of O makes Li 2 O powder can be used as a lithium supplement additive, thereby increasing the theoretical specific capacity to 1794mAh / g, greatly improving the battery capacity. It can be understood that the purpose of conductive metal doping is to increase Li 2 O powder has good conductivity, therefore, any conductive metal with good conductivity and no toxic side effects on the environment can be used in this application.

[0011] Preferably, the conductive metal doping is copper doping.

[0012] It should be noted that copper not only has good electrical conductivity and is non-toxic, but is also abundant, cheap and easy to obtain. Therefore, in a preferred implementation of the present application, copper doping is used to improve Li 2 O powder conductivity.

[0013] Preferably, the specific method of copper doping includes: mixing CuO powder and Li 2 O powders were mixed and then ball milled to form Cu-doped Li 2 O powder.

[0014] Preferably, the ball milling condition is 300rpm-600rpm, ball milling 1h-50h;

[0015] More preferably, the ball milling condition is 300 rpm-600 rpm, and the ball milling time is 5 h-24 h.

[0016] It should be noted that copper doping by CuO powder is only a preferred solution of the present application, and copper doping by other methods is not excluded, as long as copper doping can improve Li 2 The purpose of ball milling is to fully dope the copper element into the Li 2 O powder, it can be understood that the rotation speed and time of ball milling can be optimized according to the amount of CuO powder processed, and are not specifically limited here.

[0017] Preferably, the doping amount of the conductive metal is 5%-33% of the total weight of the lithium supplement additive.

[0018] It should be noted that the purpose of conductive metal doping is to improve Li 2 O powder has good conductivity. Therefore, in theory, as long as there is conductive metal doping, the Li 2 O powder conductivity, and the more conductive metal doping, the better the 2 The more conductive metal doping is, the more obvious the improvement effect of the conductivity of the O powder is; however, the more conductive metal doping is, the more dilution of Li 2 O powder, affecting its lithium supplement effect. Taking the above factors into consideration, the preferred doping amount of the present application is that the conductive metal element accounts for 5%-33% of the total weight of the lithium supplement additive. It can be understood that for lower requirements or for other purposes, for Li 2 When the conductivity requirement of O powder is low, or the requirement for lithium supplementation is low, the doping amount can be lower or higher than the range specified in this application. The specific situation depends on production requirements and is not limited here.

[0019] In addition, it should be noted that when the lithium supplement additive of the present application is actually used in the battery, gas may be generated when charged to different cut-off voltages depending on the positive electrode material. This can be done by optimizing the amount of lithium supplement additive to adjust the gas production voltage. Alternatively, the gas generated after pre-charging can be discharged by designing the battery structure. For example, in practical applications, the battery structure is preferably a battery that can be vented after formation, such as a soft-pack battery.

[0020] Another aspect of the present application discloses the application of the lithium supplement additive of the present application in positive electrode materials, lithium ion batteries or lithium source materials.

[0021] It can be understood that the lithium supplement additive of the present application is designed for lithium supplementation of positive electrode materials of lithium-ion batteries. Therefore, it can be used in positive electrode materials and lithium-ion batteries to supplement lithium and thus increase the battery capacity. As a lithium source material, it is mainly considered that for positive electrode materials that do not contain lithium, such as V 2 O 5 , FeF 3 When it is combined with a lithium-free negative electrode such as graphite or silicon to form a full battery, the lithium supplement additive of the present application can be used as a lithium source to provide active lithium ions for the system.

[0022] Another aspect of the present application discloses a conductive metal-doped Li 2 Application of O powder as a lithium supplement additive for the positive electrode of lithium-ion batteries.

[0023] Preferably, the conductive metal is doped with copper. Preferably, the copper is doped by mixing CuO powder and Li 2 O powders were mixed and then ball-milled to form Cu-doped Li 2 O powder. Preferably, the doping amount of the conductive metal is 5%-33% of the total weight of the conductive metal element.

[0024] Another aspect of the present application discloses a positive electrode material for a lithium-ion battery, wherein the positive electrode material contains the lithium supplement additive of the present application.

[0025] Preferably, in the positive electrode material, the amount of the lithium supplement additive is 0.1%-10% of the total weight of the positive electrode material.

[0026] Preferably, the positive electrode active material of the positive electrode material includes but is not limited to LiCoO 2 、LiMnO 2 、LiFePO 4 , NCM and NCA.

[0027] Among them, NCM is a nickel-cobalt-manganese ternary positive electrode material, and NCA is a nickel-cobalt-aluminum ternary positive electrode material.

[0028] It should be noted that the lithium supplement additive of the present application can be used in various lithium-ion battery positive electrode materials to play the role of lithium supplement; LiCoO 2 、LiMnO 2 、LiFePO 4 , NCM and NCA are just a few active materials that are currently commonly used. The lithium replenishing additive of the present application is not limited to replenishing lithium to these positive electrode active materials.

[0029] Another aspect of the present application discloses a lithium ion battery containing the lithium supplement additive of the present application or using the positive electrode material of the present application.

[0030] Preferably, the negative electrode of the lithium-ion battery is one or more of graphite, silicon, tin alloy, silicon-oxygen composite material or silicon-carbon composite material.

[0031] It should be noted that the lithium-ion battery of the present application has no special restrictions on the negative electrode material of the battery, and the negative electrode materials suitable for lithium-ion batteries, such as graphite, silicon, tin alloy, silicon-oxygen composite material and silicon-carbon composite material, can be used in the present invention. However, the negative electrode materials with low initial efficiency, such as silicon, silicon-oxygen composite material and silicon-carbon composite material, are matched with the positive electrode material containing lithium supplement additives of the present application, and the effect of improving the battery capacity is more obvious.

[0032] The beneficial effects of this application are:

[0033] The lithium supplement additive of the present application is provided by 2 O powder is doped with copper to improve the Li 2 The conductivity of O powder enables it to be used as a lithium supplement additive. Compared with the existing positive electrode lithium supplement additives, the lithium supplement additive of the present application can have a maximum theoretical specific capacity of up to 1794 mAh / g. In addition, the lithium supplement additive of the present application is safe, environmentally friendly, and non-toxic, laying a foundation for the preparation of high-capacity lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 3 is a curve diagram of the change of discharge capacity of the batteries prepared in the examples and comparative examples of the present application with the number of cycles, wherein the “▲” curve is the test curve of the example battery, and the “■” curve is the test curve of the comparative example battery. DETAILED DESCRIPTION

[0035] The positive electrode lithium supplement additive can supplement the positive electrode with lithium, which can avoid the defects and shortcomings of negative electrode lithium supplement. However, Li 2 O powder has poor conductivity and is highly polarized when used in batteries, so it cannot be used as a lithium supplement additive.

[0036] The inventor of this application has found through extensive research that if the Li 2 The conductivity of O powder, Li 2 The electrochemical reaction equation for the generation of lithium peroxide when the battery is charged is as follows:

[0037] 2Li 2 O→Li 2 O 2 +2Li + +2e - E 0 =2.87V vs.Li + / Li

[0038] At this point, the theoretical capacity is 897 mAh / g. Further increasing the charging voltage will cause the following reaction:

[0039] Li 2 O 2 →O 2 +2Li + +2e -

[0040] At this time, the theoretical specific capacity is as high as 1794 mAh / g. 2 If O is used as a lithium supplement additive, it has a very high theoretical specific capacity.

[0041] In view of the above research and discovery, the inventor of this application creatively 2 O powder is doped with conductive metals to improve the Li 2 O powder conductivity, thereby obtaining the lithium supplement additive of the present application, namely, the conductive metal-doped Li 2 O powder. Due to the conductive metal doping, it is possible to reduce the Li 2 The oxidative delithiation overpotential of O in the battery increases its delithiation capacity at low potential and reduces the amount of gas generated.

[0042] In a preferred implementation of the present application, the conductive metal doping is preferably copper doping. Compared with other elements such as Co doping, copper has good conductivity, abundant reserves, cheap and easy to obtain, and non-toxic. 2 O is used as a lithium supplement additive for the positive electrode of lithium-ion batteries. During the first charging process of the battery, it releases an appropriate amount of lithium ions, which effectively compensates for the lithium ions consumed by the formation of SEI film at the negative electrode and improves the battery capacity. 2 O is used as a lithium supplement additive for lithium-ion batteries. The gas generated by lithium desorption during battery pre-charging is removed by vacuuming during battery secondary sealing, which does not affect the safety of the battery and can reduce the mass of the additive. 2 Compared with negative electrode additives or other additives, lithium supplement additives do not change the internal structure and production process of the battery, and the cost of lithium supplement additives is low. It is a lithium supplement method for the positive electrode of lithium-ion batteries that is easy to industrialize and mass produce.

[0043] The present application is further described in detail below through specific examples. The following examples are only used to further illustrate the present application and should not be construed as limiting the present application.

[0044] Example

[0045] The lithium supplement additive in this example is copper-doped Li 2 O powder, the specific preparation method is as follows:

[0046] Take 13.596g Li2 O powder and 7.160 g CuO powder were used as raw materials. The two were mixed and ball milled at 600 rpm for 25 h to obtain copper-doped Li 2 O powder, that is, the lithium supplement additive for the positive electrode material of the lithium-ion battery in this example.

[0047] In this example, copper-doped Li 2 O powder is used in 406696 soft pack batteries, as follows:

[0048] 3000g LiCoO 2 After dry mixing with 100g of the lithium supplement additive of this example for 1h, the prepared conductive glue was added, stirred slowly for 20min, then stirred rapidly for 2.5h, and vacuumed to obtain the positive electrode slurry. The conductive glue of this example was prepared by mixing 21.3g CNT, 24.25g PVDF and 381.5g NMP.

[0049] The above positive electrode slurry was pressurized at 20 mg / cm 2 The single-sided surface density is double-coated on 10μm aluminum foil, with the large surface coating area being 93.7cm long and the small surface coating area being 80.6cm long. After drying, the positive electrode sheet after lithium supplementation is obtained. After rolling into a 109μm thick electrode sheet, it is cut into a positive electrode sheet with a length of 99.9cm and a width of 8.8cm, and the tabs are welded and the tab protective glue is affixed.

[0050] The NP ratio of positive and negative electrodes is set to 1.04, and the negative electrode uses a silicon-based negative electrode with a specific capacity of 483mAh / g and an initial efficiency of 83.5%. The negative electrode ratio is active material: SP:CMC:SBR:H 2 O=100:1:1.3:2.9:85. Negative electrode single surface density 7.21mg / cm 2 The negative electrode slurry was coated on both sides of a 6um thick copper foil, with the large side being 94.2cm long and the small side being 82cm long. After drying, it was rolled to 98um and cut into negative electrode sheets with a length of 100cm and a width of 9.0cm, and the tabs were welded and taped.

[0051] The positive and negative electrodes and the 9um separator were wound into a 15-fold dry battery cell. The rolled battery cell was placed in a punched aluminum-plastic film shell, the top and side were sealed, and then 11g of standard electrolyte was injected and sealed once to assemble the soft-pack battery of this example.

[0052] The sealed soft-pack battery is pre-charged to a charge cut-off voltage of 4.4V to complete the entire gas production process of the positive electrode lithium supplement additive decomposition and the negative electrode SEI film formation. The battery is then vacuum-sealed for a second time to discharge the gas generated in the battery, and the air bag is cut off to obtain a lithium-ion battery after lithium supplementation.

[0053] Comparative Example

[0054] 3000g LiCoO 2 The prepared conductive adhesive was mixed, stirred slowly for 20 minutes, then stirred rapidly for 2.5 hours, and vacuumed to obtain the positive electrode slurry. The conductive adhesive in this example was prepared by mixing 21.3g CNT, 24.25g PVDF and 381.5g NMP.

[0055] The above positive electrode slurry was heated to 21 mg / cm 2 The single-sided surface density is coated on 10μm aluminum foil on both sides, with the large surface coating area being 93.8cm long and the small surface coating area being 80.6cm long. After drying, the positive electrode sheet is obtained. After rolling into a 114μm thick electrode sheet, it is cut into a positive electrode sheet with a length of 99.9cm and a width of 8.8cm, and the tabs are welded and the tab protective glue is affixed.

[0056] The NP ratio of positive and negative electrodes is set to 1.04, and the negative electrode uses a silicon-based negative electrode with a specific capacity of 483mAh / g and an initial efficiency of 83.5%. The negative electrode ratio is active material: SP:CMC:SBR:H 2 O = 100:1:1.3:2.9:85. The NP ratio of positive and negative electrodes is set to 1.04, and the single-sided surface density of the negative electrode is 6.98 mg / cm 2 The negative electrode slurry was coated on both sides of a 6um thick copper foil, with the large side being 94.3cm long and the small side being 82.3cm long. After drying, it was rolled to 94um and cut into negative electrode sheets with a length of 100cm and a width of 9.0cm, and the tabs were welded and taped.

[0057] The positive and negative electrodes and the 9um separator were wound into a 15-fold dry cell, and the rolled cell was placed in a punched aluminum-plastic film shell, top and side sealed, and then 11g of standard electrolyte was injected and sealed once to assemble into a soft-pack battery. The sealed soft-pack battery was pre-charged to a charge cut-off voltage of 4.4V, vacuumed and sealed twice, and the air bag was removed to obtain a lithium-ion battery comparison sample.

[0058] The batteries of the embodiment and the comparative example were subjected to constant current charge and discharge test at a current of 0.2C. When charged to 4.4V, they were charged at a constant voltage until the current was less than 0.01C, and the discharge cut-off voltage was 2.5V. The discharge capacity of the embodiment and the comparative example changed with the number of cycles as shown in FIG. Figure 1 shown.

[0059] Figure 1 In the figure, the “▲” curve is the test curve of the battery of the embodiment, and the “■” curve is the test curve of the battery of the comparative example; Figure 1The results show that, under the same battery model, the lithium-ion battery to which the lithium-supplementing additive of the present application is added to the positive electrode material, i.e., the lithium-ion battery of the embodiment, has a higher discharge capacity than the lithium-ion battery of the comparative example without adding the lithium-supplementing additive. It can be seen that although the addition of the lithium-supplementing additive of the present application adds some inert components to the positive electrode material, it makes full use of the gram capacity of the positive electrode material by supplementing the lithium ion loss during the first charging of the battery, thereby improving the battery capacity as a whole.

[0060] The above contents are further detailed descriptions of the present application in combination with specific implementation methods, and it cannot be determined that the specific implementation of the present application is limited to these descriptions. For ordinary technicians in the technical field to which the present application belongs, several simple deductions or substitutions can be made without departing from the concept of the present application.

Claims

1. A lithium supplement additive for lithium ion battery positive electrode, Features: The lithium supplement additive is Li doped with a conductive metal 2 O powder; the doping amount of the conductive metal doping is 5%-33% of the total weight of the lithium supplement additive.

2. The lithium supplement additive according to claim 1, Features: The conductive metal doping is copper doping.

3. The lithium supplement additive according to claim 2, Features: The specific method of copper doping includes: mixing CuO powder and Li 2 O powders were mixed and then ball milled to form Cu-doped Li 2 O powder.

4. The lithium supplement additive according to claim 3, Features: The ball milling conditions are 300 rpm-600 rpm, and the ball milling time is 1 h-50 h.

5. The lithium supplement additive according to claim 3, Features: The ball milling conditions are 300 rpm-600 rpm, and the ball milling time is 5 h-24 h.

6. A conductive metal-doped Li 2 O powder is used as a lithium supplement additive for the positive electrode of a lithium ion battery; the doping amount of the conductive metal doping is 5%-33% of the total weight of the conductive metal element.

7. The use according to claim 6, Features: The conductive metal doping is copper doping.

8. The use according to claim 7, Features: The copper doping method is to mix CuO powder and Li 2 O powders were mixed and then ball-milled to form Cu-doped Li 2 O powder.

9. A positive electrode material for a lithium-ion battery, Features: The positive electrode material contains the lithium supplement additive according to any one of claims 1 to 5.

10. The positive electrode material according to claim 9, Features: The amount of the lithium supplement additive is 0.1%-10% of the total weight of the positive electrode material.

11. The positive electrode material according to claim 9 or 10, Features: The positive electrode active material of the positive electrode material is not limited to LiCoO 2 、LiMnO 2 、LiFePO 4 , NCM and NCA.

12. A lithium ion battery containing the lithium supplement additive according to any one of claims 1 to 5 or using the positive electrode material according to any one of claims 9 to 11.

13. The lithium ion battery according to claim 12, Features: The negative electrode of the lithium-ion battery is one or more of graphite, silicon, tin alloy, silicon-oxygen composite material or silicon-carbon composite material.

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