Lithium supplement agent and preparation method thereof, positive electrode material and lithium ion battery

Abstract

The invention provides a lithium supplement agent. The lithium supplement agent comprises lithium oxalate particles, conductive carbon particles and additive particles, the conductive carbon particles comprise at least one of carbon black, carbon nanotubes, graphene and ketjen black; the additive particles comprise at least one of MnO2, NiO, Co3O4, TiO2, Fe3O4, MnC, TiC, Mo2C and MoO3, and the additive particles comprise at least one of MnO2, NiO, Co3O4, TiO2, Fe3O4, MnC, TiC, Mo2C and MoO3. According to the lithium supplementing agent disclosed by the invention, by limiting the structure and components of the lithium oxalate lithium supplementing agent, the carbon material is respectively coated in the lithium oxalate and the additive to form a good conductive network, and finally a composite material of the lithium oxalate, the carbon material and the additive is formed, so that the decomposition voltage can be sufficiently reduced; the lithium supplement effect of the lithium oxalate can be exerted to the maximum extent.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a lithium supplement and a preparation method thereof, a positive electrode material and a lithium ion battery. Background Art

[0002] The formation of the SEI film inside the battery will irreversibly consume the active lithium stored in the positive electrode material in the battery, causing the active lithium content in the battery system to decrease, resulting in a decrease in the energy density of the battery. At the same time, the loss of lithium causes the positive electrode to be in a "lithium-deficient" state for a long time, resulting in a reduction in the battery cycle life. In order to avoid the irreversible loss of lithium ions caused by the formation of the SEI film on the surface of the negative electrode material, it is usually necessary to introduce a lithium supplement to supplement the lithium ion loss during the first charge and discharge. Commonly used positive electrode lithium supplements include lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, lithium oxalate, etc. Among them, lithium oxalate has attracted widespread attention due to its advantages such as stability in the air, non-water absorption, and no residue after decomposition. However, the decomposition voltage of lithium oxalate is relatively high, which needs to reach above 4.7V, which makes lithium oxalate unsuitable for low-voltage systems, especially low-voltage lithium iron phosphate systems.

[0003] At present, lithium oxalate is mostly physically mixed with conductive agents, additives, etc. through mechanical methods (such as ball milling and sand milling) to reduce the decomposition voltage of lithium oxalate and promote the decomposition of lithium oxalate. However, the binding properties of lithium oxalate with conductive agents and additives are poor, and it is difficult to play the role of reducing the decomposition voltage. Therefore, how to effectively reduce the decomposition voltage of lithium oxalate and maximize the capacity of lithium oxalate is a technical problem that needs to be solved urgently in this field. Summary of the invention

[0004] In view of the above technical problems, the present invention proposes a lithium supplement and a preparation method thereof, a positive electrode material, and a lithium ion battery.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a lithium supplement, characterized in that it includes the following steps: adding a first conductive carbon during the synthesis of lithium oxalate to obtain a first mixture; adding a second conductive carbon during the synthesis of an additive to obtain a second mixture; and subjecting the first mixture and the second mixture to high-speed mechanical dispersion treatment to obtain the lithium oxalate lithium supplement.

[0006] In the second aspect, the first conductive carbon is at least one or two of carbon black, carbon nanotubes, graphene, and Ketjen black, and the second conductive carbon is also at least one or two of carbon black, carbon nanotubes, graphene, and Ketjen black. The first conductive carbon and the second conductive carbon can be the same or different.

[0007] Further, the additive particles include at least one of MnO2, NiO, Co3O4, TiO2, Fe3O4, MnC, TiC, Mo2C, and MoO3.

[0008] Further, the particle size of the lithium oxalate particles is 30 - 900 nm, the D50 of the conductive carbon particles is ≤ 50 nm, the D50 of the additive particles is ≤ 3 μm, and the D50 of the lithium oxalate lithium supplement agent is ≤ 3 μm.

[0009] Further, the lithium supplement agent comprises, by mass percentage: 40 - 97.9% of lithium oxalate, 0.5 - 30% of conductive carbon, and 1 - 20% of additive.

[0010] Further, the average decomposition voltage of the lithium supplement agent is < 4.45 V, and the decomposition capacity is 300 - 500 mAh / g.

[0011] Further, the rotation speed of the high-speed mechanical dispersion treatment is 300 - 3000 rpm, and the time is 1 - 8 h.

[0012] Further, the molar ratio of the lithium source to the compound containing oxalate is 1:(0.4 - 5); the compound containing oxalate includes at least one of ammonium oxalate, oxalic acid, and its hydrates; the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, and lithium citrate.

[0013] In a third aspect, the present invention provides a cathode material, which includes the lithium supplement agent described in any one of the above or the lithium supplement agent prepared by the preparation method described in any one of the above.

[0014] In a fourth aspect, the present invention provides a lithium-ion battery, which includes the cathode material described above.

[0015] The lithium supplement agent of the present invention includes lithium oxalate-conductive carbon particles and additive-conductive carbon particles. Among them, the conductive carbon particles can be respectively added with one having a larger specific surface area and one having higher conductivity, which can better play a synergistic effect when reducing the decomposition voltage, and are added during the synthesis process, greatly increasing the contact area between the carbon material and the lithium oxalate particles or additive particles, forming a good combination, and at the same time improving the conductivity of the lithium oxalate and the additive itself, which helps to reduce the decomposition voltage of the matrix particles and increase the charging capacity; at the same time, the introduction of the additive can further reduce the decomposition voltage of the lithium oxalate particles, and can release lithium elements by decomposition to the maximum extent during the charging process, providing additional lithium elements for the cathode material, thereby maximizing the lithium supplementing effect of the lithium oxalate particles. Applying this lithium oxalate lithium supplement agent to the cathode material can maximize the lithium supplementing effect of the lithium oxalate.

[0016] The preparation method of the lithium supplement of the present invention can obtain lithium oxalate lithium supplement particles with smaller particle size through high-speed dispersion mechanical mixing, reduce the decomposition voltage of lithium oxalate, and the preparation process is simple and easy to operate, which is conducive to realizing mass production.

[0017] The positive electrode material using the lithium supplement of the present invention and the lithium ion battery using the positive electrode material are beneficial to improving the capacity and initial efficiency of the battery. Brief Description of the Drawings

[0018] Figure 1 It is the SEM image of the lithium supplement of the present invention; Figure 2 It is the SEM image of the lithium supplement of Example 1 of the present invention; Figure 3 It is the SEM image of the lithium supplement prepared in Comparative Example 1 of the present invention; Figure 4 It is the XRD pattern of the lithium supplements prepared in Example 1 and Comparative Example 2 of the present invention. Detailed Description of the Invention Examples

[0019] (1) 47 g of lithium hydroxide, 240 g of oxalic acid dihydrate, and 10 g of Ketjen black were placed in a high-speed mixer and mixed for 2 min for reaction to obtain the first mixture A1; (2) 100 g of potassium permanganate, 5 g of graphene, and 5 g of carbon nanotubes were stirred in 500 mL of pure water, then 50 mL of concentrated sulfuric acid was added, stirred for 30 min, heated at 80 °C for 3 h, and then washed and filtered to obtain the second mixture B1; (3) The first mixture and the second mixture were jointly added to a sand mill and mixed at a rotation speed of 2000 rpm for 2 h, and the mixture was spray-dried to obtain the lithium oxalate lithium supplement C1. Examples

[0020] It is basically the same as the preparation process of Example 1, except that in step (2), "5 g of graphene and 5 g of carbon nanotubes" is replaced by "10 g of carbon nanotubes", and other conditions remain unchanged, to obtain the lithium oxalate lithium supplement C2 of this example. Examples

[0021] It is basically the same as the preparation process of Example 1, except that in step (1), "10 g of Ketjen black" is replaced by "10 g of carbon nanotubes", and other conditions remain unchanged, to obtain the lithium oxalate lithium supplement C3 of this example. Examples

[0022] It is basically the same as the preparation process of Example 1, except that in step (1), "10 g of Ketjen black" is replaced by "10 g of graphene", and other conditions remain unchanged, to obtain the lithium oxalate lithium supplement C4 of this example. Example

[0023] It is basically the same as the preparation process of Example 1, except that in step (2), "5 g of graphene plus 5 g of carbon nanotubes" is replaced with "10 g of Ketjen black", and other conditions remain unchanged, obtaining the lithium oxalate lithium supplement C5 of this example. Example

[0024] It is basically the same as the preparation process of Example 1, except that in step (1), "240 g of oxalic acid dihydrate" is replaced with "180 g of oxalic acid dihydrate", and other conditions remain unchanged, obtaining the lithium oxalate lithium supplement C6 of this example. Example

[0025] It is basically the same as the preparation process of Example 1, except that in step (1), "240 g of oxalic acid dihydrate" is replaced with "144 g of oxalic acid dihydrate", and other conditions remain unchanged, obtaining the lithium oxalate lithium supplement C7 of this example. Example

[0026] It is basically the same as the preparation process of Example 1, except that in step (1), "47 g of lithium hydroxide" is replaced with "71 g of lithium hydroxide", and other conditions remain unchanged, obtaining the lithium oxalate lithium supplement C8 of this example. Example

[0027] It is basically the same as the preparation process of Example 1, except that in step (1), "47 g of lithium hydroxide" is replaced with "57 g of lithium hydroxide", and other conditions remain unchanged, obtaining the lithium oxalate lithium supplement C9 of this example. Example

[0028] It is basically the same as the preparation process of Example 1, except that in step (1), "47 g of lithium hydroxide" is replaced with "71 g of lithium hydroxide"; in step (1), "240 g of oxalic acid dihydrate" is replaced with "180 g of oxalic acid dihydrate", and other conditions remain unchanged, obtaining the lithium oxalate lithium supplement C10 of this example. Example

[0029] It is basically the same as the preparation process of Example 1, except that in step (1), "47 g of lithium hydroxide" is replaced with "57 g of lithium hydroxide", and in step (1), "240 g of oxalic acid dihydrate" is replaced with "144 g of oxalic acid dihydrate", and other conditions remain unchanged, obtaining the lithium oxalate lithium supplement C11 of this example. Example

[0030] The preparation process is basically the same as that of Example 1, except that in step (1), "10 g of Ketjen black" is replaced with "10 g of carbon nanotubes", and "240 g of oxalic acid dihydrate" is replaced with "209 g of ammonium oxalate monohydrate", and other conditions remain unchanged, to obtain the lithium oxalate lithium supplement C12 of this example. Example

[0031] The preparation process is basically the same as that of Example 1, except that in step (1), "10 g of Ketjen black" is replaced with "10 g of carbon nanotubes", and "240 g of oxalic acid dihydrate" is replaced with "140 g of ammonium oxalate monohydrate", and other conditions remain unchanged, to obtain the lithium oxalate lithium supplement C13 of this example. Example

[0032] The preparation process is basically the same as that of Example 1, except that in step (2), "50 g of concentrated sulfuric acid" is replaced with "152 g of manganese sulfate monohydrate", and other conditions remain unchanged, to obtain the lithium oxalate lithium supplement C14 of this example. Example

[0033] The preparation process is basically the same as that of Example 1, except that in step (2), "50 g of concentrated sulfuric acid" is replaced with "152 g of manganese sulfate monohydrate", and in step (1), "240 g of oxalic acid dihydrate" is replaced with "140 g of ammonium oxalate monohydrate", and other conditions remain unchanged, to obtain the lithium oxalate lithium supplement C15 of this example. Example

[0034] (1) Place 47 g of lithium hydroxide, 240 g of oxalic acid dihydrate, and 10 g of Ketjen black in a high-speed mixer and mix for 2 min for reaction to obtain the first mixture A16; (2) First, keep 120 g of melamine, 24 g of ammonium molybdate, and 10 g of graphene at 500 °C for 3 h in an Ar gas environment, and then keep it at 800 °C for 2 h to obtain the second mixture B16; (3) Add the first mixture and the second mixture together to a sand mill, mix at a rotation speed of 2000 rpm for 2 h, and spray-dry the mixture to obtain the lithium oxalate lithium supplement C16. Example

[0035] The preparation process is basically the same as that of Example 14, except that in step (2), "10 g of graphene" is replaced with "10 g of carbon nanotubes", and other conditions remain unchanged, to obtain the lithium oxalate lithium supplement C17 of this example. Example

[0036] It is basically the same as the preparation process of Example 14, except that "10 g of Ketjen black" in step (1) is replaced with "10 g of carbon nanotubes", and other conditions remain unchanged, obtaining the lithium oxalate lithium supplement C18 of this example. Example

[0037] It is basically the same as the preparation process of Example 14, except that "47 g of lithium hydroxide" in step (1) is replaced with "73 g of lithium carbonate", and "240 g of oxalic acid dihydrate" is replaced with 120 g of oxalic acid dihydrate, and other conditions remain unchanged, obtaining the lithium oxalate lithium supplement C19 of this example. Example

[0038] It is basically the same as the preparation process of Example 14, except that "10 g of graphene" in step (2) is replaced with "10 g of Ketjen black", and other conditions remain unchanged, obtaining the lithium oxalate lithium supplement C20 of this example. Example

[0039] It is basically the same as the preparation process of Example 14, except that "10 g of graphene" in step (2) is replaced with "5 g of carbon nanotubes and 5 g of graphene", and other conditions remain unchanged, obtaining the lithium oxalate lithium supplement C21 of this example. Example

[0040] It is basically the same as the preparation process of Example 14, except that "10 g of Ketjen black" in step (1) is replaced with "5 g of Ketjen black and 5 g of graphene", and other conditions remain unchanged, obtaining the lithium oxalate lithium supplement C22 of this example. Example

[0041] It is basically the same as the preparation process of Example 14, except that "120 g of melamine" in step (2) is replaced with "100 g of dicyandiamide", and other conditions remain unchanged, obtaining the lithium oxalate lithium supplement C23 of this example. Example

[0042] It is basically the same as the preparation process of Example 14, except that "120 g of melamine" in step (2) is replaced with "100 g of dicyandiamide", and "10 g of graphene" is replaced with "5 g of carbon nanotubes and 5 g of graphene", and other conditions remain unchanged, obtaining the lithium oxalate lithium supplement C24 of this example.

[0043] Comparative Example 1 (1) 100 g of commercial lithium oxalate and 10 g of Ketjen black are placed in a high-speed mixer and mixed for 2 h to obtain the first mixture D1; (2) Add 100 g of potassium permanganate, 5 g of graphene, and 5 g of carbon nanotubes to 500 mL of pure water and stir. Then add 50 mL of concentrated sulfuric acid and stir for 30 min. Heat at 80 °C for 3 h, and then wash and filter to obtain the second mixture E1; (3) Add the first mixture and the second mixture together to a sand mill and mix at a speed of 2000 rpm for 2 h. Spray dry the mixture to obtain the lithium oxalate lithium supplement F1.

[0044] Comparative Example 2 (1) Add 47 g of lithium hydroxide, 240 g of oxalic acid dihydrate, and 10 g of Ketjen black to a high-speed mixer and mix for 2 min to react, obtaining the first mixture D2; (2) Add 20 g of MnO2, 5 g of graphene, and 5 g of carbon nanotubes to 500 mL of pure water and stir. After spray drying, obtain the second mixture E2; (3) Add the first mixture and the second mixture together to a sand mill and mix at a speed of 2000 rpm for 2 h. Spray dry the mixture to obtain the lithium oxalate lithium supplement F2.

[0045] Comparative Example 3 (1) Add 100 g of commercial lithium oxalate and 10 g of Ketjen black to a high-speed mixer and mix for 2 h to obtain the first mixture D3; (2) Add 20 g of MnO2, 5 g of graphene, and 5 g of carbon nanotubes to 500 mL of pure water and stir. After spray drying, obtain the second mixture E3; (3) Add the first mixture and the second mixture together to a sand mill and mix at a speed of 2000 rpm for 2 h. Spray dry the mixture to obtain the lithium oxalate lithium supplement F3.

[0046] Comparative Example 4 It is basically the same as the preparation process of Comparative Example 3, except that in step (1), "10 g of Ketjen black" is replaced with "10 g of carbon nanotubes", and other conditions remain unchanged, obtaining the lithium oxalate lithium supplement F4 of this example.

[0047] Comparative Example 5 It is basically the same as the preparation process of Comparative Example 3, except that in step (1), "10 g of Ketjen black" is replaced with "10 g of graphene", and other conditions remain unchanged, obtaining the lithium oxalate lithium supplement F5 of this example.

[0048] Test Example Electrochemical performance test: The lithium oxalate lithium supplement of the examples and comparative examples was assembled into a CR2430 coin-type half-cell (with metallic lithium as the negative electrode), and the charging capacity and average charging voltage were tested under the conditions of a voltage window of 2.5 - 4.5 V, a nominal capacity of 525 mAh / g, and constant current plus constant voltage at 0.1C.

[0049] The SEM image of the lithium oxalate lithium supplement prepared in Example 1 is as Figure 2 shown. The particle size of the lithium oxalate lithium supplement is between 100 nm and 10 µm, with small particle size, narrow particle size distribution range, and uniform particle size. After spray drying, the lithium oxalate particles, conductive carbon particles, and additive particles are tightly adhered together.

[0050] The SEM image of the lithium oxalate lithium supplement prepared in Comparative Example 1 is as Figure 3 shown. The particle size of the lithium oxalate lithium supplement is between 200 nm and 15 µm. The XRD patterns of Example 1 and Comparative Example 2 are as Figure 4 shown. The main peak after spraying is still lithium oxalate, and the peak corresponding to 2θ = 30° is MnO2.

[0051] In summary, the average decomposition voltage of the lithium oxalate lithium supplement in the examples is not higher than 4.43 V, and the decomposition capacity is not lower than 410 mAh / g. The addition amounts of conductive carbon and catalyst in Example 1 and Comparative Example 2 are the same. Comparing with Comparative Example 2 where commercial MnO2 and conductive carbon are directly mixed, in Example 1, conductive carbon is added during the synthesis of MnO2, which can not only closely combine conductive carbon with additives but also significantly reduce the average decomposition voltage of the lithium oxalate lithium supplement. The addition amounts of conductive carbon and catalyst in Example 1 and Example 5 are also the same. Among them, Example 5 uses the same conductive carbon, while Example 1 uses three different conductive carbons. Ketjenblack with a relatively large specific surface area and graphene with high conductivity play a good synergistic role in reducing the decomposition voltage.

[0052] For the lithium supplement of the present invention, by defining the structure and components of the lithium oxalate lithium supplement, good combination of lithium oxalate with carbon materials and additives can be achieved, which can reduce the decomposition voltage. Applying this lithium oxalate lithium supplement to the positive electrode material can maximize the lithium supplement effect of lithium oxalate.

[0053] For the preparation method of the lithium supplement of the present invention, through high-speed dispersion mechanical mixing, lithium oxalate lithium supplement particles with smaller particle size can be prepared, the decomposition voltage of lithium oxalate can be reduced, and the preparation process is simple and easy to operate, which is conducive to realizing mass production.

[0054] The positive electrode material using the lithium supplement of the present invention and the lithium-ion battery using the positive electrode material are beneficial to improving the capacity and initial efficiency of the battery.

[0055] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not limited to the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A lithium oxalate lithium supplement, characterized in that: The following steps are involved: A first conductive carbon is added during the synthesis of lithium oxalate to obtain a first mixture; a second conductive carbon is added during the synthesis of the additive to obtain a second mixture; and the first mixture and the second mixture are subjected to high-speed mechanical dispersion treatment to obtain the lithium oxalate supplement.

2. The method for preparing a lithium supplement according to claim 1, characterized in that: The first conductive carbon is at least one or two of carbon black, carbon nanotubes, graphene, and Ketjen black, and the second conductive carbon is also at least one or two of carbon black, carbon nanotubes, graphene, and Ketjen black. The first conductive carbon and the second conductive carbon can be the same or different.

3. The method for preparing a lithium supplement according to claim 1, characterized in that: The additive particles include at least one of MnO2, NiO, Co3O4, TiO2, Fe3O4, MnC, TiC, Mo2C, and MoO3.

4. A lithium supplement according to claim 1, characterized in that: The particle size of the lithium oxalate particles is 30 to 900 nm, the D50 of the conductive carbon particles is ≤50 nm, the D50 of the additive particles is ≤3 μm, and the D50 of the lithium oxalate supplement is ≤3 μm.

5. A lithium supplement according to claim 1, characterized in that: The lithium supplement comprises, by mass percentage, 40-97.9% lithium oxalate, 0.5-30% conductive carbon, and 1-20% additives.

6. A lithium supplement according to claim 1, characterized in that: The average decomposition voltage of the lithium supplement is less than 4.45V, and the decomposition capacity is 300-500 mAh / g.

7. A lithium supplement according to claim 1, characterized in that: The high-speed mechanical dispersion treatment has a rotation speed of 300 to 3000 rpm and a time of 1 to 8 hours.

8. A lithium supplement according to claim 1, characterized in that: The molar ratio of the lithium source to the compound containing oxalate is 1:(0.4-5); the compound containing oxalate includes at least one of ammonium oxalate, oxalic acid and its hydrate; the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate and lithium citrate.

9. A positive electrode material, characterized in that: The positive electrode material comprises the lithium supplement agent according to any one of claims 4 to 8 or the lithium supplement agent prepared by the preparation method according to any one of claims 1 to 3.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode material according to claim 9.

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