Manganese-based composite lithium supplement agent, preparation method thereof and positive plate

Abstract

The invention provides a manganese-based composite lithium supplement agent, a preparation method thereof and a positive plate, and belongs to the field of lithium batteries. According to the manganese-based composite lithium supplement agent provided by the invention, Li6MnO4 with an anti-fluorite phase structure and LiMnO2 with a layered phase structure are compounded, so that the phase structure stability of Li6MnO4 can be improved, the first-circle charging specific capacity of the prepared positive plate is further improved, and the first-circle coulombic efficiency of the prepared positive plate is reduced. The result of the embodiment shows that the first-circle charging specific capacity can reach 788.37 mAh / g and the first-circle coulombic efficiency can be as low as 2.65% when a positive plate prepared from the manganese-based composite lithium supplement agent provided by the invention is tested.

Description

Technical Field

[0001] The present invention relates to the field of lithium batteries, and in particular to a manganese-based composite lithium supplement and a preparation method thereof and a positive electrode sheet. Background Art

[0002] During the first charge of a lithium-ion battery, the formation of a solid electrolyte interface film (SEI film) on the negative electrode surface will irreversibly consume the active lithium in the battery system, affecting the energy density and cycle life of the battery. Additional active lithium supplementation through lithium replenishment technology is an effective way to solve this problem.

[0003] The current lithium replenishment technology is mainly divided into negative electrode lithium replenishment and positive electrode lithium replenishment. Among them, positive electrode lithium replenishment technology refers to adding lithium-containing compounds with high irreversible capacity, i.e. lithium replenishers, to the positive electrode of lithium-ion batteries. Common lithium replenishers include Li2NiO2, Li5FeO4, Li6CoO4, etc., but these lithium replenishers have low first-cycle charging capacity. For example, the first-cycle charging capacity of Li2NiO2 is only 400mAh / g.

[0004] At present, manganese-based lithium supplements have attracted widespread attention due to their high theoretical specific capacity. For example, the theoretical specific capacity of Li6MnO4 with an inverse fluorite structure is 1001 mAh / g. However, the poor stability of the Li6MnO4 phase structure leads to a low actual first-cycle charge specific capacity. The first-cycle charge specific capacity of Li6MnO4 obtained in the prior art is only 334.1 mAh / g. Summary of the invention

[0005] The object of the present invention is to provide a manganese-based composite lithium supplement and a preparation method thereof and a positive electrode sheet. The manganese-based composite lithium supplement provided by the present invention has a stable phase structure, and the prepared positive electrode sheet has a high first charge specific capacity and a low first coulombic efficiency.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a manganese-based composite lithium supplement, wherein the chemical composition of the manganese-based composite lithium supplement is xLi6MnO4·(1-x)LiMnO2, wherein 0.3 <x<1;

[0008] The phase composition of the manganese-based composite lithium supplement is Li6MnO4 with an inverse fluorite phase structure and LiMnO2 with a layered phase structure.

[0009] Preferably, the chemical composition of the manganese-based composite lithium supplement is xLi6MnO4·(1-x)LiMnO2, wherein 0.5≤x≤0.9.

[0010] Preferably, the chemical composition of the manganese-based composite lithium supplement is 0.5Li6MnO4·0.5LiMnO2, 0.6Li6MnO4·0.4LiMnO2, 0.7Li6MnO4·0.3LiMnO2 or 0.8Li6MnO4·0.2LiMnO2.

[0011] The present invention also provides a method for preparing the manganese-based composite lithium supplement agent described in the above technical solution, comprising the following steps:

[0012] (1) mixing water / organic solvent with a lithium source and a manganese source to obtain a manganese-based composite lithium supplement agent precursor;

[0013] (2) The manganese-based composite lithium supplement agent precursor obtained in step (1) is subjected to a first sintering and a second sintering in sequence to obtain a manganese-based composite lithium supplement agent.

[0014] Preferably, the ratio of the amount of lithium in the lithium source to the amount of manganese in the manganese source in step (1) is (2-10):1.

[0015] Preferably, the lithium source in step (1) comprises one or two of Li2O, LiOH, LiNO3, LiCOOH, Li2CO3 and Li2C2O4.

[0016] Preferably, the manganese source in step (1) includes one or two of MnO, MnO2, Mn3O4, MnSO4, MnCO3, Mn(NO3)2 and Mn(COOH)2.

[0017] Preferably, in the step (2), the temperature of the first sintering is 300-600° C., the heating rate of the first sintering is 1-10° C. / min, and the time of the first sintering is 1-30 h.

[0018] Preferably, in the step (2), the temperature of the second sintering is 600-1000° C., the heating rate of the second sintering is 1-10° C. / min, and the time of the second sintering is 1-70 h.

[0019] The present invention also provides a positive electrode sheet, comprising a current collector and a positive electrode material coated on the surface of the current collector, wherein the positive electrode material comprises a lithium active material, a manganese-based composite lithium supplement, a conductive agent and an adhesive, and the manganese-based composite lithium supplement is the manganese-based composite lithium supplement described in the above technical scheme or the manganese-based composite lithium supplement prepared by the preparation method described in the above technical scheme.

[0020] The present invention provides a manganese-based composite lithium supplement, with a chemical composition of xLi6MnO4·(1-x)LiMnO2, where 0.3 < x < 1; the phase structure of Li6MnO4 is an anti-fluorite phase structure; the phase structure of LiMnO2 is a layered phase structure. The manganese-based composite lithium supplement provided by the present invention combines Li6MnO4 with an anti-fluorite phase structure and LiMnO2 with a layered phase structure. The introduction of LiMnO2 can promote the structure formation and stable existence of Li6MnO4, thereby improving the phase structure stability of Li6MnO4, and further increasing the first-cycle charge specific capacity of the prepared positive electrode sheet and reducing the first-cycle Coulombic efficiency of the prepared positive electrode sheet. The results of the examples show that when testing the positive electrode sheet prepared with the manganese-based composite lithium supplement provided by the present invention, the first-cycle charge specific capacity can reach 788.37 mAh / g, and the first-cycle Coulombic efficiency can be as low as 2.65%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 XRD diagrams of the manganese-based composite lithium supplements of Example 1 and Example 2 of the present invention;

[0022] Figure 2 First-cycle charge-discharge curves of the positive electrode sheets prepared in Application Example 1 and Application Example 2 of the present invention;

[0023] Figure 3 Cycling performance diagram of the positive electrode sheet prepared in Application Example 11 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention provides a manganese-based composite lithium supplement, the chemical composition of the manganese-based composite lithium supplement is xLi6MnO4·(1-x)LiMnO2, where 0.3 < x < 1; the phase composition of the manganese-based composite lithium supplement is Li6MnO4 with an anti-fluorite phase structure and LiMnO2 with a layered phase structure. In the present invention, Li6MnO4 with an anti-fluorite phase structure and LiMnO2 with a layered phase structure are combined, which can improve the phase structure stability of Li6MnO4, and further increase the first-cycle charge specific capacity of the prepared positive electrode sheet and reduce the first-cycle Coulombic efficiency of the prepared positive electrode sheet.

[0025] In the present invention, the chemical composition of the manganese-based composite lithium supplement is preferably xLi6MnO4·(1-x)LiMnO2, wherein 0.5≤x≤0.9; more preferably 0.5Li6MnO4·0.5LiMnO2, 0.6Li6MnO4·0.4LiMnO2, 0.7Li6MnO4·0.3LiMnO2 or 0.8Li6MnO4·0.2LiMnO2. The present invention limits the chemical composition of the manganese-based composite lithium supplement to make the Li6MnO4 with an inverse fluorite phase structure and the LiMnO2 with a layered phase structure more fully composited, further improve the phase structure stability of Li6MnO4, and further improve the first cycle charge specific capacity of the prepared positive electrode sheet and reduce the first cycle coulomb efficiency of the prepared positive electrode sheet.

[0026] The manganese-based composite lithium supplement provided by the present invention composites Li6MnO4 with an inverse fluorite phase structure and LiMnO2 with a layered phase structure, which can improve the phase structure stability of Li6MnO4, thereby improving the first-cycle charging capacity of the prepared positive electrode sheet and reducing the first-cycle coulomb efficiency of the prepared positive electrode sheet.

[0027] The present invention also provides a method for preparing the manganese-based composite lithium supplement agent described in the above technical solution, comprising the following steps:

[0028] (1) mixing water / organic solvent with a lithium source and a manganese source to obtain a manganese-based composite lithium supplement agent precursor;

[0029] (2) The manganese-based composite lithium supplement agent precursor obtained in step (1) is subjected to a first sintering and a second sintering in sequence to obtain a manganese-based composite lithium supplement agent.

[0030] The present invention mixes water / organic solvent, lithium source and manganese source to obtain a manganese-based composite lithium supplement agent precursor.

[0031] In the present invention, different types of lithium sources can affect the crystal structure and performance of the prepared manganese-based composite lithium supplement, and thus affect the first cycle charge capacity and coulombic efficiency of the positive electrode. In the present invention, the lithium source preferably includes one or two of Li2O, LiOH, LiNO3, LiCOOH, Li2CO3 and Li2C2O4. The present invention further improves the crystal structure of the prepared manganese-based composite lithium supplement by limiting the type of lithium source, thereby improving the first cycle charge capacity and coulombic efficiency of the positive electrode.

[0032] In the present invention, the manganese source preferably includes one or two of MnO, MnO2, Mn3O4, MnSO4, MnCO3, Mn(NO3)2 and Mn(COOH)2. The present invention can prepare a manganese-based composite lithium supplement by limiting the type of manganese source to react more fully with the lithium source.

[0033] In the present invention, the ratio of the amount of lithium in the lithium source to the amount of manganese in the manganese source is preferably (2-10): 1. In an embodiment of the present invention, the ratio of the amount of lithium in the lithium source to the amount of manganese in the manganese source may be specifically 2: 1, 3: 1, 4: 1, 5: 1, 6: 1, 7: 1, 8: 1, 9: 1 or 10: 1. In the present invention, by limiting the ratio of the amount of lithium in the lithium source to the amount of manganese in the manganese source, a manganese-based composite lithium supplement having different composition ratios of Li6MnO4 and LiMnO2 can be obtained more fully.

[0034] In the present invention, the organic solvent is preferably one or more of anhydrous ethanol, tetrahydrofuran and N-methylpyrrolidone. The present invention allows the lithium source and the manganese source to be dissolved more fully by limiting the type of organic solvent.

[0035] The present invention has no special limitation on the mixing of the water / organic solvent, the lithium source and the manganese source, and any mixing method known in the art can be used.

[0036] After the water / organic solvent, the lithium source and the manganese source are mixed, the present invention preferably grinds, separates and dries the mixed slurry in sequence to obtain a manganese-based composite lithium supplement agent precursor.

[0037] In the present invention, the solid content of the slurry obtained by mixing the water / organic solvent, the lithium source and the manganese source is preferably 10-40%. In an embodiment of the present invention, the solid content of the slurry obtained by mixing the water / organic solvent, the lithium source and the manganese source can be specifically 10%, 20%, 30% or 40%. The present invention can effectively improve the mixing effect of the lithium source and the manganese source and regulate the particle size of the raw materials by limiting the solid content of the manganese-based composite lithium supplement precursor.

[0038] In the present invention, the grinding method is preferably sand milling or ball milling. In the present invention, the rotation speed of the sand milling or ball milling is preferably 100-2000rpm. In an embodiment of the present invention, the rotation speed of the sand milling or ball milling may be specifically 100rpm, 200rpm, 300rpm, 400rpm, 500rpm, 600rpm, 700rpm, 800rpm, 900rpm, 1000rpm, 1200rpm, 1400rpm, 1600rpm, 1800rpm or 2000rpm. In the present invention, the time of the sand milling or ball milling is preferably 5-100h. In an embodiment of the present invention, the time of the sand milling or ball milling may be specifically 5h, 10h, 20h, 30h, 40h, 50h, 60h, 70h, 80h, 90h or 100h. The present invention has no special limitation on the separation, and the separation method well known in the art can be used. In the present invention, the drying temperature is preferably 50-200°C. In an embodiment of the present invention, the drying temperature may be specifically 50°C, 80°C, 100°C, 120°C, 150°C, 180°C or 200°C. In the present invention, the drying time is preferably 1 to 20 hours. In an embodiment of the present invention, the drying time may be specifically 1 hour, 5 hours, 10 hours, 15 hours or 20 hours.

[0039] After obtaining the manganese-based composite lithium supplement agent precursor, the present invention sequentially performs a first sintering and a second sintering on the obtained manganese-based composite lithium supplement agent precursor to obtain the manganese-based composite lithium supplement agent.

[0040] In the present invention, the temperature of the first sintering is preferably 300-600°C. In an embodiment of the present invention, the temperature of the first sintering may be specifically 300°C, 400°C, 500°C or 600°C. In the present invention, the heating rate of the first sintering is preferably 1-10°C / min. In an embodiment of the present invention, the heating rate of the first sintering may be specifically 1°C / min, 2°C / min, 5°C / min, 8°C / min or 10°C / min. In the present invention, the time of the first sintering is preferably 1-30h. In an embodiment of the present invention, the time of the first sintering may be specifically 1h, 5h, 10h, 15h, 20h, 25h or 30h. The present invention limits the parameters of the first sintering to ensure that the lithium source decomposes lithium ions more fully.

[0041] In the present invention, during the second sintering process, under high temperature conditions, the lithium source and the manganese source undergo a solid solution reaction to form a manganese-based composite lithium supplement. In the present invention, the temperature of the second sintering is preferably 600-1000°C. In an embodiment of the present invention, the temperature of the first sintering may be specifically 600°C, 700°C, 800°C, 900°C or 1000°C. In the present invention, the heating rate of the second sintering is preferably 1-10°C / min. In an embodiment of the present invention, the heating rate of the second sintering may be specifically 1°C / min, 2°C / min, 5°C / min, 8°C / min or 10°C / min. In the present invention, the time of the second sintering is preferably 1-30h. In an embodiment of the present invention, the time of the second sintering may be specifically 1h, 5h, 10h, 15h, 20h, 25h or 30h. The present invention limits the parameters of the second sintering to ensure that lithium ions react more fully with the manganese source to obtain a manganese-based composite lithium supplement.

[0042] In the present invention, the pressure of the first sintering and the second sintering is preferably independently 1 to 50 Pa. In the present invention, the sintering is preferably carried out under an inert atmosphere. In the present invention, the inert gas introduction rate is preferably 1 to 20 m / s. 3 In an embodiment of the present invention, the inert gas introduction rate may be specifically 1 m 3 / h,5m 3 / h,10m 3 / h or 20m 3 / h.

[0043] The present invention can adjust the phase structure composition ratio of the obtained manganese-based composite lithium supplement by limiting the ratio of the amount of lithium in the lithium source to the amount of manganese in the manganese source, and limiting the temperature and time of the first sintering and the second sintering, thereby improving the phase structure stability of Li6MnO4, thereby improving the first-cycle charging specific capacity of the obtained positive electrode sheet and reducing the first-cycle coulomb efficiency of the obtained positive electrode sheet.

[0044] The present invention also provides a positive electrode sheet, comprising a current collector and a positive electrode material coated on the surface of the current collector, wherein the positive electrode material comprises a lithium active material, a manganese-based composite lithium supplement, a conductive agent and an adhesive, and the manganese-based composite lithium supplement is the manganese-based composite lithium supplement described in the above technical scheme or the manganese-based composite lithium supplement obtained by the above preparation method.

[0045] In the present invention, the mass of the manganese-based composite lithium supplement is preferably 0.1% to 10% of the positive electrode material, preferably 0.5% to 8%. In an embodiment of the present invention, the mass of the manganese-based composite lithium supplement can be specifically 0.1%, 0.5%, 1%, 3%, 5%, 7% or 10% of the positive electrode material.

[0046] As an embodiment of the present invention, the preparation method of the positive electrode sheet may include: mixing a manganese-based composite lithium supplement, a positive electrode material, a conductive agent and a binder, and coating the mixture on the surface of a current collector to obtain a positive electrode sheet.

[0047] In the present invention, the positive electrode material is preferably LiFePO4. In the present invention, the conductive agent is preferably SuperP. In the present invention, the binder is preferably polyvinylidene fluoride (PVDF). The present invention has no special limitation on the current collector, and a current collector well known in the art can be used. In the present invention, the mass ratio of the sum of the mass of the manganese-based composite lithium supplement and the positive electrode material to the mass ratio of the conductive agent is preferably (8 to 16):1. In the present invention, the mass ratio of the sum of the mass of the manganese-based composite lithium supplement and the positive electrode material to the mass ratio of the binder is preferably (8 to 16):1.

[0048] The positive electrode sheet prepared by the invention has high initial charging specific capacity and low initial coulombic efficiency.

[0049] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] Example 1

[0051] A manganese-based composite lithium supplement, the chemical composition of which is 0.78Li6MnO4·0.22LiMnO2; the phase composition of the manganese-based composite lithium supplement is Li6MnO4 with an inverse fluorite phase structure and LiMnO2 with a layered phase structure;

[0052] The preparation method of the above manganese-based composite lithium supplement is as follows:

[0053] (1) Anhydrous ethanol, Li2O and MnO are mixed and placed in a ball mill at 100 rpm for 5 hours, then filtered and placed in a 120° C. forced air drying oven for 5 hours to obtain a manganese-based composite lithium supplement precursor; the ratio of the amount of Li in the Li2O to the amount of Mn in the MnO is 6:1; the solid content of the slurry obtained by mixing the anhydrous ethanol, Li2O and MnO is 20%;

[0054] (2) placing the manganese-based composite lithium supplement agent precursor obtained in step (1) in a corundum crucible, performing a first sintering in a tube furnace under an argon atmosphere, heating to 400° C. at 2° C. / min, sintering at 5 Pa for 8 h, and then performing a second sintering, heating to 770° C. at 4° C. / min, sintering at 5 Pa for 24 h, to obtain a manganese-based composite lithium supplement agent; the argon gas introduction rate is 10 m / s. 3 / h.

[0055] The structure of the manganese-based composite lithium supplement prepared in Example 1 was characterized by X-ray diffractometer. Figure 1 As shown in the figure, it can be seen that the XRD spectrum shows the existence of two crystal structures, Li6MnO4 and LiMnO2, indicating that the manganese-based composite lithium supplement agent is prepared in Example 1 of the present invention.

[0056] Example 2

[0057] The difference between this embodiment and embodiment 1 is that the chemical composition of the manganese-based composite lithium supplement is 0.8Li6MnO4·0.2LiMnO2; the temperature of the second sintering is 800° C., and the rest is the same as embodiment 1.

[0058] The structure of the manganese-based composite lithium supplement prepared in Example 2 was characterized by X-ray diffractometer. Figure 1 As shown in the figure, the XRD graph shows the presence of two crystal structures, Li6MnO4 and LiMnO2, indicating that the manganese-based composite lithium supplement agent is prepared in Example 2 of the present invention; and compared with the XRD graph of the manganese-based composite lithium supplement agent prepared in Example 1, it can be found that the peak intensity is different, indicating that the content of the two crystals of Li6MnO4 and LiMnO2 is different.

[0059] Example 3

[0060] The difference between this embodiment and embodiment 1 is that the chemical composition of the manganese-based composite lithium supplement is 0.75Li6MnO4·0.25LiMnO2; Li2O is replaced by LiOH, the temperature of the second sintering is 850°C, and the rest is the same as embodiment 1.

[0061] Example 4

[0062] The difference between this embodiment and embodiment 3 is that the chemical composition of the manganese-based composite lithium supplement is 0.65Li6MnO4·0.35LiMnO2; the second sintering time is 48h, and the rest is the same as embodiment 3.

[0063] Example 5

[0064] The difference between this embodiment and embodiment 4 is that the chemical composition of the manganese-based composite lithium supplement is 0.73Li6MnO4·0.27LiMnO2; LiOH is replaced by Li2CO3, and the ratio of the amount of Li in the Li2CO3 to the amount of Mn in MnO is 6.6:1, and the rest is the same as embodiment 4.

[0065] Example 6

[0066] The difference between this embodiment and embodiment 2 is that the chemical composition of the manganese-based composite lithium supplement is 0.64Li6MnO4·0.36LiMnO2; Li2O is replaced by LiOH, and MnO is replaced by MnCO3; the second sintering time is 48h, and the rest is the same as embodiment 2.

[0067] Example 7

[0068] The difference between this embodiment and embodiment 2 is that the chemical composition of the manganese-based composite lithium supplement is 0.82Li6MnO4·0.18LiMnO2; Li2O is replaced by LiCOOH, and the rest is the same as embodiment 2.

[0069] Example 8

[0070] The difference between this embodiment and embodiment 2 is that the chemical composition of the manganese-based composite lithium supplement is 0.81Li6MnO4·0.19LiMnO2; Li2O is replaced by LiCOOH, and MnO is replaced by Mn(COOH)2; the second sintering time is 48h, and the rest is the same as embodiment 2.

[0071] Example 9

[0072] The difference between this embodiment and embodiment 1 is that the chemical composition of the manganese-based composite lithium supplement is 0.85Li6MnO4·0.15LiMnO2; the ratio of the amount of Li in the Li2O to the amount of Mn in the MnO is 6.6:1, and the rest is the same as embodiment 1.

[0073] Example 10

[0074] The difference between this embodiment and embodiment 1 is that the chemical composition of the manganese-based composite lithium supplement is 0.89Li6MnO4·0.11LiMnO2; the ratio of the amount of Li in the Li2O and the amount of Mn in the MnO is 6.6:1, the temperature of the second sintering is 800°C, and the rest is the same as embodiment 1.

[0075] Application Examples 1 to 10

[0076] The manganese-based composite lithium supplement agent, SuperP and polyvinylidene fluoride (PVDF) prepared in Examples 1 to 10 were mixed respectively, placed in a coating machine for single-sided coating on the surface of an aluminum foil current collector, and then dried in a vacuum oven at 120° C. to obtain corresponding positive electrode sheets; the mass ratio of the SuperP, the manganese-based composite lithium supplement agent and the polyvinylidene fluoride (PVDF) was 5:90:5.

[0077] The positive electrode sheets prepared in Application Examples 1 to 10 were die-cut into discs with a diameter of 12 mm, assembled with lithium metal negative electrodes into button-type half-cells, and then electrochemical tests were performed. The first cycle charge and discharge specific capacity and coulomb efficiency of the positive electrode sheets prepared in Application Examples 1 to 10 were shown in Table 1.

[0078] Application Example 11

[0079] The manganese-based composite lithium supplement agent, LiFePO4, Super P and polyvinylidene fluoride (PVDF) prepared in Example 10 were mixed, placed in a coating machine and coated on one side of the aluminum foil current collector surface, and then dried in a vacuum oven at 120°C to obtain corresponding positive electrode sheets; the mass ratio of the total mass of the manganese-based composite lithium supplement agent and LiFePO4 to the mass ratio of Super P was 16:1; the mass ratio of the total mass of the manganese-based composite lithium supplement agent and LiFePO4 to polyvinylidene fluoride (PVDF) was 16:1. At the same time, a group of electrode sheets without manganese-based composite lithium supplement agent were added.

[0080] The prepared positive electrode sheet was die-cut into 8*4cm and assembled with the graphite negative electrode sheet into a soft-pack battery cell, wherein the NP ratio was 1.15:1. Then an electrochemical test was performed. Then an electrochemical test was performed to obtain the cycle performance diagram of the positive electrode sheet prepared in Application Example 11 as shown in FIG. Figure 3 shown.

[0081] Table 1 The first cycle charge and discharge performance data of the positive electrode sheets prepared in application examples 1 to 10

[0082] Example Charge capacity (mAh / g) Discharge specific capacity (mAh / g) Coulomb efficiency (%) Example 1 745.46 40.71 5.46 Example 2 756.37 26.31 3.48 Example 3 739.88 25.44 3.44 Example 4 665.46 44.17 6.64 Example 5 730.65 32.11 4.39 Example 6 672.28 42.23 6.28 Example 7 770.24 24.79 3.22 Example 8 769.35 28.46 3.70 Example 9 785.68 41.72 5.31 Example 10 788.37 20.89 2.65

[0083] Depend on Figure 2 As shown in Table 1, the positive electrode sheets prepared in Application Examples 1 to 10 of the present invention have high first charge specific capacity, which can reach up to 788.37 mAh / g, and low first cycle coulomb efficiency, which can be as low as 2.65%.

[0084] Depend on Figure 3 It can be seen that the soft-pack battery assembled with the positive electrode sheet prepared in Application Example 11 of the present invention has almost no capacity loss after 400 cycles, while the capacity of the positive electrode sheet without the manganese-based composite lithium supplement agent shows a continuous downward trend.

[0085] In summary, the manganese-based composite lithium supplement provided by the present invention has a stable phase structure, and the prepared positive electrode sheet has a high initial charge specific capacity and a low initial coulombic efficiency.

[0086] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A manganese-based composite lithium supplement, characterized in that: The chemical composition of the manganese-based composite lithium supplement is xLi6MnO4·(1-x)LiMnO2, wherein 0.3 <x<1; The phase composition of the manganese-based composite lithium supplement is Li6MnO4 with an inverse fluorite phase structure and LiMnO2 with a layered phase structure.

2. The manganese-based composite lithium supplement according to claim 1, characterized in that: The chemical composition of the manganese-based composite lithium supplement is xLi6MnO4·(1-x)LiMnO2, wherein 0.5≤x≤0.

9.

3. The manganese-based composite lithium supplement according to claim 2, characterized in that: The chemical composition of the manganese-based composite lithium supplement is 0.5Li6MnO4·0.5LiMnO2, 0.6Li6MnO4·0.4LiMnO2, 0.7Li6MnO4·0.3LiMnO2 or 0.8Li6MnO4·0.2LiMnO2.

4. The method for preparing the manganese-based composite lithium supplement according to any one of claims 1 to 3, comprising the following steps: (1) mixing water / organic solvent with a lithium source and a manganese source to obtain a manganese-based composite lithium supplement agent precursor; (2) The manganese-based composite lithium supplement agent precursor obtained in step (1) is subjected to a first sintering and a second sintering in sequence to obtain a manganese-based composite lithium supplement agent.

5. The preparation method according to claim 4, characterized in that: The ratio of the amount of lithium in the lithium source to the amount of manganese in the manganese source in the step (1) is (2-10):

1.

6. The preparation method according to claim 4, characterized in that: The lithium source in step (1) includes one or two of Li2O, LiOH, LiNO3, LiCOOH, Li2CO3 and Li2C2O4.

7. The preparation method according to claim 4, characterized in that: The manganese source in step (1) includes one or two of MnO, MnO2, Mn3O4, MnSO4, MnCO3, Mn(NO3)2 and Mn(COOH)2.

8. The preparation method according to claim 4, characterized in that: In the step (2), the temperature of the first sintering is 300-600° C., the heating rate of the first sintering is 1-10° C. / min, and the time of the first sintering is 1-30 hours.

9. The preparation method according to claim 4, characterized in that: In the step (2), the temperature of the second sintering is 600-1000° C., the heating rate of the second sintering is 1-10° C. / min, and the time of the second sintering is 1-70 hours.

10. A positive electrode sheet, comprising a current collector and a positive electrode material coated on the surface of the current collector, characterized in that: The positive electrode material comprises a lithium active material, a manganese-based composite lithium supplement, a conductive agent and a binder. The manganese-based composite lithium supplement is the manganese-based composite lithium supplement described in any one of claims 1 to 3 or the manganese-based composite lithium supplement prepared by the preparation method described in any one of claims 4 to 9.

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