Formation method of lithium ion battery and lithium ion battery

Abstract

The invention provides a formation method of a lithium ion battery and the lithium ion battery, and belongs to the technical field of batteries, and the formation method of the lithium ion battery comprises the steps that the lithium ion battery comprises a positive electrode active material, and the positive electrode active material comprises lithium iron manganese phosphate and a lithium-rich manganese-based material; wherein the upper limit voltage of the lithium ion battery during formation charging is greater than 4.45 V. According to the embodiment of the invention, the upper limit voltage of the formation charging of the lithium ion battery is set to be greater than 4.45 V, and the gram volume of the lithium-rich manganese-based material can be fully released in the formation charging process of the lithium ion battery, so that the gram volume and the cycle performance of the lithium ion battery can be both improved in the subsequent application process.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a formation method of a lithium ion battery and a lithium ion battery. Background Art

[0002] Lithium manganese iron phosphate (LMFP) is a new generation of lithium-ion battery cathode material and an upgraded material of lithium iron phosphate (LFP) material. Due to the presence of transition metal manganese (Mn) in LFP material, the voltage platform of LFP is higher than that of LFP, and the energy density of LFP is also more advantageous than that of LFP.

[0003] However, due to the presence of transition metal manganese in lithium iron phosphate materials, the lithium ion diffusion rate and electronic conductivity of lithium iron phosphate are also lower than those of lithium iron phosphate materials (the lithium ion diffusion rate of lithium iron phosphate is 10-15cm 2 / S, the lithium ion diffusion rate of lithium iron phosphate is 10-14cm 2 / S; the electronic conductivity of lithium manganese iron phosphate is 10-13S / cm, and the electronic conductivity of lithium iron phosphate is 10-9S / cm), so that the gram capacity of lithium manganese iron phosphate is lower than that of lithium iron phosphate. In addition, the lithium hexafluorophosphate in the electrolyte will react with the trace water in the battery, and the generated hydrofluoric acid will destroy the structure of lithium manganese iron phosphate. In addition, the Jahn-Teller effect of manganese ions exists, and manganese will be dissolved during the cycle, reducing the stability of the positive electrode material. In addition, the dissolved manganese ions will be reduced and precipitated at the negative electrode, destroying the SEI film, making the cycle performance of lithium manganese iron phosphate more insufficient than that of lithium iron phosphate.

[0004] In the related art, in order to solve the shortage of lithium iron manganese phosphate in terms of gram capacity, lithium supplement is usually added. However, simply adding lithium supplement cannot achieve both gram capacity and cycle performance. Summary of the invention

[0005] The embodiments of the present application provide a lithium-ion battery formation method and a lithium-ion battery, which can simultaneously improve the battery's gram capacity and cycle performance, and improve the battery's comprehensive electrochemical performance.

[0006] In a first aspect, an embodiment of the present application provides a formation method of a lithium-ion battery, wherein the lithium-ion battery includes a positive electrode active material, and the positive electrode active material includes lithium iron manganese phosphate and a lithium-rich manganese-based material;

[0007] Among them, the upper limit voltage of lithium-ion batteries during formation charging is greater than 4.45V.

[0008] In some embodiments, the upper limit voltage of the lithium-ion battery during formation charging is 4.55V-4.6V.

[0009] In some embodiments, the particle size D50 of lithium iron manganese phosphate is d1, the particle size D50 of the lithium-rich manganese-based material is d2, and 0.04≤d1 / d2≤0.30.

[0010] In some embodiments, the particle size D50 of lithium manganese iron phosphate satisfies: 0.4 μm≤d1≤1.2 μm;

[0011] And / or, the particle size D50 of the lithium-rich manganese-based material satisfies: 4μm≤d2≤10μm 。

[0012] In some embodiments, the lithium-rich manganese-based material is added to the positive electrode active material in a mass ratio of 1% to 30%.

[0013] In some embodiments, the lithium-rich manganese-based material is added to the positive electrode active material in a mass ratio of 10%-20%.

[0014] In some embodiments, the mass ratio of the lithium-rich manganese-based material added to the positive electrode active material is greater than 20% and less than or equal to 30%.

[0015] In some embodiments, the specific surface area of ​​lithium iron manganese phosphate is S1, the specific surface area of ​​the lithium-rich manganese-based material is S2, and 8≤S1 / S2≤85.

[0016] In some embodiments, the specific surface area of ​​lithium manganese iron phosphate satisfies: 16m 2 / g≤S1≤26m 2 / g;

[0017] And / or, the specific surface area of ​​the lithium-rich manganese-based material meets the following requirements: 0.3m 2 / g≤S2≤2m 2 / g.

[0018] In some embodiments, the lithium-rich manganese-based material has a molecular formula of Li w Ni x Co y Mn z O2, wherein 1.05<w<1.13, 0<x<1, 0<y<1, 0<z<1.

[0019] In a second aspect, an embodiment of the present application provides a lithium-ion battery, which is formed using the lithium-ion battery formation method described above.

[0020] In some embodiments, the charge and discharge voltage range of the lithium-ion battery after formation is 2.5V-4.2V.

[0021] Beneficial effects of the embodiments of the present application:

[0022] In an embodiment of the present application, a formation method of a lithium-ion battery is provided, wherein the positive electrode active material of the lithium-ion battery includes lithium iron manganese phosphate and lithium-rich manganese-based materials. Lithium iron manganese phosphate has a relatively high voltage platform, and the lithium-rich manganese-based material has the characteristics of high gram capacity. By combining the two, it is possible to form complementary advantages in terms of voltage platform and gram capacity, thereby improving the cycle performance of the battery. By setting the mass ratio of the lithium-rich manganese-based material in the positive electrode active material to 1%-30%, the lithium supplement effect of the lithium-rich manganese-based material can be exerted, while the problem of aggravated phase change of the positive electrode active material caused by excessive addition ratio can be reduced. In addition, by setting the upper limit voltage of the formation charge of the lithium-ion battery to greater than 4.45V, the gram capacity of the lithium-rich manganese-based material can be fully released during the formation charge process of the lithium-ion battery, so that the lithium-ion battery can take into account both the improvement of gram capacity and cycle performance in the subsequent application process. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application. In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0024] In a first aspect, an embodiment of the present application provides a formation method of a lithium-ion battery, wherein the lithium-ion battery comprises a positive electrode active material, wherein the positive electrode active material comprises lithium iron manganese phosphate and a lithium-rich manganese-based material, and the mass ratio of the lithium-rich manganese-based material added to the positive electrode active material is 1%-30%. The upper limit voltage of the lithium-ion battery during formation charging is greater than 4.45V.

[0025] The positive electrode active materials of lithium-ion batteries include lithium iron manganese phosphate and lithium-rich manganese-based materials. Lithium iron manganese phosphate has a relatively high voltage platform, and lithium-rich manganese-based materials have the characteristics of high gram capacity. By combining the two, it is possible to form complementary advantages in terms of voltage platform and gram capacity, thereby improving the battery's cycle performance. In addition, by setting the upper limit voltage of the formation charge of the lithium-ion battery to greater than 4.45V, the gram capacity of the lithium-rich manganese-based material can be fully released during the formation charge of the lithium-ion battery, so that the lithium-ion battery can take into account both the improvement of gram capacity and cycle performance in the subsequent application process.

[0026] Among them, formation refers to the process of charging the battery for the first time. During the formation process of the battery, the positive and negative electrode materials in the battery are charged and form an electrochemical reaction, so that the chemical reaction system inside the battery reaches a stable state.

[0027] The upper limit voltage of formation charge refers to the highest voltage value that the battery can reach during the first charging process.

[0028] The charging cut-off voltage of lithium-ion batteries is usually 4.2V, and the discharging cut-off voltage is usually 2.5V. In the related art, when lithium-ion batteries are charged during formation, the upper limit voltage of the formation charge is usually set to 4.2V. For lithium-ion batteries doped with lithium-rich manganese-based materials, when the upper limit voltage of the formation charge is set to 4.2V, the cycle performance of the lithium-ion battery can only be improved to a certain extent, and the lithium replenishment effect of the lithium-rich manganese-based materials cannot be fully utilized. The effect of improving the gram capacity of the lithium-ion battery is poor, resulting in the lithium-ion battery being unable to take into account both high gram capacity and high cycle performance, affecting the comprehensive electrochemical performance of the lithium-ion battery.

[0029] Specifically, by setting the upper limit voltage of the formation charge to be greater than 4.45V, more lithium ions can be embedded in the lithium-rich manganese-based material during the formation process, thereby increasing the amount of lithium embedded in the lithium-rich manganese-based material, thereby increasing the capacity and energy density of the lithium-ion battery. A higher upper limit voltage of the formation charge can also stimulate more electrochemically active sites, so that the lithium-ion battery exhibits a higher reaction rate and better cycle stability during the charge and discharge process. In addition, since the positive electrode active material of the lithium-ion battery in the embodiment of the present application includes both lithium iron manganese phosphate and lithium-rich manganese-based material, and lithium iron manganese phosphate has the advantage of a high voltage platform, the safety of the formation charge is guaranteed when the upper limit voltage of the formation charge is increased.

[0030] In some embodiments, the upper limit voltage of the lithium-ion battery during formation charging is 4.55V-4.6V.

[0031] By setting the upper limit voltage during formation charging to 4.55V-4.6V, the amount of lithium embedded in the lithium-rich manganese-based material can be increased during the formation charging process, so that the gram capacity of the lithium-rich manganese-based material can be fully released, thereby increasing the capacity and energy density of the lithium-ion battery. It can also reduce the problems of increased side reactions, voltage attenuation, and irreversible phase changes of lithium-rich manganese-based materials caused by the excessively high upper limit voltage of the formation charging. In addition, it can also improve the safety of the formation charging process and reduce the investment cost of safety measures such as thermal management and overcharge protection.

[0032] Exemplarily, the upper limit voltage during formation charging may be 4.55V, 4.56V, 4.57V, 4.58V, 4.59V or 4.6V.

[0033] In some embodiments, the particle size D50 of lithium iron manganese phosphate is d1, the particle size D50 of the lithium-rich manganese-based material is d2, and 0.04≤d1 / d2≤0.30.

[0034] That is, in the lithium-ion battery provided in the embodiment of the present application, the particle size of lithium iron manganese phosphate is relatively small, while the particle size of the lithium-rich manganese-based material is relatively large. When the small-particle lithium iron manganese phosphate and the large-particle lithium-rich manganese-based material are compounded, a better stacking effect can be formed, so that the lithium iron manganese phosphate and the lithium-rich manganese-based material can establish a more effective conductive network, thereby playing the role of improving the gram capacity and cycle performance, and maintaining good rate performance.

[0035] Specifically, when the larger lithium-rich manganese-based material is compounded with the smaller lithium iron manganese phosphate, the larger lithium-rich manganese-based material can be stacked, and there will be gaps between adjacent lithium-rich manganese-based material particles, while the smaller lithium iron manganese phosphate particles will fill in these gaps, allowing the lithium iron manganese phosphate and the lithium-rich manganese-based material to be evenly distributed and in contact with each other, reducing or avoiding problems such as stratification of lithium iron manganese phosphate and lithium-rich manganese-based materials, allowing the two to fully interact to better exert their effects.

[0036] Illustratively, d1 / d2 may be 0.04, 0.05, 0.08, 0.1, 0.15, 0.2, 0.25 or 0.3.

[0037] In some embodiments, the particle size D50 of the lithium manganese iron phosphate satisfies: 0.4 μm≤d1≤1.2 μm.

[0038] The particle size D50 of lithium manganese iron phosphate is small, which is beneficial to improving the discharge performance and cycle life of the battery when used in batteries. This is because materials with small particle sizes have larger specific surface areas and shorter ion diffusion paths, which are beneficial to the insertion and extraction reactions of lithium ions, thereby improving the charge and discharge rate performance of the battery and reducing the internal resistance of the battery. However, if the particle size D50 of lithium manganese iron phosphate is too small, it is easy to form agglomerates, increasing the difficulty of preparing battery materials, and too small particle sizes may also cause the mechanical strength of the material to decrease, thereby reducing the cycle life and stability of the material.

[0039] Illustratively, the particle size D50 of lithium manganese iron phosphate is 0.4 μm, 0.6 μm, 0.8 μm, 1.0 μm or 1.2 μm.

[0040] In some embodiments, the particle size D50 of the lithium-rich manganese-based material satisfies: 4 μm ≤ d2 ≤ 10 μm 。

[0041] The particle size D50 of the lithium-rich manganese-based material is larger, which can form a better stacking effect with the small-particle lithium iron manganese phosphate, thereby establishing a more effective conductive network, thereby better playing the role of improving the gram capacity and cycle performance. The small-particle lithium iron manganese phosphate surrounds the large-particle lithium-rich ferric acid, so that the lithium-rich manganese-based material and the lithium iron manganese phosphate material interact better.

[0042] Exemplarily, the particle size D50 of the lithium-rich lithium ferrite is 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

[0043] It should be noted that D50 refers to the particle size corresponding to when the cumulative particle size distribution percentage of a sample reaches 50%, also known as the median particle size or median particle size.

[0044] In some embodiments, the lithium-rich manganese-based material is added to the positive electrode active material in a mass ratio of 1% to 30%.

[0045] By setting the mass ratio of lithium-rich manganese-based materials in the positive electrode active materials to 1%-30%, the lithium-supplementing effect of the lithium-rich manganese-based materials can be brought into play, while reducing the problem of aggravated phase change of the positive electrode active materials caused by excessive addition ratio, and reducing excessive oxygen release caused by excessive proportion of lithium-rich manganese-based materials, thereby causing lithium ion defects.

[0046] Illustratively, the mass ratio of the lithium-rich manganese-based material added to the positive electrode active material is 1%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 25% or 30%.

[0047] In some embodiments, the mass ratio of the lithium-rich manganese-based material added to the positive electrode active material is 10%-20%. When the addition ratio of the lithium-rich manganese-based material is within this range, it can have a more obvious effect on increasing the gram capacity and improve the cycle performance, thereby compensating for the defects of lithium iron manganese phosphate relative to lithium iron phosphate to a certain extent and improving its comprehensive performance.

[0048] Illustratively, the mass ratio of the lithium-rich manganese-based material added to the positive electrode active material is 10%, 12%, 15%, 18% or 20%.

[0049] In some embodiments, the mass ratio of the lithium-rich manganese-based material added to the positive electrode active material is greater than 20% and less than or equal to 30%. Relative to the mass ratio of the lithium-rich manganese-based material added to the positive electrode active material being 10%-20%, when the addition ratio of the lithium-rich manganese-based material is greater than 20% and less than or equal to 30%, the cycle performance can be further improved, but the gram capacity will decrease to a certain extent.

[0050] Exemplarily, the mass ratio of the lithium-rich manganese-based material added to the positive electrode active material is 21%, 23%, 25%, 28% or 30%.

[0051] In some embodiments, the specific surface area of ​​lithium iron manganese phosphate is S1, the specific surface area of ​​the lithium-rich manganese-based material is S2, and 8≤S1 / S2≤85.

[0052] The particle size of lithium manganese iron phosphate is small and its specific surface area is large, while the particle size of lithium-rich manganese-based materials is large and its specific surface area is small. By setting the specific surface area of ​​the two to meet the condition of 8≤S1 / S2≤85, it is beneficial for the two to form a better stacking effect, thereby establishing a more effective conductive network and exerting a better effect.

[0053] Illustratively, S1 / S2 may be 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, or 85.

[0054] It is understandable that the specific surface area of ​​the material is inversely proportional to the particle size, that is, the larger the particle size, the smaller the specific surface area, and the smaller the particle size, the larger the specific surface area. When the specific surface area is larger, more reaction sites can be provided, and when the specific surface area is smaller, it has relatively more stable properties. As the main material of the positive electrode active material, lithium iron manganese phosphate has a small particle size and a large specific surface area, which can provide more reaction sites and is conducive to improving the energy density. The proportion of lithium-rich manganese-based materials added is relatively small, and it is mainly to provide lithium supplementation and other functions. Its particle size is larger, the specific surface area is smaller, and it has a certain stability and can play a better role.

[0055] In some embodiments, the specific surface area of ​​lithium manganese iron phosphate satisfies: 16m 2 / g≤S1≤26m 2 / g. If the specific surface area of ​​lithium manganese iron phosphate is too small, it is easy to affect the gram capacity, making the gram capacity less than expected. When its specific surface area is large, problems such as agglomeration are likely to occur during the preparation of positive electrode slurry using positive electrode active materials.

[0056] For example, the specific surface area of ​​lithium manganese iron phosphate can be 16m 2 / g, 18m 2 / g, 20m 2 / g, 22m 2 / g, 24m 2 / g or 26m 2 / g.

[0057] In some embodiments, the specific surface area of ​​the lithium-rich manganese-based material satisfies: 0.3 m 2 / g≤S2≤2m 2 / g. If the specific surface area of ​​lithium-rich manganese-based materials is too small, it will also affect the gram capacity, making the gram capacity less than expected. If the specific surface area is too large, it will easily lead to a large amount of gas production in the battery, which is difficult to completely eliminate during the production process, thus affecting the performance of the battery.

[0058] For example, the specific surface area of ​​the lithium-rich manganese-based material can be 0.3 m 2 / g, 0.5m 2 / g, 0.7m2 / g, 1m 2 / g, 1.2m 2 / g, 1.5m 2 / g, 1.8m 2 / g or 2.0m 2 / g.

[0059] In some embodiments, the lithium-rich manganese-based material has a molecular formula of Li w Ni x Co y Mn z O2, wherein 1.05<w<1.13, 0<x<1, 0<y<1, 0<z<1.

[0060] By making the lithium-rich manganese-based material satisfy the above molecular formula, the proportion of lithium (Li) in the lithium-rich manganese-based material can be controlled within a reasonable range, thereby ensuring the lithium replenishment effect of the lithium-rich manganese-based material, improving the gram capacity and cycle performance of the lithium-ion battery, and reducing the phase change problem caused by the excessive lithium content in the lithium-rich manganese-based material, as well as the problem of excessive release of oxygen from the lattice, reducing side reactions, and ensuring the stability of the lithium-ion battery.

[0061] In a second aspect, an embodiment of the present application provides a lithium-ion battery, which is formed using the lithium-ion battery formation method described above.

[0062] The beneficial effects of the lithium-ion battery provided in the embodiments of the present application are basically consistent with the formation method of the lithium-ion battery, and will not be described in detail here.

[0063] In some embodiments, the charge and discharge voltage range of the lithium-ion battery after formation is 2.5V-4.2V.

[0064] That is, during the application of lithium-ion batteries, the minimum discharge voltage is 2.5V and the maximum charge voltage is 4.2V. By setting the charge and discharge voltage range of lithium-ion batteries within this range, the safety and effectiveness of lithium-ion batteries during use can be guaranteed. Since the upper limit voltage of lithium-ion batteries during the formation and charging process is greater than 4.45V, the gram capacity of lithium-rich manganese-based materials is fully released during the formation and charging process, so that when lithium-ion batteries are used in the charge and discharge voltage range of 2.5V-4.2V, they can take into account both gram capacity and cycle performance and maintain good comprehensive electrochemical performance.

[0065] The following examples are further described in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods in the following examples that do not specify specific conditions are usually based on the conditions recommended by the manufacturer.

[0066] It should be noted that, except for the differences already explained, the other conditions in the embodiments of the present application and the comparative examples remain the same.

[0067] The manufacturing process of the lithium-ion battery in the embodiments and comparative examples of the present application includes: compounding lithium iron manganese phosphate and lithium-rich lithium ferrate in proportion to form a positive electrode active material; mixing the positive electrode active material with a conductive agent, a binder, a dispersant and a solvent to prepare a positive electrode slurry; the positive electrode active material accounts for 97.5%, the conductive agent is carbon black, accounting for 0.7%, the binder is polyvinylidene fluoride, accounting for 1.5%, and the dispersant is a polyester substance, accounting for 0.3%. Artificial graphite is used as the negative electrode active material, mixed with a conductive agent and a binder to prepare a negative electrode slurry; the negative electrode active material accounts for 96.9%, the conductive agent is carbon black, accounting for 0.5%, and the binder is sodium carboxycellulose and styrene-butadiene rubber, among which sodium carboxycellulose accounts for 1.1% and styrene-butadiene rubber accounts for 1.5%. The positive electrode slurry and the negative electrode slurry are respectively obtained through coating and sheet making processes to obtain positive electrode sheets and negative electrode sheets; the positive electrode sheets, negative electrode sheets and separators, electrolytes, cover plates and aluminum shells are assembled together into square aluminum shell batteries, and then the finished batteries are obtained after chemical composition and capacity division.

[0068] Example 1

[0069] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium iron manganese phosphate and lithium-rich manganese-based materials, and the mass ratio of the lithium-rich manganese-based materials in the positive electrode active material is 0.5%. 0.5 Mn 0.5 PO4, with a D50 of 0.8 μm and a specific surface area of ​​21 m 2 / g; the molecular formula of lithium-rich manganese-based materials is Li 1.07 Ni 0.36 Co 0.06 Mn 0.51 O2, its D50 is 7μm and its specific surface area is 1m 2 / g.

[0070] The lithium-ion battery is charged at a voltage of 4.6 V and then divided into different capacities to obtain a finished lithium battery.

[0071] Example 2

[0072] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium iron manganese phosphate and lithium-rich manganese-based materials, and the mass ratio of the lithium-rich manganese-based materials in the positive electrode active material is 5%. Among them, the molecular formula of lithium iron manganese phosphate is LiMn 0.5 Mn 0.5 PO4, with a D50 of 0.8 μm and a specific surface area of ​​21 m 2 / g; the molecular formula of lithium-rich manganese-based materials is Li 1.07 Ni0.36 Co 0.06 Mn 0.51 O2, its D50 is 7μm and its specific surface area is 1m 2 / g.

[0073] The lithium-ion battery is charged at a voltage of 4.6 V and then divided into different capacities to obtain a finished lithium battery.

[0074] Example 3

[0075] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium iron manganese phosphate and lithium-rich manganese-based materials, and the mass ratio of the lithium-rich manganese-based materials in the positive electrode active material is 15%. Among them, the molecular formula of lithium iron manganese phosphate is LiMn 0.5 Mn 0.5 PO4, with a D50 of 0.8 μm and a specific surface area of ​​21 m 2 / g; the molecular formula of lithium-rich manganese-based materials is Li 1.07 Ni 0.36 Co 0.06 Mn 0.51 O2, its D50 is 7μm and its specific surface area is 1m 2 / g.

[0076] The lithium-ion battery is charged at a voltage of 4.6 V and then divided into different capacities to obtain a finished lithium battery.

[0077] Example 4

[0078] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium iron manganese phosphate and lithium-rich manganese-based materials, and the mass ratio of the lithium-rich manganese-based materials in the positive electrode active material is 25%. Among them, the molecular formula of lithium iron manganese phosphate is LiMn 0.5 Mn 0.5 PO4, with a D50 of 0.8 μm and a specific surface area of ​​21 m 2 / g; the molecular formula of lithium-rich manganese-based materials is Li 1.07 Ni 0.36 Co 0.06 Mn 0.51 O2, its D50 is 7μm and its specific surface area is 1m 2 / g.

[0079] The lithium-ion battery is charged at a voltage of 4.6 V and then divided into different capacities to obtain a finished lithium battery.

[0080] Example 5

[0081] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium iron manganese phosphate and lithium-rich manganese-based materials, and the mass ratio of the lithium-rich manganese-based materials in the positive electrode active material is 35%. Among them, the molecular formula of lithium iron manganese phosphate is LiMn 0.5 Mn 0.5 PO4, with a D50 of 0.8 μm and a specific surface area of ​​21 m 2 / g; the molecular formula of lithium-rich manganese-based materials is Li 1.07 Ni 0.36 Co 0.06 Mn 0.51 O2, its D50 is 7μm and its specific surface area is 1m 2 / g.

[0082] The lithium-ion battery is charged at a voltage of 4.6 V and then divided into different capacities to obtain a finished lithium battery.

[0083] Example 6

[0084] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium iron manganese phosphate and lithium-rich manganese-based materials, and the mass ratio of the lithium-rich manganese-based materials in the positive electrode active material is 15%. Among them, the molecular formula of lithium iron manganese phosphate is LiMn 0.5 Mn 0.5 PO4, with a D50 of 0.8 μm and a specific surface area of ​​21 m 2 / g; the molecular formula of lithium-rich manganese-based materials is Li 1.07 Ni 0.36 Co 0.06 Mn 0.51 O2, its D50 is 7μm and its specific surface area is 1m 2 / g.

[0085] The lithium-ion battery is charged at a voltage of 4.7 V and then divided into different capacities to obtain a finished lithium battery.

[0086] Example 7

[0087] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium iron manganese phosphate and lithium-rich manganese-based materials, and the mass ratio of the lithium-rich manganese-based materials in the positive electrode active material is 15%. Among them, the molecular formula of lithium iron manganese phosphate is LiMn 0.5 Mn 0.5 PO4, with a D50 of 0.8 μm and a specific surface area of ​​21 m 2 / g; the molecular formula of lithium-rich manganese-based materials is Li 1.02 Ni 0.43 Co 0.07 Mn 0.47 O2, its D50 is 7μm and its specific surface area is 1m 2 / g.

[0088] The lithium-ion battery is charged at a voltage of 4.6 V and then divided into different capacities to obtain a finished lithium battery.

[0089] Example 8

[0090] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium iron manganese phosphate and lithium-rich manganese-based materials, and the mass ratio of the lithium-rich manganese-based materials in the positive electrode active material is 15%. Among them, the molecular formula of lithium iron manganese phosphate is LiMn 0.5 Mn 0.5 PO4, with a D50 of 0.8 μm and a specific surface area of ​​21 m 2 / g; the molecular formula of lithium-rich manganese-based materials is Li 1.16 Ni 0.23 Co 0.04 Mn 0.56 O2, its D50 is 7μm and its specific surface area is 1m 2 / g.

[0091] The lithium-ion battery is charged at a voltage of 4.6 V and then divided into different capacities to obtain a finished lithium battery.

[0092] Example 9

[0093] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium iron manganese phosphate and lithium-rich manganese-based materials, and the mass ratio of the lithium-rich manganese-based materials in the positive electrode active material is 15%. Among them, the molecular formula of lithium iron manganese phosphate is LiMn 0.5 Mn 0.5 PO4, with a D50 of 0.3 μm and a specific surface area of ​​23 m 2 / g; the molecular formula of lithium-rich manganese-based materials is Li 1.07 Ni 0.36 Co 0.06 Mn 0.51 O2, its D50 is 12μm, and its specific surface area is 0.8m 2 / g.

[0094] The lithium-ion battery is charged at a voltage of 4.6 V and then divided into different capacities to obtain a finished lithium battery.

[0095] Example 10

[0096] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium iron manganese phosphate and lithium-rich manganese-based materials, and the mass ratio of the lithium-rich manganese-based materials in the positive electrode active material is 15%. Among them, the molecular formula of lithium iron manganese phosphate is LiMn 0.5 Mn 0.5 PO4, with a D50 of 1 μm and a specific surface area of ​​14 m 2 / g; the molecular formula of lithium-rich manganese-based materials is Li 1.07 Ni 0.36 Co 0.06 Mn 0.51 O2, its D50 is 8.5μm, and its specific surface area is 0.2m 2 / g.

[0097] The lithium-ion battery is charged at a voltage of 4.6 V and then divided into different capacities to obtain a finished lithium battery.

[0098] Comparative Example 1

[0099] In this comparative example, the positive electrode active material of the lithium-ion battery is composed of lithium iron manganese phosphate and lithium-rich manganese-based materials, and the mass ratio of the lithium-rich manganese-based materials in the positive electrode active material is 15%. Among them, the molecular formula of lithium iron manganese phosphate is LiMn 0.5 Mn 0.5 PO4, with a D50 of 0.8 μm and a specific surface area of ​​21 m 2 / g; the molecular formula of lithium-rich manganese-based materials is Li 1.07 Ni 0.36 Co 0.06 Mn 0.51 O2, its D50 is 7μm and its specific surface area is 1m 2 / g.

[0100] The lithium-ion battery is charged at a voltage of 4.2 V and then divided into different capacities to obtain a finished lithium battery.

[0101] Comparative Example 2

[0102] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium iron manganese phosphate and lithium-rich manganese-based materials, and the mass ratio of the lithium-rich manganese-based materials in the positive electrode active material is 15%. Among them, the molecular formula of lithium iron manganese phosphate is LiMn 0.5 Mn 0.5 PO4, with a D50 of 0.8 μm and a specific surface area of ​​21 m 2 / g; the molecular formula of lithium-rich manganese-based materials is Li 1.07 Ni 0.36 Co 0.06 Mn 0.51 O2, its D50 is 7μm and its specific surface area is 1m 2 / g.

[0103] The lithium-ion battery is charged at a voltage of 4.4 V and then divided into different capacities to obtain a finished lithium battery.

[0104] Comparative Example 3

[0105] In this comparative example, the positive electrode active material of the lithium-ion battery is lithium iron manganese phosphate. The molecular formula of lithium iron manganese phosphate is LiMn 0.5 Mn 0.5 PO4, with a D50 of 0.8 μm and a specific surface area of ​​21 m 2 / g.

[0106] The lithium-ion battery is charged at a voltage of 4.2 V and then divided into different capacities to obtain a finished lithium battery.

[0107] Comparative Example 4

[0108] In this comparative example, the positive electrode active material of the lithium-ion battery is composed of lithium iron manganese phosphate and lithium-rich manganese-based materials, and the mass ratio of the lithium-rich manganese-based materials in the positive electrode active material is 0.5%. Among them, the molecular formula of lithium iron manganese phosphate is LiMn 0.5 Mn 0.5 PO4, with a D50 of 0.8 μm and a specific surface area of ​​21 m 2 / g; the molecular formula of lithium-rich manganese-based materials is Li 1.07 Ni 0.36 Co 0.06 Mn 0.51 O2, its D50 is 7μm and its specific surface area is 1m 2 / g.

[0109] The lithium-ion battery is charged at a voltage of 4.2 V and then divided into different capacities to obtain a finished lithium battery.

[0110] Comparative Example 5

[0111] In this comparative example, the positive electrode active material of the lithium-ion battery is composed of lithium iron manganese phosphate and lithium-rich manganese-based materials, and the mass ratio of the lithium-rich manganese-based materials in the positive electrode active material is 35%. Among them, the molecular formula of lithium iron manganese phosphate is LiMn 0.5 Mn 0.5 PO4, with a D50 of 0.8 μm and a specific surface area of ​​21 m 2 / g; the molecular formula of lithium-rich manganese-based materials is Li 1.07 Ni 0.36 Co 0.06 Mn 0.51 O2, its D50 is 7μm and its specific surface area is 1m 2 / g.

[0112] The lithium-ion battery is charged at a voltage of 4.2 V and then divided into different capacities to obtain a finished lithium battery.

[0113] Comparative Example 6

[0114] In this comparative example, the positive electrode active material of the lithium-ion battery is composed of lithium iron manganese phosphate and lithium-rich manganese-based materials, and the mass ratio of the lithium-rich manganese-based materials in the positive electrode active material is 15%. Among them, the molecular formula of lithium iron manganese phosphate is LiMn 0.5 Mn 0.5 PO4, with a D50 of 0.8 μm and a specific surface area of ​​21 m 2 / g; the molecular formula of lithium-rich manganese-based materials is Li 1.02 Ni 0.43 Co 0.07 Mn 0.47 O2, its D50 is 7μm and its specific surface area is 1m 2 / g.

[0115] The lithium-ion battery is charged at a voltage of 4.2 V and then divided into different capacities to obtain a finished lithium battery.

[0116] Comparative Example 7

[0117] In this comparative example, the positive electrode active material of the lithium-ion battery is composed of lithium iron manganese phosphate and lithium-rich manganese-based materials, and the mass ratio of the lithium-rich manganese-based materials in the positive electrode active material is 15%. Among them, the molecular formula of lithium iron manganese phosphate is LiMn 0.5 Mn 0.5 PO4, with a D50 of 0.8 μm and a specific surface area of ​​21 m 2 / g; the molecular formula of lithium-rich manganese-based materials is Li 1.16 Ni 0.23 Co 0.04 Mn 0.56 O2, its D50 is 7μm and its specific surface area is 1m 2 / g.

[0118] The lithium-ion battery is charged at a voltage of 4.2 V and then divided into different capacities to obtain a finished lithium battery.

[0119] Comparative Example 8

[0120] In this comparative example, the positive electrode active material of the lithium-ion battery is composed of lithium iron manganese phosphate and lithium-rich manganese-based materials, and the mass ratio of the lithium-rich manganese-based materials in the positive electrode active material is 15%. Among them, the molecular formula of lithium iron manganese phosphate is LiMn 0.5 Mn 0.5 PO4, with a D50 of 0.3 μm and a specific surface area of ​​23 m 2 / g; the molecular formula of lithium-rich manganese-based materials is Li 1.07 Ni 0.36 Co 0.06 Mn 0.51 O2, its D50 is 12μm, and its specific surface area is 0.8m 2 / g.

[0121] The lithium-ion battery is charged at a voltage of 4.2 V and then divided into different capacities to obtain a finished lithium battery.

[0122] Comparative Example 9

[0123] In this comparative example, the positive electrode active material of the lithium-ion battery is composed of lithium iron manganese phosphate and lithium-rich manganese-based materials, and the mass ratio of the lithium-rich manganese-based materials in the positive electrode active material is 15%. Among them, the molecular formula of lithium iron manganese phosphate is LiMn 0.5 Mn 0.5 PO4, with a D50 of 1 μm and a specific surface area of ​​14 m 2 / g; the molecular formula of lithium-rich manganese-based materials is Li 1.07 Ni 0.36 Co 0.06 Mn 0.51 O2, its D50 is 8.5μm, and its specific surface area is 0.2m 2 / g.

[0124] The lithium-ion battery is charged at a voltage of 4.2 V and then divided into different capacities to obtain a finished lithium battery.

[0125] The batteries in Examples 1-11 and Comparative Examples 1-9 were subjected to gram capacity tests and cycle tests, respectively. The gram capacity test method includes: placing the battery in a 25±2°C constant temperature box, charging to 4.2V at 0.33C constant current and constant voltage, with a cut-off current of 0.05C; leaving for 30 minutes; discharging to 2.5V at 0.33C constant current; the capacity of the discharge process / the weight of the active substance is the gram capacity. The cycle test method includes: placing the battery in a 25±2°C constant temperature box, charging to 4.2V at 1C constant current and constant voltage, with a cut-off current of 0.05C; leaving for 30 minutes; discharging to 2.5V at 1C constant current; leaving for 30 minutes; repeating the above steps until the discharge capacity / initial discharge capacity = 80%, which is recorded as the number of cycles. The results are shown in Table 1:

[0126] Table 1 Performance test results of different embodiments and comparative examples

[0127]

[0128]

[0129] By comparing Example 3 with Comparative Example 1, it can be seen that for a lithium-ion battery including lithium iron manganese phosphate and a lithium-rich manganese-based material in the positive electrode active material, setting the formation charge voltage to 4.6V can increase the gram capacity of the lithium-ion battery while having good cycle performance.

[0130] Comparing Example 3, Example 6 and Comparative Example 2, it can be seen that Example 3, Example 6 and Comparative Example 2 respectively adopt the formation charging voltage of 4.6V, 4.7V and 4.4V, and the other price adjustments are all consistent. Among them, the gram capacity and cycle performance of the lithium ion battery in Example 3 (the formation charging voltage is 4.6V) are maintained at a higher level, the gram capacity and cycle performance of the lithium ion battery in Example 6 (the formation charging voltage is 4.7V) are reduced compared with Example 3, and the cycle performance of the lithium ion battery in Comparative Example 2 (the formation charging voltage is 4.4V) is basically the same as that in Example 3, but the gram capacity decreases significantly relative to Example 3 and Example 6. It can be seen that controlling the formation charging voltage at 4.6V and 4.7V can significantly improve the gram capacity of the lithium ion battery, taking into account good gram capacity and cycle performance.

[0131] Comparing Comparative Example 1 with Comparative Example 3, it can be seen that since no lithium-rich manganese-based material is added to the lithium-ion battery in Comparative Example 3, the number of cycles of the lithium-ion battery in Comparative Example 3 decreases. This indicates that when the formation voltage is 4.2V, the addition of lithium-rich manganese-based materials only affects the cycle performance and cannot play a role in increasing the gram capacity. The cycle performance of the lithium-ion battery in Comparative Example 1 is improved by 18% compared with Comparative Example 3.

[0132] By comparing Examples 1-5, it can be seen that when the mass ratio of the lithium-rich manganese-based material in the positive electrode active material is 15% (Example 3), the gram capacity and cycle number of the lithium-ion battery are maintained at a high level. When the mass ratio of the lithium-rich manganese-based material in the positive electrode active material increases or decreases, at least one of the gram capacity and the cycle number will decrease. In particular, when the mass ratio of the lithium-rich manganese-based material in the positive electrode active material is 0.5% (Example 1) and 35% (Example 5), the gram capacity and cycle number of the lithium-ion battery are significantly reduced relative to Example 3.

[0133] By comparing Example 3 with Examples 7-10, it can be seen that the lithium content in the lithium-rich manganese-based material (Examples 7 and 8), as well as the particle size and specific surface area of ​​lithium iron manganese phosphate and the lithium-rich manganese-based material (Examples 9 and 10) will also have a certain impact on the gram capacity and cycle performance of the lithium-ion battery.

[0134] By comparing Example 1 with Comparative Example 4, it can be seen that by changing the formation charging voltage, the gram capacity and cycle performance of the lithium-ion battery can be improved.

[0135] By comparing Example 5 with Comparative Example 5, it can be seen that by changing the formation charging voltage, the gram capacity and cycle performance of the lithium-ion battery can be improved.

[0136] By comparing Example 7 with Comparative Example 6, it can be seen that by changing the formation charging voltage, the gram capacity and cycle performance of the lithium-ion battery can be improved.

[0137] By comparing Example 8 with Comparative Example 7, it can be seen that by changing the formation charging voltage, the gram capacity and cycle performance of the lithium-ion battery can be improved.

[0138] By comparing Example 9 with Comparative Example 8, it can be seen that by changing the formation charging voltage, the gram capacity and cycle performance of the lithium-ion battery can be improved.

[0139] By comparing Example 10 with Comparative Example 9, it can be seen that by changing the formation charging voltage, the gram capacity and cycle performance of the lithium-ion battery can be improved.

[0140] In summary, the embodiments of the present application enable the finished lithium-ion battery after formation charging to have both good gram capacity and cycle performance by using the positive electrode active material of the lithium-ion battery including lithium iron manganese phosphate and lithium-rich manganese-based material, and setting the upper limit voltage of the formation charge to >4.45V during the formation charge.

[0141] The embodiments of the present application are introduced in detail above. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. At the same time, for technical personnel in this field, according to the idea of ​​the present application, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A formation method for a lithium ion battery, characterized in that: The lithium-ion battery comprises a positive electrode active material, wherein the positive electrode active material comprises lithium iron manganese phosphate and a lithium-rich manganese-based material; Wherein, the upper limit voltage of the lithium-ion battery during formation charging is greater than 4.45V.

2. The formation method of a lithium ion battery according to claim 1, characterized in that: The upper limit voltage of the lithium ion battery during formation charging is 4.55V-4.6V.

3. The formation method of a lithium ion battery according to claim 1, characterized in that: The particle size D50 of the lithium manganese iron phosphate is d1, the particle size D50 of the lithium-rich manganese-based material is d2, and 0.04≤d1 / d2≤0.

30.

4. The formation method of a lithium ion battery according to claim 3, characterized in that: The particle size D50 of the lithium manganese iron phosphate satisfies: 0.4 μm≤d1≤1.2 μm; And / or, the particle size D50 of the lithium-rich manganese-based material satisfies: 4 μm≤d2≤10 μm 。 5. The lithium ion battery formation method according to claim 1, characterized in that: The lithium-rich manganese-based material is added to the positive electrode active material in a mass ratio of 1% to 30%.

6. The lithium ion battery formation method according to claim 5, characterized in that: The lithium-rich manganese-based material is added to the positive electrode active material in a mass ratio of 10% to 20%.

7. The lithium ion battery formation method according to claim 5, characterized in that: The lithium-rich manganese-based material is added to the positive electrode active material in a mass ratio greater than 20% and less than or equal to 30%.

8. The lithium ion battery formation method according to claim 1, characterized in that: The specific surface area of ​​the lithium iron manganese phosphate is S1, and the specific surface area of ​​the lithium-rich manganese-based material is S2, 8≤S1 / S2≤85.

9. The lithium ion battery formation method according to claim 8, characterized in that: The specific surface area of ​​the lithium manganese iron phosphate meets the following requirements: 16m 2 / g≤S1≤26m 2 / g; And / or, the specific surface area of ​​the lithium-rich manganese-based material satisfies: 0.3m 2 / g≤S2≤2m 2 / g.

10. The lithium ion battery formation method according to any one of claims 1 to 9, characterized in that: The molecular formula of the lithium-rich manganese-based material is Li w Ni x Co y Mn z O2, wherein 1.05<w<1.13, 0<x<1, 0<y<1, 0<z<1.

11. A lithium ion battery, characterized in that: The formation is carried out by using the lithium ion battery formation method according to any one of claims 1 to 10.

12. The lithium ion battery according to claim 11, characterized in that The charging and discharging voltage range of the lithium-ion battery after formation is 2.5V-4.2V.

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