Formation method of lithium ion battery and lithium ion battery

Abstract

The application provides a formation method of a lithium ion battery and the lithium ion battery, and belongs to the technical field of batteries. The formation method of the lithium ion battery comprises: 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 application, the upper limit voltage of the formation charging of the lithium ion battery is set to be greater than 4.45 V, so that the gram capacity of the lithium-rich manganese-based material can be fully released during the formation charging of the lithium ion battery, and the gram capacity and the cycle performance of the lithium ion battery can be improved in subsequent application.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a method for forming a lithium-ion battery and a lithium-ion battery. Background Technology

[0002] Lithium manganese iron phosphate (LMFP) is a next-generation cathode material for lithium-ion batteries and an upgrade from lithium iron phosphate (LFP). Due to the presence of the transition metal manganese (Mn) in LMFP, its voltage platform is higher than that of lithium iron phosphate, and its energy density is also superior.

[0003] However, due to the presence of the transition metal manganese in lithium manganese iron phosphate materials, the lithium-ion diffusion rate and electronic conductivity of lithium manganese iron phosphate are also lower than those of lithium iron phosphate materials (the lithium-ion diffusion rate of lithium manganese iron phosphate is 10-15 cm⁻¹). 2 / S, the lithium-ion diffusion rate of lithium iron phosphate is 10⁻¹⁴ cm⁻¹. 2 The electronic conductivity of lithium manganese iron phosphate (LMP) is 10⁻¹³ S / cm, while that of lithium iron phosphate (LFP) is 10⁻⁹ S / cm, resulting in a lower specific capacity for LMP compared to LFP. Furthermore, lithium hexafluorophosphate in the electrolyte reacts with trace amounts of moisture in the battery, generating hydrofluoric acid that damages the structure of LMP. Combined with the Jahn-Teller effect of manganese ions, manganese dissolution occurs during cycling, reducing the stability of the cathode material. The dissolved manganese ions are also reduced and precipitated at the anode, damaging the SEI film, further contributing to the significantly inferior cycle performance of LMP compared to LFP.

[0004] In related technologies, to address the insufficient specific capacity of lithium manganese iron phosphate, lithium replenishment agents are typically added. However, simply adding lithium replenishment agents cannot achieve a balance between specific capacity and cycle performance. Summary of the Invention

[0005] The embodiments of this application provide a lithium-ion battery formation method and a lithium-ion battery, which can simultaneously improve the specific capacity and cycle performance of the battery, and enhance the overall electrochemical performance of the battery.

[0006] In a first aspect, embodiments of this application provide a method for forming a lithium-ion battery, the lithium-ion battery including a positive electrode active material, the positive electrode active material including lithium manganese iron phosphate and lithium-rich manganese-based materials;

[0007] Among them, the upper limit voltage of lithium-ion batteries during formation charging is >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 manganese iron phosphate is d1, and the particle size D50 of lithium-rich manganese-based material is d2, where 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 lithium-rich manganese-based materials satisfies: 4μm≤d2≤10μm 。

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

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

[0014] In some embodiments, the mass ratio of lithium-rich manganese-based materials 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 manganese iron phosphate is S1, the specific surface area of ​​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: 16 m² / g. 2 / g≤S1≤26m 2 / g;

[0017] And / or, the specific surface area of ​​lithium-rich manganese-based materials satisfies: 0.3 m² / s². 2 / g≤S2≤2m 2 / g.

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

[0019] Secondly, embodiments of this application provide a lithium-ion battery, which is formed using the lithium-ion battery formation method described above.

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

[0021] The beneficial effects of the embodiments of this application are as follows:

[0022] In embodiments of this application, a method for forming a lithium-ion battery is provided, wherein the positive electrode active material of the lithium-ion battery includes lithium manganese iron phosphate and lithium-rich manganese-based materials. Lithium manganese iron phosphate has a high voltage plateau, while lithium-rich manganese-based materials have high specific capacity. By combining the two, complementary advantages in voltage plateau and specific capacity can be achieved, thereby improving the cycle performance of the battery. By setting the mass ratio of lithium-rich manganese-based materials in the positive electrode active material to 1%-30%, the lithium replenishment effect of lithium-rich manganese-based materials can be utilized while reducing the problem of accelerated phase transition of the positive electrode active material caused by excessive addition. Furthermore, by setting the upper limit voltage for the formation and charging of the lithium-ion battery to greater than 4.45V, the specific capacity of the lithium-rich manganese-based materials can be fully released during the formation and charging process, thereby enabling the lithium-ion battery to simultaneously improve specific capacity and cycle performance in subsequent applications. Detailed Implementation

[0023] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Furthermore, it should be understood that the specific implementation methods described herein are only for illustration and explanation of this application and are not intended to limit this application.

[0024] In a first aspect, embodiments of this application provide a method for the formation of a lithium-ion battery. The lithium-ion battery includes a positive electrode active material, which includes lithium manganese iron phosphate and lithium-rich manganese-based materials, wherein 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 >4.45V.

[0025] The positive electrode active materials for lithium-ion batteries include lithium manganese iron phosphate (LFP) and lithium-rich manganese-based materials. LFP has a high voltage plateau, while lithium-rich manganese-based materials have high specific capacity. Combining the two allows for complementary advantages in voltage plateau and specific capacity, thereby improving the battery's cycle performance. Furthermore, by setting the upper limit voltage for the formation and charging of lithium-ion batteries to greater than 4.45V, the specific capacity of lithium-rich manganese-based materials can be fully released during the formation and charging process, enabling lithium-ion batteries to balance improved specific capacity and cycle performance in subsequent applications.

[0026] Formation refers to the process of initially charging a battery. During the formation process, the positive and negative electrode materials inside the battery are charged and undergo electrochemical reactions, bringing the internal chemical reaction system of the battery to a stable state.

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

[0028] The charging cutoff voltage of lithium-ion batteries is typically 4.2V, and the discharging cutoff voltage is typically 2.5V. In related technologies, the upper limit voltage for formation charging of lithium-ion batteries is usually set to 4.2V. For lithium-ion batteries doped with lithium-rich manganese-based materials, setting the upper limit voltage for formation charging to 4.2V can only improve the cycle performance of the lithium-ion battery to a certain extent. It cannot fully utilize the lithium replenishment effect of the lithium-rich manganese-based material, resulting in a poor improvement in the specific capacity of the lithium-ion battery. Consequently, the lithium-ion battery cannot simultaneously achieve high specific capacity and high cycle performance, affecting its overall electrochemical performance.

[0029] Specifically, by setting the upper limit voltage of the formation charge to greater than 4.45V, more lithium ions can be intercalated into the lithium-rich manganese-based material during the formation process, thereby increasing the lithium intercalation capacity of the lithium-rich manganese-based material and thus improving the capacity and energy density of the lithium-ion battery. A higher upper limit voltage of the formation charge can also stimulate more electrochemical active sites, resulting in a higher reaction rate and better cycle stability of the lithium-ion battery during charge and discharge. Furthermore, since the positive electrode active material of the lithium-ion battery in this embodiment includes both lithium manganese iron phosphate and lithium-rich manganese-based materials, and lithium manganese iron phosphate has the advantage of a high voltage platform, increasing the upper limit voltage of the formation charge ensures the safety of the formation charge process.

[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 lithium intercalation amount in lithium-rich manganese-based materials can be increased during the formation charging process, allowing for the full release of the specific capacity of the lithium-rich manganese-based materials and improving the capacity and energy density of lithium-ion batteries. Furthermore, it can reduce problems such as increased side reactions, voltage decay, and irreversible phase transitions in lithium-rich manganese-based materials caused by excessively high upper limit voltages during formation charging. In addition, it can improve the safety of the formation charging process and reduce the investment costs of safety measures such as thermal management and overcharge protection.

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

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

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

[0035] Specifically, when large-particle-size lithium-rich manganese-based materials are combined with small-particle-size lithium iron phosphate, the large-particle-size lithium-rich manganese-based materials can stack up, and there will be gaps between adjacent lithium-rich manganese-based material particles. The small-particle-size lithium iron phosphate particles will fill these gaps, so that lithium iron phosphate and lithium-rich manganese-based materials can be evenly distributed and in contact with each other, reducing or avoiding problems such as stratification of lithium iron phosphate and lithium-rich manganese-based materials, and enabling the two to fully interact and achieve better results.

[0036] For example, d1 / d2 can 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 lithium manganese iron phosphate satisfies: 0.4 μm ≤ d1 ≤ 1.2 μm.

[0038] Lithium iron manganese phosphate (LFP) has a relatively small particle size (D50), which is beneficial for improving the discharge performance and cycle life of batteries. This is because smaller particle sizes result in a larger specific surface area and shorter ion diffusion paths, which facilitates lithium-ion insertion and extraction reactions, thereby improving the battery's charge-discharge rate performance and reducing internal resistance. However, if the D50 of LFP is too small, it is prone to agglomeration, increasing the difficulty of battery material preparation. Furthermore, excessively small particle sizes may also lead to a decrease in the material's mechanical strength, thus reducing its cycle life and stability.

[0039] For example, 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: 4μm≤d2≤10μm 。

[0041] The larger particle size (D50) of lithium-rich manganese-based materials allows for better packing with smaller-sized lithium iron phosphate (LFP) particles, resulting in a more efficient conductive network and thus better performance in improving specific capacity and cycle life. The smaller LFP particles surround the larger LFP particles, facilitating better interaction between the lithium-rich manganese-based materials and the LFP materials.

[0042] For example, the particle size D50 of lithium iron ferrite rich in lithium 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 at which 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 mass ratio of lithium-rich manganese-based materials added to the positive electrode active material is 1%-30%.

[0045] By setting the mass ratio of lithium-rich manganese-based material in the positive electrode active material to 1%-30%, the lithium supplementation effect of lithium-rich manganese-based material can be brought into play, while reducing the problem of accelerated phase transition of positive electrode active material caused by excessive addition ratio, and reducing the excessive oxygen release caused by excessive proportion of lithium-rich manganese-based material, which in turn causes lithium-ion defects.

[0046] For example, the mass ratio of 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 lithium-rich manganese-based material added to the positive electrode active material is 10%-20%. When the addition ratio of lithium-rich manganese-based material is within this range, it can have a significant effect on improving the specific capacity and improving the cycle performance, thereby making up for the defects of lithium manganese iron phosphate compared with lithium iron phosphate to a certain extent and improving its overall performance.

[0048] For example, the mass ratio of 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 lithium-rich manganese-based material added to the positive electrode active material is greater than 20% and less than or equal to 30%. Compared to a mass ratio of 10%-20% for lithium-rich manganese-based material added to the positive electrode active material, when the addition ratio of lithium-rich manganese-based material is in the range of greater than 20% and less than or equal to 30%, the cycle performance can be further improved, but the specific capacity will decrease to some extent.

[0050] For example, the mass ratio of 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 manganese iron phosphate is S1, the specific surface area of ​​lithium-rich manganese-based material is S2, and 8≤S1 / S2≤85.

[0052] Lithium manganese iron phosphate has a smaller particle size and a larger specific surface area, while lithium-rich manganese-based materials have a larger particle size and a smaller specific surface area. By setting the specific surface areas of both materials to satisfy the condition 8 ≤ S1 / S2 ≤ 85, it is beneficial for them to form a better stacking effect, thereby establishing a more efficient conductive network and achieving better results.

[0053] For example, S1 / S2 can 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 ​​a material is inversely proportional to its particle size; that is, the larger the particle size, the smaller the specific surface area, and vice versa. A larger specific surface area provides more reaction sites, while a smaller specific surface area generally results in more stable properties. Lithium manganese iron phosphate, as the main material for the positive electrode, has a small particle size and a large specific surface area, providing more reaction sites and thus improving energy density. Meanwhile, lithium-rich manganese-based materials are added in smaller proportions, primarily for lithium supplementation; their larger particle size and smaller specific surface area contribute to stability and allow them to perform their functions more effectively.

[0055] In some embodiments, the specific surface area of ​​lithium manganese iron phosphate satisfies: 16 m² / g. 2 / g≤S1≤26m 2 / g. If the specific surface area of ​​lithium manganese iron phosphate is too small, it can easily affect the specific capacity, causing the specific capacity to fall short of expectations. If 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 16 m². 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 m² / s². 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 specific capacity, causing the specific capacity to fall short of expectations. 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 manufacturing process, thus affecting the battery performance.

[0058] For example, the specific surface area of ​​lithium-rich manganese-based materials can be 0.3 m². 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 molecular formula of the lithium-rich manganese-based material is Li w Ni x Co y Mn z O2, where 1.05 < w < 1.13, 0 < x < 1, 0 < y < 1, 0 < z < 1.

[0060] By ensuring that the lithium-rich manganese-based material meets the above molecular formula, the proportion of lithium (Li) in the lithium-rich manganese-based material can be controlled within a reasonable range. This ensures the lithium replenishment effect of the lithium-rich manganese-based material, improves the specific capacity and cycle performance of lithium-ion batteries, and reduces the phase transition problem caused by excessive lithium content in the lithium-rich manganese-based material, as well as the problem of excessive oxygen escaping from the crystal lattice, thereby reducing side reactions and ensuring the stability of lithium-ion batteries.

[0061] Secondly, embodiments of this application provide 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 this application embodiment are basically the same as the formation method of lithium-ion battery, and will not be repeated here.

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

[0064] In other words, the minimum discharge voltage of a lithium-ion battery during application is 2.5V, and the maximum charge voltage is 4.2V. By setting the charge and discharge voltage range within this range, the safety and effectiveness of the lithium-ion battery during use can be guaranteed. Because the upper limit voltage during the formation and charging process of a lithium-ion battery is >4.45V, the specific capacity of the lithium-rich manganese-based material is fully released during the formation and charging process. This allows the lithium-ion battery to maintain good overall electrochemical performance in terms of both specific capacity and cycle performance when applied within the charge and discharge voltage range of 2.5V-4.2V.

[0065] The embodiments of this application are further illustrated below with reference to specific examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application. Experimental methods in the following embodiments that do not specify specific conditions are generally performed according to the conditions recommended by the manufacturer.

[0066] It should be noted that, apart from the differences already described, all other conditions in the embodiments and comparative examples of this application are the same.

[0067] The manufacturing process of the lithium-ion battery in the embodiments and comparative examples of this application includes: combining lithium manganese iron phosphate and lithium iron phosphate in a specified ratio to form a positive electrode active material; mixing and stirring the positive electrode active material with a conductive agent, binder, dispersant, and solvent to prepare a positive electrode slurry; the positive electrode active material accounts for 97.5%, the conductive agent is carbon black (0.7%), the binder is polyvinylidene fluoride (1.5%), and the dispersant is a polyester material (0.3%). Artificial graphite is used as the negative electrode active material, and mixed and stirred with a conductive agent and binder to prepare a negative electrode slurry; the negative electrode active material accounts for 96.9%, the conductive agent is carbon black (0.5%), and the binder is sodium carboxycellulose and styrene-butadiene rubber, wherein sodium carboxycellulose accounts for 1.1% and styrene-butadiene rubber accounts for 1.5%. Positive and negative electrode slurries are coated and sheet-making processes to obtain positive and negative electrode sheets respectively. The positive and negative electrode sheets, along with the separator, electrolyte, cover plate, and aluminum shell, are assembled into a square aluminum-shell battery. After formation and capacity testing, the finished battery is obtained.

[0068] Example 1

[0069] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium manganese iron phosphate and lithium-rich manganese-based material, with the mass ratio of lithium-rich manganese-based material in the positive electrode active material being 0.5%. The molecular formula of lithium manganese iron phosphate is LiMn. 0.5 Mn 0.5 PO4 has a D50 of 0.8 μm and a specific surface area of ​​21 m². 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 has a D50 of 7 μm and a specific surface area of ​​1 m². 2 / g.

[0070] The lithium-ion battery described above was formed and charged at a voltage of 4.6V, and then subjected to capacity testing to obtain the finished lithium battery.

[0071] Example 2

[0072] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium manganese iron phosphate and lithium-rich manganese-based material, with the lithium-rich manganese-based material accounting for 5% of the mass of the positive electrode active material. The molecular formula of lithium manganese iron phosphate is LiMn. 0.5 Mn 0.5 PO4 has a D50 of 0.8 μm and a specific surface area of ​​21 m². 2 / g; The molecular formula of lithium-rich manganese-based materials is Li 1.07 Ni0.36 Co 0.06 Mn 0.51 O2 has a D50 of 7 μm and a specific surface area of ​​1 m². 2 / g.

[0073] The lithium-ion battery described above was formed and charged at a voltage of 4.6V, and then subjected to capacity testing to obtain the finished lithium battery.

[0074] Example 3

[0075] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium manganese iron phosphate and lithium-rich manganese-based material, with the lithium-rich manganese-based material accounting for 15% of the mass of the positive electrode active material. The molecular formula of lithium manganese iron phosphate is LiMn. 0.5 Mn 0.5 PO4 has a D50 of 0.8 μm and a specific surface area of ​​21 m². 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 has a D50 of 7 μm and a specific surface area of ​​1 m². 2 / g.

[0076] The lithium-ion battery described above was formed and charged at a voltage of 4.6V, and then subjected to capacity testing to obtain the finished lithium battery.

[0077] Example 4

[0078] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium manganese iron phosphate and lithium-rich manganese-based material, with the lithium-rich manganese-based material accounting for 25% of the mass of the positive electrode active material. The molecular formula of lithium manganese iron phosphate is LiMn. 0.5 Mn 0.5 PO4 has a D50 of 0.8 μm and a specific surface area of ​​21 m². 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 has a D50 of 7 μm and a specific surface area of ​​1 m². 2 / g.

[0079] The lithium-ion battery described above was formed and charged at a voltage of 4.6V, and then subjected to capacity testing to obtain the finished lithium battery.

[0080] Example 5

[0081] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium manganese iron phosphate and lithium-rich manganese-based material, with the lithium-rich manganese-based material accounting for 35% of the mass of the positive electrode active material. The molecular formula of lithium manganese iron phosphate is LiMn. 0.5 Mn 0.5 PO4 has a D50 of 0.8 μm and a specific surface area of ​​21 m². 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 has a D50 of 7 μm and a specific surface area of ​​1 m². 2 / g.

[0082] The lithium-ion battery described above was formed and charged at a voltage of 4.6V, and then subjected to capacity testing to obtain the finished lithium battery.

[0083] Example 6

[0084] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium manganese iron phosphate and lithium-rich manganese-based material, with the lithium-rich manganese-based material accounting for 15% of the mass of the positive electrode active material. The molecular formula of lithium manganese iron phosphate is LiMn. 0.5 Mn 0.5 PO4 has a D50 of 0.8 μm and a specific surface area of ​​21 m². 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 has a D50 of 7 μm and a specific surface area of ​​1 m². 2 / g.

[0085] The lithium-ion battery described above was formed and charged at a voltage of 4.7V, and then subjected to capacity testing to obtain the finished lithium battery.

[0086] Example 7

[0087] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium manganese iron phosphate and lithium-rich manganese-based material, with the lithium-rich manganese-based material accounting for 15% of the mass of the positive electrode active material. The molecular formula of lithium manganese iron phosphate is LiMn. 0.5 Mn 0.5 PO4 has a D50 of 0.8 μm and a specific surface area of ​​21 m². 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 has a D50 of 7 μm and a specific surface area of ​​1 m². 2 / g.

[0088] The lithium-ion battery described above was formed and charged at a voltage of 4.6V, and then subjected to capacity testing to obtain the finished lithium battery.

[0089] Example 8

[0090] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium manganese iron phosphate and lithium-rich manganese-based material, with the lithium-rich manganese-based material accounting for 15% of the mass of the positive electrode active material. The molecular formula of lithium manganese iron phosphate is LiMn. 0.5 Mn 0.5 PO4 has a D50 of 0.8 μm and a specific surface area of ​​21 m². 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 has a D50 of 7 μm and a specific surface area of ​​1 m². 2 / g.

[0091] The lithium-ion battery described above was formed and charged at a voltage of 4.6V, and then subjected to capacity testing to obtain the finished lithium battery.

[0092] Example 9

[0093] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium manganese iron phosphate and lithium-rich manganese-based material, with the lithium-rich manganese-based material accounting for 15% of the mass of the positive electrode active material. The molecular formula of lithium manganese iron phosphate is LiMn. 0.5 Mn 0.5 PO4 has a D50 of 0.3 μm and a specific surface area of ​​23 m². 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 has a D50 of 12 μm and a specific surface area of ​​0.8 m². 2 / g.

[0094] The lithium-ion battery described above was formed and charged at a voltage of 4.6V, and then subjected to capacity testing to obtain the finished lithium battery.

[0095] Example 10

[0096] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium manganese iron phosphate and lithium-rich manganese-based material, with the lithium-rich manganese-based material accounting for 15% of the mass of the positive electrode active material. The molecular formula of lithium manganese iron phosphate is LiMn. 0.5 Mn 0.5 PO4 has a D50 of 1 μm and a specific surface area of ​​14 m². 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 has a D50 of 8.5 μm and a specific surface area of ​​0.2 m². 2 / g.

[0097] The lithium-ion battery described above was formed and charged at a voltage of 4.6V, and then subjected to capacity testing to obtain the 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 manganese iron phosphate and lithium-rich manganese-based material, with the lithium-rich manganese-based material accounting for 15% of the mass of the positive electrode active material. The molecular formula of lithium manganese iron phosphate is LiMn. 0.5 Mn 0.5 PO4 has a D50 of 0.8 μm and a specific surface area of ​​21 m². 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 has a D50 of 7 μm and a specific surface area of ​​1 m². 2 / g.

[0100] The above-mentioned lithium-ion batteries were formed and charged at a voltage of 4.2V, and then subjected to capacity testing to obtain the finished lithium batteries.

[0101] Comparative Example 2

[0102] In this embodiment, the positive electrode active material of the lithium-ion battery is composed of lithium manganese iron phosphate and lithium-rich manganese-based material, with the lithium-rich manganese-based material accounting for 15% of the mass of the positive electrode active material. The molecular formula of lithium manganese iron phosphate is LiMn. 0.5 Mn 0.5 PO4 has a D50 of 0.8 μm and a specific surface area of ​​21 m². 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 has a D50 of 7 μm and a specific surface area of ​​1 m². 2 / g.

[0103] The lithium-ion battery described above was formed and charged at a voltage of 4.4V, and then subjected to capacity testing to obtain the 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 has a D50 of 0.8 μm and a specific surface area of ​​21 m². 2 / g.

[0106] The above-mentioned lithium-ion batteries were formed and charged at a voltage of 4.2V, and then subjected to capacity testing to obtain the finished lithium batteries.

[0107] Comparative Example 4

[0108] In this comparative example, the positive electrode active material of the lithium-ion battery is composed of lithium manganese iron phosphate and lithium-rich manganese-based material, with the mass ratio of lithium-rich manganese-based material in the positive electrode active material being 0.5%. The molecular formula of lithium manganese iron phosphate is LiMn. 0.5 Mn 0.5 PO4 has a D50 of 0.8 μm and a specific surface area of ​​21 m². 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 has a D50 of 7 μm and a specific surface area of ​​1 m². 2 / g.

[0109] The above-mentioned lithium-ion batteries were formed and charged at a voltage of 4.2V, and then subjected to capacity testing to obtain the finished lithium batteries.

[0110] Comparative Example 5

[0111] In this comparative example, the positive electrode active material of the lithium-ion battery is composed of lithium manganese iron phosphate and lithium-rich manganese-based material, with the lithium-rich manganese-based material accounting for 35% of the mass of the positive electrode active material. The molecular formula of lithium manganese iron phosphate is LiMn. 0.5 Mn 0.5 PO4 has a D50 of 0.8 μm and a specific surface area of ​​21 m². 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 has a D50 of 7 μm and a specific surface area of ​​1 m². 2 / g.

[0112] The above-mentioned lithium-ion batteries were formed and charged at a voltage of 4.2V, and then subjected to capacity testing to obtain the finished lithium batteries.

[0113] Comparative Example 6

[0114] In this comparative example, the positive electrode active material of the lithium-ion battery is composed of lithium manganese iron phosphate and lithium-rich manganese-based material, with the lithium-rich manganese-based material accounting for 15% of the mass of the positive electrode active material. The molecular formula of lithium manganese iron phosphate is LiMn. 0.5 Mn 0.5 PO4 has a D50 of 0.8 μm and a specific surface area of ​​21 m². 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 has a D50 of 7 μm and a specific surface area of ​​1 m². 2 / g.

[0115] The above-mentioned lithium-ion batteries were formed and charged at a voltage of 4.2V, and then subjected to capacity testing to obtain the finished lithium batteries.

[0116] Comparative Example 7

[0117] In this comparative example, the positive electrode active material of the lithium-ion battery is composed of lithium manganese iron phosphate and lithium-rich manganese-based material, with the lithium-rich manganese-based material accounting for 15% of the mass of the positive electrode active material. The molecular formula of lithium manganese iron phosphate is LiMn. 0.5 Mn 0.5 PO4 has a D50 of 0.8 μm and a specific surface area of ​​21 m². 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 has a D50 of 7 μm and a specific surface area of ​​1 m². 2 / g.

[0118] The above-mentioned lithium-ion batteries were formed and charged at a voltage of 4.2V, and then subjected to capacity testing to obtain the finished lithium batteries.

[0119] Comparative Example 8

[0120] In this comparative example, the positive electrode active material of the lithium-ion battery is composed of lithium manganese iron phosphate and lithium-rich manganese-based material, with the lithium-rich manganese-based material accounting for 15% of the mass of the positive electrode active material. The molecular formula of lithium manganese iron phosphate is LiMn. 0.5 Mn 0.5 PO4 has a D50 of 0.3 μm and a specific surface area of ​​23 m². 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 has a D50 of 12 μm and a specific surface area of ​​0.8 m². 2 / g.

[0121] The above-mentioned lithium-ion batteries were formed and charged at a voltage of 4.2V, and then subjected to capacity testing to obtain the finished lithium batteries.

[0122] Comparative Example 9

[0123] In this comparative example, the positive electrode active material of the lithium-ion battery is composed of lithium manganese iron phosphate and lithium-rich manganese-based material, with the lithium-rich manganese-based material accounting for 15% of the mass of the positive electrode active material. The molecular formula of lithium manganese iron phosphate is LiMn. 0.5 Mn 0.5 PO4 has a D50 of 1 μm and a specific surface area of ​​14 m². 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 has a D50 of 8.5 μm and a specific surface area of ​​0.2 m². 2 / g.

[0124] The above-mentioned lithium-ion batteries were formed and charged at a voltage of 4.2V, and then subjected to capacity testing to obtain the finished lithium batteries.

[0125] The batteries in Examples 1-11 and Comparative Examples 1-9 were subjected to specific capacity and cycle tests, respectively. The specific capacity test method included: placing the battery in a constant temperature chamber at 25±2℃, charging it at a constant current and constant voltage of 0.33C to 4.2V, with a cutoff current of 0.05C; resting for 30 minutes; discharging it at a constant current of 0.33C to 2.5V; the discharge capacity divided by the weight of the active material was the specific capacity. The cycle test method included: placing the battery in a constant temperature chamber at 25±2℃, charging it at a constant current and constant voltage of 1C to 4.2V, with a cutoff current of 0.05C; resting for 30 minutes; discharging it at a constant current of 1C to 2.5V; resting for 30 minutes; repeating the above steps until the discharge capacity / initial discharge capacity = 80%, which was 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] A comparison of Example 3 and Comparative Example 1 shows that for lithium-ion batteries whose positive electrode active materials include lithium manganese iron phosphate and lithium-rich manganese-based materials, setting the formation charging voltage to 4.6V can improve the specific capacity of the lithium-ion battery and also provide good cycle performance.

[0130] A comparison of Examples 3, 6, and Comparative Example 2 shows that Examples 3, 6, and 2 used formation charging voltages of 4.6V, 4.7V, and 4.4V, respectively, while other adjustments remained consistent. Specifically, in Example 3 (formation charging voltage of 4.6V), the lithium-ion battery maintained high specific capacity and cycle performance. In Example 6 (formation charging voltage of 4.7V), the specific capacity and cycle performance of the lithium-ion battery were lower than in Example 3. In Comparative Example 2 (formation charging voltage of 4.4V), the cycle performance of the lithium-ion battery was basically the same as in Example 3, but the specific capacity was significantly lower than in Examples 3 and 6. Therefore, controlling the formation charging voltage at 4.6V and 4.7V can significantly improve the specific capacity of lithium-ion batteries, achieving a good balance between specific capacity and cycle performance.

[0131] Comparing Comparative Example 1 and Comparative Example 3, it can be seen that the lithium-ion battery in Comparative Example 3, lacking the addition of lithium-rich manganese-based materials, resulted in a decrease in the number of cycles. This indicates that when the formation voltage is 4.2V, the addition of lithium-rich manganese-based materials only affects cycle performance and cannot improve specific capacity. The cycle performance of the lithium-ion battery in Comparative Example 1 is 18% higher than that of Comparative Example 3.

[0132] A comparison of Examples 1-5 shows that when the mass ratio of lithium-rich manganese-based material in the positive electrode active material is 15% (Example 3), the specific capacity and cycle life of the lithium-ion battery remain at a high level. When the mass ratio of lithium-rich manganese-based material in the positive electrode active material increases or decreases, at least one of the specific capacity and cycle life decreases. In particular, when the mass ratio of lithium-rich manganese-based material in the positive electrode active material is 0.5% (Example 1) and 35% (Example 5), the specific capacity and cycle life of the lithium-ion battery show a significant decrease compared to Example 3.

[0133] A comparison of Examples 3 and 7-10 shows that the lithium content in lithium-rich manganese-based materials (Examples 7 and 8), as well as the particle size and specific surface area of ​​lithium manganese iron phosphate and lithium-rich manganese-based materials (Examples 9 and 10), also have a certain impact on the specific capacity and cycle performance of lithium-ion batteries.

[0134] A comparison of Example 1 and Comparative Example 4 shows that by changing the formation charging voltage, both the specific capacity and cycle performance of the lithium-ion battery can be improved.

[0135] A comparison of Example 5 and Comparative Example 5 shows that by changing the formation charging voltage, both the specific capacity and cycle performance of the lithium-ion battery can be improved.

[0136] A comparison of Example 7 and Comparative Example 6 shows that by changing the formation charging voltage, both the specific capacity and cycle performance of the lithium-ion battery can be improved.

[0137] A comparison of Example 8 and Comparative Example 7 shows that by changing the formation charging voltage, both the specific capacity and cycle performance of the lithium-ion battery can be improved.

[0138] A comparison of Example 9 and Comparative Example 8 shows that by changing the formation charging voltage, both the specific capacity and cycle performance of the lithium-ion battery can be improved.

[0139] A comparison of Example 10 and Comparative Example 9 shows that by changing the formation charging voltage, both the specific capacity and cycle performance of the lithium-ion battery can be improved.

[0140] In summary, the embodiments of this application, by using lithium iron manganese phosphate and lithium-rich manganese-based materials as the positive electrode active materials of lithium-ion batteries, and setting the upper limit voltage of formation charging to >4.45V, enable the finished lithium-ion batteries after formation and capacity testing to achieve both good specific capacity and cycle performance.

[0141] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for forming a lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode active material, which includes lithium manganese iron phosphate and lithium-rich manganese-based materials. The upper limit voltage of the lithium ion battery during formation charging is 4.55V-4.6V; the molecular formula of the lithium-rich manganese-based material is Li w Ni x Co y Mn z O2, wherein 1.05 2. 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, and the particle size D50 of the lithium-rich manganese-based material is d2, with 0.04≤d1 / d2≤0.

30.

3. The formation method of a lithium-ion battery according to claim 2, characterized in that, The particle size D50 of the lithium manganese iron phosphate satisfies: 0.4μm≤d1≤1.2μm; And / or, the particle size D50 of the lithium-rich manganese-based material satisfies: 4μm≤d2≤10μm.

4. The formation method of a lithium-ion battery according to claim 1, characterized in that, The lithium-rich manganese-based material is added to the positive electrode active material at a mass ratio of 1%-30%.

5. The formation method of a lithium-ion battery according to claim 4, characterized in that, The lithium-rich manganese-based material is added to the positive electrode active material at a mass ratio of 10%-20%.

6. The formation method of a lithium-ion battery according to claim 4, characterized in that, The lithium-rich manganese-based material is added to the positive electrode active material at a mass ratio greater than 20% and less than or equal to 30%.

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

8. The formation method of a lithium-ion battery according to claim 7, characterized in that, The specific surface area of ​​the lithium manganese iron phosphate meets the following requirement: 16 m² 2 / g≤S1≤26m 2 / g; And / or, the specific surface area of ​​the lithium-rich manganese-based material satisfies: 0.3 m² / s². 2 / g≤S2≤2m 2 / g.

9. A lithium-ion battery, characterized in that, The lithium-ion battery is formed using the formation method described in any one of claims 1-8.

10. The lithium-ion battery according to claim 9, characterized in that, The lithium-ion battery has a charge / discharge voltage range of 2.5V-4.2V after formation.

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