Lithium ion battery and preparation method thereof

Abstract

The invention discloses a lithium ion battery and a preparation method thereof. The lithium ion battery comprises a battery shell and a battery pole group in the battery shell; electrolyte is injected into the battery shell; the battery pole group comprises a positive pole piece, a negative pole piece and a diaphragm; the positive pole piece comprises a positive current collector; the upper and lower sides of the positive current collector are respectively coated with a positive active material coating; the positive electrode active material coating comprises a positive electrode active material, a binder, a conductive agent and a positive electrode lithium supplement agent; the negative pole piece comprises a negative current collector; the upper and lower sides of the negative current collector are respectively coated with a negative active material coating; the negative electrode active material coating comprises a negative electrode active material, a dispersant, a binder and a conductive agent; according to the invention, the key problem that the electrochemical performance of the lithium ion battery is remarkably reduced in a low-temperature environment can be effectively solved, the large-current discharge capacity of the lithium ion battery in the low-temperature environment is remarkably improved through a special electrode formula design and an electrolyte optimization design, and the lithium ion battery has a wide application prospect.

Description

Technical Field

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

[0002] With the rapid development of lithium-ion battery technology, its application in many fields is becoming increasingly extensive. However, in low-temperature environments, the electrochemical performance of lithium-ion batteries decreases significantly, limiting their application in special fields such as low-altitude flight and aerospace.

[0003] Especially at low temperatures below -40°C, the discharge capacity and energy of lithium-ion batteries are significantly reduced. As the temperature drops, the viscosity of the electrolyte in lithium-ion batteries increases, the charge transfer impedance increases, and the ion migration speed slows down. Especially when discharging at high currents (such as 3C), the battery voltage drops significantly and may even lose its discharge capacity.

[0004] Therefore, there is an urgent need to develop a lithium-ion battery that can solve the above technical problems. Summary of the Invention

[0005] The purpose of the present invention is to provide a lithium ion battery and a preparation method thereof in view of the technical defects existing in the prior art.

[0006] To this end, the present invention provides a lithium-ion battery comprising a battery housing and a battery electrode group located in the battery housing;

[0007] The battery shell is filled with electrolyte;

[0008] A battery electrode group, comprising a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet;

[0009] Among them, the positive electrode sheet includes a positive electrode current collector;

[0010] The upper and lower surfaces of the positive electrode current collector are respectively coated with a positive electrode active material coating;

[0011] A positive electrode active material coating, comprising a positive electrode active material, a binder, a conductive agent and a positive electrode lithium supplement;

[0012] The mass ratio of the positive electrode active material, the binder, the conductive agent and the positive electrode lithium supplement is: (90-96): (1-4): (1-5): (2-6);

[0013] Among them, the negative electrode sheet includes a negative electrode current collector;

[0014] The upper and lower surfaces of the negative electrode current collector are respectively coated with a negative electrode active material coating;

[0015] A negative electrode active material coating, comprising a negative electrode active material, a dispersant, a binder and a conductive agent;

[0016] The mass ratio of the negative electrode active material, the dispersant, the binder and the conductive agent is: (85-95): (1-4): (1-3): (1-5).

[0017] In addition, the present invention also provides a method for preparing the lithium ion battery as described above, which comprises the following steps:

[0018] The first step is the preparation of positive electrode slurry;

[0019] Specifically, the positive electrode active material, binder, conductive agent and positive electrode lithium supplement are mixed uniformly according to a preset mass ratio, and then a solvent is added and stirred until a preset solid content is reached to prepare a positive electrode slurry;

[0020] The second step is the production of positive electrode;

[0021] Specifically, the positive electrode slurry obtained in the first step is evenly coated on the upper and lower surfaces of the positive electrode current collector, and then subjected to rolling, slitting and punching processes to obtain the positive electrode sheet;

[0022] The third step is the preparation of negative electrode slurry;

[0023] Specifically, the negative electrode active material, dispersant, binder and conductive agent are mixed uniformly according to a preset mass ratio, and then a solvent is added and stirred until a preset solid content is reached to prepare a positive electrode slurry;

[0024] The fourth step is the production of negative electrode;

[0025] Specifically, the negative electrode slurry obtained in the third step is evenly coated on the upper and lower surfaces of the negative electrode current collector, and then subjected to rolling, slitting and punching processes to obtain the negative electrode sheet;

[0026] Step 5: Production of finished lithium-ion batteries;

[0027] Specifically, the positive electrode sheet obtained in the second step, the negative electrode sheet obtained in the fourth step, and the separator are wound or stacked to prepare a battery electrode group, and then the battery electrode group is subjected to the external tab welding, shell insertion, hot pressing, liquid injection and formation processes in sequence to obtain a finished lithium-ion battery.

[0028] It can be seen from the technical solution provided by the present invention above that, compared with the prior art, the present invention provides a lithium-ion battery and a preparation method, specifically a high-energy-density, low-temperature lithium-ion battery and a preparation method thereof, which can effectively solve the key problem of a significant decrease in the electrochemical performance of lithium-ion batteries in low-temperature environments. The present invention significantly improves the high-current discharge capacity of lithium-ion batteries in low-temperature environments through special electrode formulation design and electrolyte optimization design, and the battery preparation process is simple and efficient, has broad application prospects, and has great practical significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A flowchart of a lithium-ion battery and a preparation method provided by the present invention;

[0030] Figure 2 Schematic diagram of the discharge capacity curve of the lithium-ion battery prepared in Example 2 of the present invention and the lithium-ion battery prepared in Comparative Example 1 using the prior art process. The curve shows the corresponding relationship between the battery's depth of discharge DOD (which is the percentage of the battery's discharge amount to the battery's rated capacity) and the battery voltage. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0032] In the description of this patent, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," "connected," and "set" should be understood in a broad sense. For example, they can refer to fixed connection or set, detachable connection or set, or integral connection or set. Those skilled in the art will understand the specific meanings of the above terms in this patent based on the specific circumstances.

[0033] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0034] The present invention provides a lithium ion battery, which is a high-energy, low-temperature lithium ion battery, specifically comprising a battery housing and a battery electrode group located in the battery housing;

[0035] The battery shell is filled with electrolyte;

[0036] A battery electrode group, comprising a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet;

[0037] Among them, the positive electrode sheet includes a positive electrode current collector;

[0038] The upper and lower surfaces of the positive electrode current collector are respectively coated with a positive electrode active material coating;

[0039] A positive electrode active material coating, comprising a positive electrode active material, a binder, a conductive agent and a positive electrode lithium supplement;

[0040] The mass ratio of the positive electrode active material, the binder, the conductive agent and the positive electrode lithium supplement is: (90-96): (1-4): (1-5): (2-6);

[0041] Among them, the negative electrode sheet includes a negative electrode current collector;

[0042] The upper and lower surfaces of the negative electrode current collector are respectively coated with a negative electrode active material coating;

[0043] A negative electrode active material coating, comprising a negative electrode active material, a dispersant, a binder and a conductive agent;

[0044] The mass ratio of the negative electrode active material, the dispersant, the binder and the conductive agent is: (85-95): (1-4): (1-3): (1-5).

[0045] In the present invention, in a specific implementation, the battery electrode group is a battery electrode group prepared by a winding method or a lamination method.

[0046] In the present invention, in specific implementation, the diaphragm includes any one of a PE diaphragm, a PP diaphragm, a PE ceramic diaphragm, a PP ceramic diaphragm, an aramid diaphragm and a PI diaphragm.

[0047] In the present invention, in a specific implementation, the positive electrode current collector is preferably aluminum foil.

[0048] In the present invention, in a specific implementation, the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium-rich manganese-based materials, layered lithium manganese oxide and spinel lithium manganese oxide, or includes a coated modified material of at least one of lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium-rich manganese-based materials, layered lithium manganese oxide and spinel lithium manganese oxide;

[0049] Preferably, the positive electrode active material is nickel cobalt manganese oxide (NCM).

[0050] In the present invention, in a specific implementation, for the positive electrode active material coating, the conductive agent includes at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive carbon black, conductive graphite, carbon fibers and Ketjen black, which is used to form a three-dimensional conductive network; this three-dimensional conductive network constructs a three-dimensional conductive path through the connection of points, lines and surfaces: by forming a continuous conductive path, the resistance is reduced and the electron transmission efficiency is improved; the gaps in the three-dimensional conductive network are conducive to the penetration of the electrolyte and the improvement of the ion transmission rate.

[0051] In the present invention, in a specific implementation, for the positive electrode active material coating, the positive electrode lithium supplement comprises at least one of a binary lithium compound, a ternary lithium-containing compound, Li2O, and Li2O2;

[0052] It should be noted that the positive electrode lithium replenisher is used to replenish the active lithium consumed in the first cycle and improve the capacity and energy density of the battery.

[0053] Preferably, the positive electrode lithium supplement is a ternary lithium-containing compound.

[0054] In a specific implementation, the ternary lithium-containing compound includes at least one of Li2NiO2, Li5FeO4, Li6CoO4 and Li2CuO2. Preferably, the ternary lithium-containing compound is Li2NiO2 (LNO).

[0055] In the present invention, in a specific implementation, for the positive electrode active material coating, the binder is PVDF (polyvinylidene fluoride).

[0056] In the present invention, in a specific implementation, the negative electrode current collector is preferably copper foil.

[0057] In the present invention, in a specific implementation, for the negative electrode active material coating, the negative electrode active material includes at least one of artificial graphite, natural graphite and silicon-carbon material, or includes a coated modified material of at least one of artificial graphite, natural graphite and silicon-carbon material.

[0058] In the present invention, in a specific implementation, for the negative electrode active material coating, the binder is SBR (styrene-butadiene rubber);

[0059] The dispersant is CMC (carboxymethyl cellulose);

[0060] In the present invention, in a specific implementation, for the negative electrode active material coating, the conductive agent includes at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive carbon black, conductive graphite, carbon fibers and Ketjen black, which is used to form a three-dimensional conductive network and construct a three-dimensional conductive path of points, lines and surfaces: the active material is supported by the network structure to reduce the volume change during the charge and discharge process; by forming a continuous conductive path, the resistance is reduced and the electron transmission efficiency is improved; the gaps in the three-dimensional conductive network are conducive to the penetration of the electrolyte and the ion transmission rate is improved.

[0061] In the present invention, in a specific implementation, the electrolyte includes a lithium salt, an organic solvent and an additive; in the electrolyte, the mass percentage content of the lithium salt is 10% to 15%; the mass percentage content of the organic solvent is 70% to 80%; the mass percentage content of the additive is 10-20%; the technical effect brought about by this proportion design is to ensure that the electrolyte has good stability and electrochemical properties while providing sufficient lithium ion conduction, which helps to improve the overall performance of the battery, especially the performance in low temperature environments.

[0062] Among them, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4) and lithium fluorosulfonate (LiFSI), which is used to improve the ion conductivity and low-temperature stability of the battery;

[0063] The organic solvent is a carbonate solvent, including at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC), for providing good solubility and conductivity.

[0064] The additives include at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), lithium difluorophosphate (LiPO2F2), lithium bis(fluorosulfonyl)imide (LiFSl), diethylene sulfate (DTD), lithium dioxalatoborate (LiODFB), 1,3-propane sultone (PS) and vinylene carbonate (VC) to improve the cycle performance and low-temperature performance of the battery.

[0065] In order to prepare the lithium ion battery provided by the present invention, see Figure 1 The present invention also provides a method for preparing a lithium-ion battery, which is a method for preparing a high-energy, low-temperature lithium-ion battery, comprising the following steps:

[0066] The first step is the preparation of positive electrode slurry;

[0067] Specifically, the positive electrode active material, binder, conductive agent and positive electrode lithium supplement are mixed uniformly according to a preset mass ratio, and then a solvent is added and stirred until a preset solid content is reached to prepare a positive electrode slurry;

[0068] In the first step, the solid content of the cathode slurry is 50-65%;

[0069] In the first step, the solvent in the positive electrode slurry is NMP (N-methylpyrrolidone).

[0070] In the first step, the mass ratio of the positive electrode active material, the binder, the conductive agent and the positive electrode lithium supplement agent is: (90-96): (1-4): (1-5): (2-6);

[0071] It should be noted that in the present invention, the positive electrode active material includes at least one of lithium cobaltate, lithium nickelate, lithium nickel cobalt manganate, lithium-rich manganese-based materials, layered lithium manganate and spinel lithium manganate, or a coated modified material including at least one of lithium cobaltate, lithium nickelate, lithium nickel cobalt manganate, lithium-rich manganese-based materials, layered lithium manganate and spinel lithium manganate;

[0072] Preferably, the positive electrode active material is lithium nickel cobalt manganese oxide.

[0073] In the first step, for the positive electrode slurry, the conductive agent includes at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive carbon black, conductive graphite, carbon fiber and Ketjen black to form a three-dimensional conductive network.

[0074] In the first step, for the positive electrode slurry, the positive electrode lithium supplement includes at least one of a binary lithium compound, a ternary lithium-containing compound, Li2O, and Li2O2;

[0075] It should be noted that the positive electrode lithium replenisher is used to replenish the active lithium consumed in the first cycle and improve the capacity and energy density of the battery.

[0076] Preferably, the positive electrode lithium supplement is a ternary lithium-containing compound.

[0077] In a specific implementation, the ternary lithium-containing compound includes at least one of Li2NiO2, Li5FeO4, Li6CoO4 and Li2CuO2. Preferably, the ternary lithium-containing compound is Li2NiO2 (LNO).

[0078] It should be noted that, in the present invention, the capacity and energy density of the lithium-ion battery can be effectively improved by using the pre-lithiation technology of adding a positive electrode lithium supplement during the positive electrode homogenization process.

[0079] In the first step, for the positive electrode slurry, the binder is PVDF (polyvinylidene fluoride).

[0080] The second step is to prepare the positive electrode sheet. Specifically, the positive electrode slurry obtained in the first step is evenly coated on the upper and lower surfaces of the positive electrode current collector, and then the positive electrode sheet is obtained through rolling, slitting and punching (i.e., a mature process in the existing technology).

[0081] In the second step, the positive electrode current collector is aluminum foil;

[0082] The thickness of the positive electrode sheet ranges from 90 to 120 μm.

[0083] The third step is the preparation of negative electrode slurry;

[0084] Specifically, the negative electrode active material, dispersant, binder and conductive agent are mixed uniformly according to a preset mass ratio, and then a solvent is added and stirred until a preset solid content is reached to prepare a positive electrode slurry;

[0085] In the third step, the solid content of the negative electrode slurry is 35-50%;

[0086] In the third step, the solvent in the negative electrode slurry is deionized water;

[0087] In the third step, the mass ratio between the negative electrode active material, the dispersant, the binder and the conductive agent is: (85-95): (1-4): (1-3): (1-5).

[0088] It should be noted that in the present invention, for the negative electrode slurry, the negative electrode active material includes at least one of artificial graphite, natural graphite and silicon-carbon material, or includes a coated modified material of at least one of artificial graphite, natural graphite and silicon-carbon material.

[0089] In the third step, in a specific implementation, for the negative electrode slurry, the binder is SBR (styrene-butadiene rubber);

[0090] The dispersant is CMC (carboxymethyl cellulose);

[0091] In the third step, in specific implementation, for the negative electrode slurry, the conductive agent includes at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive carbon black, conductive graphite, carbon fiber and Ketjen black, which are used to form a three-dimensional conductive network.

[0092] The fourth step is the production of negative electrode;

[0093] Specifically, the negative electrode slurry obtained in the third step is evenly coated on the upper and lower surfaces of the negative electrode current collector, and then subjected to rolling, slitting and punching processes (i.e., processes with mature existing technologies) to obtain negative electrode sheets;

[0094] In the fourth step, the negative electrode current collector is copper foil;

[0095] The thickness of the negative electrode sheet ranges from 100 to 120 μm.

[0096] Step 5: Production of finished lithium-ion batteries (such as soft-pack batteries);

[0097] Specifically, the positive electrode sheet obtained in the second step, the negative electrode sheet obtained in the fourth step, and the separator are wound or stacked (i.e., using the existing conventional stacked battery or wound battery production process) to prepare a battery electrode group, and then the battery electrode group is successively subjected to external electrode ear welding (specifically including welding of the positive electrode ear and the positive electrode sheet, and welding of the negative electrode ear and the negative electrode sheet), shelling, hot pressing, liquid injection and formation processes (all using the existing conventional battery production processes) to obtain a finished lithium-ion battery.

[0098] In the fifth step, for the present invention, the arrangement and thickness of the electrode sheets need to be precisely controlled to ensure the stability and safety of the battery electrode group.

[0099] In the fifth step, the present invention makes an innovative design for the electrolyte injected into the battery housing during the injection process.

[0100] In the fifth step, the electrolyte used in the injection process includes a lithium salt, an organic solvent and an additive. In the electrolyte, the mass percentage content of the lithium salt is 10% to 15%; the mass percentage content of the organic solvent is 70% to 80%; and the mass percentage content of the additive is 10-20%.

[0101] Among them, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4) and lithium fluorosulfonate (LiFSI), which is used to improve the ion conductivity and low-temperature stability of the battery;

[0102] The organic solvent is a carbonate solvent, including at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC), for providing good solubility and conductivity.

[0103] The additives include at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), lithium difluorophosphate (LiPO2F2), lithium bis(fluorosulfonyl)imide (LiFSl), diethylene sulfate (DTD), lithium dioxalatoborate (LiODFB), 1,3-propane sultone (PS) and vinylene carbonate (VC) to improve the cycle performance and low-temperature performance of the battery.

[0104] It should be noted that, in the present invention, regarding the preparation of the electrolyte, the ratio of each component and the preparation conditions need to be strictly controlled to ensure the stability of the electrolyte and the performance of the battery cell.

[0105] It should be noted that, in the present invention, the mass percentage content of the lithium salt in the electrolyte is 10% to 15%; the mass percentage content of the organic solvent is 70% to 80%; and the mass percentage content of the additive is 10 to 20%. The technical effect brought about by this proportion design is that it ensures that the electrolyte has good stability and electrochemical properties while providing sufficient lithium ion conduction, which helps to improve the overall performance of the battery, especially the performance in low temperature environments.

[0106] Regarding the electrolyte, the preparation conditions are as follows: slowly add lithium salt and stir thoroughly under low temperature conditions (low temperature is usually between 0 and 10°C) to fully dissolve the lithium salt in the solvent, and avoid excessively high temperature that may cause decomposition of the lithium salt or ineffectiveness of the additive.

[0107] It should be noted that, in the present invention, the organic solvent is a carbonate solvent, which is a low melting point solvent. The lithium ion battery of the present invention achieves high rate discharge performance in a low temperature environment by adding a low melting point solvent and additives to the electrolyte.

[0108] In the present invention, a low-melting-point solvent refers to a carbonate solvent with a relatively low melting point used in the electrolyte. This type of solvent can remain liquid at low temperatures, improving battery performance. At low temperatures, the viscosity of the electrolyte increases significantly, slowing ion migration and thus affecting the battery's discharge performance. The addition of a low-melting-point solvent lowers the electrolyte's overall melting point, allowing it to maintain good fluidity at low temperatures. This allows lithium ions to migrate more smoothly within the electrolyte, reducing resistance to ion transport and ensuring normal battery charge and discharge at low temperatures.

[0109] In the present invention, the melting point of the low melting point solvent should be lower than the conventional operating temperature range (such as below 0° C.) to ensure that it can remain liquid in a low temperature environment.

[0110] In order to more clearly understand the technical solution of the present invention, the technical solution of the present invention is described below through specific embodiments and comparative examples.

[0111] Table 1: Schematic table of battery cell (battery electrode group) formulas for examples and comparative examples

[0112]

[0113] Example 1

[0114] The present invention provides a method for preparing a lithium-ion battery, which is a method for preparing a high-energy, low-temperature lithium-ion battery, comprising the following steps:

[0115] The first step is to prepare the positive electrode slurry: the positive electrode active material NCM-1, the lithium supplement agent LNO, the conductive agent (the conductive agent includes conductive carbon black and carbon nanotubes) and the binder PVDF are mixed evenly in a mass ratio of 92:5:1.5:1.5, and evenly stirred and dispersed in the solvent NMP to form a positive electrode slurry.

[0116] It should be noted that, in the first step, the conductive agent includes conductive carbon black and carbon nanotubes, and the mass percentages of the two can be any ratio, as long as the sum of the percentages of the two is 100%.

[0117] The second step is the production of positive electrode sheets: the positive electrode slurry is evenly coated on both sides of the aluminum foil, and after processes such as rolling, slitting and punching, a positive electrode sheet with a thickness of 90-120μm is obtained.

[0118] The third step is to prepare the negative electrode slurry: the graphite material as the negative electrode active material, the silicon carbon material SC as the negative electrode active material, the conductive carbon black, the carboxymethyl cellulose and the styrene-butadiene rubber SBR are mixed evenly in a mass ratio of 78:15:2.5:2:2.5, and are evenly stirred and dispersed in the solvent deionized water to prepare the negative electrode slurry.

[0119] The fourth step is the production of negative electrode sheets: the negative electrode slurry is evenly coated on both sides of the copper foil, and the negative electrode sheets with a thickness of 100-120μm are obtained through the same processes of rolling, slitting and punching.

[0120] The fifth step is the production of soft-pack batteries: The battery produced by the present invention is a 5Ah soft-pack battery, and the method includes: stacking the negative electrode sheet, diaphragm, positive electrode, diaphragm, and negative electrode sheet in this order; after completing the welding of the outer tabs (specifically including the welding of the positive tab and the positive electrode sheet and the welding of the negative tab and the negative electrode sheet), placing it in an aluminum-plastic shell outer packaging (i.e., the battery shell) (i.e., performing the shelling operation), and sequentially undergoing hot pressing, liquid injection, and formation processes (all of which are existing preparation processes) to obtain a soft-pack lithium-ion battery.

[0121] In Example 1, in the fifth step, the electrolyte added in the injection process, the lithium salt in the electrolyte is LiPF6 with a concentration of 1.3 mol / L;

[0122] The mass ratio of the components contained in the solvent in the electrolyte is EMC:EC:PC=80:10:10;

[0123] The specific requirements for the mass percentage of each component of the film-forming additive in the electrolyte to the total mass of the electrolyte are: VC: 0.8%; PS: 1%; DTD: 1.2%; LiTFSI: 1.5%; LiODFB: 1.5%; LiPO2F2: 1%; FEC: 8%.

[0124] The low-temperature additive in the electrolyte is: LiFSI accounting for 4% of the total mass of the electrolyte.

[0125] Example 2

[0126] In Example 2, the preparation operations of the positive electrode slurry, positive electrode sheet, negative electrode slurry, negative electrode sheet and soft-pack battery involved in the first to fifth steps are basically the same as those in Example 1, as shown in Table 1, with the difference that the mass percentage of the silicon-carbon material SC in the negative electrode slurry solute in Example 2 is 18%.

[0127] Example 3

[0128] In Example 3, the preparation operations of the positive electrode slurry, positive electrode sheet, negative electrode slurry, negative electrode sheet and soft-pack battery involved in the first to fifth steps are basically the same as those in Example 1, as shown in Table 1, with the difference that: Example 3 does not add 5% of lithium supplement agent, and the mass percentage of the positive electrode active material NCM-1 is 97%, that is, the mass ratio between the positive electrode active material NCM-1, the conductive agent (the conductive agent includes conductive carbon black and carbon nanotubes) and the binder PVDF is 97:1.5:1.5.

[0129] Example 4

[0130] In Example 4, the preparation operations of the positive electrode slurry, positive electrode sheet, negative electrode slurry, negative electrode sheet and soft-pack battery involved in the first to fifth steps are basically the same as those in Example 1, as shown in Table 1, with the difference that: Example 4 does not add 5% of lithium supplement agent, and the mass percentage of the positive electrode active material NCM-2 is 97%, that is, the mass ratio between the positive electrode active material NCM-2, the conductive agent (the conductive agent includes conductive carbon black and carbon nanotubes) and the binder PVDF is 97:1.5:1.5.

[0131] Example 5

[0132] In Example 5, the preparation operations of the positive electrode slurry, positive electrode sheet, negative electrode slurry, negative electrode sheet and soft-pack battery involved in the first to fifth steps are basically the same as those in Example 1, as shown in Table 1, with the difference that: the mass percentage of the silicon-carbon material SC in the negative electrode slurry solute in Example 5 is 18%, and no 5% lithium supplement agent is added in Example 5, and the mass percentage of the positive electrode active material NCM-3 is 97%, that is, the mass ratio between the positive electrode active material NCM-3, the conductive agent (the conductive agent includes conductive carbon black and carbon nanotubes) and the binder PVDF is 97:1.5:1.5.

[0133] Comparative Example 1

[0134] In Comparative Example 1, the preparation operations of the positive electrode slurry, positive electrode sheet, negative electrode slurry, negative electrode sheet, and soft-pack battery involved in the first to fifth steps are basically the same as those in Example 1, as shown in Table 1, except that: in Comparative Example 1, no 5% lithium supplement agent is added, no carbon material SC is added, and no 4% low-temperature additive LiFSI is added;

[0135] In Comparative Example 1, since 5% of the lithium supplement agent was not added, the mass percentage of the positive electrode active material NCM-1 was 97%, that is, the mass ratio between the positive electrode active material NCM-1, the conductive agent (the conductive agent includes conductive carbon black and carbon nanotubes) and the binder PVDF was 97:1.5:1.5.

[0136] In addition, in Comparative Example 1, the mass ratio of the components contained in the solvent in the electrolyte is EMC:EC:PC=65:20:15;

[0137] In addition, in Comparative Example 1, the specific requirements for the mass percentage of each component of the film-forming additive in the electrolyte to the total mass of the electrolyte are: VC: 1%; PS: 1%; DTD: 1.5%; LiTFSI: 1.5%; LiODFB: 1%; LiPO2F2: 1%.

[0138] Comparative Example 2

[0139] In Comparative Example 2, the preparation operations of the positive electrode slurry, positive electrode sheet, negative electrode slurry, negative electrode sheet, and soft-pack battery involved in the first to fifth steps are basically the same as those in Example 1, as shown in Table 1, with the following differences: In Comparative Example 2, no 5% lithium supplement agent is added, no carbon material SC is added, and no 4% low-temperature additive LiFSI is added; the positive electrode active material is NCM-2;

[0140] In Comparative Example 2, since 5% of the lithium supplement agent was not added, the mass percentage of the positive electrode active material NCM-2 was 97%, that is, the mass ratio between the positive electrode active material NCM-2, the conductive agent (the conductive agent includes conductive carbon black and carbon nanotubes) and the binder PVDF was 97:1.5:1.5.

[0141] In addition, in Comparative Example 2, the mass ratio of the components contained in the solvent in the electrolyte is EMC:EC:PC=65:20:15;

[0142] In addition, in Comparative Example 2, the specific requirements for the mass percentage of each component of the film-forming additive in the electrolyte to the total mass of the electrolyte are: VC: 1%; PS: 1%; DTD: 1.5%; LiTFSI: 1.5%; LiODFB: 1%; LiPO2F2: 1%.

[0143] Comparative Example 3

[0144] In Comparative Example 3, the preparation operations of the positive electrode slurry, positive electrode sheet, negative electrode slurry, negative electrode sheet, and soft-pack battery involved in the first to fifth steps are basically the same as those in Example 1, as shown in Table 1, with the following differences: In Comparative Example 3, no 5% lithium supplement agent is added, no carbon material SC is added, and no 4% low-temperature additive LiFSI is added; the positive electrode active material is NCM-3;

[0145] In Comparative Example 3, since 5% of the lithium supplement agent is not added, the mass percentage of the positive electrode active material NCM-3 is 97%, that is, the mass ratio between the positive electrode active material NCM-3, the conductive agent (the conductive agent includes conductive carbon black and carbon nanotubes) and the binder PVDF is 97:1.5:1.5.

[0146] In addition, in Comparative Example 2, the mass ratio of the components contained in the solvent in the electrolyte is EMC:EC:PC=65:20:15;

[0147] In addition, in Comparative Example 2, the specific requirements for the mass percentage of each component of the film-forming additive in the electrolyte to the total mass of the electrolyte are: VC: 1%; PS: 1%; DTD: 1.5%; LiTFSI: 1.5%; LiODFB: 1%; LiPO2F2: 1%.

[0148] The soft-pack lithium-ion batteries prepared in Examples 1-5 and the soft-pack lithium-ion batteries prepared in Comparative Examples 1-3 were respectively subjected to discharge performance tests. The test results are shown in Table 2.

[0149] Table 2: Schematic table of discharge performance of soft-pack batteries prepared in Examples and Comparative Examples

[0150]

[0151] It should be noted that, as shown in Table 2 above, for the present invention, the 1C discharge capacity at 25°C refers to the amount of electricity released by the battery when the battery is discharged at a discharge rate of 1C (5A) at an ambient temperature of 25°C, with a cut-off voltage of 2.5V.

[0152] As shown in Table 2 above, the energy density of a battery represents the energy stored per unit mass of the battery at 25°C per 1 discharge cycle, expressed in watt-hours per kilogram (Wh / kg). Energy density = discharge capacity × average discharge voltage / weight.

[0153] As shown in Table 2 above, the 1C (5A) discharge capacity at -40°C represents the amount of energy released by the battery when discharged at a 1C rate after standing at -40°C for 6 hours, with a cutoff voltage of 2.0V. The unit is ampere-hour (Ah). This data reflects the battery's discharge capability in low-temperature environments.

[0154] As shown in Table 2 above, the 1C (15A) discharge capacity at -40°C represents the amount of energy released by the battery when discharged at a 1C rate after standing at -40°C for 6 hours, with a cutoff voltage of 2.0V. The unit is ampere-hour (Ah). This data reflects the battery's discharge capability in low-temperature environments.

[0155] As shown in Table 2, a comparative analysis of the soft-pack batteries prepared in Examples 1-5 and Comparative Examples 1-3 shows that the introduction of the silicon-carbon material SC effectively improves the capacity and energy density of the battery; and with the addition of low-temperature additives and lithium supplements, the low-temperature discharge capability of the battery is further enhanced. At a temperature of -40°C, the discharge efficiency of the battery under 3C conditions can reach 71.68%.

[0156] Figure 2 This is a schematic diagram of the discharge capacity curve of the lithium-ion battery prepared in Example 2 of the present invention and the lithium-ion battery prepared in Comparative Example 1 using the prior art process. The curve shows the corresponding relationship between the battery's depth of discharge DOD (which is the percentage of the battery's discharge capacity to the battery's rated capacity) and the battery voltage. Figure 2 It can be seen that compared with Comparative Example 1, the battery prepared in Example 2 of the present invention has a higher discharge voltage platform at room temperature, which improves the discharge energy of the battery. Under low temperature conditions (-40°C), the discharge capacity curve of the battery in Example 2 of the present invention shows a relatively gentle voltage drop during the entire discharge process; while the voltage drop of the discharge capacity curve of the battery in Comparative Example 1 is faster, especially in the later stage of discharge, when the voltage drop is greater. Therefore, it can be shown that the battery prepared in the present invention has a higher discharge capacity, which fully demonstrates that the battery prepared in Example 2 of the present invention has obvious advantages in capacity and discharge voltage stability, has better performance in low temperature environments, and can better meet the needs of actual applications.

[0157] Compared with the prior art, the lithium-ion battery and preparation method provided by the present invention have the following beneficial effects:

[0158] 1. The preparation method of the present invention is simple to operate in terms of electrode production and battery assembly, has low professional requirements for employees, is low in cost, and does not consume unnecessary resources.

[0159] 2. The preparation method of this invention utilizes a pre-lithiation technique involving the addition of a lithium replenisher during the positive electrode homogenization process. This introduces a lithium replenisher with a high specific capacity and a delithiation potential below the upper voltage limit of the positive electrode material. This approach effectively replenishes the active lithium consumed by SEI formation during the initial cycle, thereby significantly increasing the battery's capacity and energy density. This step is simple to operate and inexpensive to manufacture.

[0160] 3. The electrolyte used in the preparation method of the present invention can effectively improve the process of lithium ion migration, increase the conductivity of the electrolyte, reduce viscosity and impedance, and effectively achieve high-rate discharge performance of lithium-ion batteries in low-temperature environments by adding low-melting-point solvents and additive components.

[0161] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A lithium-ion battery, characterized in that: comprising a battery casing and a battery electrode group located in the battery casing; The battery shell is filled with electrolyte; A battery electrode group, comprising a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet; Among them, the positive electrode sheet includes a positive electrode current collector; The upper and lower surfaces of the positive electrode current collector are respectively coated with a positive electrode active material coating; A positive electrode active material coating, comprising a positive electrode active material, a binder, a conductive agent and a positive electrode lithium supplement; The mass ratio of the positive electrode active material, the binder, the conductive agent and the positive electrode lithium supplement is: (90-96): (1-4): (1-5): (2-6); Among them, the negative electrode sheet includes a negative electrode current collector; The upper and lower surfaces of the negative electrode current collector are respectively coated with a negative electrode active material coating; A negative electrode active material coating, comprising a negative electrode active material, a dispersant, a binder and a conductive agent; The mass ratio of the negative electrode active material, the dispersant, the binder and the conductive agent is: (85-95): (1-4): (1-3): (1-5).

2. The lithium-ion battery according to claim 1, wherein The positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium-rich manganese-based materials, layered lithium manganese oxide and spinel lithium manganese oxide, or a coated modified material including at least one of lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium-rich manganese-based materials, layered lithium manganese oxide and spinel lithium manganese oxide.

3. The lithium-ion battery according to claim 2, wherein The positive electrode active material is lithium nickel cobalt manganese oxide.

4. The lithium-ion battery according to claim 1, wherein For the positive electrode active material coating, the conductive agent includes at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive carbon black, conductive graphite, carbon fiber and Ketjen black; For the positive electrode active material coating, the positive electrode lithium supplement comprises at least one of a binary lithium compound, a ternary lithium-containing compound, Li2O, and Li2O2; For the positive electrode active material coating, the binder is PVDF.

5. The lithium-ion battery according to claim 4, wherein The ternary lithium-containing compound includes at least one of Li2NiO2, Li5FeO4, Li6CoO4 and Li2CuO2.

6. The lithium-ion battery according to claim 1, wherein For the negative electrode active material coating, the negative electrode active material includes at least one of artificial graphite, natural graphite and silicon-carbon material, or includes a coating modified material of at least one of artificial graphite, natural graphite and silicon-carbon material.

7. The lithium-ion battery according to claim 1, wherein For the negative electrode active material coating, the binder is styrene-butadiene rubber (SBR); The dispersant is carboxymethyl cellulose CMC; For the negative electrode active material coating, the conductive agent includes at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive carbon black, conductive graphite, carbon fiber and Ketjen black.

8. The lithium-ion battery according to claim 1, wherein electrolyte, including lithium salt, organic solvent and additives; In the electrolyte, the mass percentage content of the lithium salt is 10% to 15%; the mass percentage content of the organic solvent is 70% to 80%; the mass percentage content of the additive is 10-20%; The lithium salt includes at least one of lithium hexafluorophosphate LiPF6, lithium tetrafluoroborate LiBF4 and lithium fluorosulfonate LiFSI. The organic solvent is a carbonate solvent, including at least one of ethylene carbonate EC, propylene carbonate PC, dimethyl carbonate DMC and ethyl methyl carbonate EMC; The additive includes at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), lithium difluorophosphate (LiPO2F2), lithium bis(fluorosulfonyl)imide (LiFSl), vinyl sulfate (DTD), lithium dioxalatoborate (LiODFB), 1,3-propane sultone (PS), and vinylene carbonate (VC).

9. A method for preparing a lithium ion battery according to any one of claims 1 to 8, characterized in that: The following steps are involved: The first step is the preparation of positive electrode slurry; Specifically, the positive electrode active material, binder, conductive agent and positive electrode lithium supplement are mixed uniformly according to a preset mass ratio, and then a solvent is added and stirred until a preset solid content is reached to prepare a positive electrode slurry; The second step is the production of positive electrode; Specifically, the positive electrode slurry obtained in the first step is evenly coated on the upper and lower surfaces of the positive electrode current collector, and then subjected to rolling, slitting and punching processes to obtain the positive electrode sheet; The third step is the preparation of negative electrode slurry; Specifically, the negative electrode active material, dispersant, binder and conductive agent are mixed uniformly according to a preset mass ratio, and then a solvent is added and stirred until a preset solid content is reached to prepare a positive electrode slurry; The fourth step is the production of negative electrode; Specifically, the negative electrode slurry obtained in the third step is evenly coated on the upper and lower surfaces of the negative electrode current collector, and then subjected to rolling, slitting and punching processes to obtain the negative electrode sheet; Step 5: Production of finished lithium-ion batteries; Specifically, the positive electrode sheet obtained in the second step, the negative electrode sheet obtained in the fourth step, and the separator are wound or stacked to prepare a battery electrode group, and then the battery electrode group is subjected to the external tab welding, shell insertion, hot pressing, liquid injection and formation processes in sequence to obtain a finished lithium-ion battery.

10. The method for preparing a lithium-ion battery according to claim 9, wherein: In the first step, the solid content of the cathode slurry is 50-65%; In the first step, the solvent in the cathode slurry is NMP; In the second step, the positive electrode current collector is aluminum foil; the thickness of the positive electrode sheet ranges from 90 to 120 μm; In the third step, the solid content of the negative electrode slurry is 35-50%; In the third step, the solvent in the negative electrode slurry is deionized water; In the fourth step, the negative electrode current collector is copper foil; the thickness of the negative electrode sheet ranges from 100 to 120 μm; In the fifth step, the electrolyte used in the injection process includes a lithium salt, an organic solvent and an additive. In the electrolyte, the mass percentage content of the lithium salt is 10% to 15%; the mass percentage content of the organic solvent is 70% to 80%; and the mass percentage content of the additive is 10-20%. The lithium salt includes at least one of lithium hexafluorophosphate LiPF6, lithium tetrafluoroborate LiBF4 and lithium fluorosulfonate LiFSI. The organic solvent is a carbonate solvent, including at least one of ethylene carbonate EC, propylene carbonate PC, dimethyl carbonate DMC and ethyl methyl carbonate EMC; The additive includes at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), lithium difluorophosphate (LiPO2F2), lithium bis(fluorosulfonyl)imide (LiFSl), vinyl sulfate (DTD), lithium dioxalatoborate (LiODFB), 1,3-propane sultone (PS), and vinylene carbonate (VC).

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