Negative electrode slurry, method of preparing the same, and lithium secondary battery and method of preparing the same

Abstract

The present application provides a kind of negative electrode slurry and its preparation method and lithium secondary battery and its preparation method.The negative electrode slurry includes negative electrode active material, conductive agent, binder and composite additive, wherein, the composite additive includes the combination of organic additive and inorganic additive, the organic additive includes one or more of cyclodextrin and alcohol amine compound, and the inorganic additive includes one or more of alkali metal and / or alkaline earth metal nitrate.The present application uses organic additive and inorganic additive as composite additive in the negative electrode slurry, through the synergistic effect of composite additive, can form thin and uniform coating on the surface of negative electrode material, which is thinner SEI film of negative electrode, lower battery resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to a negative electrode slurry and a preparation method thereof, and a lithium secondary battery and a preparation method thereof, in particular to a negative electrode slurry for reducing the internal resistance of a battery and a preparation method thereof, and a lithium secondary battery comprising the negative electrode slurry and a preparation method thereof, and belongs to the field of lithium ion batteries. BACKGROUND

[0002] The direct current resistance of a lithium ion battery is mainly composed of ohmic impedance, charge transfer resistance and charge transport resistance. Among them, the charge transfer resistance is mainly contributed by the shuttle of lithium ions between the interface electrolyte layer between the positive electrode, the negative electrode active material particles and the electrolyte. And Li + The impedance of the SEI film on the surface of the negative electrode is the main contribution to the charge transfer resistance, which is greatly affected by the structure and thickness of the SEI film.

[0003] The prior art mainly realizes the regulation of the structure and composition of the SEI film through surface modification / modification of the negative electrode main material, electrolyte composition and formation strategy. The regulation content includes the composition of the SEI film, such as the ratio and composition of organic / inorganic components, and the regulation of the overall thickness of the SEI film. Such regulation technology mainly focuses on: (1) the use of solvents, organic small molecule additives and lithium salt additives in the electrolyte, which realizes the protection of the negative electrode surface SEI film through the specific oxidation-reduction reaction of the additives; (2) the introduction of artificial SEI film, such as organic polymer, organic small molecule coated graphite or negative electrode sheet surface layer; (3) formation system regulation.

[0004] Some documents disclose a negative electrode slurry which improves the cycle stability and conductivity of the battery by adding sodium alginate and cyclodextrin as organic additives. However, the introduction of organic small molecule additives may cause the SEI film on the surface of the negative electrode to thicken, causing the battery resistance to increase.

[0005] Some documents disclose a negative electrode slurry comprising a negative electrode material, a conductive agent, a binder and a stable lithium salt, wherein the stable lithium salt comprises inorganic additives such as lithium fluoride, lithium carbonate, lithium phosphate, lithium oxalate or lithium nitrate. By introducing the stable lithium salt, a degradation reaction occurs during the first charge and discharge of the battery to form a coating on the negative electrode, which can reduce the loss of lithium ions in the first charge and discharge of the positive electrode, thereby improving the energy density of the lithium battery, and also helps to improve the cycle performance of the battery. However, due to the low adhesion between inorganic particles and graphite, the contact between the formed protective layer and the negative electrode material is limited, so the improvement degree of the SEI film structure is limited.

[0006] It can be seen that although the prior art has made certain research on the regulation of the composition of the negative electrode slurry to control the structure of the SEI film, it is not sufficient to reduce the battery resistance, and there is still room for further research. SUMMARY

[0007] The invention addresses the problem

[0008] As described above, it is necessary to provide a negative electrode slurry with appropriate components and a slurry preparation process to achieve the optimization and thickness control of the SEI film structure on the surface of the negative electrode to achieve the purpose of reducing the internal resistance of the battery.

[0009] The solution to the problem

[0010] The present application uses organic additives and inorganic additives in combination in the negative electrode slurry. On the one hand, due to the strong intermolecular forces of the organic additives, they can be adsorbed on the surface of the negative electrode material; on the other hand, the specific organic additives of the present application have a cavity structure or a cavity structure formed by assembling the organic additives, which can anchor the inorganic additives, so that part of the inorganic additives is embedded inside the organic additive molecules and the other part exists between the organic additive molecules, and the whole forms a reticular or core-shell structure on the surface of the negative electrode. In the process of forming the SEI film, a synergistic effect is produced, which thins the SEI film and obtains a more dense, uniform and thinner SEI film, and finally achieves the purpose of significantly reducing the internal resistance of the battery.

[0011] The inorganic additive used in the present application is one or more of the nitrate salts of alkali metal and / or alkaline earth metal. In the first charging process of the full battery, the NO3 - can undergo a reduction reaction to form LiN x O y and Li3N and other compounds with high lithium ion conductivity, and at the same time, due to the good adhesion and coating of the organic additives on the surface of the negative electrode material, based on the anchoring effect of the inorganic additives, the compound layer obtained after the reduction of the inorganic additives can be firmly fixed on the surface of the negative electrode material, and finally a thin and uniform coating is formed on the surface of the negative electrode material, which is manifested as a thinner SEI film on the negative electrode and a lower battery internal resistance.

[0012] In the preparation method of the negative electrode slurry of the present application, the addition sequence of the organic additive and the inorganic additive is adjusted, so as to adjust the distribution of the organic / inorganic components in the SEI, which overall shows a more dense, uniform and thinner SEI film, thereby significantly reducing the internal resistance of the battery.

[0013] The present application first provides a negative electrode slurry, which comprises a negative electrode active material, a conductive agent, a binder and a composite additive,

[0014] wherein the composite additive comprises a combination of an organic additive and an inorganic additive,

[0015] The organic additive includes one or more of cyclodextrin and alcohol amine compounds,

[0016] The inorganic additive includes one or more of nitrate salts of alkali metal and / or alkaline earth metal.

[0017] According to the negative electrode slurry of the present application, the cyclodextrin includes one or more of a-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, and derivatives thereof; and / or,

[0018] The alcohol amine compound includes one or more of methanol amine compound, ethanol amine compound, and propanol amine compound.

[0019] Preferably, the ethanol amine compound includes one or more of ethanol amine, diethanol amine, and triethanol amine; and / or,

[0020] The nitrate salt of alkali metal and / or alkaline earth metal includes one or more of LiNO3, NaNO3, Ca(NO3)2, and Mg(NO3)2.

[0021] According to the negative electrode slurry of the present application, the organic additive is coated on the surface of the negative electrode active material, and a part of the inorganic additive is embedded inside the organic additive molecule, and another part of the inorganic additive exists between the organic additive molecules.

[0022] According to the negative electrode slurry of the present application, the weight ratio of the inorganic additive to the organic additive is 20:1 to 3:1.

[0023] According to the negative electrode slurry of the present application, the weight ratio of the negative electrode active material, the conductive agent, the binder, and the composite additive is 93 to 98 wt%: 0.5 to 1.5 wt%: 0.5 to 3.5 wt%: 0.1 to 2 wt%; and / or,

[0024] The negative electrode active material includes one or more of graphite, hard carbon, silicon-carbon material, lithium metal, and tin-based material; and / or,

[0025] The conductive agent includes one or more of conductive graphite, graphene, acetylene black, carbon black, and carbon nanotube; and / or,

[0026] The binder includes one or more of sodium carboxymethyl cellulose, chitosan, sodium lignocellulose, butadiene-styrene rubber, styrene-butadiene rubber, sodium polymethacrylate, lithium polymethacrylate, polymethacrylate, and polyvinylidene fluoride.

[0027] In addition, the present application also provides a preparation method of the negative electrode slurry, which includes the following steps:

[0028] Step S1: stirring the negative electrode active material, the conductive agent and the solvent to obtain a slurry;

[0029] Step S2: adding the composite additive to the slurry obtained in Step S1 and stirring, and then adding the solvent to adjust the viscosity of the slurry;

[0030] Step S3: adding the binder and stirring to obtain a negative electrode slurry,

[0031] wherein the composite additive comprises a combination of an organic additive and an inorganic additive,

[0032] the organic additive comprises one or more of cyclodextrin and alcohol amine compounds,

[0033] the inorganic additive comprises one or more of nitrate salts of alkali metal and / or alkaline earth metal.

[0034] According to the preparation method of the present application, the cyclodextrin comprises one or more of a-cyclodextrin, β-cyclodextrin, γ-cyclodextrin and derivatives thereof; and / or

[0035] the alcohol amine compound comprises one or more of methanol amine compound, ethanol amine compound and propanol amine compound;

[0036] Preferably, the ethanol amine compound comprises one or more of ethanol amine, diethanol amine and triethanol amine; and / or,

[0037] the nitrate salt of alkali metal and / or alkaline earth metal comprises one or more of LiNO3, NaNO3, Ca(NO3)2 and Mg(NO3)2; and / or

[0038] the weight ratio of the total amount of the inorganic additive to the total amount of the organic additive is 20:1 to 3:1; and / or

[0039] the weight ratio of the negative electrode active material, the conductive agent, the binder and the composite additive is 93-98 wt%: 0.5-1.5 wt%: 0.5-3.5 wt%: 0.1-2 wt%; and / or

[0040] the negative electrode active material comprises one or more of graphite, hard carbon, silicon-carbon material, lithium metal and tin-based material; and / or

[0041] the conductive agent comprises one or more of conductive graphite, graphene, acetylene black, carbon black and carbon nanotube; and / or,

[0042] the binder comprises one or more of sodium carboxymethyl cellulose, chitosan, sodium lignocellulose, butadiene-styrene rubber, styrene-butadiene rubber, sodium polymethacrylate, lithium polymethacrylate, polymethacrylate and polyvinylidene fluoride.

[0043] According to the preparation method, the slurry in step S1 further comprises a dispersant.

[0044] Preferably, the dispersant comprises one or more of sodium carboxymethyl cellulose, chitosan, sodium lignocellulose, styrene butadiene rubber, styrene propylene rubber, sodium polymethacrylate, lithium polymethacrylate, and polymethacrylate.

[0045] According to the preparation method, in step S2, the composite additive is added in the following manner: first, 50-100% of the total amount of organic additive is added, then 50-100% of the total amount of inorganic additive is added, then optionally, the remaining organic additive is added, and then optionally, the remaining inorganic additive is added.

[0046] Preferably, the composite additive is added in the following manner: first, 50-80% of the total amount of organic additive is added, then 100% of the total amount of inorganic additive is added, and then the remaining organic additive is added.

[0047] Further, the present application also provides a lithium secondary battery comprising a negative electrode sheet, a positive electrode sheet, a separator, an electrolyte, and a battery shell,

[0048] wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode layer on the negative electrode current collector,

[0049] the negative electrode layer is formed from the negative electrode slurry of the present application or from the negative electrode slurry obtained by the preparation method of the present application.

[0050] Further, the present application also provides a preparation method of the lithium secondary battery according to the present application, which comprises the following steps: assembling the negative electrode sheet and the positive electrode sheet with the separator, the electrolyte, and the battery shell, and then performing a formation process.

[0051] According to the preparation method, the formation process comprises the following steps: after the lithium battery is assembled, the battery is injected with electrolyte and then left to stand, and then the battery is charged.

[0052] wherein the charging step comprises the following steps in sequence:

[0053] Step a: charging for a time T1 using a current I1, and then standing for 5-20 min; wherein I1=0.06-0.12C, and T1=30-60 min.

[0054] Step b: charging for a time T2 using a current I2, and then standing for 5-20 min; wherein I2=0.06-0.24C, and T2=15-60 min.

[0055] Step c: charging with current I3 for time T3, and standing for 5-20 min; wherein I3=0.12-0.48C, T3=90-360 min.

[0056] Wherein, I1≤I2, I2≤I3, and I1, I2, I3 are not equal at the same time.

[0057] According to the preparation method, wherein,

[0058] When I1=I2, optionally, the charging step comprises in sequence:

[0059] Step ab: charging with current I1 for time T1+T2, and standing for 5-20 min; wherein I1=0.06-0.12C, T1+T2=45-120 min.

[0060] Step c: charging with current I3 for time T3, and standing for 5-20 min; wherein I3=0.12-0.48C, T3=90-360 min; or,

[0061] When I2=I3, optionally, the charging step comprises in sequence:

[0062] Step a: charging with current I1 for time T1, and standing for 5-20 min; wherein I1=0.06-0.12C, T1=30-60 min.

[0063] Step bc: charging with current I2 for time T2+T3, and standing for 5-20 min; wherein I2=0.12-0.24C, T2+T3=105-420 min.

[0064] Effects of the invention

[0065] The above technical solutions of the present application have the following beneficial effects:

[0066] 1) The negative electrode slurry provided by the present application introduces organic additives and inorganic additives as composite additives. The organic additives have strong intermolecular forces, can be adsorbed on the surface of the negative electrode material, and anchor the inorganic additives through the cavity structure of the specific organic additives, forming a reticular or core-shell structure on the surface of the negative electrode. In the process of forming the SEI film of the negative electrode, a synergistic effect is produced, the SEI film is thinned, a more dense, uniform and thin SEI film is obtained, and the purpose of significantly reducing the internal resistance of the battery is finally achieved.

[0067] 2) The preparation method of the negative electrode slurry provided by the present application can improve the utilization rate of the electrochemical reaction product of the composite additive, increase the effective coating degree of the negative electrode material, and guide the distribution of the organic / inorganic components in the SEI, and the overall performance is a more dense, uniform and thin SEI film, and the effect is a significant reduction in the internal resistance of the battery.

[0068] 3) The formation process of the lithium secondary battery provided by the present application can promote the double-electron reduction reaction of the organic additive under a large current, and further reduce the internal resistance of the battery in cooperation with the components of the SEI film formed by the inorganic additive. BRIEF DESCRIPTION OF DRAWINGS

[0069] Figure 1 A schematic structural diagram of the negative electrode slurry of the present application is shown. DETAILED DESCRIPTION

[0070] Various exemplary embodiments, features and aspects of the present application will be described in detail below. The word "exemplary" used herein means "serving as an example, an embodiment or illustrative". Any embodiment described herein as "exemplary" is not necessarily to be construed as being superior to or preferable over other embodiments.

[0071] In addition, in order to better illustrate the present application, numerous specific details are given in the following detailed description. Those skilled in the art should understand that the present application can be implemented without certain specific details. In some other examples, methods, means, apparatus and steps that are well known to those skilled in the art are not described in detail, in order to highlight the main idea of the present application.

[0072] Unless otherwise stated, the units used in the specification are international standard units, and the numerical values and numerical ranges appearing in the present application should be understood to include the systematic errors that are inevitable in industrial production.

[0073] In the present specification, the meaning of "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

[0074] In the present specification, "some specific / preferred embodiments", "some other specific / preferred embodiments", "embodiments" and the like refer to the specific elements (e.g. features, structures, properties and / or characteristics) described in relation to the embodiment, which are included in at least one embodiment described herein, and can be present in other embodiments or can not be present in other embodiments. In addition, it should be understood that the elements can be combined in various embodiments in any suitable manner.

[0075] In the present specification, a numerical range indicated using "numerical value A ~ numerical value B" means a range including the end point numerical values A and B.

[0076] <First aspect>

[0077] The first aspect of the present application provides a negative electrode slurry including a negative electrode active material, a conductive agent, a binder, and a composite additive,

[0078] The composite additive includes a combination of an organic additive and an inorganic additive,

[0079] The organic additive includes one or more of a cyclodextrin and an alcohol amine compound,

[0080] The inorganic additive includes one or more of a nitrate salt of an alkali metal and / or an alkaline earth metal.

[0081] In some specific embodiments, the cyclodextrin can include one or more of an a-cyclodextrin, a β-cyclodextrin, a γ-cyclodextrin, and derivatives thereof, and the like, and preferably a β-cyclodextrin. Cyclodextrin has a cavity that can accommodate lithium ions in the inorganic additive, thereby improving the binding force with the inorganic additive. Among the cyclodextrins, β-cyclodextrin is preferred, mainly because β-cyclodextrin has a more suitable cavity volume and can better accommodate lithium ions in the inorganic additive, thereby exhibiting a higher binding force between the organic additive and the inorganic additive.

[0082] In some specific embodiments, the alcohol amine compound can include one or more of a methanol amine compound, an ethanol amine compound, a propanol amine compound, and the like, and preferably an ethanol amine compound, and more preferably the ethanol amine compound can include one or more of ethanol amine, diethanol amine, triethanol amine, and the like, and preferably diethanol amine. Through the assembly of the alcohol amine compound, a cavity structure can be formed to anchor the inorganic additive, achieving a synergistic effect.

[0083] In some specific embodiments, the nitrate salt of the alkali metal and / or the alkaline earth metal includes one or more of LiNO3, NaNO3, Ca(NO3)2, Mg(NO3)2, and the like, and preferably LiNO3.

[0084] In some specific embodiments, the combination of the composite additive can be a combination of one organic additive with one or more inorganic additives, or a combination of one inorganic additive with multiple organic additives.

[0085] In some preferred embodiments, the organic additive coats the surface of the negative electrode active material, and part of the inorganic additive is embedded inside the organic additive molecules and part of the inorganic additive exists between the organic additive molecules. The whole forms a reticular or core-shell structure on the surface of the negative electrode, and a thin and uniform SEI film is formed on the negative electrode by synergistic effect, thereby achieving the purpose of significantly reducing the internal resistance of the battery. The reticular structure herein refers to a network-like structure formed by the organic additive molecules covering the surface of the active material; the core-shell structure refers to a structure in which the organic additive wraps the inorganic additive.

[0086] Figure 1 A schematic structural diagram of the negative electrode slurry of the present application is shown. From the diagram, it can be seen that the organic additive coats the surface of the negative electrode active material, and most of the inorganic additive is embedded in the organic additive molecules, and a small part is between the organic additive molecules. Finally, the outermost layer is an organic additive layer, which is not shown in the drawing. Figure 1

[0087] In some specific embodiments, the weight ratio of the inorganic additive to the organic additive is 20:1 to 3:1, for example, 18:1, 16:1, 13:1, 11:1, 9:1, 7:1, 5:1, etc. When the weight ratio of the inorganic additive to the organic additive is too high, it will cause waste of the inorganic additive, and may cause the SEI film to thicken, thereby increasing the internal resistance of the battery; when the weight ratio of the inorganic additive to the organic additive is too low, the fixing effect of the organic additive on the inorganic additive will be weakened, thereby weakening the synergistic effect.

[0088] In some specific embodiments, the weight ratio of the negative electrode active material, the conductive agent, the binder and the composite additive is 93-98 wt%: 0.5-1.5 wt%: 0.5-3.5 wt%: 0.1-2 wt%.

[0089] For the negative electrode active material, the present application is not particularly limited and can be the active material commonly used in the art, for example, can include one or more of graphite, hard carbon, silicon-carbon material, lithium metal, tin-based material, etc.

[0090] For the conductive agent, the present application is not particularly limited and can be the conductive agent commonly used in the art, for example, can include one or more of conductive graphite, graphene, acetylene black, carbon black, carbon nanotube (CNT).

[0091] For the binder, the present application is not particularly limited and can be the binder commonly used in the art, for example, can include one or more of sodium carboxymethyl cellulose, chitosan, sodium lignocellulose, styrene butadiene rubber (SBR), phenylpropyl rubber, sodium polymethacrylate, lithium polymethacrylate, polymethacrylate, polyvinylidene fluoride (PVDF).​

[0092] In some preferred embodiments, by adding the composite additive described in the present application, the internal resistance of the lithium battery can be reduced by 5% to 15% under the conventional formulation system.

[0093] <Second aspect>

[0094] The second aspect of the present application provides a preparation method of the negative electrode slurry according to the first aspect, comprising the following steps:

[0095] Step S1: stirring the negative electrode active material, the conductive agent and the solvent to obtain a slurry;

[0096] Step S2: adding the composite additive to the slurry obtained in step S1 and stirring, and then adding the solvent to adjust the viscosity of the slurry;

[0097] Step S3: adding the binder and stirring to obtain the negative electrode slurry,

[0098] wherein the composite additive comprises a combination of an organic additive and an inorganic additive,

[0099] the organic additive comprises one or more of cyclodextrin and alcohol amine compounds,

[0100] the inorganic additive comprises one or more of nitrate salts of alkali metal and / or alkaline earth metal.

[0101] The types, amounts, and usage ratios of the components of the negative electrode active material, the conductive agent, the binder, the cyclodextrin, the alcohol amine compound, the nitrate salt of alkali metal and / or alkaline earth metal, and the like in the present aspect are the same as those in the first aspect, and will not be described here.

[0102] As for the solvent, the present application is not particularly limited and can be a commonly used solvent in the art, for example, can include one of N-methyl pyrrolidone, deionized water, and the like.

[0103] In some specific embodiments, the slurry of step S1 can further comprise a dispersing agent. As for the type of the dispersing agent, it is not particularly limited and can be selected as needed, for example, can include one or more of sodium carboxymethyl cellulose, chitosan, sodium lignocellulose, butadiene styrene rubber, phenylpropyl rubber, sodium polymethacrylate, lithium polymethacrylate, and polymethacrylate.

[0104] In some preferred embodiments, step S1 comprises: mixing the negative electrode active material with the conductive agent, adding the dispersing agent, and forming a kneaded state by stirring; and continuously adding the dispersing agent or the solvent and stirring to achieve a flowable state to obtain the slurry.

[0105] In some specific embodiments, the adding of the composite additive in step S2 can include: first adding 50-100% by mass, for example 60%, 70%, 80%, 90% by mass, of the total amount of the organic additive, then adding 50-100% by mass, for example 60%, 70%, 80%, 90% by mass, of the total amount of the inorganic additive, and then optionally adding the remaining organic additive, and then optionally adding the remaining inorganic additive.

[0106] In some specific embodiments, the adding of the composite additive can include: first adding 50-80% by mass, for example 55%, 60%, 65%, 70%, 75% by mass, of the total amount of the organic additive, then adding 100% by mass of the total amount of the inorganic additive, and then adding the remaining organic additive.

[0107] The first part of the organic additive adheres to the surface of the negative active material and binds with the negative active material, then the inorganic additive is added, and the inorganic additive is attached to the inside or surface of the organic additive through the anchoring effect of the organic additive; finally, the organic additive is added to further uniformly coat the exposed surface of the inorganic additive. The whole forms a network or core-shell structure on the surface of the negative electrode. The batched addition of the organic additive can provide additional pre-coating for the inorganic additive, thereby preventing the problem of uneven dispersion of the inorganic additive caused by one-time addition of the organic additive.

[0108] In some more specific embodiments, after the composite additive is added and stirred in step S2, a solvent needs to be added to adjust the viscosity of the slurry. The viscosity of the slurry can be 2000-5000 cp, for example, 2500 cp, 3000 cp, 3500 cp, 4000 cp, 4500 cp, etc.

[0109] In some specific embodiments, in step S3, in order to more uniformly mix the raw materials, the stirring can be performed at a slow stirring rate, which can be 20-200 r / min. In addition, in order to further improve the quality of the negative electrode slurry, the stirring can further include the steps of removing bubbles and filtering. The method for removing bubbles is not particularly limited and can be performed by a method commonly used in the art, such as vacuum degassing.

[0110] <Third aspect>

[0111] The third aspect of the present application provides a lithium secondary battery, which comprises a negative electrode sheet, a positive electrode sheet, a separator, an electrolyte and a battery shell. The negative electrode sheet comprises a negative electrode current collector and a negative electrode layer on the negative electrode current collector, and the negative electrode layer is formed by the negative electrode slurry of the first aspect or the negative electrode slurry obtained by the preparation method of the second aspect.

[0112] The negative electrode current collector is not particularly limited in the present application and can be a conventional negative electrode current collector in the art.

[0113] The positive electrode sheet is not particularly limited in the present application and can be a conventional positive electrode sheet in the art, for example, a lithium iron phosphate electrode sheet, a lithium iron manganese phosphate electrode sheet, a lithium manganese electrode sheet, and a ternary electrode sheet such as a lithium nickel manganese cobalt oxide electrode sheet, a lithium nickel cobalt aluminum oxide electrode sheet, and the like.

[0114] The separator is not particularly limited in the present application and can be a conventional separator in the art.

[0115] The electrolyte is not particularly limited in the present application and can be a conventional electrolyte in the art.

[0116] <Fourth aspect>

[0117] The fourth aspect of the present application provides a preparation method of the lithium secondary battery according to the third aspect, which comprises the following steps: assembling the negative electrode sheet and the positive electrode sheet with the separator, the electrolyte and the battery shell, and then performing a formation process.

[0118] In some specific embodiments, the formation process comprises the following steps: after the lithium battery is assembled, the battery is injected with electrolyte and then is left to stand, and then is charged. The standing mode is not particularly limited and can be selected as required, for example, the standing step can comprise standing at 30-55℃ for 24-48h.

[0119] The formation process of the present application can use a conventional formation system or an optimized formation system.

[0120] In the optimized formation system, the charging step comprises the following steps in sequence:

[0121] Step a: charging for a time T1 using a current I1 and then standing for 5-20min; wherein I1=0.06-0.12C and T1=30-60min;

[0122] Step b: charging for a time T2 using a current I2 and then standing for 5-20min; wherein I2=0.06-0.24C and T2=15-60min;

[0123] Step c: charging with current I3 for time T3, and standing for 5-20 min; wherein, I3 = 0.12-0.48C, T3 = 90-360 min.

[0124] Wherein, I1≤I2, I2≤I3, and I1, I2, I3 are not equal at the same time.

[0125] When I1 = I2, the charging steps comprise in sequence:

[0126] Step ab: charging with current I1 for time T1+T2, and standing for 5-20 min; wherein, I1 = 0.06-0.12C, T1+T2 = 45-120 min.

[0127] Step c: charging with current I3 for time T3, and standing for 5-20 min; wherein, I3 = 0.12-0.48C, T3 = 90-360 min.

[0128] When I2 = I3, the charging steps comprise in sequence:

[0129] Step a: charging with current I1 for time T1, and standing for 5-20 min; wherein, I1 = 0.06-0.12C, T1 = 30-60 min.

[0130] Step bc: charging with current I2 for time T2+T3, and standing for 5-20 min; wherein, I2 = 0.12-0.24C, T2+T3 = 105-420 min.

[0131] By the optimized formation system of the present application, the proportion and composition of organic / inorganic components in SEI film can be changed, thereby further reducing the internal resistance of lithium battery.

[0132] In some preferred embodiments, under the optimized formation system, the internal resistance of lithium battery can be reduced by 20%-35%.

[0133] In some specific embodiments, the preparation method of lithium secondary battery further comprises the steps of aging, capacity grading, K value testing, etc. The aging method is not particularly limited and can be selected as required. Preferably, the aging step comprises aging at 30-55℃ for 24-48 hours.

[0134] Examples

[0135] The embodiments of the present application will be described in detail below with reference to Examples, but those skilled in the art will understand that the following Examples are only for illustration of the present application and should not be considered as limiting the scope of the present application. The specific conditions not noted in the Examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not noted by the manufacturer, which are all conventional products that can be obtained by purchase.

[0136] Comparative Example 1

[0137] (1) The composition of the negative electrode slurry: the weight ratio of active material: conductive agent: binder: composite additive is 96%: 1.0%: 3.0%: 0. Wherein, the active material is graphite, the conductive agent is carbon nanotube CNT, and the binder is butadiene rubber SBR.

[0138] (2) The preparation method of the negative electrode slurry:

[0139] Step S1: uniformly mix the active material powder and the conductive agent material, and form a kneaded state by stirring; continue to add deionized water and stir to achieve a flowable state, and the slurry viscosity is 3600cp;

[0140] Step S3: add the binder, slowly stir, vacuum to remove bubbles, filter, and discharge.

[0141] (3) The preparation method of the lithium secondary battery:

[0142] The negative electrode slurry in (2) is further made into a pole piece, assembled with a lithium iron phosphate positive electrode pole piece, an electrolyte, a separator, and a battery shell to obtain a lithium battery. After the lithium battery is injected with liquid and placed at 50°C for 24-48h, formation is carried out.

[0143] The formation process includes:

[0144] Step a: charge the battery at 0.04C for 60min, and stand for 20min;

[0145] Step b: charge at 0.08C for 60min, and stand for 20min;

[0146] Step c: charge at 0.16C for 300min; stand for 20min;

[0147] After aging at 50°C for another 48h, the K value is measured to obtain the lithium secondary battery.

[0148] Example 1

[0149] (1) The composition of the negative electrode slurry: the weight ratio of active material: conductive agent: binder: composite additive is 96%: 1.0%: 2.0%: 1.0%. Wherein, the active material is graphite, the conductive agent is carbon nanotube CNT, and the binder is butadiene rubber SBR.

[0150] (2) Preparation method of negative electrode slurry:

[0151] Step S1: uniformly mix the active material powder and the conductive agent material, and form a kneaded state by stirring; continue to add deionized water and stir to achieve a flowable state;

[0152] Step S2: add a composite additive, which contains 0.08 mass% β-cyclodextrin and 0.92 mass% LiNO3, first add 0.04 mass% (50 mass% of the total amount of β-cyclodextrin addition) β-cyclodextrin, stir for 10 min, then add 0.92 mass% LiNO3 (100 mass% of the total amount of LiNO3 addition) and continue to stir, after stirring for 20 min, add 0.04 mass% (50 mass% of the total amount of β-cyclodextrin addition) β-cyclodextrin, stir for 10 min, and add deionized water to adjust the slurry viscosity to 2900 cp;

[0153] Step S3: add a binder, slowly stir, vacuum degassing to remove bubbles, filter, and discharge.

[0154] (3) Preparation method of lithium secondary battery:

[0155] The negative electrode slurry in (2) is further subjected to electrode sheet making, assembled with lithium iron phosphate positive electrode sheet, electrolyte, separator, and battery shell to obtain a lithium battery. After the lithium battery is injected with liquid and is placed at 50°C for 24-48h, formation is performed.

[0156] The formation process includes:

[0157] Step a: charge the battery at 0.04C for 60 min, and stand for 20 min;

[0158] Step b: charge at 0.08C current for 60 min, and stand for 20 min;

[0159] Step c: charge at 0.16C current for 300 min; stand for 20 min;

[0160] After aging at 50°C for another 48h, the lithium secondary battery is obtained by capacity distribution and K value measurement.

[0161] Example 2

[0162] (1) Composition of negative electrode slurry: the weight ratio of active material: conductive agent: binder: composite additive is 96%: 1.0%: 2.0%: 1.0%. Among them, the active material is graphite, the conductive agent is carbon nanotube CNT, and the binder is butadiene rubber SBR.

[0163] (2) Preparation method of negative electrode slurry:

[0164] Step S1: mix the active material powder and the conductive agent material uniformly, form a kneaded state by stirring; continue to add deionized water and stir to achieve a flowable state;

[0165] Step S2: add the composite additive, the composite additive contains 0.08 mass% β-cyclodextrin and 0.92 mass% LiNO3, add 0.08 mass% (100 mass% of the total amount of β-cyclodextrin addition) β-cyclodextrin, stir for 20 min, then add 0.92 mass% LiNO3 (100 mass% of the total amount of LiNO3 addition) and continue to stir for 20 min, add deionized water to adjust the slurry viscosity to 2600 cp;

[0166] Step S3: add the binder, slow stirring, vacuum degassing, filtration, and discharge.

[0167] (3) Preparation method of lithium secondary battery:

[0168] The negative electrode slurry in (2) is further subjected to tab making, and lithium phosphate positive electrode tabs, electrolyte, separator, and battery shell are assembled to obtain a lithium battery. After the lithium battery is injected with liquid and is placed at 50°C for 24-48h, formation is performed.

[0169] The formation process includes:

[0170] Step a: charge the battery at 0.04C for 60 min, and stand for 20 min;

[0171] Step b: charge at 0.08C for 60 min, and stand for 20 min;

[0172] Step c: charge at 0.16C for 300 min; stand for 20 min;

[0173] After aging at 50°C for another 48h, the K value is measured, and a lithium secondary battery is obtained.

[0174] Example 3

[0175] (1) Composition of the negative electrode slurry: the weight ratio of active material: conductive agent: binder: composite additive is 96%: 1.0%: 2.0%: 1.0%. Among them, the active material is graphite, the conductive agent is carbon nanotube CNT, and the binder is butadiene rubber SBR.

[0176] (2) Preparation method of the negative electrode slurry:

[0177] Step S1: mix the active material powder and the conductive agent material uniformly, form a kneaded state by stirring; continue to add deionized water and stir to achieve a flowable state;

[0178] Step S2: Add composite additive, the composite additive contains 0.08 mass% β-cyclodextrin and 0.92 mass% LiNO3, add 0.92 mass% (100 mass% of the total amount of LiNO3 addition) LiNO3, stir uniformly, then add 0.08 mass% β-cyclodextrin (100 mass% of the total amount of β-cyclodextrin addition) and continue to stir, add deionized water to adjust the slurry viscosity to 3250 cp;

[0179] Step S3: Add binder, slow stirring, vacuum degassing to remove bubbles, filter, and discharge.

[0180] (3) A method for preparing a lithium secondary battery:

[0181] The negative electrode slurry in (2) is further subjected to tab making, and a lithium phosphate iron lithium positive electrode tab, an electrolyte, a separator, and a battery shell are assembled to obtain a lithium battery. After the lithium battery is injected with liquid and is placed at 50°C for 24-48h, formation is performed.

[0182] The formation process includes:

[0183] Step a: charge the battery at 0.04C for 60 min, and stand for 20 min;

[0184] Step b: charge at 0.08C for 60 min, and stand for 20 min;

[0185] Step c: charge at 0.16C for 300 min; stand for 20 min;

[0186] After aging at 50°C for another 48h, the K value is measured, and a lithium secondary battery is obtained.

[0187] Example 4

[0188] (1) The composition of the negative electrode slurry: the weight ratio of active material: conductive agent: binder: composite additive is 96%: 1.0%: 2.0%: 1.0%. Among them, the active material is graphite, the conductive agent is carbon nanotube CNT, and the binder is butadiene rubber SBR.

[0189] (2) A method for preparing a negative electrode slurry:

[0190] Step S1: uniformly mix the active material powder and the conductive agent material, and form a kneaded state by stirring; continue to add deionized water and stir to achieve a flowable state;

[0191] Step S2: Add the composite additive, which contains 0.08 mass% of β-cyclodextrin and 0.92 mass% of LiNO3, first mix 0.08 mass% (100 mass% of the total amount of β-cyclodextrin added) of β-cyclodextrin and 0.92 mass% of LiNO3 (100 mass% of the total amount of LiNO3 added) uniformly, add them to the slurry at one time, stir for 40 min, and add deionized water to adjust the viscosity of the slurry to 3600 cp;

[0192] Step S3: Add the binder, stir slowly, vacuum to remove bubbles, filter, and discharge.

[0193] (3) A method for preparing a lithium secondary battery:

[0194] The negative electrode slurry in (2) is further subjected to tab making, and a lithium phosphate positive electrode tab, an electrolyte, a separator, and a battery shell are assembled to obtain a lithium battery. After the lithium battery is injected with liquid and is left to stand at 50°C for 24-48 h, formation is performed.

[0195] The formation process includes:

[0196] Step a: Charge the battery at 0.04C for 60 min, and leave it to stand for 20 min;

[0197] Step b: Charge the battery at 0.08C for 60 min, and leave it to stand for 20 min;

[0198] Step c: Charge the battery at 0.16C for 300 min; leave it to stand for 20 min;

[0199] After aging at 50°C for another 48 h, the K value is measured, and a lithium secondary battery is obtained.

[0200] Example 5

[0201] (1) The composition of the negative electrode slurry: the weight ratio of active material: conductive agent: binder: composite additive is 95.4%: 1.0%: 2.0%: 1.6%. Among them, the active material is graphite, the conductive agent is carbon nanotube CNT, and the binder is butadiene rubber SBR.

[0202] (2) A method for preparing a negative electrode slurry:

[0203] Step S1: Mix the active material powder and the conductive agent material uniformly, and form a kneaded state by stirring; continue to add deionized water and stir to achieve a flowable state;

[0204] Step S2: Add the composite additive, which contains 0.16 mass% of β-cyclodextrin and 1.44 mass% of LiNO3, first add 0.16 mass% (100 mass% of the total amount of β-cyclodextrin added) of β-cyclodextrin, stir for 20 min, then add 1.44 mass% of LiNO3 (100 mass% of the total amount of LiNO3 added), continue to stir for 20 min, and add deionized water to adjust the slurry viscosity to 2800 cp;

[0205] Step S3: Add the binder, stir slowly, vacuum to remove bubbles, filter, and discharge.

[0206] (3) A method for preparing a lithium secondary battery:

[0207] The negative electrode slurry in (2) is further subjected to tab making, and a lithium phosphate positive electrode tab, an electrolyte, a separator, and a battery shell are assembled to obtain a lithium battery. After the lithium battery is injected with liquid and is placed at 50°C for 24-48h, formation is performed.

[0208] The formation process includes:

[0209] Step a: Charge the battery at 0.04C for 60 min, and stand for 20 min;

[0210] Step b: Charge the battery at 0.08C for 60 min, and stand for 20 min;

[0211] Step c: Charge the battery at 0.16C for 300 min; stand for 20 min;

[0212] After aging at 50°C for another 48h, the lithium secondary battery is obtained by measuring the K value.

[0213] Example 6

[0214] (1) The composition of the negative electrode slurry: the weight ratio of active material: conductive agent: binder: composite additive is 95.4%: 1.0%: 2.0%: 1.6%. Among them, the active material is graphite, the conductive agent is carbon nanotube CNT, and the binder is butadiene rubber SBR.

[0215] (2) A method for preparing a negative electrode slurry:

[0216] Step S1: Mix the active material powder and the conductive agent material uniformly, and form a kneaded state by stirring; continue to add deionized water and stir to achieve a flowable state;

[0217] Step S2: Add the composite additive, which contains 0.08 mass% β-cyclodextrin, 0.08 mass% ethylene glycol amine and 1.44 mass% LiNO3, first add 0.08 mass% (100 mass% of the total amount of β-cyclodextrin added) β-cyclodextrin, 0.08 mass% (100 mass% of the total amount of ethylene glycol amine added) ethylene glycol amine, stir for 20 min, then add 1.44 mass% LiNO3 (100 mass% of the total amount of LiNO3 added), continue to stir for 20 min, add deionized water to adjust the slurry viscosity to 3800 cp;

[0218] Step S3: Add the binder, slow stirring, vacuum degassing to remove bubbles, filter, and discharge.

[0219] (3) A method for preparing a lithium secondary battery:

[0220] The negative electrode slurry in (2) is further subjected to tab making, and a lithium iron phosphate positive electrode tab, an electrolyte, a separator, and a battery shell are assembled to obtain a lithium battery. After the lithium battery is injected with liquid and is left to stand at 50°C for 24-48 h, formation is performed.

[0221] The formation process includes:

[0222] Step a: charge the battery at 0.04C for 60 min, and leave to stand for 20 min;

[0223] Step b: charge at a current of 0.08C for 60 min, and leave to stand for 20 min;

[0224] Step c: charge at a current of 0.16C for 300 min; leave to stand for 20 min;

[0225] After aging at 50°C for another 48 h, the lithium secondary battery is obtained by equalizing and measuring the K value.

[0226] Example 7

[0227] (1) The composition of the negative electrode slurry: the weight ratio of active material: conductive agent: binder: composite additive is 95.4%: 1.0%: 2.0%: 1.6%. Among them, the active material is graphite, the conductive agent is carbon nanotube CNT, and the binder is butadiene rubber SBR.

[0228] (2) A method for preparing a negative electrode slurry:

[0229] Step S1: uniformly mix the active material powder and the conductive agent material, and form a kneaded state by stirring; continue to add deionized water and stir to achieve a flowable state;

[0230] Step S2: Add composite additive, the composite additive contains 0.16 mass% ethylene glycol amine and 1.44 mass% Mg(NO3)2, add 0.16 mass% (100 mass% of the total amount of ethylene glycol amine addition) ethylene glycol amine, stir for 20 min, then add 1.44 mass% Mg(NO3)2 (100 mass% of the total amount of Mg(NO3)2 addition), continue to stir for 20 min, add deionized water to adjust the slurry viscosity to 3300 cp;

[0231] Step S3: Add binder, slow stirring, vacuum degassing to remove bubbles, filter, and discharge.

[0232] (3) A method for preparing a lithium secondary battery:

[0233] The negative electrode slurry in (2) is further subjected to tab making, and a lithium phosphate positive electrode tab, an electrolyte, a separator, and a battery shell are assembled to obtain a lithium battery. After the lithium battery is injected with liquid and is left to stand at 50°C for 24-48 h, formation is performed.

[0234] The formation process includes:

[0235] Step a: 0.04C battery charging for 60 min, and standing for 20 min;

[0236] Step b: 0.08C current charging for 60 min, and standing for 20 min;

[0237] Step c: 0.16C current charging for 300 min; and standing for 20 min;

[0238] After aging at 50°C for another 48 h, the lithium secondary battery is obtained by capacity distribution and K value measurement.

[0239] Example 8

[0240] (1) Composition of the negative electrode slurry: the weight ratio of active material: conductive agent: binder: composite additive is 96%: 1.0%: 2.0%: 1.0%. Among them, the active material is graphite, the conductive agent is carbon nanotube CNT, and the binder is butadiene rubber SBR.

[0241] (2) Preparation method of the negative electrode slurry:

[0242] Step S1: uniformly mix the active material powder and the conductive agent material, and form a kneaded state by stirring; continue to add deionized water and stir to achieve a flowable state;

[0243] Step S2: Add the composite additive, which contains 0.04 mass% of β-cyclodextrin and 0.96 mass% of LiNO3. First, add 0.02 mass% (50 mass% of the total amount of β-cyclodextrin added) of β-cyclodextrin and stir for 10 min. Then, add 0.96 mass% of LiNO3 (100 mass% of the total amount of LiNO3 added) and continue stirring. After stirring for 20 min, add 0.02 mass% (50 mass% of the total amount of β-cyclodextrin added) of β-cyclodextrin and stir for 10 min. Add deionized water to adjust the slurry viscosity to 3250 cp.

[0244] Step S3: Add the binder, stir slowly, vacuum to remove bubbles, filter, and discharge.

[0245] (3) Method for preparing a lithium secondary battery:

[0246] The negative electrode slurry in (2) is further subjected to tab production, and a lithium iron phosphate positive electrode tab, an electrolyte, a separator, and a battery shell are assembled to obtain a lithium battery. After the lithium battery is injected with liquid and is left to stand at 50°C for 24-48 h, formation is performed.

[0247] The formation process includes:

[0248] Step a: Charge the battery at 0.04C for 60 min and leave it to stand for 20 min.

[0249] Step b: Charge the battery at 0.08C for 60 min and leave it to stand for 20 min.

[0250] Step c: Charge the battery at 0.16C for 300 min and leave it to stand for 20 min.

[0251] After aging at 50°C for another 48 h, the lithium secondary battery is obtained by performing capacity distribution and measuring the K value.

[0252] Example 9

[0253] (1) Composition of the negative electrode slurry: The weight ratio of active material: conductive agent: binder: composite additive is 96%: 1.0%: 2.0%: 1.0%. The active material is graphite, the conductive agent is carbon nanotube CNT, and the binder is butadiene styrene rubber SBR.

[0254] (2) Method for preparing the negative electrode slurry:

[0255] Step S1: Mix the active material powder and the conductive agent material uniformly, and form a kneaded state by stirring. Continue to add deionized water and stir to achieve a flowable state.

[0256] Step S2: Add the composite additive, which contains 0.26 mass% of β-cyclodextrin and 0.74 mass% of LiNO3, first add 0.13 mass% (50 mass% of the total amount of β-cyclodextrin added) of β-cyclodextrin, stir for 10 min, then add 0.74 mass% of LiNO3 (100 mass% of the total amount of LiNO3 added) and continue stirring, after stirring for 20 min, add 0.13 mass% (50 mass% of the total amount of β-cyclodextrin added) of β-cyclodextrin, stir for 10 min, and add deionized water to adjust the slurry viscosity to 2600 cp;

[0257] Step S3: Add the binder, stir slowly, vacuum to remove bubbles, filter, and discharge.

[0258] (3) A method for preparing a lithium secondary battery:

[0259] The negative electrode slurry in (2) is further subjected to tab making, and a lithium iron phosphate positive electrode tab, an electrolyte, a separator, and a battery shell are assembled to obtain a lithium battery. After the lithium battery is injected with liquid and is left to stand at 50°C for 24-48 h, formation is performed.

[0260] The formation process includes:

[0261] Step a: charge the battery at 0.04C for 60 min, and leave to stand for 20 min;

[0262] Step b: charge at a current of 0.08C for 60 min, and leave to stand for 20 min;

[0263] Step c: charge at a current of 0.16C for 300 min; leave to stand for 20 min;

[0264] After aging at 50°C for another 48 h, the lithium secondary battery is obtained by equalizing and measuring the K value.

[0265] Example 10

[0266] (1) The composition of the negative electrode slurry: the weight ratio of active material: conductive agent: binder: composite additive is 96%: 1.0%: 2.0%: 1.0%. Among them, the active material is graphite, the conductive agent is carbon nanotube CNT, and the binder is butadiene rubber SBR.

[0267] (2) A method for preparing a negative electrode slurry:

[0268] Step S1: uniformly mix the active material powder and the conductive agent material, and form a kneaded state by stirring; continue to add deionized water and stir to achieve a flowable state;

[0269] Step S2: Add composite additive, the composite additive contains 0.08 mass% β-cyclodextrin and 0.92 mass% LiNO3, add 0.08 mass% (100 mass% of the total amount of β-cyclodextrin addition) β-cyclodextrin, stir for 20 min, then add 0.92 mass% LiNO3 (100 mass% of the total amount of LiNO3 addition) and continue stirring for 20 min, add deionized water to adjust the slurry viscosity to 2900 cp;

[0270] Step S3: Add binder, slow stirring, vacuum degassing to remove bubbles, filter, and discharge.

[0271] (3) A method for preparing a lithium secondary battery:

[0272] The negative electrode slurry in (2) is further subjected to tab production, and a lithium iron phosphate positive electrode tab, an electrolyte, a separator, and a battery shell are assembled to obtain a lithium battery. After the lithium battery is injected with liquid and is left to stand at 50°C for 24-48h, formation is performed.

[0273] The formation process includes:

[0274] Step a: 0.08C battery charging for 30 min, and standing for 20 min;

[0275] Step b: 0.08C current charging for 60 min, and standing for 20 min;

[0276] Step c: 0.16C current charging for 300 min; and standing for 20 min;

[0277] After aging at 50°C for another 48h, the lithium secondary battery is obtained by capacity distribution and K value measurement.

[0278] Example 11

[0279] (1) Composition of the negative electrode slurry: the weight ratio of active material: conductive agent: binder: composite additive is 96%: 1.0%: 2.0%: 1.0%. Among them, the active material is graphite, the conductive agent is carbon nanotube CNT, and the binder is butadiene rubber SBR.

[0280] (2) Preparation method of the negative electrode slurry:

[0281] Step S1: uniformly mix the active material powder and the conductive agent material, and form a kneaded state by stirring; continue to add deionized water and stir to achieve a flowable state;

[0282] Step S2: Add composite additive, the composite additive contains 0.08 mass% β-cyclodextrin and 0.92 mass% LiNO3, add 0.08 mass% (100 mass% of the total amount of β-cyclodextrin addition) β-cyclodextrin, stir for 20 min, then add 0.92 mass% LiNO3 (100 mass% of the total amount of LiNO3 addition) and continue stirring for 20 min, add deionized water to adjust the slurry viscosity to 3250 cp;

[0283] Step S3: Add binder, slow stirring, vacuum degassing to remove bubbles, filter, and discharge.

[0284] (3) A method for preparing a lithium secondary battery:

[0285] The negative electrode slurry in (2) is further subjected to tab production, and a lithium iron phosphate positive electrode tab, an electrolyte, a separator, and a battery shell are assembled to obtain a lithium battery. After the lithium battery is injected with liquid and is left to stand at 50°C for 24-48 h, formation is performed.

[0286] The formation process includes:

[0287] Step a: 0.08C battery charging for 30 min, standing for 20 min;

[0288] Step b: 0.16C current charging for 30 min, standing for 20 min;

[0289] Step c: 0.16C current charging for 300 min; standing for 20 min;

[0290] After aging at 50°C for another 48 h, the lithium secondary battery is obtained by capacity distribution and K value measurement.

[0291] Example 12

[0292] (1) Composition of the negative electrode slurry: the weight ratio of active material: conductive agent: binder: composite additive is 96%: 1.0%: 2.0%: 1.0%. Among them, the active material is graphite, the conductive agent is carbon nanotube CNT, and the binder is butadiene rubber SBR.

[0293] (2) Preparation method of the negative electrode slurry:

[0294] Step S1: uniformly mix the active material powder and the conductive agent material, and form a kneaded state by stirring; continue to add deionized water and stir to achieve a flowable state;

[0295] Step S2: adding composite additive, the composite additive comprises 0.08 mass% β-cyclodextrin and 0.92 mass% LiNO3, 0.08 mass% (100 mass% of the total amount of β-cyclodextrin added) β-cyclodextrin is added, stirred for 20 min, then 0.92 mass% LiNO3 (100 mass% of the total amount of LiNO3 added) is added and stirring is continued for 20 min, and deionized water is added to adjust the slurry viscosity to 2550 cp;

[0296] Step S3: adding binder, slow stirring, vacuum degassing to remove bubbles, filtering, and discharging.

[0297] (3) A method for preparing a lithium secondary battery:

[0298] The negative electrode slurry in (2) is further subjected to tab production, and a lithium battery is obtained by assembling the lithium iron phosphate positive electrode tab, an electrolyte, a separator, and a battery shell. After the lithium battery is injected with liquid and is left to stand at 50°C for 24-48 h, formation is performed.

[0299] The formation process comprises:

[0300] Step a: charging at 0.08C for 30 min, and leaving to stand for 20 min;

[0301] Step b: charging at 0.16C for 30 min, and leaving to stand for 20 min;

[0302] Step c: charging at 0.32C for 150 min, and leaving to stand for 20 min;

[0303] After aging at 50°C for another 48 h, the lithium secondary battery is obtained by capacity matching and K value measurement.

[0304] Performance test

[0305] The lithium secondary batteries obtained in Comparative Example 1 and Examples 1-12 are subjected to DCR testing, and the results are shown in Table 1. In addition, Table 1 also shows the amount of composite additive used in Comparative Example 1 and Examples 1-12, the addition sequence, and the formation mode adopted.

[0306] Table 1: Amount of composite additive used in Comparative Example 1 and Examples 1-12, addition sequence, formation mode, and DCR test results

[0307]

[0308]

[0309] As can be seen from Table 1, by comparing Examples 1-9 with Comparative Example 1, the use of composite additive can significantly reduce the internal resistance of the battery, with a reduction of 2%-12.4%.

[0310] From the comparison of Examples 1-4, it can be seen that the order of adding the organic additive and the inorganic additive in the composite additive greatly affects the battery internal resistance, and the optimal effect of reducing the battery internal resistance is achieved by adding the organic additive step by step and adding the inorganic additive in the middle. At the same time, the effect of adding the organic additive first and then adding the inorganic additive is obviously better than that of adding the inorganic additive first and then adding the organic additive or mixing the two and then adding.

[0311] From the comparison of Example 2 and Example 5, it can be seen that when the content of the composite additive exceeds a certain value, the further reduction of the battery internal resistance has no promoting effect.

[0312] From Examples 6 and 7, it can be seen that the effect of reducing the internal resistance can be achieved by one or more different specific organic additives and inorganic additives. The most preferred combination is the combination of LiNO3 and β-cyclodextrin.

[0313] From the comparison of Example 2 and Examples 10-12, it can be seen that by optimizing the formation process, the battery internal resistance can be further reduced by 12%-17%.

[0314] It should be noted that although the technical solutions of the present application are described by specific examples, those skilled in the art can understand that the present application should not be limited thereto.

[0315] The above has described various embodiments of the present application, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles, practical applications, or technical improvements in the market of the embodiments, or to enable other ordinary skilled persons in the art to understand the embodiments disclosed herein.

Claims

1. A negative electrode slurry, characterized by, It comprises negative active material, conductive agent, binder and composite additive, The composite additive comprises a combination of organic additive and inorganic additive, The organic additive comprises one or more of cyclodextrin and alcohol amine compound, The inorganic additive comprises one or more of nitrate of alkali metal and / or alkaline earth metal, The cyclodextrin comprises one or more of a-cyclodextrin, b-cyclodextrin, g-cyclodextrin and derivatives thereof; The alcohol amine compound comprises one or more of methanol amine compound, ethanol amine compound and propanol amine compound; The nitrate of alkali metal and / or alkaline earth metal comprises one or more of LiNO3, NaNO3, Ca(NO3)2 and Mg(NO3)2, The weight ratio of the inorganic additive to the organic additive is 20:1 to 3:

1.

2. The negative electrode slurry of claim 1, wherein The ethanol amine compound comprises one or more of ethanol amine, diethanol amine and triethanol amine.

3. The negative electrode slurry according to claim 1 or 2, characterized by, The organic additive is coated on the surface of the negative active material, and part of the inorganic additive is embedded in the interior of the organic additive molecules and the other part exists between the organic additive molecules.

4. The negative electrode slurry according to claim 1 or 2, wherein The weight ratio of the negative active material, conductive agent, binder and composite additive is 93-98 wt%: 0.5-1.5 wt%: 0.5-3.5 wt%: 0.1-2 wt%; and / or The negative active material comprises one or more of graphite, hard carbon, silicon-carbon material, lithium metal and tin-based material; and / or The conductive agent comprises one or more of conductive graphite, graphene, acetylene black, carbon black and carbon nanotube; and / or The binder comprises one or more of sodium carboxymethyl cellulose, chitosan, sodium lignocellulose, butadiene rubber, styrene-butadiene rubber, sodium polymethacrylate, lithium polymethacrylate, polymethacrylate and polyvinylidene fluoride.

5. A method for preparing a negative electrode slurry, characterized by, It comprises the following steps: Step S1: stirring negative active material, conductive agent and solvent to obtain slurry; Step S2: adding composite additive to the slurry obtained in step S1 and stirring, and then adding solvent to adjust the viscosity of the slurry; Step S3: adding binder and stirring to obtain negative electrode slurry, The composite additive comprises a combination of organic additive and inorganic additive, The organic additive comprises one or more of cyclodextrin and alcohol amine compound, The inorganic additive comprises one or more of nitrate of alkali metal and / or alkaline earth metal, The cyclodextrin comprises one or more of a-cyclodextrin, b-cyclodextrin, g-cyclodextrin and derivatives thereof; The alcohol amine compound comprises one or more of methanol amine compound, ethanol amine compound and propanol amine compound; The nitrate of alkali metal and / or alkaline earth metal comprises one or more of LiNO3, NaNO3, Ca(NO3)2 and Mg(NO3)2, The weight ratio of the inorganic additive to the organic additive is 20:1 to 3:

1.

6. The production method according to claim 5, wherein The ethanol amine compound comprises one or more of ethanol amine, diethanol amine and triethanol amine; and / or The weight ratio of the negative active material, the conductive agent, the binder, and the composite additive is 93-98 wt%: 0.5-1.5 wt%: 0.5-3.5 wt%: 0.1-2 wt%; and / or The negative active material comprises one or more of graphite, hard carbon, silicon-carbon material, lithium metal, tin-based material; and / or The conductive agent comprises one or more of conductive graphite, graphene, acetylene black, carbon black, carbon nanotube; and / or The binder comprises one or more of sodium carboxymethyl cellulose, chitosan, sodium lignocellulose, butadiene-styrene rubber, styrene-butadiene rubber, sodium polymethacrylate, lithium polymethacrylate, polymethacrylate, polyvinylidene fluoride.

7. The production method according to claim 5 or 6, characterized by, The slurry of step S1 further comprises a dispersant.

8. The preparation method according to claim 7, characterized in that, The dispersant comprises one or more of sodium carboxymethyl cellulose, chitosan, sodium lignocellulose, butadiene-styrene rubber, styrene-butadiene rubber, sodium polymethacrylate, lithium polymethacrylate, polymethacrylate.

9. The production method according to claim 5 or 6, characterized by, In step S2, the composite additive is added in the following manner: first, 50-100 mass% of the total amount of organic additive is added, then 50-100 mass% of the total amount of inorganic additive is added, then optionally the remaining organic additive is added, and then optionally the remaining inorganic additive is added.

10. The method of claim 9, wherein, The composite additive is added in the following manner: first, 50-80 mass% of the total amount of organic additive is added, then 100 mass% of the total amount of inorganic additive is added, and then the remaining organic additive is added.

11. A lithium secondary battery, characterized by comprising: It comprises a negative electrode sheet, a positive electrode sheet, a separator, an electrolyte, and a battery shell, The negative electrode sheet comprises a negative electrode current collector and a negative electrode layer on the negative electrode current collector, The negative electrode layer is formed from the negative electrode slurry of any one of claims 1-4 or from the negative electrode slurry obtained by the preparation method of any one of claims 5-10.

12. A method of manufacturing a lithium secondary battery according to claim 11, characterized by, It comprises the following steps: The negative electrode sheet and the positive electrode sheet are assembled with the separator, the electrolyte, and the battery shell, and then a formation process is performed.

13. The method of claim 12, wherein, The formation process comprises the following steps: The charging step comprises the following steps in sequence: Step a: charging for a time T1 using a current I1, and then standing for 5-20 min; wherein I1=0.06-0.12C and T1=30-60 min; Step b: charging for a time T2 using a current I2, and then standing for 5-20 min; wherein I2=0.06-0.24C and T2=15-60 min; Step c: charging for a time T3 using a current I3, and then standing for 5-20 min; wherein I3=0.12-0.48C and T3=90-360 min; 。 14. The preparation method of claim 13, wherein, When I1=I2, the charging step comprises the following steps in sequence: Step ab: charging for a time T1+T2 using a current I1, and then standing for 5-20 min; wherein I1=0.06-0.12C and T1+T2=45-120 min; Step c: charging with current I3for time T3, resting for 5-20 min; wherein I3= 0.12-0.48 C, T3= 90-360 min; or, When I2= I3, optionally, the charging step comprises in sequence: Step a: charging with current I1for time T1, resting for 5-20 min, wherein I1= 0.06-0.12 C, T1= 30-60 min; 。

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