Negative electrode slurry and preparation method thereof, and lithium secondary battery and preparation method thereof

Abstract

The invention provides negative electrode slurry and a preparation method thereof, and a lithium secondary battery and a preparation method thereof. The negative electrode slurry comprises a negative electrode active material, a conductive agent, a binder and a composite additive, the composite additive comprises a combination of an organic additive and an inorganic additive, the organic additive comprises one or more of cyclodextrin and an alcohol amine compound, and the inorganic additive comprises one or more of a binder and a binder. The inorganic additive comprises one or more of nitrates of alkali metal and / or alkaline earth metal. The organic additive and the inorganic additive are combined and used as the composite additive in the negative electrode slurry, and thin and uniform coating can be formed on the surface of the negative electrode material through the synergistic effect of the composite additive, so that a negative electrode SEI film is thinner, and the internal resistance of the battery is lower.

Description

Technical Field

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

[0002] The DC internal resistance of lithium-ion batteries is mainly composed of ohmic impedance, charge transfer resistance and charge transmission resistance. Among them, the charge transfer resistance is mainly contributed by the shuttling of lithium ions in the interface electrolyte layer between the positive and negative electrode active material particles and the electrolyte. + The impedance across the SEI on the negative electrode surface is the main contribution to the charge transfer resistance, and this impedance is greatly affected by the structure and thickness of the SEI film.

[0003] Existing technologies mainly achieve the regulation of the structure / composition of the SEI film through surface modification / modification of the main negative electrode material, electrolyte composition preparation and formation strategy. The regulation content includes the composition of the SEI film, such as the ratio and composition of organic components / inorganic components, and the regulation of the overall thickness of the SEI film. This type of regulation technology mainly focuses on: (1) the use of solvents, organic small molecule additives, and lithium salt additives in the electrolyte, and the protection of the negative electrode surface SEI film through specific oxidation-reduction reactions of the additives; (2) the introduction of artificial SEI film, such as organic polymers, organic small molecules coated on graphite or the surface of the negative electrode; (3) formation system regulation.

[0004] Some documents disclose a negative electrode slurry that 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 negative electrode surface to thicken, causing the internal resistance of the battery to increase.

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

[0006] It can be seen that although the existing technology has conducted certain research on regulating the composition of the negative electrode slurry to control the structure of the SEI film, it cannot be said to be sufficient to reduce the internal resistance of the battery, and there is room for further research. Summary of the invention

[0007] Problem that the invention aims to solve

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

[0009] Solutions for solving problems

[0010] The present invention uses a combination of organic additives and inorganic additives in the negative electrode slurry. On the one hand, since the organic additive has a strong intermolecular force, it can be adsorbed on the surface of the negative electrode material; on the other hand, the cavity structure of the specific organic additive of the present invention or the cavity structure formed by the assembly of the organic additive can anchor the inorganic additive, so that a part of the inorganic additive is embedded in the organic additive molecule, and the other part exists between the organic additive molecules, and the whole forms a mesh or core-shell structure on the negative electrode surface. In the process of forming the negative electrode SEI film, a synergistic effect is generated, the SEI film is thinned, and a denser, uniform, and thinner SEI film is obtained, and finally the purpose of significantly reducing the internal resistance of the battery is achieved.

[0011] The inorganic additive used in the present invention is one or more nitrates of alkali metals and / or alkaline earth metals. During the first charge of the full battery, the NO3 in the nitrates of alkali metals and / or alkaline earth metals as inorganic additives is - Can undergo reduction reaction to form LiN x O y At the same time, since the organic additives have formed good adhesion and coating on the surface of the negative electrode material in advance, based on their anchoring effect on 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 reflected in the thinner negative electrode SEI film and lower battery internal resistance.

[0012] In the preparation method of the negative electrode slurry of the present invention, the distribution of organic / inorganic components in SEI is adjusted by adjusting the order of adding organic additives and inorganic additives, which generally presents a denser, more uniform, and thinner SEI film, thereby significantly reducing the internal resistance of the battery.

[0013] The present invention first provides a negative electrode slurry, which includes 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 additives include one or more of cyclodextrin and alcoholamine compounds.

[0016] The inorganic additive includes one or more nitrates of alkali metals and / or alkaline earth metals.

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

[0018] The alcoholamine compounds include one or more of methanolamine compounds, ethanolamine compounds, and propanolamine compounds;

[0019] Preferably, the ethanolamine compound includes one or more of ethanolamine, diethanolamine, and triethanolamine; and / or,

[0020] The nitrate of the 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 invention, the organic additive is coated on the surface of the negative electrode active material, a part of the inorganic additive is embedded in the organic additive molecules, and another part exists between the organic additive molecules.

[0022] According to the negative electrode slurry of the present invention, 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 invention, the weight ratio of the negative electrode active material, the conductive agent, the binder and the composite additive is 93-98 weight %: 0.5-1.5 weight %: 0.5-3.5 weight %: 0.1-2 weight %; 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 nanotubes; and / or,

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

[0027] In addition, the present invention also provides a method for preparing a negative electrode slurry, which comprises 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 a solvent to adjust the viscosity of the slurry;

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

[0031] The composite additive comprises a combination of an organic additive and an inorganic additive.

[0032] The organic additives include one or more of cyclodextrin and alcoholamine compounds.

[0033] The inorganic additive includes one or more nitrates of alkali metals and / or alkaline earth metals.

[0034] According to the preparation method of the present invention, the cyclodextrin includes one or more of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, and derivatives thereof; and / or

[0035] The alcoholamine compounds include one or more of methanolamine compounds, ethanolamine compounds, and propanolamine compounds;

[0036] Preferably, the ethanolamine compound includes one or more of ethanolamine, diethanolamine, and triethanolamine; and / or,

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

[0038] The weight ratio of the total amount of the inorganic additives to the total amount of the organic additives 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 weight %: 0.5-1.5 weight %: 0.5-3.5 weight %: 0.1-2 weight %; and / or

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

[0041] The conductive agent includes one or more of conductive graphite, graphene, acetylene black, carbon black, and carbon nanotubes; and / or,

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

[0043] According to the preparation method of the present invention, the slurry in step S1 further includes a dispersant;

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

[0045] According to the preparation method of the present invention, in step S2, the method of adding the composite additive includes: first adding 50-100% by mass of organic additives accounting for the total amount of organic additives, then adding 50-100% by mass of inorganic additives accounting for the total amount of inorganic additives, then optionally adding the remaining organic additives, and then optionally adding the remaining inorganic additives;

[0046] Preferably, the method of adding the composite additive includes: first adding 50-80 mass % of the organic additives accounting for the total amount of the organic additives, then adding 100 mass % of the inorganic additives accounting for the total amount of the inorganic additives, and then adding the remaining organic additives.

[0047] Furthermore, the present invention also provides a lithium secondary battery, which includes a negative electrode sheet, a positive electrode sheet, a separator, an electrolyte and a battery casing.

[0048] 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 invention or from the negative electrode slurry obtained by the preparation method of the present invention.

[0050] Furthermore, the present invention also provides a method for preparing the lithium secondary battery according to the present invention, which comprises the following steps: assembling the negative electrode plate and the positive electrode plate with the separator, the electrolyte, and the battery casing, and then performing a formation process.

[0051] According to the preparation method of the present invention, the formation process comprises: injecting liquid into the assembled lithium battery, leaving it to stand, and then charging it.

[0052] The charging steps include:

[0053] Step a: Use current I1 to charge for time T1, and let it stand for 5 to 20 minutes; wherein I1 = 0.06 to 0.12C, T1 = 30 to 60 minutes;

[0054] Step b: Use current I2 to charge for time T2, and let stand for 5 to 20 minutes; wherein I2 = 0.06 to 0.24C, T2 = 15 to 60 minutes;

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

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

[0057] According to the preparation method of the present invention,

[0058] When I1=I2, optionally, the charging steps sequentially include:

[0059] Step ab: Use current I1 to charge for time T1+T2, and let stand for 5 to 20 minutes, where I1=0.06 to 0.12C, T1+T2=45 to 120 minutes;

[0060] Step c: Use current I3 to charge for time T3, and let stand for 5 to 20 minutes; wherein I3 = 0.12 to 0.48C, T3 = 90 to 360 minutes; or,

[0061] When I2=I3, optionally, the charging steps sequentially include:

[0062] Step a: Use current I1 to charge for time T1, and let it stand for 5 to 20 minutes, where I1 = 0.06 to 0.12C, T1 = 30 to 60 minutes;

[0063] Step bc: Use current I2 to charge for time T2+T3, and let stand for 5 to 20 minutes; wherein, I2=0.12 to 0.24C, T2+T3=105 to 420 minutes.

[0064] Effects of the Invention

[0065] The above technical solution of the present invention has the following beneficial effects:

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

[0067] 2) The preparation method of the negative electrode slurry provided by the present invention can improve the utilization rate of the electrochemical reaction products of the composite additives, increase the effective coating degree of the negative electrode material, and guide the distribution of organic / inorganic components in SEI by adopting specific composite additives and adjusting the addition order of organic additives and inorganic additives. The overall performance is a denser, uniform, and thinner 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 invention can promote the two-electron reduction reaction of the organic additive under large current, cooperate with the SEI film components formed by the inorganic additive, and further reduce the internal resistance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0070] Various exemplary embodiments, features and aspects of the present invention will be described in detail below. The word "exemplary" used here means "used as an example, embodiment or illustrative". Any embodiment described here as "exemplary" is not necessarily interpreted as being superior or better than other embodiments.

[0071] In addition, in order to better illustrate the present invention, numerous specific details are provided in the following specific embodiments. It should be understood by those skilled in the art that the present invention can be implemented without certain specific details. In other examples, methods, means, equipment and steps well known to those skilled in the art are not described in detail in order to highlight the subject matter of the present invention.

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

[0073] In this specification, the word "may" includes both performing a certain process and not performing a certain process.

[0074] In this specification, the references to "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", etc., mean that the specific elements (e.g., features, structures, properties and / or characteristics) described in connection with the embodiments are included in at least one embodiment described herein, and may or may not exist in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0075] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints A and B.

[0076] <First aspect>

[0077] A first aspect of the present invention provides a negative electrode slurry, which includes a negative electrode active material, a conductive agent, a binder and a composite additive.

[0078] Wherein, the composite additive comprises a combination of an organic additive and an inorganic additive,

[0079] The organic additives include one or more of cyclodextrin and alcoholamine compounds.

[0080] The inorganic additive includes one or more nitrates of alkali metals and / or alkaline earth metals.

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

[0082] In some specific embodiments, the alcoholamine compound may include one or more of methanolamine compounds, ethanolamine compounds, propanolamine compounds, etc., wherein ethanolamine compounds are preferred, and more preferably, the ethanolamine compound may include one or more of ethanolamine, diethanolamine, triethanolamine, etc., wherein diethanolamine is preferred. Through the assembly of alcoholamine compounds, a cavity structure can be formed, thereby anchoring the inorganic additives to achieve synergistic effects.

[0083] In some specific embodiments, the nitrate of alkali metal and / or alkaline earth metal includes one or more of LiNO3, NaNO3, Ca(NO3)2, Mg(NO3)2, etc., among which LiNO3 is preferred.

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

[0085] In some preferred embodiments, the organic additive is coated on the surface of the negative electrode active material, a part of the inorganic additive is embedded in the organic additive molecules, and another part exists between the organic additive molecules. The whole forms a mesh or core-shell structure on the negative electrode surface, and a thin and uniform SEI film is formed on the negative electrode through synergistic action, thereby achieving the purpose of significantly reducing the internal resistance of the battery. The mesh structure here refers to a network-like structure formed by 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 Schematic diagram of the structure of the negative electrode slurry of the present invention is shown. Figure 1 It can be seen that the organic additives are coated on the surface of the negative electrode active material, and most of the inorganic additives are embedded in the organic additive molecules, and a small part is between the organic additive molecules. The last outermost layer is an organic additive layer, which is not shown in the attached figure.

[0087] In some specific embodiments, the weight ratio of the inorganic additive to the organic additive is 20:1 to 3:1, such as 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 lead to waste of the inorganic additive, and may cause the SEI film to thicken, causing the internal resistance of the battery to increase; 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, 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 weight %: 0.5-1.5 weight %: 0.5-3.5 weight %: 0.1-2 weight %.

[0089] The present invention does not specifically limit the negative electrode active material, and it may be an active material commonly used in the art, for example, it may include one or more of graphite, hard carbon, silicon-carbon material, lithium metal, tin-based material, and the like.

[0090] The present invention does not specifically limit the conductive agent, and it may be a conductive agent commonly used in the art, for example, it may include one or more of conductive graphite, graphene, acetylene black, carbon black, and carbon nanotubes (CNTs).

[0091] The present invention does not specifically limit the binder, and it may be a binder commonly used in the art, for example, it may include one or more of sodium carboxymethyl cellulose, chitosan, sodium lignocellulose, styrene-butadiene rubber (SBR), styrene-acrylic rubber, sodium polymethacrylate, lithium polymethacrylate, polymethacrylate, and polyvinylidene fluoride (PVDF).

[0092] In some preferred embodiments, by adding the composite additive of the present invention, the internal resistance of the lithium battery can be reduced by 5% to 15% under conventional formation conditions.

[0093] <Second Aspect>

[0094] A second aspect of the present invention provides a method for preparing 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 a solvent to adjust the viscosity of the slurry;

[0097] Step S3: adding a binder and stirring to obtain a negative electrode slurry.

[0098] The composite additive comprises a combination of an organic additive and an inorganic additive.

[0099] The organic additives include one or more of cyclodextrin and alcoholamine compounds.

[0100] The inorganic additive includes one or more nitrates of alkali metals and / or alkaline earth metals.

[0101] The types, amounts, and proportions of the negative electrode active material, conductive agent, binder, cyclodextrin, amine compounds, nitrates of alkali metals and / or alkaline earth metals, etc. in this aspect are the same as those in the first aspect and will not be repeated here.

[0102] The present invention does not specifically limit the solvent, and it may be a commonly used solvent in the art, for example, it may include one of N-methylpyrrolidone, deionized water, and the like.

[0103] In some specific embodiments, the slurry in step S1 may further include a dispersant. The type of the dispersant is not particularly limited and may be selected as needed. For example, the dispersant may include one or more of sodium carboxymethyl cellulose, chitosan, sodium lignocellulose, styrene-butadiene rubber, styrene-acrylic rubber, sodium polymethacrylate, lithium polymethacrylate, and polymethacrylate.

[0104] In some preferred embodiments, the step S1 comprises: mixing the negative electrode active material with the conductive agent, adding a dispersant, and stirring to form a kneaded state; and continuing to add a dispersant or a solvent and stirring to reach a fluid state to obtain a slurry.

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

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

[0107] The first added organic additives will adhere to the surface of the negative electrode active material and combine with the negative electrode active material. Then the inorganic additives are added. The inorganic additives are attached to the inside or surface of the organic additives through the anchoring effect of the organic additives. Finally, the organic additives are added to further coat the exposed inorganic additive surface evenly. A mesh or core-shell structure is formed on the negative electrode surface as a whole. The organic additives added in batches can additionally pre-coat the inorganic additives, thereby preventing the problem of uneven dispersion of the inorganic additives due to the one-time addition of the organic additives.

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

[0109] In some specific embodiments, in step S3, in order to make the raw materials more evenly mixed, the stirring can be slow stirring, and the slow stirring rate can be 20 to 200 r / min. In addition, in order to further improve the quality of the negative electrode slurry, the stirring can also include the steps of removing bubbles and filtering. There is no particular limitation on the method of removing bubbles, and the commonly used methods in the art can be used, such as vacuuming to remove bubbles.

[0110] <Third Aspect>

[0111] The third aspect of the present invention provides a lithium secondary battery, comprising a negative electrode sheet, a positive electrode sheet, a separator, an electrolyte and a battery case. 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 described in the first aspect or by the negative electrode slurry obtained by the preparation method described in the second aspect.

[0112] The present invention has no particular limitation on the negative electrode current collector, and it can be any negative electrode current collector commonly used in the art.

[0113] The present invention has no particular limitation on the positive electrode plate, and it can be a positive electrode plate commonly used in the art, such as lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, and ternary positive electrode plates such as lithium nickel manganese cobalt oxide, lithium nickel cobalt aluminum oxide, etc.

[0114] The present invention has no particular limitation on the diaphragm, and it may be a diaphragm commonly used in the art.

[0115] The present invention has no particular limitation on the electrolyte, and it can be any electrolyte commonly used in the art.

[0116] <Fourth Aspect>

[0117] The fourth aspect of the present invention provides a method for preparing a lithium secondary battery according to the third aspect, comprising the following steps: assembling a negative electrode plate and a positive electrode plate with a separator, an electrolyte, and a battery casing, and then performing a formation process.

[0118] In some specific embodiments, the formation process includes: filling the assembled lithium battery with liquid, allowing it to stand, and then charging. There is no particular limitation on the standing method, which can be selected as needed. For example, the standing step can include: standing at 30-55° C. for 24-48 hours.

[0119] The chemical formation process of the present invention can adopt a conventional chemical formation system or an optimized chemical formation system.

[0120] In the optimized formation system, the charging steps include:

[0121] Step a: Use current I1 to charge for time T1, and let it stand for 5 to 20 minutes; wherein I1 = 0.06 to 0.12C, T1 = 30 to 60 minutes;

[0122] Step b: Use current I2 to charge for time T2, and let stand for 5 to 20 minutes; wherein I2 = 0.06 to 0.24C, T2 = 15 to 60 minutes;

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

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

[0125] When I1=I2, the charging steps sequentially include:

[0126] Step ab: Use current I1 to charge for time T1+T2, and let stand for 5 to 20 minutes, where I1=0.06 to 0.12C, T1+T2=45 to 120 minutes;

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

[0128] When I2=I3, the charging steps sequentially include:

[0129] Step a: Use current I1 to charge for time T1, and let it stand for 5 to 20 minutes, where I1 = 0.06 to 0.12C, T1 = 30 to 60 minutes;

[0130] Step bc: Use current I2 to charge for time T2+T3, and let stand for 5 to 20 minutes; wherein, I2=0.12 to 0.24C, T2+T3=105 to 420 minutes.

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

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

[0133] In some specific embodiments, the preparation method of the lithium secondary battery further includes aging, capacity separation, K value measurement and other steps. There is no particular limitation on the aging method, which can be selected as needed. Preferably, the aging step includes: aging at 30-55°C for 24-48 hours.

[0134] Example

[0135] The embodiments of the present invention will be described in detail below in conjunction with the examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific conditions are specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be obtained commercially.

[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. Among them, the active material is graphite, the conductive agent is carbon nanotube CNT, and the binder is styrene butadiene rubber SBR.

[0138] (2) Preparation method of negative electrode slurry:

[0139] Step S1: Mix the active material powder and the conductive agent material evenly and stir to form a kneaded state; continue to add deionized water and stir until the mixture has fluidity and the slurry viscosity is 3600cp;

[0140] Step S3: adding a binder, stirring slowly, vacuuming to remove bubbles, filtering, and discharging.

[0141] (3) Preparation method of lithium secondary battery:

[0142] The negative electrode slurry in (2) is further used to make a pole piece, and assembled with a lithium iron phosphate positive pole piece, an electrolyte, a separator, and a battery case to obtain a lithium battery. After the lithium battery is filled with liquid, it is allowed to stand at 50° C. for 24 to 48 hours before being formed.

[0143] The chemical process includes:

[0144] Step a: Charge the battery with 0.04C for 60 minutes and let it stand for 20 minutes;

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

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

[0147] After aging at 50°C for 48h, the capacity was divided and the K value was measured to obtain a 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 nanotubes CNT, and the binder is styrene-butadiene rubber SBR.

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

[0151] Step S1: Mix the active material powder and the conductive agent material uniformly and stir to form a kneaded state; continue to add deionized water and stir to achieve a fluid state;

[0152] Step S2: adding a composite additive, the composite additive comprising 0.08 mass% β-cyclodextrin and 0.92 mass% LiNO3, first adding 0.04 mass% (accounting for 50 mass% of the total amount of β-cyclodextrin added) β-cyclodextrin, stirring for 10 minutes, then adding 0.92 mass% LiNO3 (accounting for 100 mass% of the total amount of LiNO3 added) and continuing to stir, after stirring for 20 minutes, adding 0.04 mass% (accounting for 50 mass% of the total amount of β-cyclodextrin added) β-cyclodextrin, stirring for 10 minutes, and adding deionized water to adjust the slurry viscosity to 2900cp;

[0153] Step S3: adding a binder, stirring slowly, vacuuming to remove bubbles, filtering, and discharging.

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

[0155] The negative electrode slurry in (2) is further used to make a pole piece, and assembled with a lithium iron phosphate positive pole piece, an electrolyte, a separator, and a battery case to obtain a lithium battery. After the lithium battery is filled with liquid, it is allowed to stand at 50° C. for 24 to 48 hours before being formed.

[0156] The chemical process includes:

[0157] Step a: Charge the battery with 0.04C for 60 minutes and let it stand for 20 minutes;

[0158] Step b: Charge at 0.08C for 60 min and let stand for 20 min;

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

[0160] After aging at 50°C for 48h, the capacity was divided and the K value was measured to obtain a lithium secondary battery.

[0161] Example 2

[0162] (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 nanotubes CNT, and the binder is styrene-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 and stir to form a kneaded state; continue to add deionized water and stir to achieve a fluid state;

[0165] Step S2: adding a composite additive, the composite additive comprising 0.08 mass% β-cyclodextrin and 0.92 mass% LiNO3, adding 0.08 mass% (accounting for 100 mass% of the total amount of β-cyclodextrin added) β-cyclodextrin, stirring for 20 minutes, then adding 0.92 mass% LiNO3 (accounting for 100 mass% of the total amount of LiNO3 added) and continuing to stir for 20 minutes, adding deionized water to adjust the slurry viscosity to 2600cp;

[0166] Step S3: adding a binder, stirring slowly, vacuuming to remove bubbles, filtering, and discharging.

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

[0168] The negative electrode slurry in (2) is further used to make a pole piece, and assembled with a lithium iron phosphate positive pole piece, an electrolyte, a separator, and a battery case to obtain a lithium battery. After the lithium battery is filled with liquid, it is allowed to stand at 50° C. for 24 to 48 hours before being formed.

[0169] The chemical process includes:

[0170] Step a: Charge the battery with 0.04C for 60 minutes and let it stand for 20 minutes;

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

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

[0173] After aging at 50°C for 48h, the capacity was divided and the K value was measured to obtain a lithium secondary battery.

[0174] Example 3

[0175] (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 nanotubes CNT, and the binder is styrene-butadiene rubber SBR.

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

[0177] Step S1: Mix the active material powder and the conductive agent material uniformly and stir to form a kneaded state; continue to add deionized water and stir to achieve a fluid state;

[0178] Step S2: adding a composite additive, the composite additive comprising 0.08 mass% β-cyclodextrin and 0.92 mass% LiNO3, adding 0.92 mass% (accounting for 100 mass% of the total amount of LiNO3 added) LiNO3, stirring evenly, then adding 0.08 mass% β-cyclodextrin (accounting for 100 mass% of the total amount of β-cyclodextrin added) and continuing to stir, adding deionized water to adjust the slurry viscosity to 3250cp;

[0179] Step S3: adding a binder, stirring slowly, vacuuming to remove bubbles, filtering, and discharging.

[0180] (3) Preparation method of lithium secondary battery:

[0181] The negative electrode slurry in (2) is further used to make a pole piece, and assembled with a lithium iron phosphate positive pole piece, an electrolyte, a separator, and a battery case to obtain a lithium battery. After the lithium battery is filled with liquid, it is allowed to stand at 50° C. for 24 to 48 hours before being formed.

[0182] The chemical process includes:

[0183] Step a: Charge the battery with 0.04C for 60 minutes and let it stand for 20 minutes;

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

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

[0186] After aging at 50°C for 48h, the capacity was divided and the K value was measured to obtain a lithium secondary battery.

[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%, wherein the active material is graphite, the conductive agent is carbon nanotubes CNT, and the binder is styrene-butadiene rubber SBR.

[0189] (2) Preparation method of negative electrode slurry:

[0190] Step S1: Mix the active material powder and the conductive agent material uniformly and stir to form a kneaded state; continue to add deionized water and stir to achieve a fluid state;

[0191] Step S2: adding a composite additive, the composite additive comprising 0.08 mass% β-cyclodextrin and 0.92 mass% LiNO3, firstly mixing 0.08 mass% (accounting for 100 mass% of the total amount of β-cyclodextrin added) β-cyclodextrin and 0.92 mass% LiNO3 (accounting for 100 mass% of the total amount of LiNO3 added) evenly, adding them to the slurry at one time, stirring for 40 minutes, and adding deionized water to adjust the slurry viscosity to 3600cp;

[0192] Step S3: adding a binder, stirring slowly, vacuuming to remove bubbles, filtering, and discharging.

[0193] (3) Preparation method of lithium secondary battery:

[0194] The negative electrode slurry in (2) is further used to make a pole piece, and assembled with a lithium iron phosphate positive pole piece, an electrolyte, a separator, and a battery case to obtain a lithium battery. After the lithium battery is filled with liquid, it is allowed to stand at 50° C. for 24 to 48 hours before being formed.

[0195] The chemical process includes:

[0196] Step a: Charge the battery with 0.04C for 60 minutes and let it stand for 20 minutes;

[0197] Step b: Charge at 0.08C for 60 min and let stand for 20 min;

[0198] Step c: charge at 0.16C for 300 min; let stand for 20 min;

[0199] After aging at 50°C for 48h, the capacity was divided and the K value was measured to obtain a lithium secondary battery.

[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 nanotubes CNT, and the binder is styrene butadiene rubber SBR.

[0202] (2) Preparation method of negative electrode slurry:

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

[0204] Step S2: adding a composite additive, the composite additive comprising 0.16 mass% β-cyclodextrin and 1.44 mass% LiNO3, first adding 0.16 mass% (accounting for 100 mass% of the total amount of β-cyclodextrin added) β-cyclodextrin, stirring for 20 minutes, then adding 1.44 mass% LiNO3 (accounting for 100 mass% of the total amount of LiNO3 added), continuing to stir for 20 minutes, and adding deionized water to adjust the slurry viscosity to 2800cp;

[0205] Step S3: adding a binder, stirring slowly, vacuuming to remove bubbles, filtering, and discharging.

[0206] (3) Preparation method of lithium secondary battery:

[0207] The negative electrode slurry in (2) is further used to make a pole piece, and assembled with a lithium iron phosphate positive pole piece, an electrolyte, a separator, and a battery case to obtain a lithium battery. After the lithium battery is filled with liquid, it is allowed to stand at 50° C. for 24 to 48 hours before being formed.

[0208] The chemical process includes:

[0209] Step a: Charge the battery with 0.04C for 60 minutes and let it stand for 20 minutes;

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

[0211] Step c: charge at 0.16C for 300 min; let stand for 20 min;

[0212] After aging at 50°C for 48h, the capacity was divided and the K value was measured to obtain a lithium secondary battery.

[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 nanotubes CNT, and the binder is styrene butadiene rubber SBR.

[0215] (2) Preparation method of negative electrode slurry:

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

[0217] Step S2: adding a composite additive, the composite additive comprising 0.08 mass% β-cyclodextrin, 0.08 mass% ethylene glycol amine and 1.44 mass% LiNO3, first 0.08 mass% (accounting for 100 mass% of the total amount of β-cyclodextrin added) β-cyclodextrin, 0.08 mass% (accounting for 100 mass% of the total amount of ethylene glycol amine added) ethylene glycol amine, stirring for 20 minutes, then adding 1.44 mass% LiNO3 (accounting for 100 mass% of the total amount of LiNO3 added), continuing to stir for 20 minutes, adding deionized water to adjust the slurry viscosity to 3800cp;

[0218] Step S3: adding a binder, stirring slowly, vacuuming to remove bubbles, filtering, and discharging.

[0219] (3) Preparation method of lithium secondary battery:

[0220] The negative electrode slurry in (2) is further used to make a pole piece, and assembled with a lithium iron phosphate positive pole piece, an electrolyte, a separator, and a battery case to obtain a lithium battery. After the lithium battery is filled with liquid, it is allowed to stand at 50° C. for 24 to 48 hours before being formed.

[0221] The chemical process includes:

[0222] Step a: Charge the battery with 0.04C for 60 minutes and let it stand for 20 minutes;

[0223] Step b: Charge at 0.08C for 60 min and let stand for 20 min;

[0224] Step c: charge at 0.16C for 300 min; let stand for 20 min;

[0225] After aging at 50°C for 48h, the capacity was divided and the K value was measured to obtain a lithium secondary battery.

[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 nanotubes CNT, and the binder is styrene butadiene rubber SBR.

[0228] (2) Preparation method of negative electrode slurry:

[0229] Step S1: Mix the active material powder and the conductive agent material uniformly and stir to form a kneaded state; continue to add deionized water and stir to achieve a fluid state;

[0230] Step S2: adding a composite additive, the composite additive comprising 0.16 mass % ethylene glycol amine and 1.44 mass % Mg(NO3)2, adding 0.16 mass % (accounting for 100 mass % of the total amount of ethylene glycol amine added) ethylene glycol amine, stirring for 20 minutes, then adding 1.44 mass % Mg(NO3)2 (accounting for 100 mass % of the total amount of Mg(NO3)2 added), continuing to stir for 20 minutes, adding deionized water to adjust the slurry viscosity to 3300cp;

[0231] Step S3: adding a binder, stirring slowly, vacuuming to remove bubbles, filtering, and discharging.

[0232] (3) Preparation method of lithium secondary battery:

[0233] The negative electrode slurry in (2) is further used to make a pole piece, and assembled with a lithium iron phosphate positive pole piece, an electrolyte, a separator, and a battery case to obtain a lithium battery. After the lithium battery is filled with liquid, it is allowed to stand at 50° C. for 24 to 48 hours before being formed.

[0234] The chemical process includes:

[0235] Step a: Charge the battery with 0.04C for 60 minutes and let it stand for 20 minutes;

[0236] Step b: Charge at 0.08C for 60 min and let stand for 20 min;

[0237] Step c: charge at 0.16C for 300 min; let stand for 20 min;

[0238] After aging at 50°C for 48h, the capacity was divided and the K value was measured to obtain a lithium secondary battery.

[0239] Example 8

[0240] (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 nanotubes CNT, and the binder is styrene-butadiene rubber SBR.

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

[0242] Step S1: Mix the active material powder and the conductive agent material uniformly and stir to form a kneaded state; continue to add deionized water and stir to achieve a fluid state;

[0243] Step S2: adding a composite additive, the composite additive comprising 0.04 mass% β-cyclodextrin and 0.96 mass% LiNO3, first adding 0.02 mass% (accounting for 50 mass% of the total amount of β-cyclodextrin added) β-cyclodextrin, stirring for 10 minutes, then adding 0.96 mass% LiNO3 (accounting for 100 mass% of the total amount of LiNO3 added) and continuing to stir, after stirring for 20 minutes, adding 0.02 mass% (accounting for 50 mass% of the total amount of β-cyclodextrin added) β-cyclodextrin, stirring for 10 minutes, adding deionized water to adjust the slurry viscosity to 3250cp;

[0244] Step S3: adding a binder, stirring slowly, vacuuming to remove bubbles, filtering, and discharging.

[0245] (3) Preparation method of lithium secondary battery:

[0246] The negative electrode slurry in (2) is further used to make a pole piece, and assembled with a lithium iron phosphate positive pole piece, an electrolyte, a separator, and a battery case to obtain a lithium battery. After the lithium battery is filled with liquid, it is allowed to stand at 50° C. for 24 to 48 hours before being formed.

[0247] The chemical process includes:

[0248] Step a: Charge the battery with 0.04C for 60 minutes and let it stand for 20 minutes;

[0249] Step b: Charge at 0.08C for 60 min and let stand for 20 min;

[0250] Step c: charge at 0.16C for 300 min; let stand for 20 min;

[0251] After aging at 50°C for 48h, the capacity was divided and the K value was measured to obtain a lithium secondary battery.

[0252] Example 9

[0253] (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 nanotubes CNT, and the binder is styrene-butadiene rubber SBR.

[0254] (2) Preparation method of negative electrode slurry:

[0255] Step S1: Mix the active material powder and the conductive agent material uniformly and stir to form a kneaded state; continue to add deionized water and stir to achieve a fluid state;

[0256] Step S2: adding a composite additive, the composite additive comprising 0.26 mass% β-cyclodextrin and 0.74 mass% LiNO3, first adding 0.13 mass% (accounting for 50 mass% of the total amount of β-cyclodextrin added) β-cyclodextrin, stirring for 10 minutes, then adding 0.74 mass% LiNO3 (accounting for 100 mass% of the total amount of LiNO3 added) and continuing to stir, after stirring for 20 minutes, adding 0.13 mass% (accounting for 50 mass% of the total amount of β-cyclodextrin added) β-cyclodextrin, stirring for 10 minutes, and adding deionized water to adjust the slurry viscosity to 2600cp;

[0257] Step S3: adding a binder, stirring slowly, vacuuming to remove bubbles, filtering, and discharging.

[0258] (3) Preparation method of lithium secondary battery:

[0259] The negative electrode slurry in (2) is further used to make a pole piece, and assembled with a lithium iron phosphate positive pole piece, an electrolyte, a separator, and a battery case to obtain a lithium battery. After the lithium battery is filled with liquid, it is allowed to stand at 50° C. for 24 to 48 hours before being formed.

[0260] The chemical process includes:

[0261] Step a: Charge the battery with 0.04C for 60 minutes and let it stand for 20 minutes;

[0262] Step b: Charge at 0.08C for 60 min and let stand for 20 min;

[0263] Step c: charge at 0.16C for 300 min; let stand for 20 min;

[0264] After aging at 50°C for 48h, the capacity was divided and the K value was measured to obtain a lithium secondary battery.

[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%, wherein the active material is graphite, the conductive agent is carbon nanotubes CNT, and the binder is styrene-butadiene rubber SBR.

[0267] (2) Preparation method of negative electrode slurry:

[0268] Step S1: Mix the active material powder and the conductive agent material uniformly and stir to form a kneaded state; continue to add deionized water and stir to achieve a fluid state;

[0269] Step S2: adding a composite additive, the composite additive comprising 0.08 mass% β-cyclodextrin and 0.92 mass% LiNO3, adding 0.08 mass% (accounting for 100 mass% of the total amount of β-cyclodextrin added) β-cyclodextrin, stirring for 20 minutes, then adding 0.92 mass% LiNO3 (accounting for 100 mass% of the total amount of LiNO3 added) and continuing to stir for 20 minutes, adding deionized water to adjust the slurry viscosity to 2900cp;

[0270] Step S3: adding a binder, stirring slowly, vacuuming to remove bubbles, filtering, and discharging.

[0271] (3) Preparation method of lithium secondary battery:

[0272] The negative electrode slurry in (2) is further used to make a pole piece, and assembled with a lithium iron phosphate positive pole piece, an electrolyte, a separator, and a battery case to obtain a lithium battery. After the lithium battery is filled with liquid, it is allowed to stand at 50° C. for 24 to 48 hours before being formed.

[0273] The chemical process includes:

[0274] Step a: Charge the battery with 0.08C for 30 minutes and let it stand for 20 minutes;

[0275] Step b: Charge at 0.08C for 60 min and let stand for 20 min;

[0276] Step c: charge at 0.16C for 300 min; let stand for 20 min;

[0277] After aging at 50°C for 48h, the capacity was divided and the K value was measured to obtain a lithium secondary battery.

[0278] Embodiment 11

[0279] (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 nanotubes CNT, and the binder is styrene-butadiene rubber SBR.

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

[0281] Step S1: Mix the active material powder and the conductive agent material uniformly and stir to form a kneaded state; continue to add deionized water and stir to achieve a fluid state;

[0282] Step S2: adding a composite additive, the composite additive comprising 0.08 mass% β-cyclodextrin and 0.92 mass% LiNO3, adding 0.08 mass% (accounting for 100 mass% of the total amount of β-cyclodextrin added) β-cyclodextrin, stirring for 20 minutes, then adding 0.92 mass% LiNO3 (accounting for 100 mass% of the total amount of LiNO3 added) and continuing to stir for 20 minutes, adding deionized water to adjust the slurry viscosity to 3250cp;

[0283] Step S3: adding a binder, stirring slowly, vacuuming to remove bubbles, filtering, and discharging.

[0284] (3) Preparation method of lithium secondary battery:

[0285] The negative electrode slurry in (2) is further used to make a pole piece, and assembled with a lithium iron phosphate positive pole piece, an electrolyte, a separator, and a battery case to obtain a lithium battery. After the lithium battery is filled with liquid, it is allowed to stand at 50° C. for 24 to 48 hours before being formed.

[0286] The chemical process includes:

[0287] Step a: Charge the battery with 0.08C for 30 minutes and let it stand for 20 minutes;

[0288] Step b: Charge at 0.16C for 30 minutes and let stand for 20 minutes;

[0289] Step c: charge at 0.16C for 300 min; let stand for 20 min;

[0290] After aging at 50°C for 48h, the capacity was divided and the K value was measured to obtain a lithium secondary battery.

[0291] Example 12

[0292] (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 nanotubes CNT, and the binder is styrene-butadiene rubber SBR.

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

[0294] Step S1: Mix the active material powder and the conductive agent material uniformly and stir to form a kneaded state; continue to add deionized water and stir to achieve a fluid state;

[0295] Step S2: adding a composite additive, the composite additive comprising 0.08 mass% β-cyclodextrin and 0.92 mass% LiNO3, adding 0.08 mass% (accounting for 100 mass% of the total amount of β-cyclodextrin added) β-cyclodextrin, stirring for 20 minutes, then adding 0.92 mass% LiNO3 (accounting for 100 mass% of the total amount of LiNO3 added) and continuing to stir for 20 minutes, adding deionized water to adjust the slurry viscosity to 2550cp;

[0296] Step S3: adding a binder, stirring slowly, vacuuming to remove bubbles, filtering, and discharging.

[0297] (3) Preparation method of lithium secondary battery:

[0298] The negative electrode slurry in (2) is further used to make a pole piece, and assembled with a lithium iron phosphate positive pole piece, an electrolyte, a separator, and a battery case to obtain a lithium battery. After the lithium battery is filled with liquid, it is allowed to stand at 50° C. for 24 to 48 hours before being formed.

[0299] The chemical process includes:

[0300] Step a: Charge the battery with 0.08C for 30 minutes and let it stand for 20 minutes;

[0301] Step b: Charge at 0.16C for 30 minutes and let stand for 20 minutes;

[0302] Step c: charge for 150 min using 0.32C current; let stand for 20 min;

[0303] After aging at 50°C for 48h, the capacity was divided and the K value was measured to obtain a lithium secondary battery.

[0304] Performance Testing

[0305] The lithium secondary batteries obtained in Comparative Example 1 and Examples 1 to 12 were subjected to DCR tests, and the results are shown in Table 1. In addition, Table 1 also shows the amounts of composite additives used in Comparative Example 1 and Examples 1 to 12, the order of addition, and the chemical formation systems used.

[0306] Table 1 Amounts of composite additives used, order of addition, chemical formulation and DCR test results of Comparative Example 1 and Examples 1 to 12

[0307]

[0308]

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

[0310] By comparing Examples 1 to 4, it can be seen that the order of adding the organic additive and the inorganic additive in the composite additive has a great influence on the internal resistance of the battery. The best effect of reducing the internal resistance of the battery is to add the organic additive in steps and add the inorganic additive in the middle. At the same time, the effect of adding the organic additive first and then the inorganic additive is obviously better than adding the inorganic additive first and then the organic additive or mixing the two and then adding them.

[0311] By comparing Example 2 with Example 5, it can be seen that when the content of the composite additive exceeds a certain value, it has no promoting effect on further reducing the internal resistance of the battery.

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

[0313] By comparing Example 2 with Examples 10 to 12, it can be seen that by optimizing the formation process, the internal resistance of the battery can be further reduced by 12% to 17%.

[0314] It should be noted that, although the technical solution of the present invention is introduced with specific examples, those skilled in the art will appreciate that the present invention should not be limited thereto.

[0315] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill 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 of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A negative electrode slurry, characterized in that: It includes negative electrode active material, conductive agent, binder and composite additives. Wherein, the composite additive comprises a combination of an organic additive and an inorganic additive, The organic additives include one or more of cyclodextrin and alcoholamine compounds. The inorganic additive includes one or more nitrates of alkali metals and / or alkaline earth metals.

2. The negative electrode slurry according to claim 1, characterized in that The cyclodextrin includes one or more of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, and derivatives thereof; and / or The alcoholamine compounds include one or more of methanolamine compounds, ethanolamine compounds, and propanolamine compounds; Preferably, the ethanolamine compound includes one or more of ethanolamine, diethanolamine, triethanolamine; and / or The nitrate of the alkali metal and / or alkaline earth metal includes one or more of LiNO3, NaNO3, Ca(NO3)2, and Mg(NO3)2.

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

4. The negative electrode slurry according to any one of claims 1 to 3, characterized in that: The weight ratio of the inorganic additive to the organic additive is 20:1 to 3:

1.

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

6. A method for preparing a negative electrode slurry, characterized in that: It includes the following steps: Step S1: stirring the negative electrode active material, the conductive agent and the solvent to obtain a slurry; Step S2: adding the composite additive to the slurry obtained in step S1 and stirring, and then adding a solvent to adjust the viscosity of the slurry; Step S3: adding a binder and stirring to obtain a negative electrode slurry. The composite additive comprises a combination of an organic additive and an inorganic additive. The organic additives include one or more of cyclodextrin and alcoholamine compounds. The inorganic additive includes one or more nitrates of alkali metals and / or alkaline earth metals.

7. The preparation method according to claim 6, characterized in that: The cyclodextrin includes one or more of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, and derivatives thereof; and / or, The alcoholamine compounds include one or more of methanolamine compounds, ethanolamine compounds, and propanolamine compounds; Preferably, the ethanolamine compound includes one or more of ethanolamine, diethanolamine, triethanolamine; and / or The nitrate of the alkali metal and / or alkaline earth metal includes one or more of LiNO3, NaNO3, Ca(NO3)2, Mg(NO3)2; and / or The weight ratio of the total amount of the inorganic additives to the total amount of the organic additives is 20:1 to 3:1; and / or The weight ratio of the negative electrode active material, the conductive agent, the binder and the composite additive is 93-98 weight %: 0.5-1.5 weight %: 0.5-3.5 weight %: 0.1-2 weight %; and / or The negative electrode active material includes one or more of graphite, hard carbon, silicon-carbon material, lithium metal, and tin-based material; and / or The conductive agent includes one or more of conductive graphite, graphene, acetylene black, carbon black, and carbon nanotubes; and / or The binder includes one or more of sodium carboxymethyl cellulose, chitosan, sodium lignocellulose, styrene-butadiene rubber, styrene-propylene rubber, sodium polymethacrylate, lithium polymethacrylate, polymethacrylate, and polyvinylidene fluoride.

8. The preparation method according to claim 6 or 7, characterized in that: The slurry in step S1 also includes a dispersant; Preferably, the dispersant includes one or more of sodium carboxymethyl cellulose, chitosan, sodium lignocellulose, styrene-butadiene rubber, styrene-acrylic rubber, sodium polymethacrylate, lithium polymethacrylate, and polymethacrylate.

9. The preparation method according to any one of claims 6 to 8, characterized in that: In the step S2, the method of adding the composite additive includes: first adding 50-100% by mass of the organic additive accounting for the total amount of the organic additive, then adding 50-100% by mass of the inorganic additive accounting for the total amount of the inorganic additive, then optionally adding the remaining organic additive, and then optionally adding the remaining inorganic additive; Preferably, the method of adding the composite additive includes: first adding 50-80 mass % of the organic additives accounting for the total amount of the organic additives, then adding 100 mass % of the inorganic additives accounting for the total amount of the inorganic additives, and then adding the remaining organic additives.

10. A lithium secondary battery, characterized in that: It includes a negative electrode sheet, a positive electrode sheet, a separator, an electrolyte and a battery casing. 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 according to any one of claims 1 to 5 or is formed from the negative electrode slurry obtained by the preparation method according to any one of claims 6 to 9.

11. A method for preparing a lithium secondary battery according to claim 10, characterized in that: It includes the following steps: The negative electrode sheet and the positive electrode sheet are assembled with the separator, the electrolyte, and the battery case, and then the formation process is carried out.

12. The preparation method according to claim 11, characterized in that: The formation process includes: injecting liquid into the assembled lithium battery, letting it stand, and then charging it. The charging steps include: Step a: Use current I1 to charge for time T1, and let it stand for 5 to 20 minutes; wherein I1 = 0.06 to 0.12C, T1 = 30 to 60 minutes; Step b: Use current I2 to charge for time T2, and let it stand for 5 to 20 minutes; wherein I2 = 0.06 to 0.24C, T2 = 15 to 60 minutes; Step c: using current I3 to charge for time T3, and standing for 5 to 20 minutes; wherein I3 = 0.12 to 0.48C, T3 = 90 to 360 minutes; Among them, I1≤I2, I2≤I3, and I1, I2, and I3 are not equal at the same time.

13. The preparation method according to claim 12, characterized in that: When I1=I2, optionally, the charging steps sequentially include: Step ab: Use current I1 to charge for time T1+T2, and let stand for 5 to 20 minutes, where I1=0.06 to 0.12C, T1+T2=45 to 120 minutes; Step c: Use current I3 to charge for time T3, and let stand for 5 to 20 minutes; wherein I3 = 0.12 to 0.48C, T3 = 90 to 360 minutes; or, When I2=I3, optionally, the charging steps sequentially include: Step a: Use current I1 to charge for time T1, and let it stand for 5 to 20 minutes, where I1 = 0.06 to 0.12C, T1 = 30 to 60 minutes; Step bc: Use current I2 to charge for time T2+T3, and let stand for 5 to 20 minutes; wherein, I2=0.12 to 0.24C, T2+T3=105 to 420 minutes.

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