Lithium ion battery

Abstract

The invention relates to a lithium ion battery in the technical field of lithium batteries, the lithium ion battery comprises a composite positive electrode and a negative electrode plate, the composite positive electrode comprises a positive electrode lithium supplement agent, the negative electrode plate comprises a negative electrode composite layer and a negative electrode current collector, the negative electrode composite layer comprises a negative electrode active material layer and a slow-release lithium supplement layer, the negative active material layer is prepared by a dry method; the slow-release lithium supplementing layer is compounded on one side, far away from the negative electrode current collector, of the negative electrode active material layer; and the slow-release lithium supplementing layer comprises a lithium-silicon alloy. And the slow-release lithium supplementing layer is matched with the negative plate to realize slow release of lithium ions. According to the brand-new lithium ion battery provided by the invention, the positive electrode lithium supplement agent is added into the positive electrode to realize first-charge lithium supplement, the negative electrode is compounded with the negative electrode plate prepared by the dry method through the lithium-silicon alloy, and the lithium-silicon alloy can slowly release active lithium ions by compounding the negative electrode plate prepared by the dry method with the lithium-silicon alloy, so that the cycle performance of the battery is improved.

Description

Technical Field

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

[0002] Rechargeable lithium-ion batteries are widely used in portable electronic devices, hybrid electric vehicles and renewable energy storage systems. Generally, lithium-ion batteries are usually composed of a transition metal oxide positive electrode and a graphite negative electrode. During the charge and discharge process, lithium ions migrate between the positive and negative electrodes, but during the first charge process, 5-20% of the Li+ is consumed by forming a solid electrolyte interface (SEI) at the negative electrode, resulting in problems such as excessive irreversible capacity loss and low first cycle coulomb efficiency. On the other hand, there are many reasons that cause the slow and continuous consumption of lithium ions during the battery cycle, further affecting the battery's capacity retention rate and cycle performance.

[0003] Based on the lithium ion consumption problem caused by the above-mentioned first charge and cycle, the current common solution is to replenish lithium to the positive electrode alone or to the negative electrode alone.

[0004] Common positive electrode lithium replenishment usually involves directly adding a lithium replenisher to the positive electrode to compensate for the irreversible loss of active lithium caused by the formation of the negative electrode SEI film. Common negative electrode lithium replenishment methods are direct pre-lithiation through metallic lithium powder / metal lithium foil. Metal lithium powder pre-lithiation usually involves adding metallic lithium powder into the negative electrode active material slurry or directly coating the metallic lithium powder on the negative electrode surface to achieve the purpose of lithium replenishment. Metal lithium foil pre-lithiation usually involves directly pressing ultra-thin lithium foil or alloy lithium foil onto the negative electrode to form a lithium replenished negative electrode.

[0005] However, no matter whether it is the positive electrode or the negative electrode that is replenishing lithium, in most cases only the first cycle of lithium replenishment can be achieved, and continuous lithium replenishment throughout the life cycle cannot be achieved. Therefore, how to sustainably replenish lithium throughout the life cycle is an important issue facing the lithium battery industry. Summary of the invention

[0006] In order to solve the problem that the lithium battery industry cannot sustainably replenish lithium throughout the life cycle of lithium batteries, the present invention proposes a lithium-ion battery, which realizes the initial lithium replenishment by adding a positive electrode lithium replenisher to the positive electrode, and the negative electrode is compounded with a negative electrode sheet prepared by a dry method through a lithium-silicon alloy. The compounding of the negative electrode sheet prepared by the dry method and the lithium-silicon alloy can make the lithium-silicon alloy slowly release active lithium ions, thereby improving the battery cycle performance. The technical solution of the present invention is implemented as follows:

[0007] A lithium-ion battery comprises a composite positive electrode and a negative electrode sheet, wherein the composite positive electrode comprises a positive electrode lithium replenisher, the negative electrode sheet comprises a negative electrode composite layer and a negative electrode current collector, the negative electrode composite layer comprises a negative electrode active material layer and a slow-release lithium replenisher layer, wherein:

[0008] The negative electrode active material layer is prepared by a dry method;

[0009] The slow-release lithium supplement layer is composited on a side of the negative electrode active material layer away from the negative electrode current collector;

[0010] The slow-release lithium supplementing layer comprises a lithium-silicon alloy.

[0011] Preferably, the composite positive electrode comprises a positive electrode current collector and a positive electrode active material layer; wherein the positive electrode active material layer comprises a positive electrode active material, a positive electrode lithium replenisher, a binder and a conductive agent.

[0012] Preferably, the composite positive electrode comprises a positive electrode current collector and a positive electrode composite layer, the positive electrode composite layer comprises a positive electrode active material layer and a positive electrode lithium replenishing layer, and the positive electrode lithium replenishing layer comprises a positive electrode lithium replenishing agent.

[0013] Preferably, the sustained-release lithium supplementing layer is prepared by a dry method.

[0014] Preferably, the positive electrode lithium supplement is selected from one or more of Li2NiO2 (LNO), Li5FeO4 (LFO), Li2O, Li8ZrO6 (LZO), and Li2C2O4.

[0015] Preferably, the slow-release lithium-replenishing layer comprises a lithium-silicon alloy and a fiberizable binder, and the slow-release lithium-replenishing layer accounts for 2%-5% of the thickness of the negative electrode composite layer.

[0016] Preferably, the fiberizable binder is selected from any one of polyethylene oxide, polytetrafluoroethylene, polyvinylidene fluoride, polypropylene, polyvinyl chloride, polystyrene, polyoxymethylene, polycarbonate, polyamide, acrylic plastic, polysulfone, polyphenylene ether, and carboxymethyl cellulose, or a combination of at least two thereof.

[0017] Preferably, the negative electrode active material layer comprises a negative electrode active material, a fiberizable binder and a conductive agent, and the negative electrode active material layer accounts for 95%-98% of the thickness of the negative electrode composite layer;

[0018] The negative electrode active material is graphite-silicon carbon material, including dopamine-coated nano silicon carbon and hard carbon-coated graphite, wherein the dopamine-coated nano silicon carbon accounts for 10% to 20% of the negative electrode active material.

[0019] Preferably, the lithium-ion battery further comprises an electrolyte, and a deoxidizing additive is added to the electrolyte.

[0020] Preferably, the composite positive electrode further comprises an electrolyte coating.

[0021] Preferably, the preparation method of the lithium silicon alloy is as follows:

[0022] In an argon glove box, two raw materials, nano-Si and 10% excess metallic lithium powder, were added into a spherical ink tank according to a stoichiometric ratio, and a lithium-silicon alloy was prepared by a high-energy ball milling method using n-hexane as a lubricant;

[0023] The ball milling parameters were 800 r / min for 2.5 h, then 200 r / min for 3 h, and 800 r / min for 2.5 h.

[0024] After the ball milling, the cyclohexane was evaporated to obtain the lithium silicon alloy Li 22 Si5.

[0025] The present invention proposes a new lithium-ion battery, which realizes the initial lithium replenishment by adding a positive electrode lithium replenisher to the positive electrode, and for the first time proposes to compound the negative electrode with a negative electrode sheet prepared by a dry method through a lithium-silicon alloy. The compound of the negative electrode sheet prepared by the dry method and the lithium-silicon alloy can make the lithium-silicon alloy slowly release active lithium ions, thereby improving the battery cycle performance. DETAILED DESCRIPTION

[0026] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] In the description of the specific implementation methods of the present invention, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present invention, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0029] Reference to "embodiments" in the present invention means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in the present invention may be combined with other embodiments.

[0030] In the description of the embodiments of the present invention, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in the present invention generally indicates that the associated objects before and after are in an "or" relationship.

[0031] Throughout the present invention, numerical values ​​represent approximate measures or limits of ranges to cover minor deviations from given values ​​as well as embodiments with about the values ​​mentioned and embodiments with the exact values ​​mentioned. Except for the working examples provided at the end of the detailed description, all numerical values ​​of parameters (e.g., amounts or conditions) in this specification (including the appended claims) should be understood to be modified by the term "about" in all cases, regardless of whether "about" actually appears before the numerical value. "About" indicates that the stated numerical value allows some minor imprecision (close to the exact value of the value to some extent; approximately or reasonably close to the value; almost). If the imprecision provided by "about" is not otherwise understood in this ordinary sense in the art, "about" as used in the present invention at least indicates the variation that can be produced by the ordinary methods of measuring and using such parameters. For example, "about" may include a variation of less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in some aspects, optionally less than or equal to 0.1%.

[0032] Additionally, disclosure of ranges includes disclosure of all values ​​within the entire range and further divided ranges, including endpoints and sub-ranges given for such ranges.

[0033] Rechargeable lithium-ion batteries are widely used in portable electronic devices, hybrid electric vehicles and renewable energy storage systems. Generally, lithium-ion batteries are usually composed of a transition metal oxide positive electrode and a graphite negative electrode. During the charge and discharge process, lithium ions migrate between the positive and negative electrodes, but during the first charge process, 5-20% of the Li+ is consumed by forming a solid electrolyte interface (SEI) at the negative electrode, resulting in problems such as excessive irreversible capacity loss and low first cycle coulomb efficiency. On the other hand, there are many reasons that cause the slow and continuous consumption of lithium ions during the battery cycle, further affecting the battery's capacity retention rate and cycle performance.

[0034] The existing technology usually replenishes lithium ions consumed in the battery by replenishing lithium to the positive and negative electrodes. However, the positive electrode lithium replenishment in the existing technology can usually only release active lithium during the first charging process of the battery. At present, there are studies on the continuous lithium replenishment of the positive electrode during the battery cycle. For example, by selecting a specific lithium replenisher (such as lithium-rich manganese-based material) to be used in conjunction with the positive electrode, continuous lithium replenishment can be achieved; or, a higher content of lithium replenisher is added to the positive electrode to stepwise increase the battery charging voltage to release the lithium source in the positive electrode in stages. However, both of the above two continuous lithium replenishment methods have certain problems. The former lithium-rich manganese-based material has a large irreversible capacity loss during the first charge and discharge, and the lithium-rich manganese-based layered material structure is unstable, and it will transform into a spinel structure near 4.5V, thereby losing electrochemical activity; the latter requires a continuous increase in the upper limit of the charging voltage, and has high requirements for the pressure resistance of the materials in the battery system; however, whether it is the former or the latter, gas will continue to be generated in the process of gradually releasing active lithium. Excessive gas production in the closed environment of the battery cell will cause the battery cell to open the valve prematurely, resulting in safety risks. So far, no research has been found to achieve continuous lithium replenishment at the negative electrode.

[0035] In order to solve the above problems, the present invention proposes a lithium-ion battery. The lithium-ion battery, wherein the composite positive electrode contains a positive electrode lithium replenisher, the negative electrode sheet includes a negative electrode composite layer and a negative electrode current collector, the negative electrode composite layer includes a negative electrode active material layer and a slow-release lithium replenisher layer, wherein:

[0036] The negative electrode active material layer is prepared by a dry method; the slow-release lithium supplement layer is compounded on the side of the negative electrode active material layer away from the negative electrode current collector; the slow-release lithium supplement layer contains a lithium-silicon alloy. The slow-release lithium supplement layer cooperates with the negative electrode sheet to achieve slow release of lithium ions.

[0037] As we all know, metallic lithium is extremely active and has high safety risks of its own, which will bring uncontrollable risks to the production and use of batteries. The applicant accidentally discovered that when the negative electrode sheet prepared by the dry method is compounded with the lithium-silicon alloy, the unique properties of the dry-process negative electrode sheet enable the lithium ions of the lithium-silicon alloy to be slowly released, thereby improving safety.

[0038] Through the above configuration, both the positive and negative electrodes are provided with lithium replenishment schemes, and the positive electrode lithium replenisher provides lithium replenishment for the formation of the SEI film when the lithium-ion battery is first charged. The slow-release lithium replenishment layer of the negative electrode sheet cooperates with the negative electrode sheet prepared by the dry method to provide a lithium replenishment source for the lithium ions consumed during the cycle, achieving continuous lithium replenishment and improving the cycle performance of the battery.

[0039] The existing lithium powder or lithium foil replenishment methods can basically only replenish lithium in the first cycle, and cannot achieve continuous lithium replenishment throughout the life cycle to achieve excellent cycle stability. In this case, the negative electrode can be slowly replenished with lithium through the cooperation of the negative electrode sheet and the lithium replenishment layer.

[0040] In some embodiments, the slow-release lithium replenishing layer is prepared by a dry method. Lithium-silicon alloy has high activity. By preparing the slow-release lithium replenishing layer by a dry method, the lithium-silicon alloy can be prevented from reacting during the preparation process, thereby ensuring the amount of lithium replenishment in the battery, ensuring continuous lithium replenishment of the battery, and improving the cycle performance of the battery.

[0041] In some embodiments, the composite positive electrode includes a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer includes a positive electrode active material, a positive electrode lithium supplement, a binder and a conductive agent.

[0042] In some embodiments, the composite positive electrode comprises a positive electrode current collector and a positive electrode composite layer, the positive electrode composite layer comprises a positive electrode active material layer and a positive electrode lithium replenishing layer, and the positive electrode lithium replenishing layer comprises a positive electrode lithium replenishing agent.

[0043] In some embodiments, the positive electrode lithium supplement layer accounts for 2%-3% of the thickness of the positive electrode composite layer.

[0044] The present invention provides a lithium replenishing layer to replenish the active lithium consumed by forming a solid electrolyte interface (SEI) film during the first charging process of the lithium ion battery, thereby improving the first efficiency and the energy density of the battery and the cycle performance of the battery.

[0045] In some embodiments, the positive electrode lithium replenishment layer further includes a binder, which is used to adhere the binders in the positive electrode lithium replenishment layer together, so that the positive electrode lithium replenishment layer has a certain viscosity and can be composited with the positive electrode active material layer. Specifically, the binder is a binder used in conventional positive electrode lithium replenishment, and the conductive agent is a conductive agent used in conventional positive electrode lithium replenishment.

[0046] In some embodiments, the positive electrode lithium replenishing layer further includes a conductive agent, which is mainly used to assist and improve the conductivity in the positive electrode lithium replenishing layer. The conductive agent is not particularly limited in the present application as long as it has electronic conductivity without causing chemical changes. Specifically, the conductive agent includes any one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene or carbon nanofibers, or a combination of at least two thereof.

[0047] In some embodiments, the positive electrode lithium supplement is selected from one or more of Li2NiO2 (LNO), Li5FeO4 (LFO), Li2O, Li8ZrO6 (LZO), and Li2C2O4.

[0048] It should be noted that the "one or more" claimed in the present invention refers to the types of positive electrode lithium replenishers that can be selectively purchased by those skilled in the art based on actual needs and factors such as the price of raw materials. Whether it is one, two or even more, it does not change its ability to achieve the function and effect of initial lithium replenishment. Since this part of the technology is prior art, the types of these materials in the present invention are merely examples rather than limitations. In actual applications, materials with the same or similar properties to the above-mentioned materials can also be selected as positive electrode lithium replenishers.

[0049] In some embodiments, the composite positive electrode further includes an electrolyte coating. The electrolyte coating is a polymer and oxide solid electrolyte. Specifically, when the composite positive electrode includes a positive electrode current collector and a positive electrode active material layer, the solid electrolyte coating is arranged on the side of the positive electrode active material layer away from the positive electrode current collector; when the composite positive electrode includes a positive electrode current collector and a positive electrode composite layer, the solid electrolyte coating is arranged on the side of the positive electrode composite layer away from the positive electrode current collector. This arrangement can improve the safety of the battery.

[0050] In some embodiments, the slow-release lithium supplementation layer comprises a lithium-silicon alloy (Li 22 Si5) and a fiberizable binder, the slow-release lithium replenishing layer and the negative electrode active material layer constitute a negative electrode composite layer, and the slow-release lithium replenishing layer accounts for 2%-5% of the thickness of the negative electrode composite layer.

[0051] In practical applications, the ratio of the slow-release lithium supplement layer to the thickness of the negative electrode composite layer can be 2%, 3%, 4%, or 5%. The above values ​​are only examples and are not limiting.

[0052] In some embodiments, the fiberizable binder is selected from any one or a combination of at least two of polyethylene oxide, polytetrafluoroethylene, polyvinylidene fluoride, polypropylene, polyvinyl chloride, polystyrene, polyoxymethylene, polycarbonate, polyamide, acrylic plastic, polysulfone, polyphenylene ether or carboxymethyl cellulose.

[0053] Since lithium-silicon alloys are chemically active and easily react with water, these fiberizable binders can bind lithium-silicon alloys together after fiberization, thereby realizing the dry method for preparing negative electrode sheets. The dry method for preparing a slow-release lithium replenishment layer can maintain the activity of the lithium-silicon alloy and prevent it from losing its activity and failing to provide continuous lithium replenishment for the battery cycle.

[0054] In some embodiments, the sustained-release lithium supplementation layer further includes a conductive agent, which is mainly used to assist in improving the ionic conductivity of the sustained-release lithium supplementation layer. The conductive agent is not particularly limited in the present application as long as it has electronic conductivity without causing chemical changes. Specifically, the conductive agent includes any one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene or carbon nanofibers, or a combination of at least two thereof.

[0055] In some embodiments, the negative electrode active material layer comprises a negative electrode active material, a fibrillable binder and a conductive agent, and the negative electrode active material layer accounts for 95%-98% of the thickness of the negative electrode composite layer.

[0056] In practical applications, the proportion of the negative electrode active material layer to the thickness of the negative electrode composite layer can be 95%, 96%, 97%, or 98%. The above values ​​are only examples and are not limiting.

[0057] The "negative electrode active material" referred to in the present invention is a conventional negative electrode active material in the art, preferably a graphite-silicon carbon material.

[0058] In some preferred embodiments, the negative electrode active material includes dopamine-coated nano silicon carbon and hard carbon-coated graphite. Among them, the dopamine-coated nano silicon carbon accounts for 10% to 20% of the active material. Dopamine is coated on the outside of nano silicon, which can inhibit the expansion of nano carbon silicon, and then inhibit the expansion of the negative electrode, thereby improving the cycle performance of the battery. The rest is hard carbon-coated graphite.

[0059] The "fiberizable binder" referred to in the present invention refers to a binder commonly used in the art that can be fibrillated; the conductive agent is a conductive agent in conventional negative electrode materials, which improves the ionic conductivity of the electrode sheet.

[0060] In some embodiments, the conductive agent in the negative electrode active material layer is mainly used to assist in improving the ionic conductivity of the negative electrode active material layer. There is no particular limitation on the conductive agent in the present application, as long as it has electronic conductivity without causing chemical changes. Specifically, the conductive agent includes any one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene or carbon nanofibers, or a combination of at least two thereof.

[0061] Preferably, the lithium-ion battery further comprises an electrolyte, and a deoxidizing additive is added to the electrolyte.

[0062] The electrolyte referred to in the present invention is a commonly used electrolyte. In the present invention, deoxygenating additives such as TMSPI, TMSP, and LiBOB are added to the electrolyte to eliminate the influence of oxygen generated by the positive electrode lithium supplement additive during the first activation process on the battery performance.

[0063] Preferably, the preparation method of the lithium silicon alloy is as follows:

[0064] In an argon glove box, two raw materials, nano-Si and 10% excess metallic lithium powder, were added into a spherical ink tank according to a stoichiometric ratio, and a lithium-silicon alloy was prepared by a high-energy ball milling method using n-hexane as a lubricant;

[0065] The ball milling parameters were 800 r / min for 2.5 h, then 200 r / min for 3 h, and 800 r / min for 2.5 h.

[0066] After the ball milling, the cyclohexane was evaporated to obtain the lithium silicon alloy Li 22 Si5.

[0067] The embodiments of the present invention will be described in more detail below through examples and comparative examples. It should be noted that the embodiments of the present invention are not limited to these examples.

[0068] In addition, the diaphragms and electrolytes in the following examples and comparative examples are all common structures or materials in the art. Since they are not the core of the present invention, the present embodiment does not show specific materials or components, but those skilled in the art should know that any common diaphragm and electrolyte can be used to prepare the lithium-ion battery of the present invention. The diaphragms and electrolytes in all the examples and comparative examples of the present invention are the same.

[0069] Example 1

[0070] A lithium-ion battery includes a composite positive electrode and a negative electrode sheet arranged alternately and a separator arranged therebetween, and also includes an electrolyte, wherein the electrolyte is a lithium salt solution. The preparation method of the composite positive electrode and the negative electrode sheet is as follows:

[0071] 1. Preparation of negative electrode sheet:

[0072] 1. The negative electrode lithium supplement material lithium silicon alloy, the binder PVDF and the conductive agent acetylene black are mixed, and after fiberization treatment, the negative electrode slow-release lithium supplement layer is prepared by roller pressing.

[0073] 2. The negative electrode active material graphite, the binder PVDF and the conductive agent acetylene black are mixed and fiberized, and then roll-formed to obtain the negative electrode active material layer.

[0074] 3. Roll-press and composite the negative electrode slow-release lithium supplement layer, the negative electrode active material layer and the copper foil, wherein the slow-release lithium supplement layer accounts for 4% of the negative electrode composite layer, and the negative electrode active material layer accounts for 96% of the negative electrode composite layer.

[0075] 2. Preparation of composite positive electrode:

[0076] 1. The positive electrode active material Li(NiCoMn)O2, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are mixed to prepare a positive electrode active material layer slurry, which is then coated on an aluminum foil and dried.

[0077] 2. The positive electrode lithium supplement material Li2NiO2, the binder PVDF and the conductive agent acetylene black are mixed, coated on the positive electrode active material layer and dried.

[0078] 3. Preparation of lithium-ion batteries:

[0079] The negative electrode sheet prepared in step one and the composite positive electrode prepared in step two are prepared into a lithium-ion battery together with a separator and an electrolyte using a conventional method.

[0080] Example 2

[0081] A lithium-ion battery includes a composite positive electrode and a negative electrode sheet arranged alternately and a separator arranged therebetween, and also includes an electrolyte, wherein the electrolyte is a lithium salt solution. The preparation method of the composite positive electrode and the negative electrode sheet is as follows:

[0082] 1. Preparation of negative electrode sheet:

[0083] 1. The negative electrode lithium supplement material lithium silicon alloy, the binder PVDF and the conductive agent acetylene black are mixed, and after fiberization treatment, the negative electrode slow-release lithium supplement layer is prepared by roller pressing.

[0084] 2. The negative electrode active material graphite, the binder PVDF and the conductive agent acetylene black are mixed and fiberized, and then roll-formed to obtain the negative electrode active material layer.

[0085] 3. Roll-press and composite the negative electrode slow-release lithium supplement layer, the negative electrode active material layer and the copper foil, wherein the slow-release lithium supplement layer accounts for 4% of the negative electrode composite layer, and the negative electrode active material layer accounts for 96% of the negative electrode composite layer.

[0086] 2. Preparation of composite positive electrode:

[0087] 1. The positive electrode active material Li(NiCoMn)O2, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are mixed to prepare a positive electrode active material layer slurry, which is then coated on an aluminum foil and dried.

[0088] 2. The positive electrode lithium supplement material Li2NiO2, the binder PVDF, the solvent and the conductive agent acetylene black are mixed, coated on the positive electrode active material layer and dried.

[0089] 3. Composite the composite electrolyte layer on the surface of the positive electrode lithium replenishing layer.

[0090] 3. Preparation of lithium-ion batteries:

[0091] The negative electrode sheet prepared in step one and the composite positive electrode prepared in step two are prepared into a lithium-ion battery together with a separator and an electrolyte using a conventional method.

[0092] Example 3

[0093] A lithium-ion battery includes a composite positive electrode and a negative electrode sheet arranged alternately and a separator arranged therebetween, and also includes an electrolyte, wherein the electrolyte is a lithium salt solution. The preparation method of the composite positive electrode and the negative electrode sheet is as follows:

[0094] 1. Preparation of negative electrode sheet:

[0095] 1. The negative electrode lithium supplement material lithium silicon alloy, the binder PVDF and the conductive agent acetylene black are mixed, and after fiberization treatment, the negative electrode slow-release lithium supplement layer is prepared by roller pressing.

[0096] 2. The negative electrode active material graphite-nano silicon carbon (15% dopamine-coated nano silicon carbon, 85% hard carbon-coated graphite), the binder PVDF and the conductive agent acetylene black are mixed and fiberized, and roll-formed to obtain the negative electrode active material layer.

[0097] 3. Roll-press and composite the negative electrode slow-release lithium supplement layer, the negative electrode active material layer and the copper foil, wherein the slow-release lithium supplement layer accounts for 4% of the negative electrode composite layer, and the negative electrode active material layer accounts for 96% of the negative electrode composite layer.

[0098] 2. Preparation of composite positive electrode:

[0099] 1. The positive electrode active material Li(NiCoMn)O2, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are mixed to prepare a positive electrode active material layer slurry, which is then coated on an aluminum foil and dried.

[0100] 2. The positive electrode lithium supplement material Li2NiO2, the binder PVDF and the conductive agent acetylene black are mixed, coated on the positive electrode active material layer and dried.

[0101] 3. Composite the composite electrolyte layer on the surface of the positive electrode lithium replenishing layer.

[0102] 3. Preparation of lithium-ion batteries:

[0103] The negative electrode sheet prepared in step one and the composite positive electrode prepared in step two are prepared into a lithium-ion battery together with a separator and an electrolyte using a conventional method.

[0104] Example 4

[0105] A lithium-ion battery includes a composite positive electrode and a negative electrode sheet arranged alternately and a separator arranged therebetween, and also includes an electrolyte, wherein the electrolyte is a lithium salt solution. The preparation method of the composite positive electrode and the negative electrode sheet is as follows:

[0106] 1. Preparation of negative electrode sheet:

[0107] 1. The negative electrode lithium supplement material lithium silicon alloy, the binder PVDF and the conductive agent acetylene black are mixed, and after fiberization treatment, the negative electrode slow-release lithium supplement layer is prepared by roller pressing.

[0108] 2. The negative electrode active material graphite, the binder PVDF and the conductive agent acetylene black are mixed and fiberized, and then roll-formed to obtain the negative electrode active material layer.

[0109] 3. Roll-press and composite the negative electrode slow-release lithium supplement layer, the negative electrode active material layer and the copper foil, wherein the slow-release lithium supplement layer accounts for 2% of the negative electrode composite layer, and the negative electrode active material layer accounts for 98% of the negative electrode composite layer.

[0110] 2. Preparation of composite positive electrode:

[0111] 1. The positive electrode active material Li(NiCoMn)O2, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are mixed to prepare a positive electrode active material layer slurry, which is then coated on an aluminum foil and dried.

[0112] 2. The positive electrode lithium supplement material Li2O, the binder PVDF and the conductive agent acetylene black are mixed, coated on the positive electrode active material layer and dried.

[0113] 3. Composite the composite electrolyte layer on the surface of the positive electrode lithium replenishing layer.

[0114] 3. Preparation of lithium-ion batteries:

[0115] The negative electrode sheet prepared in step one and the composite positive electrode prepared in step two are prepared into a lithium-ion battery together with a separator and an electrolyte using a conventional method.

[0116] Example 5

[0117] A lithium-ion battery includes a composite positive electrode and a negative electrode sheet arranged alternately and a separator arranged therebetween, and also includes an electrolyte, wherein the electrolyte is a lithium salt solution. The preparation method of the composite positive electrode and the negative electrode sheet is as follows:

[0118] 1. Preparation of negative electrode sheet:

[0119] 1. The negative electrode lithium supplement material lithium silicon alloy, the binder PVDF and the conductive agent acetylene black are mixed, and after fiberization treatment, the negative electrode slow-release lithium supplement layer is prepared by roller pressing.

[0120] 2. The negative electrode active material graphite, the binder PVDF and the conductive agent acetylene black are mixed and fiberized, and then roll-formed to obtain the negative electrode active material layer.

[0121] 3. Roll-press and composite the negative electrode slow-release lithium supplement layer, the negative electrode active material layer and the copper foil, wherein the slow-release lithium supplement layer accounts for 5% of the negative electrode composite layer, and the negative electrode active material layer accounts for 95% of the negative electrode composite layer.

[0122] 2. Preparation of composite positive electrode:

[0123] 1. The positive electrode active material Li(NiCoMn)O2, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are mixed to prepare a positive electrode active material layer slurry, which is then coated on an aluminum foil and dried.

[0124] 2. The positive electrode lithium supplement material Li2NiO2, the binder PVDF and the conductive agent acetylene black are mixed, coated on the positive electrode active material layer and dried.

[0125] 3. Composite the composite electrolyte layer on the surface of the positive electrode lithium replenishing layer.

[0126] 3. Preparation of lithium-ion batteries:

[0127] The negative electrode sheet prepared in step one and the composite positive electrode prepared in step two are prepared into a lithium-ion battery together with a separator and an electrolyte using a conventional method.

[0128] Example 6

[0129] A lithium-ion battery includes a composite positive electrode and a negative electrode sheet arranged alternately and a separator arranged therebetween, and also includes an electrolyte, wherein the electrolyte is a lithium salt solution. The preparation method of the composite positive electrode and the negative electrode sheet is as follows:

[0130] 1. Preparation of negative electrode sheet:

[0131] 1. The negative electrode lithium supplement material lithium silicon alloy, the binder PVDF and the conductive agent acetylene black are mixed, and after fiberization treatment, the negative electrode slow-release lithium supplement layer is prepared by roller pressing.

[0132] 2. The negative electrode active material graphite, the binder PVDF and the conductive agent acetylene black are mixed and fiberized, and then roll-formed to obtain the negative electrode active material layer.

[0133] 3. Roll-press and composite the negative electrode slow-release lithium supplement layer, the negative electrode active material layer and the copper foil, wherein the slow-release lithium supplement layer accounts for 5% of the negative electrode composite layer, and the negative electrode active material layer accounts for 95% of the negative electrode composite layer.

[0134] 2. Preparation of composite positive electrode:

[0135] 1. The positive electrode active material Li(NiCoMn)O2, the binder polyvinylidene fluoride (PVDF), the conductive agent acetylene black are mixed, and the positive electrode lithium supplement Li2NiO2 is prepared to obtain a positive electrode active material layer slurry, which is then coated on an aluminum foil and dried to form a positive electrode active material layer on the aluminum foil.

[0136] 2. Composite the composite electrolyte layer on the surface of the positive electrode active material layer.

[0137] 3. Preparation of lithium-ion batteries:

[0138] The negative electrode sheet prepared in step one and the composite positive electrode prepared in step two are prepared into a lithium-ion battery together with a separator and an electrolyte using a conventional method.

[0139] Comparative Example 1

[0140] A lithium-ion battery includes a composite positive electrode and a negative electrode sheet arranged alternately and a separator arranged therebetween, and also includes an electrolyte, wherein the electrolyte is a lithium salt solution. The preparation method of the composite positive electrode and the negative electrode sheet is as follows:

[0141] 1. Preparation of negative electrode sheet:

[0142] 1. The negative electrode active material graphite, the binder PVDF and the conductive agent acetylene black are mixed and fiberized, and then roll-formed to obtain the negative electrode active material layer.

[0143] 2. The negative electrode active material layer and the copper foil are rolled and laminated.

[0144] 2. Preparation of composite positive electrode:

[0145] 1. The positive electrode active material Li(NiCoMn)O2, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are mixed to prepare a positive electrode active material layer slurry, which is then coated on an aluminum foil and dried.

[0146] 3. Preparation of lithium-ion batteries:

[0147] The negative electrode sheet prepared in step one and the composite positive electrode prepared in step two are prepared into a lithium-ion battery together with a separator and an electrolyte using a conventional method.

[0148] Comparative Example 2

[0149] A lithium-ion battery includes a composite positive electrode and a negative electrode sheet arranged alternately and a separator arranged therebetween, and also includes an electrolyte, wherein the electrolyte is a lithium salt solution. The preparation method of the composite positive electrode and the negative electrode sheet is as follows:

[0150] 1. Preparation of negative electrode sheet:

[0151] 1. The negative electrode active material graphite, the binder PVDF and the conductive agent acetylene black are mixed and fiberized, and then roll-formed to obtain the negative electrode active material layer.

[0152] 2. The negative electrode active material graphite, the binder PVDF and the conductive agent acetylene black are mixed and fiberized, and then roll-formed to obtain the negative electrode active material layer.

[0153] 3. Roll-press and composite the negative electrode slow-release lithium supplement layer, the negative electrode active material layer and the copper foil, wherein the slow-release lithium supplement layer accounts for 4% of the negative electrode composite layer, and the negative electrode active material layer accounts for 96% of the negative electrode composite layer.

[0154] 2. Preparation of composite positive electrode:

[0155] 1. The positive electrode active material Li(NiCoMn)O2, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are mixed to prepare a positive electrode active material layer slurry, which is then coated on an aluminum foil and dried.

[0156] 2. Composite the composite electrolyte layer on the surface of the positive electrode active material layer.

[0157] 3. Preparation of lithium-ion batteries:

[0158] The negative electrode sheet prepared in step one and the composite positive electrode prepared in step two are prepared into a lithium-ion battery together with a separator and an electrolyte using a conventional method.

[0159] Comparative Example 3

[0160] A lithium-ion battery includes a composite positive electrode and a negative electrode sheet arranged alternately and a separator arranged therebetween, and also includes an electrolyte, wherein the electrolyte is a lithium salt solution. The preparation method of the composite positive electrode and the negative electrode sheet is as follows:

[0161] 1. Preparation of negative electrode sheet:

[0162] 1. The negative electrode active material graphite, the binder PVDF and the conductive agent acetylene black are mixed and fiberized, and then roll-formed to obtain the negative electrode active material layer.

[0163] 2. The negative electrode active material layer and the copper foil are rolled and laminated.

[0164] 2. Preparation of composite positive electrode:

[0165] 1. The positive electrode active material Li(NiCoMn)O2, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are mixed to prepare a positive electrode active material layer slurry, which is then coated on an aluminum foil and dried.

[0166] 2. The positive electrode lithium supplement material Li2NiO2, the binder PVDF and the conductive agent acetylene black are mixed, coated on the positive electrode active material layer and dried.

[0167] 3. Composite the composite electrolyte layer on the surface of the positive electrode lithium replenishing layer.

[0168] 3. Preparation of lithium-ion batteries:

[0169] The negative electrode sheet prepared in step one and the composite positive electrode prepared in step two are prepared into a lithium-ion battery together with a separator and an electrolyte using a conventional method.

[0170] Comparative Example 4

[0171] A lithium-ion battery includes a composite positive electrode and a negative electrode sheet arranged alternately and a separator arranged therebetween, and also includes an electrolyte, wherein the electrolyte is a lithium salt solution. The preparation method of the composite positive electrode and the negative electrode sheet is as follows:

[0172] 1. Preparation of negative electrode sheet:

[0173] 1. The negative electrode lithium supplement material lithium silicon alloy, the binder PVDF and the conductive agent acetylene black are mixed, and after fiberization treatment, the negative electrode slow-release lithium supplement layer is prepared by roller pressing.

[0174] 2. The negative electrode active material graphite, the binder PVDF, the organic solvent and the conductive agent acetylene black are uniformly mixed to form a slurry, and the slurry is coated on the copper foil, and after drying, a negative electrode active material layer is formed on the copper foil.

[0175] 3. Composite the negative electrode slow-release lithium replenishing layer on the negative electrode active material layer, wherein the slow-release lithium replenishing layer accounts for 4% of the negative electrode composite layer, and the negative electrode active material layer accounts for 96% of the negative electrode composite layer.

[0176] 2. Preparation of composite positive electrode:

[0177] 1. The positive electrode active material Li(NiCoMn)O2, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are mixed to prepare a positive electrode active material layer slurry, which is then coated on an aluminum foil and dried.

[0178] 2. The positive electrode lithium supplement material Li2NiO2, the binder PVDF and the conductive agent acetylene black are mixed, coated on the positive electrode active material layer and dried.

[0179] 3. Composite the composite electrolyte layer on the surface of the positive electrode lithium replenishing layer.

[0180] 3. Preparation of lithium-ion batteries:

[0181] The negative electrode sheet prepared in step one and the composite positive electrode prepared in step two are prepared into a lithium-ion battery together with a separator and an electrolyte using a conventional method.

[0182] Comparative Example 5

[0183] A lithium-ion battery includes a composite positive electrode and a negative electrode sheet arranged alternately and a separator arranged therebetween, and also includes an electrolyte, wherein the electrolyte is a lithium salt solution. The preparation method of the composite positive electrode and the negative electrode sheet is as follows:

[0184] 1. Preparation of negative electrode sheet:

[0185] 1. Evenly mix the negative electrode lithium supplement material lithium silicon alloy, the binder PVDF, the organic solvent and the conductive agent acetylene black to form a slurry.

[0186] 2. The negative electrode active material graphite, the binder PVDF and the conductive agent acetylene black are mixed and fiberized, and then roll-formed to obtain the negative electrode active material layer.

[0187] 3. Roll-press the negative electrode active material layer and the copper foil, and apply the slurry on the negative electrode active material layer, and after drying, form a slow-release lithium replenishment layer on the surface of the negative electrode active material layer. The slow-release lithium replenishment layer accounts for 4% of the negative electrode composite layer, and the negative electrode active material layer accounts for 96% of the negative electrode composite layer.

[0188] 2. Preparation of composite positive electrode:

[0189] 1. The positive electrode active material Li(NiCoMn)O2, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are mixed to prepare a positive electrode active material layer slurry, which is then coated on an aluminum foil and dried.

[0190] 2. The positive electrode lithium supplement material Li2NiO2, the binder PVDF and the conductive agent acetylene black are mixed, coated on the positive electrode active material layer and dried.

[0191] 3. Composite the composite electrolyte layer on the surface of the positive electrode lithium replenishing layer.

[0192] 3. Preparation of lithium-ion batteries:

[0193] The negative electrode sheet prepared in step one and the composite positive electrode prepared in step two are prepared into a lithium-ion battery together with a separator and an electrolyte using a conventional method.

[0194] The final test result data is shown in the following table.

[0195]

[0196]

[0197] It can be seen from the above table:

[0198] Compared with Example 1, Example 2 adds a composite positive electrode without adding a solid electrolyte, so it is safer and can be punctured by needles.

[0199] Example 3 uses graphite-nano silicon carbon as the active layer material. Compared with Example 2, the capacity retention rate and the first efficiency do not change much, indicating that when graphite-nano silicon is used as the negative electrode active material, the negative electrode active material layer is prepared by a dry method, and the battery cycle performance can be improved in coordination with the slow-release lithium supplement layer.

[0200] The positive electrode lithium replenisher of Example 4 adopts Li2O. Compared with Example 2, the capacity retention rate and the first efficiency do not change much, indicating that when the positive electrode lithium replenisher adopts Li2O, the battery cycle performance can be improved in coordination with the negative electrode to set a slow-release lithium replenishment layer.

[0201] Compared with Example 2, the thickness of the sustained-release lithium supplementation layer in Example 5 is increased, and the first effect and cycle retention rate are improved.

[0202] Compared with Example 2, the composite positive electrode in Example 6 does not add a positive electrode lithium replenishing layer, but directly performs the first lithium replenishment by adding a positive electrode lithium replenishing agent. As a result, compared with Example 1, the cycle performance does not change much.

[0203] Compared with Example 2, the positive and negative electrodes of Comparative Example 1 did not supplement lithium, and the cycle performance and first-effect performance were significantly reduced, and failed the puncture test.

[0204] Compared with Example 2, the positive electrode of Comparative Example 2 does not have a positive electrode lithium replenishing layer added, and its first-effect performance is poor.

[0205] Compared with Example 2, the negative electrode of Comparative Example 3 has poor cycle performance and initial efficiency because no lithium-silicon alloy (slow-release lithium supplement layer) is added.

[0206] Compared with Example 2, in Comparative Example 4, the negative electrode active material layer is prepared by a wet process, and after being compounded with the lithium-silicon alloy and the slow-release lithium supplement layer, the cycle performance is poor.

[0207] Compared with Example 2, Comparative Example 5 adopts a wet method to prepare a sustained-release lithium supplement layer, which is composited with a negative electrode active material layer and a lithium-silicon alloy prepared by a dry method, and has poor cycle performance.

[0208] According to the above table, the present invention realizes the initial lithium replenishment by adding a positive electrode lithium replenishment layer or a positive electrode lithium replenishment agent to the composite positive electrode, and prepares the negative electrode sheet with a slow-release lithium replenishment layer by dry method and cooperates with lithium silicon alloy to slowly release lithium ions during the lithium ion battery cycle, thereby greatly improving the battery cycle performance. When graphite-nano silicon carbon is used as the material of the negative electrode active layer, the battery cycle performance can be further optimized.

[0209] It should be pointed out that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A lithium-ion battery comprising a composite positive electrode and a negative electrode sheet, wherein: The composite positive electrode comprises a positive electrode lithium replenisher, characterized in that the negative electrode sheet comprises a negative electrode composite layer and a negative electrode current collector, the negative electrode composite layer comprises a negative electrode active material layer and a slow-release lithium replenisher layer, wherein: The negative electrode active material layer is prepared by a dry method; The slow-release lithium supplement layer is composited on a side of the negative electrode active material layer away from the negative electrode current collector; The slow-release lithium supplementing layer comprises a lithium-silicon alloy.

2. The lithium-ion battery according to claim 1, characterized in that The composite positive electrode comprises a positive electrode current collector and a positive electrode active material layer; wherein the positive electrode active material layer comprises a positive electrode active material, a positive electrode lithium supplement, a binder and a conductive agent.

3. The lithium-ion battery according to claim 1, characterized in that The composite positive electrode comprises a positive electrode current collector and a positive electrode composite layer; the positive electrode composite layer comprises a positive electrode active material layer and a positive electrode lithium replenishing layer, and the positive electrode lithium replenishing layer comprises a positive electrode lithium replenishing agent.

4. The lithium-ion battery according to claim 1, characterized in that The sustained-release lithium supplement layer is prepared by a dry method.

5. The lithium-ion battery according to claim 1, characterized in that: The positive electrode lithium supplement agent is selected from one or more of Li2NiO2, Li5FeO4, Li2O, Li8ZrO6, and Li2C2O4.

6. The lithium-ion battery according to claim 1, characterized in that The slow-release lithium supplement layer comprises a lithium-silicon alloy and a fiberizable binder, and the slow-release lithium supplement layer accounts for 2%-5% of the thickness of the negative electrode composite layer.

7. The lithium-ion battery according to claim 6, characterized in that: The fiberizable binder is selected from any one of polyethylene oxide, polytetrafluoroethylene, polyvinylidene fluoride, polypropylene, polyvinyl chloride, polystyrene, polyoxymethylene, polycarbonate, polyamide, acrylic plastic, polysulfone, polyphenylene ether, and carboxymethyl cellulose, or a combination of at least two thereof.

8. The lithium-ion battery according to claim 1, characterized in that The negative electrode active material layer comprises a negative electrode active material, a fiberizable binder and a conductive agent, and the negative electrode active material layer accounts for 95%-98% of the thickness of the negative electrode composite layer; The negative electrode active material is graphite-silicon carbon material, including dopamine-coated nano silicon carbon and hard carbon-coated graphite, wherein the dopamine-coated nano silicon carbon accounts for 10% to 20% of the negative electrode active material.

9. The lithium-ion battery according to claim 1, characterized in that: The lithium-ion battery also includes an electrolyte, and a deoxidizing additive is added into the electrolyte.

10. The lithium-ion battery according to any one of claims 1 to 9, characterized in that: The composite positive electrode also includes an electrolyte coating.

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