WO2024026654A1

WO2024026654A1 - Negative electrode sheet, secondary battery and electric apparatus

Info

Publication number: WO2024026654A1
Application number: PCT/CN2022/109591
Authority: WO
Inventors: 田亚西; 石春美; 唐代春
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2022-08-02
Filing date: 2022-08-02
Publication date: 2024-02-08
Also published as: CN118511301A

Abstract

The present application relates to a negative electrode sheet, a secondary battery, and an electric apparatus. The negative electrode sheet comprises: a negative electrode current collector; a first negative electrode active material layer located on at least one surface of the negative electrode current collector, the first negative electrode active material layer comprising a first negative electrode active material; a second negative electrode active material layer located on the surface of the first negative electrode active material layer away from the negative electrode current collector, the second negative electrode active material layer comprising a second negative electrode active material; and a third negative electrode active material layer located on the surface of the second negative electrode active material layer away from the first negative electrode active material layer, the third negative electrode active material layer comprising a third negative electrode active material, and the volume expansion rates of the first negative electrode active material and the third negative electrode active material being respectively greater than that of the second negative electrode active material.

Description

Negative electrode plates, secondary batteries and electrical devices

Technical field

This application belongs to the technical field of secondary batteries, and specifically relates to a negative electrode plate, a secondary battery and an electrical device.

Background technique

Secondary batteries are widely used in various consumer electronics and electric vehicles due to their outstanding characteristics such as light weight, no pollution, and no memory effect. With the continuous development of the new energy industry, customers have put forward higher demand for secondary batteries. Among them, high energy density is the feature that customers are most concerned about, and improving the energy density of secondary batteries is an urgent need for the lithium battery industry.

Contents of the invention

In view of the technical problems existing in the background art, this application provides a negative electrode plate, a secondary battery and a power consumption device, aiming to enable the secondary battery to have higher energy density and capacity retention rate.

In order to achieve the above objectives, a first aspect of the present application provides a negative electrode plate, including:

Negative current collector;

A first negative active material layer is located on at least one surface of the negative current collector, and the first negative active material layer includes a first negative active material;

A second negative active material layer is located on the surface of the first negative active material layer away from the negative current collector, and the second negative active material layer includes a second negative active material; and

A third negative active material layer is located on the surface of the second negative active material layer away from the first negative active material layer, and the third negative active material layer includes a third negative active material;

Wherein, the volume expansion rate of the first negative electrode active material and the third negative electrode active material is respectively greater than the volume expansion rate of the second negative electrode active material.

Compared with the prior art, this application at least includes the following beneficial effects:

The negative electrode sheet of the present application is provided with three negative electrode active material layers, and the volume expansion rate of the first negative electrode active material included in the first negative electrode active material layer is higher than that of the second negative electrode included in the second negative electrode active material layer. The volume expansion rate of the active material, the volume expansion rate of the third negative active material included in the third negative active material layer is higher than the volume expansion rate of the second negative active material included in the second negative active material layer, which occurs after lithium insertion When expanding, the volume expansion multiple of the first negative active material particles and the third negative active material particles is higher than the volume expansion multiple of the second negative active material particles; compared with only containing the second negative active material layer, by arranging the first negative active material layer The active material layer and the third negative electrode active material layer can form a squeezing effect on the second negative electrode active material layer and reduce the porosity in the second negative electrode active material layer. In this way, the above-mentioned negative electrode sheet is used in secondary batteries, which can effectively reduce the amount of electrolyte and improve the energy density and capacity retention rate of the battery.

In any embodiment of the present application, the volume expansion rates of the first negative active material layer and the third negative active material layer before and after lithium insertion are respectively greater than the volume expansion of the second negative active material layer before and after lithium insertion. Rate.

In any embodiment of the present application, the volume expansion rate of the first negative electrode active material and the volume expansion rate of the third negative electrode active material are each independently 47% to 220%.

In any embodiment of the present application, the volume expansion rate of the second negative active material is 20% to 25%.

In any embodiment of the present application, the active materials in the second negative electrode active material layer are all the second negative electrode active materials; optionally, the second negative electrode active material is in the second negative electrode active material layer. The quality proportion in the product ranges from 94% to 96.8%.

In any embodiment of the present application, the active material in the first negative active material layer includes the first negative active material and the second negative active material; optionally, the first negative active material is The mass proportion of the first negative active material layer is 15% to 25%, and the mass proportion of the second negative active material in the first negative active material layer is 71.8% to 81.8%;

And/or, the active material in the third negative electrode active material layer includes the third negative electrode active material and the second negative electrode active material; optionally, the third negative electrode active material is in the third negative electrode active material layer. The mass proportion of the active material layer is 15% to 25%, and the mass proportion of the second negative active material in the third negative active material layer is 71.8% to 81.8%.

In any embodiment of the present application, the first negative active material and the third negative active material each independently include one or more of Ge, Sn, Sb, Bi and SiOx;

Among them, 0≤x<2.

In any embodiment of the present application, the second negative active material includes one or more of artificial graphite and hard carbon.

In any embodiment of the present application, the thickness of the first negative electrode active material layer before lithium insertion is denoted as L1, the thickness of the second negative electrode active material layer before lithium insertion is denoted as L2, and the thickness of the third negative electrode active material layer before lithium insertion is denoted as L2. The thickness of the material layer before lithium insertion is recorded as L3, then the first negative electrode active material layer, the second negative electrode active material layer and the third negative electrode active material layer satisfy: 0.1≤L1/L3≤1, 0.08 ≤(L1+L3)/L2≤0.2.

In any embodiment of the present application, the thickness of the first negative active material layer before lithium insertion satisfies: 1 μm ≤ L1 ≤ 10 μm; and/or the thickness of the second negative active material layer before lithium insertion satisfies: 100 μm ≤ L2 ≤ 120 μm; and/or, the thickness of the third negative active material layer before lithium insertion satisfies: 1 μm ≤ L3 ≤ 10 μm.

A second aspect of the application provides a secondary battery, which includes the negative electrode plate of the first aspect of the application;

Wherein, the volume expansion ratios of the first negative active material layer and the third negative active material layer before and after lithium insertion are respectively greater than the volume expansion ratios of the second negative active material layer before and after lithium insertion.

A third aspect of the present application provides an electrical device, which includes the secondary battery of the second aspect of the present application.

Description of the drawings

In order to explain the technical solution of the present application more clearly, the drawings used in the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on the drawings without exerting creative efforts.

FIG. 1 is a schematic diagram of an embodiment of a secondary battery.

FIG. 2 is an exploded view of FIG. 1 .

Figure 3 is a schematic diagram of an embodiment of a battery pack.

FIG. 4 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment.

Explanation of reference symbols:

1. Battery pack; 2. Upper box; 3. Lower box; 4. Secondary battery; 41. Case; 42. Electrode assembly; 43. Cover; 5. Electrical device.

Detailed ways

The present application will be further elaborated below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not intended to limit the scope of the present application.

For the sake of simplicity, only certain numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form an unexpressed range; and any lower limit can be combined with other lower limits to form an unexpressed range, and likewise any upper limit can be combined with any other upper limit to form an unexpressed range. Furthermore, each individually disclosed point or single value may itself serve as a lower or upper limit in combination with any other point or single value or with other lower or upper limits to form a range not expressly recited.

"Ranges" disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be combined in any combination, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Furthermore, if the

minimum range values

1 and 2 are listed, and if the

maximum range values

3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-5. In this application, unless stated otherwise, the numerical range "a-b" represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed in this article, and "0-5" is just an abbreviation of these numerical combinations. In addition, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

If there is no special description, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

If there is no special description, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

If there is no special instructions, all steps of the present application can be performed sequentially or randomly, and are preferably performed sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, mentioning that the method may also include step (c) means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c). , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b), etc.

If there is no special explanation, the words "include" and "include" mentioned in this application represent open expressions, which may also be closed expressions. For example, "comprising" and "comprising" may mean that other components not listed may also be included or included, or only the listed components may be included or included.

In the description of this article, it should be noted that, unless otherwise stated, "above" and "below" include the original number, and "several" in "one or several" means two or more than two.

In the description herein, the term "or" is inclusive unless stated otherwise. That is, the phrase "A or (or) B" means "A, B, or both A and B." More specifically, condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; Or both A and B are true (or exist). Unless otherwise stated, terms used in this application have their commonly understood meanings as generally understood by those skilled in the art. Unless otherwise stated, the values of each parameter mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

The negative electrode sheet provided by this application includes: a negative electrode current collector; a first negative electrode active material layer, located on at least one surface of the negative electrode current collector; the first negative electrode active material layer includes a first negative electrode active material; a second negative electrode active material layer, located on the surface of the first negative electrode active material layer away from the negative electrode current collector, the second negative electrode active material layer includes a second negative electrode active material; and a third negative electrode active material layer, located on the second negative electrode active material layer away from the first negative electrode On the surface of the active material layer, the third negative active material layer includes a third negative active material; wherein the volume expansion rates of the first negative active material and the third negative active material are respectively greater than the volume expansion rates of the second negative active material.

Without wishing to be limited to any theory, the negative electrode sheet of the present application is provided with three negative electrode active material layers on at least one surface of the negative electrode current collector, and the first negative electrode active material included in the first negative electrode active material layer has a high volume expansion rate The volume expansion rate of the second negative electrode active material included in the second negative electrode active material layer, and the volume expansion rate of the third negative electrode active material included in the third negative electrode active material layer are higher than that of the third negative electrode active material included in the second negative electrode active material layer. The volume expansion rate of the two negative electrode active materials. When expansion occurs after lithium insertion, the volume expansion multiples of the first negative electrode active material particles and the third negative electrode active material particles are higher than the volume expansion multiples of the second negative electrode active material particles; Compared with the two negative electrode active material layers, by providing the first negative electrode active material layer and the third negative electrode active material layer, a squeezing effect can be formed on the second negative electrode active material layer and the porosity in the second negative electrode active material layer can be reduced. In this way, the above-mentioned negative electrode sheet is used in secondary batteries, which can effectively reduce the amount of electrolyte and improve the energy density and capacity retention rate of the battery.

It can be understood that all the negative active materials in the first negative active material layer may be the first negative active material, or only part of the negative active material may be the first negative active material; preferably, the negative active material in the first negative active material layer may be only the first negative active material. Part of it is the first negative electrode active material.

After in-depth research, the inventor found that when the negative electrode plate of the present application meets the above design conditions and optionally meets one or more of the following conditions, the energy density of the secondary battery can be further improved. and capacity retention.

In some embodiments, the volume expansion rates of the first negative active material layer and the third negative active material layer before and after lithium insertion are respectively greater than the volume expansion rates of the second negative active material layer before and after lithium insertion. After the first negative electrode active material layer and the second negative electrode active material layer are embedded with lithium, they can form a squeezing effect on the second negative electrode active material layer, reducing the porosity in the second negative electrode active material layer, thereby reducing the amount of electrolyte. Improve battery energy density and capacity retention rate.

As an example, the first negative active material layer can use both graphite and silicon or other materials with high volume expansion rates as negative active materials, and the third negative active material layer can use both graphite and silicon or other materials with high volume expansion rates. As the negative active material, the second negative active material layer can all use graphite as the negative active material; and the volume expansion rates of the first negative active material layer and the third negative active material layer before and after lithium insertion are respectively higher than that of the second negative active material. The volume expansion rate of the layer before and after lithium insertion.

The main change in the thickness direction of the negative active material layer before and after lithium insertion. The volume expansion rate of the first negative active material layer and the volume expansion rate of the third negative active material layer mentioned above were measured using the following method: before lithium insertion Perform cross-sectional CP characterization of the negative electrode piece, and measure the thickness L1 of the first negative electrode active material layer and the thickness L3 of the third negative electrode active material layer; continue cross-sectional CP characterization of the negative electrode piece after lithium embedding, and measure the first negative electrode active material layer The thickness L11 of the third negative electrode active material layer and the thickness L31 of the third negative electrode active material layer are calculated based on the formula (L11-L1)/L1*100. The volume expansion rate of the first negative electrode active material layer is calculated based on the formula (L31-L3)/L3*100. The volume expansion rate of the three negative electrode active material layers.

In some embodiments, the volume expansion rate of the first negative active material and the third negative active material are independently 47% to 220%; for example, they can be 47%, 80%, 100%, 130%, 150%, 170%, 200% or 220% etc. Using a negative active material with a high volume expansion rate in the negative active material layer can increase the volume expansion rate of the negative active material layer. Furthermore, the volume expansion rate of the first negative active material is 170% to 220%. Furthermore, the volume expansion rate of the third negative active material is 170% to 220%.

In some embodiments, the volume expansion rate of the second negative active material is 20% to 25%; for example, it may be 20%, 21%, 22%, 23%, 24% or 25%. Further, the volume expansion rate of the second negative electrode active material is 20% to 23%.

The volume expansion rates of the first negative electrode active material, the second negative electrode active material and the third negative electrode active material mentioned above can be obtained by the following method: the first negative electrode active material, the second negative electrode active material and the third negative electrode active material can be obtained by the known method. The expansion multiple N of the negative active material before and after lithium insertion is calculated, and then the corresponding volume expansion rate is obtained based on the formula (N-1)*100%. The expansion ratio N refers to the multiple of the volume of the negative electrode active material after lithium insertion is the volume of the negative electrode active material before lithium insertion.

In some embodiments, the active materials in the second negative electrode active material layer are all second negative electrode active materials; optionally, the mass proportion of the second negative electrode active material in the second negative electrode active material layer is 94%. ~96.8%; for example, it can be 94%, 94.5%, 95%, 95.5%, 96%, 96.5% or 96.8%, etc. Further, the mass proportion of the second negative electrode active material in the second negative electrode active material layer is 95% to 96.8%.

In some embodiments, the active material in the first negative active material layer includes a first negative active material and a second negative active material; optionally, the mass of the first negative active material in the first negative active material layer The proportion is 15% to 25%, and the mass proportion of the second negative active material in the first negative active material layer is 71.8% to 81.8%; the volume expansion rate of the first negative active material is greater than the volume of the second negative active material The expansion rate. Compared with the negative active material layer containing only the second negative active material, adding part of the first negative active material to replace the second negative active material can increase the volume expansion rate of the first negative active material layer, which is more effective for the second negative electrode. The active material layer forms an effective squeeze. Technicians have found through research that when the mass ratio of the first negative active material in the first negative active material layer is set within this range, it can not only squeeze the second negative active material layer, but also prevent the subsequent long-term During the cycle, the first negative active material is pulverized, exposing more fresh surfaces, resulting in increased electrolyte consumption.

In some embodiments, the active material in the third negative active material layer includes a third negative active material and a second negative active material; optionally, the mass of the third negative active material in the third negative active material layer The proportion is 15% to 25%, and the mass proportion of the second negative active material in the third negative active material layer is 71.8% to 81.8%; the volume expansion rate of the third negative active material is greater than the volume of the second negative active material The expansion rate. Compared with the negative active material layer containing only the second negative active material, adding part of the third negative active material to replace the second negative active material can increase the volume expansion rate of the third negative active material layer, which is more effective for the second negative electrode. The active material layer forms an effective squeeze. Technicians have found through research that when the mass proportion of the third negative active material in the third negative active material layer is set within this range, it can not only squeeze the second negative active material layer, but also prevent it from being damaged in the future. During the cycle, the third negative electrode active material is pulverized, exposing more fresh surfaces, resulting in increased electrolyte consumption.

In some embodiments, the first negative active material and the third negative active material each independently include one or more of Ge, Sn, Sb, Bi and SiOx; where 0≤x<2.

The volume expansion multiples N of Ge, Sn, Sb, Bi and SiOx before and after lithium insertion can be measured by known methods and are respectively around 2.72, 2.90, 1.47, 2.15 and 3.20. According to the formula (N-1)*100% The volume expansion ratios of Ge, Sn, Sb, Bi and SiOx before and after lithium insertion were obtained to be around 172%, 190%, 47%, 115% and 220% respectively.

In some embodiments, the second negative active material includes one or more of artificial graphite and hard carbon.

In some embodiments, the thickness of the first negative active material layer before lithium insertion is marked as L1, the thickness of the second negative active material layer before lithium insertion is marked as L2, and the thickness of the third negative active material layer before lithium insertion is recorded as L2. The thickness is recorded as L3, then the first negative active material layer, the second negative active material layer and the third negative active material layer satisfy: 0.1≤L1/L3≤1, 0.08≤(L1+L3)/L2≤0.2. Technicians found through research that the thickness ratio of the first negative active material layer and the third negative active material layer before lithium embedding satisfies the above range, and the total thickness of the first negative active material layer and the third negative active material layer is less than that of the second negative active material layer. When the thickness ratio of the negative active material layer meets the above range, it can not only squeeze the second negative active material layer, but also prevent the first negative active material and the third negative active material from being pulverized during the subsequent long cycle. , exposing more fresh surfaces, resulting in increased electrolyte consumption.

Optionally, the thickness of the first negative active material layer before lithium insertion satisfies: 1 μm ≤ L1 ≤ 10 μm; for example, it can be 1 μm, 2 μm, 4 μm, 6 μm, 8 μm or 10 μm, etc. Further, the thickness of the first negative active material layer before lithium insertion satisfies: 4 μm ≤ L1 ≤ 6 μm.

Optionally, the thickness of the second negative active material layer before lithium insertion satisfies: 100 μm ≤ L2 ≤ 120 μm; for example, it may be 100 μm, 105 μm, 110 μm, 115 μm or 120 μm. Further, the thickness of the second negative active material layer before lithium insertion satisfies: 110 μm ≤ L2 ≤ 120 μm.

Optionally, the thickness of the third negative active material layer before lithium insertion satisfies: 1 μm ≤ L3 ≤ 10 μm; for example, it can be 1 μm, 2 μm, 4 μm, 6 μm, 8 μm or 10 μm, etc. Further, the thickness of the third negative active material layer before lithium insertion satisfies: 4 μm ≤ L3 ≤ 10 μm.

The thickness L1 of the first negative active material layer before lithium insertion mentioned above, the thickness L2 of the second negative active material layer before lithium insertion, and the thickness L3 of the third negative active material layer before lithium insertion were measured using the following method. : Perform cross-sectional CP characterization of the negative electrode sheet before lithium insertion, and measure the thickness L1 of the first negative active material layer, the thickness L2 of the second negative active material layer, and the thickness L3 of the third negative active material layer.

Embodiments of the present application also provide a method for preparing a negative electrode sheet, including the following steps:

S1. Prepare a first negative electrode slurry, and apply the first negative electrode slurry on at least one surface of the negative electrode current collector to form the first negative electrode active material layer;

S2. Prepare a second negative electrode slurry, and apply the second negative electrode slurry on the surface of the first negative electrode active material layer away from the negative electrode current collector to form the second negative electrode active material layer;

S3. Prepare a third negative electrode slurry, and apply the third negative electrode slurry on the surface of the second negative electrode active material layer away from the first negative electrode active material layer to form the third negative electrode active material layer. .

The negative electrode current collector can use conventional metal foil or composite current collector. As an example, the metal foil may be copper foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material. The composite current collector can be formed by forming metal materials (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

The negative active material layer usually also includes conductive agents and other optional auxiliaries.

As an example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

As an example, other optional additives may be PTC thermistor materials, etc.

The above-mentioned raw materials are all commercially available unless otherwise specified.

secondary battery

Secondary batteries refer to batteries that can be recharged to activate active materials and continue to be used after the battery is discharged.

Normally, a secondary battery includes a positive electrode sheet, the negative electrode sheet provided above in this application, a separator and an electrolyte. During the charging and discharging process of the battery, active ions are inserted and detached back and forth between the positive and negative electrodes. The isolation film is arranged between the positive electrode piece and the negative electrode piece to play the role of isolation. The electrolyte plays a role in conducting ions between the positive and negative electrodes.

Positive electrode piece

In secondary batteries, a positive electrode sheet usually includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material.

As an example, the positive electrode current collector has two surfaces facing each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

As an example, the positive electrode current collector may use a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming metal materials (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

When the secondary battery is a lithium ion battery, the cathode active material may be a cathode active material known in the art for lithium ion batteries. As an example, the cathode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials of batteries can also be used. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO ₂ ), lithium nickel oxides (such as LiNiO ₂ ), lithium manganese oxides (such as LiMnO ₂ , LiMn ₂ O ₄ ), lithium Nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (also referred to as NCM ₃₃₃ ), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (can also be abbreviated to NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (can also be abbreviated to NCM ₂₁₁ ), LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (can also be abbreviated to NCM ₆₂₂ ), LiNi At least one of _0.8 Co _0.1 Mn _0.1 O ₂ (also referred to as NCM ₈₁₁ ), lithium nickel cobalt aluminum oxide (such as LiNi _0.85 Co _0.15 Al _0.05 O ₂ ) and its modified compounds. The olivine structure contains Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO ₄ (also referred to as LFP)), composites of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO ₄ ), lithium manganese phosphate and carbon. At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.

When the secondary battery is a sodium-ion battery, the cathode active material may be a cathode active material known in the art for sodium-ion batteries. As an example, only one type of positive electrode active material may be used alone, or two or more types may be combined. Among them, the positive active material can be selected from sodium iron composite oxide (NaFeO ₂ ), sodium cobalt composite oxide (NaCoO ₂ ), sodium chromium composite oxide (NaCrO ₂ ), sodium manganese composite oxide (NaMnO ₂ ), sodium nickel Composite oxide (NaNiO ₂ ), sodium nickel titanium composite oxide (NaNi _1/2 Ti _1/2 O ₂ ), sodium nickel manganese composite oxide (NaNi _1/2 Mn _1/2 O ₂ ), sodium iron manganese composite Oxide (Na _2/3 Fe _1/3 Mn _2/3 O ₂ ), sodium nickel cobalt manganese composite oxide (NaNi _1/3 Co _1/3 Mn _1/3 O ₂ ), sodium iron phosphate compound (NaFePO ₄ ), sodium manganese phosphate compound (NaMn _P O ₄ ), sodium cobalt phosphate compound (NaCoPO ₄ ), Prussian blue materials, polyanionic materials (phosphates, fluorophosphates, pyrophosphates, sulfates), etc., but this application It is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials of sodium ion batteries can also be used in this application.

The positive electrode film layer also optionally includes binders, conductive agents and other optional auxiliaries.

As examples, the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene At least one of ethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

As an example, the positive electrode sheet can be prepared in the following manner: the above-mentioned components for preparing the positive electrode sheet, such as the positive active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methyl pyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode piece can be obtained.

Isolation film

In some embodiments, the secondary battery further includes a separator film. There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.

In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation film can be a single-layer film or a multi-layer composite film, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.

In some embodiments, the positive electrode piece, the negative electrode piece and the separator film can be made into an electrode assembly through a winding process or a lamination process.

electrolyte

The secondary battery may include an electrolyte that serves to conduct ions between a positive electrode and a negative electrode. The electrolyte solution may include electrolyte salts and solvents.

As an example, the electrolyte salt may be selected from lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium bisfluorosulfonyl imide ( LiFSI), lithium bistrifluoromethanesulfonimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoromethanesulfonate borate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO ₂ F ₂ ), one or more of lithium difluorodioxalate phosphate (LiDFOP) and lithium tetrafluorooxalate phosphate (LiTFOP).

As an example, the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), carbonic acid Dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), One or more of ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE) .

In some embodiments, additives are also included in the electrolyte. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high-temperature performance of the battery, and additives that improve the low-temperature performance of the battery. Additives etc.

In some embodiments, the secondary battery of the present application is a lithium-ion secondary battery.

The secondary battery can be prepared according to conventional methods in the art, for example, the positive electrode sheet, the separator film, and the negative electrode sheet are wound (or stacked) in order, so that the separator film is between the positive electrode sheet and the negative electrode sheet for isolation. function to obtain the battery core, place the battery core in the outer package, inject the electrolyte and seal it to obtain a secondary battery.

The embodiments of the present application have no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. FIG. 1 shows an example of a square-structured secondary battery 4 .

In some embodiments, the secondary battery may include an outer packaging. The outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.

In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag. The material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.

In some embodiments, referring to FIG. 2 , the outer package may include a housing 41 and a cover 43 . The housing 41 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 41 has an opening communicating with the accommodation cavity, and the cover plate 43 can cover the opening to close the accommodation cavity.

The positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 42 through a winding process or a lamination process. The electrode assembly 52 is packaged in the containing cavity. The electrolyte soaks into the electrode assembly 42 . The number of electrode assemblies 42 contained in the secondary battery 4 can be one or more, and can be adjusted according to requirements.

In some embodiments, the above-mentioned secondary batteries can also be assembled into a battery pack, and the number of secondary batteries contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

Figure 3 is a battery pack 1 as an example. The battery pack 1 may include a battery box and a plurality of secondary batteries 4 provided in the battery box. The battery box includes an upper box 2 and a lower box 3 . The upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the secondary battery 4 . The plurality of secondary batteries 4 can be arranged in the battery box in any manner.

electrical device

The present application also provides an electrical device, which includes at least one of the secondary battery or battery pack. The secondary battery or battery pack may be used as a power source for the device or as an energy storage unit for the device. The device may be, but is not limited to, a mobile device (such as a mobile phone, a laptop, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, or an electric golf ball). vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

The device can select secondary batteries or battery packs according to its usage requirements.

Figure 4 shows an electrical device 5 as an example. The electric device 5 is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or the like. In order to meet the device's requirements for high power and high energy density of secondary batteries, a battery pack can be used.

As another example, the device may be a mobile phone, a tablet, a laptop, etc. The device is usually required to be thin and light, and a secondary battery can be used as a power source.

The beneficial effects of the present application will be further described below in conjunction with the examples.

Example

In order to make the technical problems, technical solutions and beneficial effects solved by this application clearer, further details will be described below in conjunction with the embodiments and drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of this application.

It should be noted that in the following examples and comparative examples, the thickness of the first negative active material layer is marked as L1, the thickness of the second negative active material layer is marked as L2, and the thickness of the third negative active material layer is marked as L3. .

In the following examples and comparative examples, the volume expansion rate of the negative electrode active material _SiOx used is 220%, the volume expansion rate of the negative electrode active material Sb used is 47%, and the volume expansion rate of the negative electrode active material Bi used The volume expansion rate of the used negative electrode active material Sn is 190%, the volume expansion rate of the used negative electrode active material Ge is 172%, and the volume expansion rate of the used negative electrode active material artificial graphite is 23%.

The materials used in the examples of this application are all commercially available.

1. Preparation of negative electrode pieces

Example 1

Combine artificial graphite (as the second negative electrode active material), SiO _x (as the first negative electrode active material), conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium hydroxymethylcellulose (CMC) Dissolve in the solvent deionized water according to the weight ratio of 71.8:25:0.7:1.3:1.2, mix evenly and prepare the first negative electrode slurry; apply the first negative electrode slurry on the surface of the negative electrode current collector copper foil to form The first negative active material layer has a thickness of 4 μm;

The weight ratio of artificial graphite (as the second negative active material), conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethylcellulose (CMC) is 96.8:0.7:1.3:1.2 Dissolve in solvent deionized water, mix evenly and prepare a second negative electrode slurry; apply the second negative electrode slurry on the surface of the first negative electrode active material layer to form a second negative electrode active material layer with a thickness of 120 μm;

Combine artificial graphite (as the second negative electrode active material), SiOx (as the first negative electrode active material), conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium hydroxymethylcellulose (CMC) according to the The weight ratio is 71.8:25:0.7:1.3:1.2. Dissolve in the solvent deionized water, mix evenly and prepare a third negative electrode slurry; apply the third negative electrode slurry on the surface of the second negative electrode active material layer to form The third negative active material layer has a thickness of 10 μm; after drying, cold pressing, and cutting, the negative electrode pieces are obtained.

Example 2-20

The preparation method of the negative electrode sheet in Examples 2-20 is basically similar to the preparation method of the negative electrode sheet in Example 1. The difference lies in: when preparing the negative electrode sheet, the type and/or amount of the first negative electrode active material used, and the amount of the first negative electrode active material. At least one of the types and/or amounts of the three negative active materials, the thickness of the first negative active material layer, the thickness of the second negative active material layer, and the thickness of the third negative active material layer are different. See Table 1 for details.

Comparative example 1

The preparation method of the negative electrode sheet in Comparative Example 1 is basically similar to the preparation method of the negative electrode sheet in Example 1, except that it only includes the first negative electrode active material layer and the second negative electrode active material layer (that is, it does not contain the third negative electrode active material layer). material layer), and the thickness of the first negative active material layer is different. See Table 1 for details.

Comparative example 2

The preparation method of the negative electrode sheet in Comparative Example 2 is basically similar to the preparation method of the negative electrode sheet in Example 1, except that it only includes the second negative electrode active material layer and the third negative electrode active material layer (that is, it does not contain the first negative electrode active material layer). material layer), see Table 1 for details.

Comparative example 3

The difference between the preparation method of the negative electrode sheet in Comparative Example 3 and the negative electrode sheet in Example 1 is that it only contains a second negative electrode active material layer, and the thickness of the second negative electrode active material layer is different. See Table 1 for details.

Comparative example 4

The difference between the preparation method of the negative electrode sheet in Comparative Example 4 and the negative electrode sheet in Example 15 is that it only contains a second negative electrode active material layer, and the thickness of the second negative electrode active material layer is different. See Table 1 for details.

Comparative example 5

The difference between the preparation method of the negative electrode sheet in Comparative Example 5 and the negative electrode sheet in Example 16 is that it only contains a second negative electrode active material layer, and the thickness of the second negative electrode active material layer is different. See Table 1 for details.

The parameters of the negative electrode plates of each embodiment and each comparative example are as shown in Table 1 below.

Table 1

2. Preparation of batteries

1. Preparation of the positive electrode piece: Stir and mix the nickel cobalt manganese (NCM) ternary material, the conductive agent carbon black, and the binder polyvinylidene fluoride (PVDF) in a weight ratio of 96.7:1.7:1.6 to obtain the positive electrode. slurry; then, the positive electrode slurry is evenly coated on the positive electrode current collector, and then dried, cold pressed, and cut to obtain the positive electrode piece.

2. Isolation film: Polyethylene film (PE) with a thickness of 12 μm is used as the isolation film.

3. Preparation of electrolyte: Mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1, and then dissolve LiPF6 evenly in the above solution. , get the electrolyte. In this electrolyte, the concentration of LiPF ₆ is 1 mol/L.

4. Preparation of secondary battery: Stack and wind the positive electrode sheet, isolation film, and negative electrode sheet in the above embodiments or comparative examples in order to obtain an electrode assembly; put the electrode assembly into the outer package, and add the above After the prepared electrolyte is packaged, left to stand, formed, aged and other processes, a secondary battery is obtained. Record the amount of electrolyte added. See Table 2 for details.

It should be noted that when preparing a secondary battery, the electrolyte is mainly used to fill the pores of the electrode assembly and outer packaging as well as the pores in the second negative active material layer; when the thickness error of the second negative active material layer is within ±3 μm or When the total thickness error of the three negative active material layers is within ±6 μm, the difference in the amount of electrolyte caused can be ignored.

3. Battery performance test

1. Test the 800cls capacity retention rate of each secondary battery produced above:

The prepared secondary battery was charged to 3.8V at 1C in a constant temperature environment of 25°C, then charged to 4.2V at 0.87C, and finally charged to 4.4V at 0.33C, left for 10 minutes, and then discharged to 2.5V at 1C. . Repeat the above steps and record the battery capacity after 800 cycles.

2. Test the energy density of each secondary battery produced above:

Each prepared secondary battery was charged to 4.4V at 0.33C standard at room temperature, and charged to 0.05C at 4.4V constant voltage. After standing for 10 minutes, it was discharged to 2.5V at 0.33C. The discharge capacity was recorded, and the discharge time was then calculated. energy density. The formula is as follows:

Energy density (Wh/L) = discharge capacity (Wh)/lithium-ion secondary battery volume (L)

3. Test the negative electrode plate's full charge cycle expansion performance at 25°C for each secondary battery produced above:

At 25°C, charge the prepared secondary battery to 4.4V at a stepped rate, then charge at a constant voltage until the current is less than 0.05C, and then discharge it to 2.5V using a 1C rate; after cycling the secondary battery 100 times, Charge with constant current at 1C rate until the voltage is 4.4V, then charge with constant voltage at 4.4V until the current is less than or equal to 0.05C, then let it stand for 5 minutes. At this time, the battery is fully charged, and then disassemble it in the drying room after the cycle. Battery, obtain the negative electrode piece after full charge cycle.

Perform cross-sectional CP characterization of the negative electrode piece, and measure the thickness L11 of the first negative active material layer, the thickness L21 of the second negative active material layer, and the thickness L31 of the third negative active material layer respectively; based on the formula (L11-L1)/L1 *100 calculates the volume expansion rate of the first negative electrode active material layer, calculates the volume expansion rate of the second negative electrode active material layer based on the formula (L21-L2)/L1*100, and calculates the volume expansion rate of the second negative electrode active material layer based on the formula (L31-L3)/L3*100 The volume expansion rate of the three negative electrode active material layers.

The performance parameters of the secondary batteries prepared in each Example and Comparative Example are shown in Table 2 below.

Table 2

It can be seen from the examples and comparative examples in Table 1 and Table 2 that the negative electrode sheet is provided with three layers of negative active material, and the volume expansion rate of the first negative active material is higher than that of the second negative active material. The volume expansion rate is higher than the volume expansion rate of the second negative active material. When expansion occurs after lithium insertion, the first negative active material layer and the second active material layer can form a squeezing effect on the second negative active material layer, reducing the The porosity in the second active material layer can thereby reduce the amount of electrolyte and improve the energy density and capacity retention rate of the battery.

The main difference between Examples 1-5 is that the mass proportion of the first negative active material in the first negative active material layer is different. In Example 4, the mass proportion of the first negative active material is the smallest, and in Example 5, the mass proportion of the first negative active material is the smallest. One negative electrode active material accounts for the largest mass proportion. The amount of electrolyte used in the secondary battery in Example 4 and Example 5 is higher than that in Example 1-3, and its 800cls capacity retention rate and battery energy density are respectively lower than those in Example 1- 3. Technicians analyzed the reason. This may be due to the fact that the first negative active material has a relatively small mass proportion and cannot effectively squeeze the second negative active material layer. The second negative active material layer has more porosity, resulting in electrolyte consumption. As the amount increases, the energy density and capacity retention rate of the battery decrease; when the mass proportion of the first negative active material is large, the first negative active material pulverizes during the long cycle, exposing more fresh surfaces, resulting in electrolyte As consumption increases, the energy density and capacity retention rate of the battery decreases. Preferably, the mass proportion of the first negative active material in the first negative active material layer is 15% to 25%.

The main difference between Embodiment 1 and Embodiments 6-9 is that the mass proportion of the third negative active material in the third negative active material layer is different. In Embodiment 8, the mass proportion of the first negative active material is the smallest. In Example 9, the mass proportion of the first negative active material is the largest. The electrolyte consumption of the secondary battery in Example 8 and Example 9 is higher than that in Example 1 and Examples 7-8, and its 800cls capacity retention rate and battery energy The density is lower than Example 1 and Examples 7-8 respectively. Technicians analyzed the reason. This may be because the mass proportion of the third negative active material is relatively small and cannot effectively squeeze the second negative active material layer. The second negative active material layer has more porosity, resulting in electrolyte consumption. As the amount increases, the energy density and capacity retention rate of the battery decrease; when the mass proportion of the third negative active material is large, the first negative active material pulverizes during the long cycle, exposing more fresh surfaces, resulting in electrolyte As consumption increases, the energy density and capacity retention rate of the battery decreases. Preferably, the mass proportion of the third negative electrode active material in the third negative electrode active material layer is 15% to 25%.

The main difference between Embodiment 1 and Embodiments 10-16 is that: the thickness of the first negative active material layer, the second negative active material layer and/or the third negative active material layer is different, wherein the ratio of L1/L3 in Embodiment 13 The maximum, the ratio of (L1+L3)/L2 in Example 14 is the smallest, and the electrolyte consumption of the secondary battery in Example 8 and Example 9 is higher than that in Example 1, Examples 10-12 and Examples 15-16, And its 800cls capacity retention rate and battery energy density are lower than those in Example 1, Examples 10-12 and Examples 15-16 respectively. Preferably, 0.1≤L1/L3≤1, 0.08≤(L1+L3)/L2≤0.2, which can further reduce the amount of electrolyte and improve the 800cls capacity retention rate and energy density of the battery.

The difference between Embodiment 1 and Embodiments 17-20 mainly lies in: the types of the first negative active material and/or the second negative active material are different. Compared with Embodiments 17-20, Embodiment 1 has lower electrolyte dosage and Higher 800cls capacity rate and energy density.

The above are only specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any person familiar with the technical field can easily think of various equivalent methods within the technical scope disclosed in the present application. Modification or replacement, these modifications or replacements shall be covered by the protection scope of this application. Therefore, the protection scope of this application should be subject to the protection scope of the claims.

Claims

A negative electrode piece, including:

Negative current collector;

A first negative active material layer is located on at least one surface of the negative current collector, and the first negative active material layer includes a first negative active material;

A second negative active material layer is located on the surface of the first negative active material layer away from the negative current collector, and the second negative active material layer includes a second negative active material; and

A third negative active material layer is located on the surface of the second negative active material layer away from the first negative active material layer, and the third negative active material layer includes a third negative active material;

Wherein, the volume expansion rate of the first negative electrode active material and the third negative electrode active material is respectively greater than the volume expansion rate of the second negative electrode active material.
The negative electrode sheet according to claim 1, wherein the volume expansion rates of the first negative active material layer and the third negative active material layer before and after lithium insertion are respectively greater than that of the second negative active material layer before and after lithium insertion. Volume expansion rate before and after lithium.
The negative electrode sheet according to claims 1 to 2, wherein the volume expansion rate of the first negative electrode active material and the volume expansion rate of the third negative electrode active material are each independently 47% to 220%.
The negative electrode sheet according to claims 1 to 3, wherein the volume expansion rate of the second negative active material is 20% to 25%.
The negative electrode sheet according to claims 1 to 4, wherein the active materials in the second negative electrode active material layer are all the second negative electrode active materials; optionally, the second negative electrode active material is The mass proportion of the second negative active material layer is 94% to 96.8%.
The negative electrode sheet according to claims 1 to 5, wherein the active material in the first negative active material layer includes the first negative active material and the second negative active material; optionally, the The mass proportion of the first negative active material in the first negative active material layer is 15% to 25%, and the mass proportion of the second negative active material in the first negative active material layer is 71.8% ~81.8%;

And/or, the active material in the third negative electrode active material layer includes the third negative electrode active material and the second negative electrode active material; optionally, the third negative electrode active material is in the third negative electrode active material layer. The mass proportion of the active material layer is 15% to 25%, and the mass proportion of the second negative active material in the third negative active material layer is 71.8% to 81.8%.
The negative electrode sheet according to any one of claims 1 to 6, wherein the first negative electrode active material and the third negative electrode active material each independently include one of Ge, Sn, Sb, Bi and SiOx. or more;

Among them, 0≤x<2.
The negative electrode sheet according to any one of claims 1 to 7, wherein the second negative electrode active material includes one or more of artificial graphite and hard carbon.
The negative electrode sheet according to any one of claims 1 to 8, wherein the thickness of the first negative active material layer before lithium insertion is denoted as L1, and the thickness of the second negative active material layer before lithium insertion is Marked as L2, the thickness of the third negative active material layer before lithium insertion is marked as L3, then the first negative active material layer, the second negative active material layer and the third negative active material layer satisfy : 0.1≤L1/L3≤1, 0.08≤(L1+L3)/L2≤0.2.
The negative electrode sheet according to claim 9, wherein the thickness of the first negative active material layer before lithium insertion satisfies: 1 μm ≤ L1 ≤ 10 μm; and/or the second negative active material layer has a thickness before lithium insertion. The thickness before lithium embedding satisfies: 100 μm ≤ L2 ≤ 120 μm; and/or the thickness of the third negative active material layer before lithium embedding satisfies: 1 μm ≤ L3 ≤ 10 μm.
A secondary battery including the negative electrode plate according to any one of claims 1 to 10;

Wherein, the volume expansion ratios of the first negative active material layer and the third negative active material layer before and after lithium insertion are respectively greater than the volume expansion ratios of the second negative active material layer before and after lithium insertion.
An electrical device including the secondary battery according to claim 11.