Negative electrode sheet, method for manufacturing the same, battery, and electric device

Abstract

The application relates to a negative electrode sheet, a preparation method thereof, a battery and an electric device. The negative electrode sheet comprises a current collector and an active layer arranged on the surface of the current collector. Components of the active layer comprise at least two liquid-retaining polymers with different molecular weights. The liquid-retaining polymers contain functional groups capable of forming hydrogen bonds with water.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a negative electrode sheet and its preparation method, a battery, and an electrical device. Background Technology

[0002] Secondary batteries are increasingly widely used due to their clean and renewable characteristics. They mainly rely on the movement of active ions such as lithium ions between the positive and negative electrodes to generate electrical energy.

[0003] In recent years, with the rapid development of the new energy industry, people's demand for electric vehicles, electric bicycles and other electrical devices has been increasing, and their performance requirements have also been getting higher and higher.

[0004] As demand increases, the performance of traditional rechargeable batteries is becoming increasingly unable to meet people's needs and requires further improvement. Summary of the Invention

[0005] Therefore, it is necessary to provide a negative electrode sheet and its preparation method, a battery, and an electrical device, with the aim of improving the cycle performance and rate capability of the battery.

[0006] A first aspect of this application provides a negative electrode sheet, the negative electrode sheet comprising a current collector and an active layer disposed on the surface of the current collector, the active layer comprising at least two liquid-retaining polymers with different molecular weights;

[0007] The liquid-retaining polymer contains functional groups that can form hydrogen bonds with water.

[0008] The active layer of the aforementioned negative electrode contains at least two liquid-retaining polymers with different molecular weights. When used to prepare a battery, on the one hand, the liquid-retaining polymers in the negative electrode can adsorb electrolyte and keep the transport of active ions unobstructed. On the other hand, the combination of at least two liquid-retaining polymers with different molecular weights can maintain a high liquid absorption effect while reducing the degree to which the liquid-retaining polymers swell due to adsorbing electrolyte and cause blockage of pores, thereby slowing down the migration of active ions. All aspects work together to improve the cycle performance and rate of the battery.

[0009] In some embodiments, the gel chromatography elution curve of the liquid-retaining polymer in the active layer contains at least two peaks.

[0010] In some embodiments, the number-average molecular weights corresponding to each peak in the gel chromatography elution curve are independently selected from 50 to 600.

[0011] Optionally, at least one peak corresponds to a number-average molecular weight of 50 to 100, and at least another peak corresponds to a number-average molecular weight of 300 to 600.

[0012] By controlling the synergy of at least two specific liquid-retaining polymers with different molecular weight ranges, the consistency of the active layer of the negative electrode can be further improved, thereby enhancing the cycle performance and rate capability of the battery.

[0013] In some embodiments, the mass ratio of the liquid-retaining polymer with a number average molecular weight of 50 to 100 to the liquid-retaining polymer with a number average molecular weight of 300 to 600 is 1:(1 to 6).

[0014] In some embodiments, the gel chromatography elution curve of the liquid-retaining polymer in the active layer contains three peaks.

[0015] The gel chromatography elution curve of the liquid-retaining polymer in the active layer contains three peaks, which essentially means that the active layer contains at least three liquid-retaining polymers with different molecular weights. Furthermore, by combining at least three liquid-retaining polymers with different molecular weights within a specific molecular weight range, the cycle performance and rate of the battery can be further improved.

[0016] In some embodiments, the active layer includes a first liquid-retaining polymer with a number-average molecular weight of T1, a second liquid-retaining polymer with a number-average molecular weight of T2, and a third liquid-retaining polymer with a number-average molecular weight of T3.

[0017] Wherein, 50≤T1≤100, 100<T2≤250, 250<T3≤600; optionally, 500≤T3≤600.

[0018] By combining three liquid-retaining polymers with specific molecular weight ranges, on the one hand, while maintaining a high liquid absorption effect, the degree to which the liquid-retaining polymer swells due to the adsorption of electrolyte and causes blockage of pores, thus slowing down the migration of active ions, can be reduced. On the other hand, the liquid-retaining polymer with a smaller molecular weight also has a certain degree of migration, which can further improve the consistency of the active layer of the negative electrode and improve the cycle performance and rate of the battery.

[0019] In some embodiments, the mass ratio of the first liquid-retaining polymer, the second liquid-retaining polymer, and the third liquid-retaining polymer is (1-2):(1-4):(3-6);

[0020] Optionally, the mass ratio of the first liquid-retaining polymer, the second liquid-retaining polymer, and the third liquid-retaining polymer is 1:(1-4):(5-6).

[0021] By adjusting the mass ratio of three liquid-retaining polymers with different molecular weights, the cycle performance and rate of the battery can be further improved.

[0022] In some of these embodiments, one of the liquid-retaining polymers contains lithium ions;

[0023] The presence of lithium ions can further improve the migration rate of lithium ions between the positive and negative electrodes. The liquid-retaining polymer contains lithium ions, that is, lithium ions are connected to other elements on the molecular chain of the liquid-retaining polymer through chemical bonds. In this way, lithium ions are not easily lost, effectively improving the migration rate of lithium ions between the positive and negative electrodes, thereby improving the cycle performance and rate of the battery.

[0024] Optionally, the lithium ions account for 0.2% to 15% of the total mass, based on the mass of the liquid-retaining polymer.

[0025] By adjusting the mass ratio of lithium ions in the liquid-retaining polymer, the migration rate of lithium ions between the positive and negative electrodes can be further improved, thereby enhancing the cycle performance and rate capability of the battery.

[0026] In some embodiments, at least one of the liquid-retaining polymers contains lithium ions on the side groups of its molecular chain;

[0027] Optionally, the mass ratio of the liquid-retaining polymer containing lithium ions to the liquid-retaining polymer without lithium ions is 10:(2-5).

[0028] In some embodiments, the total mass percentage of the liquid-retaining polymer in the active layer is 0.3% to 0.8%.

[0029] Optionally, the total mass percentage of the liquid-retaining polymer in the active layer is 0.3% to 0.5%.

[0030] Adjusting the amount of liquid-retaining polymer reduces the likelihood of gelation during preparation, which could lead to a decrease in electrode uniformity.

[0031] In some embodiments, the liquid-retaining polymer satisfies at least one of the following conditions (I) to (II):

[0032] (I) The functional group includes at least one of hydroxyl, carboxyl, carbonyl and ether groups;

[0033] Optionally, each of the liquid-retaining polymers contains the same functional groups;

[0034] (II) Each of the liquid-retaining polymers has a main chain with the same structure;

[0035] Optionally, the backbone is selected from any one of polyethylene glycol backbone, polyvinyl alcohol backbone, and polyacrylic acid backbone.

[0036] In some embodiments, the liquid-retaining polymer includes at least one of lithium-ion-free polyvinyl alcohol, lithium-ion-containing polyvinyl alcohol, lithium-ion-free polyethylene glycol, lithium-ion-containing polyethylene glycol, lithium-ion-free polyacrylic acid, lithium-ion-containing polyacrylic acid, lithium-ion-free polyvinyl alcohol-acrylic acid graft polymer, lithium-ion-containing polyvinyl alcohol-acrylic acid graft polymer, lithium-ion-free polyethylene glycol acrylate, lithium-ion-containing polyethylene glycol acrylate, lithium-ion-free polyethylene glycol diacrylate, lithium-ion-containing polyethylene glycol diacrylate, lithium-ion-free polyethylene glycol acrylate, and lithium-ion-containing polyethylene glycol acrylate.

[0037] In some embodiments, the active layer further includes a binder;

[0038] Optionally, the adhesive includes a carboxymethyl cellulose adhesive, and in the active layer, the total mass ratio of the carboxymethyl cellulose adhesive to the liquid-retaining polymer is 1% to 2%.

[0039] Further optionally, the total mass ratio of the carboxymethyl cellulose binder to the liquid-retaining polymer is 1% to 1.5%.

[0040] By controlling the amount of carboxymethyl cellulose binder, it can work synergistically with the liquid-retaining polymer to maintain good liquid retention performance while maintaining good adhesion performance, thereby reducing the probability of electrode cracking.

[0041] In some embodiments, the molecular weight of the binder is different from the molecular weight of the liquid-retaining polymer;

[0042] Optionally, the number-average molecular weight of the adhesive is greater than the molecular weight of the liquid-retaining polymer;

[0043] Further optionally, the number-average molecular weight of the adhesive is ≥100,000.

[0044] A second aspect of this application provides a method for preparing a negative electrode sheet, comprising the following steps:

[0045] A negative electrode sheet is prepared by forming an active layer on the surface of a current collector using an active slurry.

[0046] The active slurry comprises at least two liquid-retaining polymers with different molecular weights; the liquid-retaining polymers contain functional groups that can form hydrogen bonds with water.

[0047] A third aspect of this application provides a battery comprising a negative electrode sheet prepared by the method of preparing a negative electrode sheet according to the first aspect or the second aspect.

[0048] A fourth aspect of this application provides an electrical device comprising the battery of the third aspect. Attached Figure Description

[0049] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0050] Figure 1 This is a schematic diagram of one embodiment of the battery;

[0051] Figure 2 yes Figure 1 Exploded view;

[0052] Figure 3 This is a schematic diagram of one embodiment of the battery pack;

[0053] Figure 4 yes Figure 3 Exploded view;

[0054] Figure 5 This is a schematic diagram of one embodiment of an electrical device in which a battery is used as a power source.

[0055] Explanation of reference numerals in the attached figures:

[0056] 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery; 41. Housing; 42. Electrode assembly; 43. Cover plate; 5. Electrical device. Detailed Implementation

[0057] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, a detailed description of specific embodiments of this application is provided below. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0058] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0059] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0060] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0061] In conclusion, traditional battery performance is increasingly unable to meet people's needs. With the rapid development of the new energy industry, people have higher and higher requirements for battery cycle performance and charging rate.

[0062] Technicians are primarily focused on developing new active materials, but this is a lengthy and arduous process, and no substantial progress has been made so far. Some technical studies have found that during battery operation, the voids in the negative electrode plate need to be filled with electrolyte to form lithium-ion liquid phase transport channels. However, during cyclic charging and discharging, the electrolyte impregnated in the pores of the negative electrode plate is squeezed out or deposited at the bottom of the cell due to gravity, resulting in insufficient electrolyte during cell cycling and thus a decrease in cell cycle performance.

[0063] Therefore, the technicians tried to introduce polymers with high liquid absorption into the negative electrode to improve its liquid retention. However, further research by the technicians revealed that polymers with high liquid absorption inevitably swell after absorbing liquid. After swelling, the polymer will block the pores of the active layer of the negative electrode, which will slow down the migration of lithium ions and have a negative impact on battery performance.

[0064] Based on this, after extensive creative exploration, the negative electrode sheet that can improve the charging rate and cycle performance of the battery was obtained in this application.

[0065] One embodiment of this application provides a negative electrode sheet, which includes a current collector and an active layer disposed on the surface of the current collector. The active layer comprises at least two liquid-retaining polymers with different molecular weights. The liquid-retaining polymers contain functional groups that can form hydrogen bonds with water.

[0066] The active layer of the aforementioned negative electrode contains at least two liquid-retaining polymers with different molecular weights. When used to prepare a battery, on the one hand, the liquid-retaining polymers in the negative electrode can adsorb electrolyte and keep the transport of active ions unobstructed. On the other hand, the combination of at least two liquid-retaining polymers with different molecular weights can maintain a high liquid absorption effect while reducing the degree to which the liquid-retaining polymers swell due to adsorbing electrolyte and cause blockage of pores, thereby slowing down the migration of active ions. All aspects work together to improve the cycle performance and rate of the battery.

[0067] It should be noted that the current collector in the negative electrode has two surfaces opposite each other in its own thickness direction, and the active layer can be disposed on either or both of the two opposite surfaces of the current collector.

[0068] In some embodiments, the gel chromatography elution profile of the liquid-retaining polymer in the active layer contains at least two peaks.

[0069] It is understandable that a peak in the gel chromatography elution curve represents a specific molecular weight or molecular weight range. The gel chromatography elution curve of the liquid-retaining polymer in the active layer contains at least two peaks, that is, the components characterizing the active layer include at least two liquid-retaining polymers with different molecular weights.

[0070] In some embodiments, the gel chromatography elution curve of the liquid-retaining polymer in the active layer contains two peaks.

[0071] Optionally, the number-average molecular weight of the liquid-retaining polymer corresponding to each peak is independently selected from 50 to 600.

[0072] In some embodiments, at least one peak corresponds to a number-average molecular weight of 50 to 100, and at least another peak corresponds to a number-average molecular weight of 300 to 600.

[0073] In some embodiments, at least one peak corresponds to a number-average molecular weight of 50 to 100, and at least another peak corresponds to a number-average molecular weight of 500 to 600.

[0074] By controlling the synergy of at least two specific liquid-retaining polymers with different molecular weight ranges, the consistency of the active layer of the negative electrode can be further improved, thereby enhancing the cycle performance and rate capability of the battery.

[0075] Optionally, the active layer includes a liquid-retaining polymer with a number-average molecular weight of 50 to 100 and a liquid-retaining polymer with a number-average molecular weight of 300 to 600.

[0076] In one embodiment, the mass ratio of the liquid-retaining polymer with a number average molecular weight of 50 to 100 and the liquid-retaining polymer with a number average molecular weight of 300 to 600 is 1:(1 to 6).

[0077] In some of these embodiments, the active layer includes a liquid-retaining polymer having a number-average molecular weight of 50 to 100 and a liquid-retaining polymer having a number-average molecular weight of 500 to 600.

[0078] In one of the embodiments, the mass ratio of the liquid-retaining polymer having a number-average molecular weight of 50 to 100 to the liquid-retaining polymer having a number-average molecular weight of 500 to 600 is 1:(1 to 6).

[0079] In the above "1:(1 to 6)", the values include the minimum and maximum values of this range, as well as each value between such minimum and maximum values. Specific examples include, but are not limited to, the point values in the embodiments and the following point values: 1:1, 1:2, 1:3, 1:4, 1:5, 1:6; or a range composed of any two numerical values, such as: 1:(1 to 5), 1:(1 to 4), 1:(1 to 3), 1:(1 to 2), 1:(2 to 6), 1:(2 to 5).

[0080] In some of these embodiments, the gel permeation chromatography elution curve of the liquid-retaining polymer in the active layer contains three peaks.

[0081] The fact that the gel permeation chromatography elution curve of the liquid-retaining polymer contains three peaks essentially means that there are at least three different molecular weight liquid-retaining polymers.

[0082] Further, through the software supporting gel permeation chromatography, after integration and normalization processing, the area ratio of each peak is calculated, which is the mass ratio of the polymer with a specific molecular weight corresponding to each peak.

[0083] It can be understood that the above molecular weight can be any one of number-average molecular weight, weight-average molecular weight, viscosity-average molecular weight, and Z-average molecular weight.

[0084] Optionally, the number-average molecular weights of the liquid-retaining polymers corresponding to the three peaks are independently selected from 50 to 600.

[0085] Further, by combining at least three different molecular weight liquid-retaining polymers within a specific molecular weight range, the cycle performance and rate of the battery are further improved.

[0086] In some of these embodiments, the active layer includes a first liquid-retaining polymer having a number-average molecular weight of T1, a second liquid-retaining polymer having a number-average molecular weight of T2, and a third liquid-retaining polymer having a number-average molecular weight of T3.

[0087] Among them, 50 ≤ T1 ≤ 100, 100 < T2 ≤ 250, 250 < T3 ≤ 600.

[0088] In some of these embodiments, 300 ≤ T3 ≤ 600.

[0089] Optionally, 500 ≤ T3 ≤ 600.

[0090] By combining three liquid-retaining polymers with specific molecular weight ranges, on the one hand, while maintaining a high liquid absorption effect, the degree to which the liquid-retaining polymer swells due to the adsorption of electrolyte and causes blockage of pores, thus slowing down the migration of active ions, can be reduced. On the other hand, the liquid-retaining polymer with a smaller molecular weight has a certain degree of migration, which can further improve the consistency of the active layer of the negative electrode and improve the cycle performance and rate of the battery.

[0091] In the above "50≤T1≤100", the value of T1 includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiment and the following point values: 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 99, 100; or any range consisting of two values, such as: 50~55, 50~60, 50~65, 50~70, 50~75, 50~80, 50~85, 50~90, 50~95, 50~99, 55~60, 55 ~65, 55~70, 55~75, 55~80, 55~85, 55~90, 55~95, 55~99, 60~65, 60~70, 60~75, 60~80, 60~85, 60~90, 60~95, 60~99, 65~70, 65~75, 65~80, 65~85, 65~90, 65~95, 65~99, 70~80, 70~85, 70~90, 70~95, 70~99, 80~85, 80~90, 80~95, 80~99, 80~100.

[0092] In the above "100<T2≤250", the value of T2 includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiment and the following point values: "101, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250"; or any range consisting of two values, such as: 101~120, 101~150, 101~160, 101~170, 101~180, 101~200, 101~220, 101~250, 1 10~120, 110~150, 110~160, 110~170, 110~180, 110~200, 110~220, 110~250, 120~150, 120~160, 120~170, 120~180, 120~200, 120~220, 120~250, 130~150, 130~160, 130~170, 130~180, 130~200, 130~220, 130~250, 150~160, 150~170, 150~180, 150~200, 150~220, 150~250.

[0093] In the above "250<T3≤600", the value of T3 includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: "260, 300, 350, 400, 450, 500, 550, 600"; or any range consisting of any two values, such as: 260~300, 260~350, 260~400, 260~450, 260~500, 2 60~550, 300~350, 300~400, 300~450, 300~500, 300~550, 300~600, 350~400, 350~450, 350~500, 350~550, 350~600, 400~450, 400~500, 400~550, 400~600, 450~500, 450~550, 450~600, 500~550, 500~600.

[0094] In some embodiments, the mass ratio of the first liquid-retaining polymer, the second liquid-retaining polymer, and the third liquid-retaining polymer is (1-2):(1-4):(3-6).

[0095] In some embodiments, the mass ratio of the first liquid-retaining polymer, the second liquid-retaining polymer, and the third liquid-retaining polymer is 1:(1-4):(5-6).

[0096] By adjusting the mass ratio of three liquid-retaining polymers with different molecular weights, the cycle performance and rate of the battery can be further improved.

[0097] In the above “(1~2):(1~4):(3~6)”, the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 1:1:5, 1:1:3, 1:1:4, 1:1:6, 1:2:5, 1:3:5, 2:2:5, 2:3:5, 1:2:6, 1:3:6, 2:2:6, 2:3:6.

[0098] In some of these embodiments, one of the liquid-retaining polymers contains lithium ions.

[0099] The presence of lithium ions can further improve the migration rate of lithium ions between the positive and negative electrodes. The molecular chain of the liquid-retaining polymer contains lithium ions, that is, lithium ions are connected to other elements on the molecular chain of the liquid-retaining polymer through chemical bonds. In this way, lithium ions are not easily lost, effectively improving the migration rate of lithium ions between the positive and negative electrodes, thereby improving the cycle performance and rate of the battery.

[0100] Optionally, the mass percentage of lithium ions is 0.2% to 15% based on the mass of the liquid-retaining polymer.

[0101] By adjusting the mass ratio of lithium ions in the liquid-retaining polymer, the migration rate of lithium ions between the positive and negative electrodes can be further improved, thereby enhancing the cycle performance and rate capability of the battery.

[0102] The values ​​in the above "0.2% to 15%" range include the minimum and maximum values ​​of this range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: "0.2%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%; or any range consisting of two values, such as: 0.2% to 15%, 0.2% to 14%, etc." 0.2%–13%, 0.2%–12%, 0.2%–11%, 0.2%–10%, 0.2%–8%, 0.2%–7%, 0.2%–6%, 0.2%–5%, 0.2%–4%, 0.2%–3%, 0.2%–2%, 0.2%–1%, 5%–15%, 5%–13%, 5%–10%, 5%–9%, ​​5%–7%, 6%–15%, 6%–13%, 6%–10%, 6%–9%, ​​6%–7%, 8%–15%, 8%–13%, 8%–10%, 8%–9%, ​​10%–15%, 10%–13%.

[0103] In some embodiments, at least one liquid-retaining polymer contains lithium ions on the side groups of its molecular chain.

[0104] It is understandable that the molecular chain of the liquid-retaining polymer includes a main chain and side groups attached to the main chain, and chemical bonds are formed between lithium ions and the group atoms on the side groups.

[0105] In some embodiments, the mass ratio of the lithium-ion-containing liquid-retaining polymer to the lithium-ion-free liquid-retaining polymer is 10:(2-5).

[0106] In the above "10:(2~5)", the value includes the minimum and maximum value of the range, as well as every value between the minimum and maximum value. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: "10:2, 10:3, 10:4, 10:5; or any range of two values".

[0107] It should be noted that the molecular weights of lithium-ion-containing and lithium-free liquid-retaining polymers may be the same or different.

[0108] In some embodiments, the total mass percentage of the liquid-retaining polymer in the active layer is 0.3% to 0.8%.

[0109] In some embodiments, the total mass percentage of the liquid-retaining polymer in the active layer is 0.3% to 0.5%.

[0110] Adjusting the amount of liquid-retaining polymer reduces the likelihood of gelation during preparation, which could lead to a decrease in electrode uniformity.

[0111] The values ​​in "0.3% to 0.8%" above include the minimum and maximum values ​​of this range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%; or any range consisting of two values, such as: 0.3% to 0.8%, 0.3% to 0.7%, 0.3% to 0.6%, 0.3% to 0.5%, 0.3% to 0.4%, 0.4% to 0.8%, 0.4% to 0.7%, 0.4% to 0.6%, 0.4% to 0.5%, 0.5% to 0.8%, 0.5% to 0.7%, 0.5% to 0.6%.

[0112] In some embodiments, the functional groups include at least one of hydroxyl, carboxyl, carbonyl and ether groups.

[0113] In some of these embodiments, each liquid-retaining polymer contains the same functional groups.

[0114] In some embodiments, each liquid-retaining polymer has a backbone with the same structure; further, the backbone is selected from any one of polyethylene glycol backbone, polyvinyl alcohol backbone and polyacrylic acid backbone.

[0115] It is understandable that the main chain of a polymer is composed of repeating units arranged in a chain-like structure, which is the polymer backbone.

[0116] In some embodiments, non-limiting examples of lithium-ion-containing liquid-retaining polymers include at least one of polyvinyl alcohol-lithium compounds and polyacrylic acid-lithium compounds.

[0117] In some embodiments, the liquid-retaining polymer includes at least one of lithium-ion-free polyvinyl alcohol, lithium-ion-containing polyvinyl alcohol, lithium-ion-free polyethylene glycol, lithium-ion-containing polyethylene glycol, lithium-ion-free polyacrylic acid, lithium-ion-containing polyacrylic acid, lithium-ion-free polyvinyl alcohol-acrylic acid graft polymer, lithium-ion-containing polyvinyl alcohol-acrylic acid graft polymer, lithium-ion-free polyethylene glycol acrylate, lithium-ion-containing polyethylene glycol acrylate, lithium-ion-free polyethylene glycol diacrylate, lithium-ion-containing polyethylene glycol diacrylate, lithium-ion-free polyethylene glycol acrylate, and lithium-ion-containing polyethylene glycol acrylate.

[0118] In some embodiments, the active layer also includes a binder.

[0119] Optionally, the total mass percentage of the adhesive in the active layer is 0.8% to 4%.

[0120] The values ​​in "0.8% to 4%" above include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%; or any range of two values.

[0121] In some embodiments, the binder includes a carboxymethyl cellulose binder, and the total mass percentage of the carboxymethyl cellulose binder and the liquid-retaining polymer in the active layer is 1% to 2%.

[0122] Optionally, the total mass percentage of carboxymethyl cellulose binder and liquid-retaining polymer is 1% to 1.5%.

[0123] By controlling the amount of carboxymethyl cellulose binder, it can work synergistically with the liquid-retaining polymer to maintain good liquid retention performance while maintaining good adhesion performance, thereby reducing the probability of electrode cracking.

[0124] The values ​​in "1% to 2%" above include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%; or any range of two values.

[0125] In some embodiments, the adhesive further includes a styrene-butadiene rubber adhesive.

[0126] Optionally, the styrene-butadiene rubber adhesive accounts for 1% to 1.8% of the mass of the active layer.

[0127] The values ​​in "1% to 1.8%" include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%; or any range of two values.

[0128] In some embodiments, the carboxymethyl cellulose binder includes at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

[0129] In some embodiments, the molecular weight of the binder differs from that of the liquid-retaining polymer.

[0130] Optionally, the number-average molecular weight of the binder is greater than the molecular weight of the liquid-retaining polymer.

[0131] Further optionally, the number average molecular weight of the adhesive is ≥100,000.

[0132] In some embodiments, the active layer further comprises a negative electrode active material and a negative electrode conductive agent.

[0133] In any embodiment of this application, the aforementioned negative electrode active material includes at least one of the following: mesophase carbon microspheres, graphite, glassy carbon, carbon nanotubes, carbon-carbon composite materials, carbon fibers, hard carbon, soft carbon, silicon-based materials, tin-based materials, magnesium-based materials, and iron-based materials.

[0134] Optionally, specific examples of the above-mentioned negative electrode active materials include, but are not limited to, at least one of the following: interphase carbon microspheres, natural graphite, artificial graphite, graphene, glassy carbon, carbon nanotubes, carbon fibers, hard carbon, soft carbon, iron oxide, tin oxide, silicon oxide, magnesium oxide, and silicon-carbon composites.

[0135] In any embodiment of this application, the mass percentage of the above-mentioned negative electrode active material in the active layer is 70% to 99.5%.

[0136] In any embodiment of this application, the aforementioned negative electrode conductive agent can be a commonly used conductive material in the art, including but not limited to at least one of graphite, carbon nanotubes, nanofibers, carbon black, and graphene. Specifically, it can be selected from at least one of SP, KS-6, acetylene black, branched Ketjen black ECP, SFG-6, vapor-grown carbon fiber VGCF, carbon nanotubes CNTs, and graphene and their composite conductive agents.

[0137] In some embodiments, the negative electrode conductive agent accounts for 0.05% to 20% of the weight of the active layer.

[0138] In any embodiment of this application, the current collector in the negative electrode can be a metal foil or a composite current collector. For example, copper foil can be used as the metal foil.

[0139] Composite current collectors may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. Composite current collectors can be formed by forming a metal material on a polymer substrate.

[0140] In some embodiments, the metallic material is selected from any one of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys.

[0141] In some embodiments, the polymer material substrate includes at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0142] According to one embodiment of this application, a method for preparing a negative electrode sheet is also provided, including the following step S10.

[0143] Step S10: An active layer is formed on the surface of the current collector using an active slurry to prepare a negative electrode sheet; the active slurry comprises at least two liquid-retaining polymers with different molecular weights; the liquid-retaining polymers contain functional groups that can form hydrogen bonds with water.

[0144] The selection of the liquid-retaining polymer is the same as described above and will not be repeated here.

[0145] In any embodiment of this application, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, liquid-retaining polymer, binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then performing processes such as drying and cold pressing to obtain the negative electrode sheet. The negative electrode slurry has a solid content of 30wt% to 70wt% and its viscosity at room temperature is adjusted to 2000 mPa·s.

[0146] ~10000 mPa·s; The obtained negative electrode slurry is coated onto the negative electrode current collector, and after a drying process, it is cold-pressed, for example, by rollers, to obtain the negative electrode sheet.

[0147] In some embodiments, the areal density of the negative electrode active material contained in the negative electrode sheet is 0.005 g / cm³. 2 ~0.03g / cm 2 .

[0148] The areal density of the negative electrode active material = the mass of the negative electrode active material / the area of ​​the negative electrode sheet.

[0149] According to one embodiment of this application, a battery is provided, which includes a negative electrode sheet as described above or a negative electrode sheet prepared by the method described above.

[0150] This battery exhibits excellent cycle performance and rate performance.

[0151] The battery also includes a positive electrode, a separator, and an electrolyte. Examples of the positive electrode, separator, and electrolyte are given below, including but not limited to the following.

[0152] [Positive electrode tablets]

[0153] The positive electrode includes a current collector and a positive electrode active layer disposed on the surface of the current collector. The components of the positive electrode active layer include positive electrode active materials.

[0154] As an example, the current collector in the positive electrode has two surfaces opposite each other in its own thickness direction, and the positive electrode active material layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0155] In any embodiment of this application, the current collector in the positive electrode may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material on a polymer material substrate.

[0156] In some embodiments, the metallic material includes at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.

[0157] In some embodiments, the polymer material substrate includes at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0158] The aforementioned positive electrode active material can be a commonly used positive electrode active material in this application, such as lithium-ion positive electrode active material or sodium-ion positive electrode active material.

[0159] Further, as an example, lithium-ion active materials may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also known as LFP)), lithium manganese phosphate (such as LiMnPO4), and lithium manganese iron phosphate.

[0160] In any embodiment of this application, the molecular formula of the lithium-ion active material is: LiFe x Mn (1-x) PO4, where x takes any number from 0 to 1.

[0161] It is understandable that when x is 0, LiFe x Mn (1-x) PO4 is lithium manganese phosphate (LiMnPO4). When x is 1, LiFePO4 is lithium iron phosphate (LiFePO4).

[0162] It should be noted that the lithium content in the cathode materials exemplified above refers to their content when unused. During battery use, repeated charging and discharging occur, resulting in the deintercalation and consumption of Li. Therefore, the molar content of Li in the cathode active material changes during charge and discharge. In other words, the molar subscript of Li in the cathode active material of the battery product will not remain constant at 1; it will change. Furthermore, the range of change can be (0–1.2). In the examples of cathode materials in this application, the molar content of Li refers to the initial state of the material, i.e., the state before feeding. When the cathode material is applied to the battery system, the molar content of Li will change after charge and discharge cycles.

[0163] Similarly, in the examples of cathode materials in this application, the molar content of O is only a theoretical value. The release of oxygen from the crystal lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0164] For example, LiFe x Mn (1-x) PO4 can be further represented as Li y Fe x Mn (1-x) PO4, y is 0 to 1.1.

[0165] For example, regarding the ternary material Li y (Ni a Co b Mn c ) 1-d M d O 2-x A z y is 0.2 to 1.2, a+b+c=1, 0≤d≤1, 0≤x<2; M is one or more of Zr, Sr, B, Ti, Mg, Sn and Al, and A is one or more of S, N, F, Cl, Br and I.

[0166] During the charging and discharging process, Li will be extracted and consumed. The molar content of Li will be different when the battery is discharged to different states. The above limitation on y includes the molar content of Li in different charging and discharging states of the battery. Furthermore, the battery voltage is usually between 2-5V.

[0167] As an example, sodium-ion active materials may include at least one of the following: sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, this application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries may also be used.

[0168] As an optional technical solution in this application, the transition metal in the sodium transition metal oxide includes at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide is Na. x MO2, wherein M includes at least one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0169] As an optional technical solution in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. Transition metals include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y includes at least one of P, S, and Si; n represents (YO4). n- The price state.

[0170] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds comprising anionic units and halide anions. Transition metals include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y includes at least one of P, S, and Si, where n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0171] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y includes at least one of P, S, and Si, and n represents (YO4). n- The valence state; Z represents a transition metal, including at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, and m represents (ZO). y ) m+ The valence state; the halogen can be at least one of F, Cl and Br.

[0172] Polyanionic compounds include, for example, NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2 (P2O7), NaM'PO4F (M' is one or more of V, Fe, Mn and Ni), and Na3(VO4) y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0173] Prussian blue compounds can be compounds containing sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. Transition metals include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue compounds are, for example, Na. a Me b Me' c (CN)6, wherein Me and Me' each independently include at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0174] Based on the total weight of the positive electrode active layer, the weight ratio of the positive electrode active material in the positive electrode active layer is 80wt% to 100wt%.

[0175] In any embodiment of this application, the positive electrode active layer further comprises a positive electrode conductive agent and a positive electrode binder.

[0176] The aforementioned positive electrode conductive agent can be a commonly used conductive agent in the art, including but not limited to at least one of graphite, carbon nanotubes, nanofibers, carbon black, and graphene. Specifically, it can be selected from at least one of SP, KS-6, acetylene black, branched Ketjen black ECP, SFG-6, vapor-grown carbon fiber VGCF, carbon nanotubes CNTs, and graphene and their composite conductive agents.

[0177] Based on the total weight of the positive electrode active layer, the weight ratio of the positive electrode conductive agent in the positive electrode active layer is 0–20 wt%.

[0178] In any embodiment of this application, the binder of the above-mentioned positive electrode binder may be at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, hydrogenated nitrile rubber, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), carboxymethyl chitosan (CMCS), and fluorinated acrylate resin.

[0179] Based on the total weight of the positive electrode active layer, the weight ratio of the positive electrode binder in the positive electrode active layer is 0–30 wt%.

[0180] In any embodiment of this application, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a current collector, and then performing processes such as drying and cold pressing to obtain the positive electrode sheet. The solid content of the positive electrode slurry is 40wt% to 80wt%, and the viscosity at room temperature is adjusted to 5000 mPa·s.

[0181] The positive electrode slurry is coated onto the surface of the positive electrode current collector at a pressure of ~25000 mPa·s, dried, and then cold-pressed through a cold rolling mill to form the positive electrode sheet; the areal density of the positive electrode powder coating is 15-35 mg / cm³. 2 The compacted density of the positive electrode sheet is 3.0–3.6 g / cm³. 3 The concentration can be selected as 3.3–3.5 g / cm³. 3 The formula for calculating compacted density is:

[0182] Compacted density = Coated surface density / (Extreme electrode thickness after extrusion - Current collector thickness).

[0183] Electrolyte

[0184] Electrolytes include electrolyte salts and solvents.

[0185] In some embodiments, the electrolyte salt may be selected from electrolyte salts commonly used in the art, such as lithium-ion electrolyte salts.

[0186] As an example, lithium-ion electrolyte salts include, but are not limited to, one or more of the following: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0187] In some embodiments, the solvent may be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0188] In some embodiments, the concentration of the electrolyte salt in the electrolyte is typically 0.5 mol / L to 15 mol / L.

[0189] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0190] [Isolation membrane]

[0191] The separator is placed between the positive electrode and the negative electrode.

[0192] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0193] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0194] The thickness of the diaphragm is controlled between 2 μm and 15 μm; optionally, the thickness of the diaphragm is controlled between 2 μm and 13 μm.

[0195] In some embodiments, the battery is a secondary battery; specifically, the battery is a lithium-ion battery.

[0196] The shape of the battery in this application is not particularly limited; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 The battery 4 is a square structure, which serves as an example.

[0197] In some embodiments, refer to Figure 2 The outer casing may include a housing 41 and a cover plate 43. The housing 41 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 41 has an opening communicating with the receiving cavity, and the cover plate 43 can be placed over the opening to close the receiving cavity.

[0198] The positive electrode, negative electrode, and separator can be formed into electrode assembly 42 by a winding or stacking process. Electrode assembly 42 is encapsulated within a receiving cavity. Electrolyte is immersed in electrode assembly 42. The battery 4 can contain one or more electrode assemblies 42, which can be adjusted according to requirements.

[0199] This application also provides an electrical device that includes the battery described above.

[0200] Furthermore, in the aforementioned electrical device, the battery can exist in the form of a single battery cell, or it can be further assembled into a battery pack.

[0201] Figure 3 and Figure 4 Here is an example of a battery pack 1. The battery pack 1 includes a battery compartment and one or more batteries 4 disposed within the battery compartment. The battery compartment includes an upper compartment 2 and a lower compartment 3, the upper compartment 2 being able to cover the lower compartment 3 and form an enclosed space for the batteries 4.

[0202] Multiple batteries 4 can be arranged in the battery box in any way.

[0203] The aforementioned battery or the battery pack assembled therefrom can be used as a power source for an electrical device or as an energy storage unit for an electrical device.

[0204] The aforementioned electrical devices may include, but are not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0205] Figure 5 This is an example of an electrical device 5. This electrical device 5 can be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this electrical device 5, a battery pack can be used.

[0206] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use batteries as their power source.

[0207] The present application will be described below with reference to specific embodiments, but the present application is not limited to the following embodiments. It should be understood that the appended claims summarize the scope of the present application. Under the guidance of the concept of the present application, those skilled in the art should realize that certain changes made to the various embodiments of the present application will be covered by the spirit and scope of the claims of the present application.

[0208] The following are specific examples.

[0209] Example 1

[0210] S1. Preparation of the positive electrode sheet: The positive electrode slurry is prepared according to the following method:

[0211] The ternary cathode active material NCM532, conductive agent acetylene black, and binder PVDF were added to a vacuum mixer at a mass ratio of 96:2:2 and mixed. Then, solvent NMP was added to the mixed slurry, and the mixed slurry was stirred until it became homogeneous under the action of the vacuum mixer, thus obtaining the cathode slurry.

[0212] The above-mentioned positive electrode slurry was uniformly coated on both surfaces of the positive electrode current collector aluminum foil. After drying at room temperature, it was transferred to an oven for further drying. After drying in the oven, a positive electrode active layer was formed. Then, it was cold-pressed and slit to obtain the positive electrode sheet to be assembled. The thickness of the positive electrode active layer was 109 μm.

[0213] S2. Preparation of the negative electrode:

[0214] The negative electrode active material graphite, conductive agent acetylene black, styrene-butadiene latex, sodium carboxymethyl cellulose, and liquid-retaining polymer were added to a vacuum mixer in a mass ratio of 96.8:0.7:1.5:0.5:0.5 and mixed. Then, deionized water was added as a solvent to the mixture, and the mixture was stirred under vacuum until homogeneous, thus obtaining the negative electrode slurry. The presence of gelation was observed. In the liquid-retaining polymer, the mass percentages of polyethylene glycol with a number average molecular weight of 80, lithium polyethylene glycol with a number average molecular weight of 80, polyethylene glycol with a number average molecular weight of 600, and lithium polyethylene glycol with a number average molecular weight of 600 were 25%, 25%, 25%, and 25%, respectively.

[0215] The above-mentioned negative electrode slurry was uniformly coated on both surfaces of the negative electrode current collector copper foil. After being dried at room temperature, it was transferred to an oven for further drying. After drying in the oven, a negative electrode active layer was formed. Then, it was cold-pressed into an electrode sheet with a thickness of 131 μm, cut into negative electrode sheets, and the presence of cracks in the negative electrode sheets was observed.

[0216] Characterization test of negative electrode sheet: The active layer of the negative electrode sheet was separated, and the binder and liquid-retaining polymer were separated by scraping, hydrothermal ultrasound, centrifugation and filtration. The weights were weighed and the mass percentage of each component was calculated. The proportion of liquid-retaining polymer in the active layer was recorded as H1, and the total mass percentage of carboxymethyl cellulose binder and liquid-retaining polymer in the active layer was recorded as H2.

[0217] Infrared spectroscopy was performed on the liquid-retaining polymer to identify the types of functional groups contained in the polymer based on the characteristic peaks. Please refer to Table 1 for details.

[0218] Gel chromatography was performed on the liquid-retaining polymers to obtain their gel chromatography elution curves. The molecular weights corresponding to the two peaks in the curves were calculated using software, namely the first liquid-retaining polymer with a number-average molecular weight of T1 and the third liquid-retaining polymer with a number-average molecular weight of T3. The integral area ratio of the two peaks was further obtained through integration and homogenization, which is the mass ratio Y1 of the first liquid-retaining polymer and the third liquid-retaining polymer.

[0219] Flame atomic absorption spectrometry was used to analyze and calculate the lithium ion mass percentage (Y2) in the liquid-retaining polymer.

[0220] Please see Table 1 for specific parameters.

[0221] S3. Preparation of electrolyte

[0222] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of EC:EMC:DEC = 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0223] S4. Separator: Polyethylene film is selected as the separator for lithium-ion batteries.

[0224] S5. Assembly of lithium-ion batteries: The positive electrode, separator, and negative electrode to be assembled are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The bare cell is then produced by winding. The bare cell is placed in the battery casing, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, the lithium-ion battery to be tested is obtained.

[0225] S6. Performance Testing of Lithium-ion Batteries

[0226] 1. At 25℃, the lithium-ion battery used as the test object was subjected to a cycle test according to the following procedure: fully charged at a 1C rate, left to stand for 30 minutes, and then fully discharged. This is considered one cycle. The initial capacity at this point was recorded. This cycle was repeated 1500 times, and the remaining capacity of the cell was recorded. The percentage of the remaining capacity to the initial capacity was recorded as P.1500 .

[0227] 2. Equivalent rate test: The three-electrode detection method is used to test the equivalent window of the battery at 25℃, which is 30% to 80%.

[0228] 3. Low-temperature lithium plating test: Using a -10℃ battery charging window, the cell was cycled 10 times at 1.1x magnification, and the cell was disassembled to confirm the lithium plating status of the negative electrode.

[0229] Example 2

[0230] Example 2 is basically the same as Example 1, except that in step S2, the mass percentages of polyethylene glycol with a number average molecular weight of 50, lithium polyethylene glycol with a number average molecular weight of 50, polyethylene glycol with a number average molecular weight of 500, and lithium polyethylene glycol with a number average molecular weight of 500 are 25%, 25%, 25%, and 25%, respectively, in the liquid-retaining polymer.

[0231] The other steps are the same as in Implementation 1. Please refer to Table 1 for specific parameters.

[0232] Example 3

[0233] Example 3 is basically the same as Example 1, except that in step S2, the mass percentages of polyethylene glycol with a number average molecular weight of 100, lithium polyethylene glycol with a number average molecular weight of 100, polyethylene glycol with a number average molecular weight of 450, and lithium polyethylene glycol with a number average molecular weight of 450 in the liquid-retaining polymer are 25%, 25%, 25%, and 25%, respectively.

[0234] The other steps are the same as in Implementation 1. Please refer to Table 1 for specific parameters.

[0235] Example 4

[0236] Example 4 is basically the same as Example 1, except that in step S2, the mass percentages of polyethylene glycol with a number average molecular weight of 80, lithium polyethylene glycol with a number average molecular weight of 80, polyethylene glycol with a number average molecular weight of 300, and lithium polyethylene glycol with a number average molecular weight of 300 in the liquid-retaining polymer are 25%, 25%, 25%, and 25%, respectively.

[0237] The other steps are the same as in Implementation 1. Please refer to Table 1 for specific parameters.

[0238] Example 5

[0239] Example 5 is basically the same as Example 1, except that in step S2, the mass percentages of polyethylene glycol with a number average molecular weight of 80, lithium polyethylene glycol with a number average molecular weight of 80, polyethylene glycol with a number average molecular weight of 600, and lithium polyethylene glycol with a number average molecular weight of 600 in the liquid-retaining polymer are 7%, 7.5%, 42.5%, and 43%, respectively.

[0240] The other steps are the same as in Implementation 1. Please refer to Table 1 for specific parameters.

[0241] Example 6

[0242] Example 6 is basically the same as Example 1, except that in step S2, the mass percentages of polyethylene glycol with a number average molecular weight of 80, lithium polyethylene glycol with a number average molecular weight of 80, polyethylene glycol with a number average molecular weight of 600, and lithium polyethylene glycol with a number average molecular weight of 600 in the liquid-retaining polymer are 12.5%, 12.5%, 37.5%, and 37.5%, respectively.

[0243] The other steps are the same as in Implementation 1. Please refer to Table 1 for specific parameters.

[0244] Example 7

[0245] Example 7 is basically the same as Example 1, except that in step S2, the number average molecular weight of polyethylene glycol (80) and the number average molecular weight of polyethylene glycol (500) in the liquid-retaining polymer are 50% and 50% respectively by mass.

[0246] The other steps are the same as in Implementation 1. Please refer to Table 1 for specific parameters.

[0247] Example 8

[0248] Example 8 is basically the same as Example 1, except that in step S2, the negative electrode active material graphite, conductive agent acetylene black, styrene-butadiene latex, sodium carboxymethyl cellulose, and liquid-retaining polymer are added to a vacuum mixer in a mass ratio of 96.8:0.7:1.5:0.5:0.5 for mixing. Then, deionized water is added to the mixed slurry as a solvent, and the mixed slurry is stirred until it becomes homogeneous under the action of the vacuum mixer, thereby obtaining the negative electrode slurry. The presence of gelation in the slurry is observed. The liquid-retaining polymer includes polyethylene glycol with a number average molecular weight of 80, lithium polyethylene glycol with a number average molecular weight of 80, polyethylene glycol with a number average molecular weight of 200, lithium polyethylene glycol with a number average molecular weight of 200, polyethylene glycol with a number average molecular weight of 500, and lithium polyethylene glycol with a number average molecular weight of 500, with a mass percentage of 5%, 5%, 20%, 20%, 25%, and 25% in the liquid-retaining polymer, respectively.

[0249] Correspondingly, the gel chromatography elution curve of the liquid-retaining polymer has three peaks, namely the first liquid-retaining polymer with a number-average molecular weight of T1, the second liquid-retaining polymer with a number-average molecular weight of T2, and the third liquid-retaining polymer with a number-average molecular weight of T3; at this time, Y1 is the mass ratio of the first liquid-retaining polymer, the second liquid-retaining polymer, and the third liquid-retaining polymer.

[0250] The other steps are the same as in Implementation 1. Please refer to Table 1 for specific parameters.

[0251] Example 9

[0252] Example 9 is basically the same as Example 8, except that in step S2, the mass ratio of the negative electrode active material graphite, the conductive agent acetylene black, styrene-butadiene latex, sodium carboxymethyl cellulose, and the liquid-retaining polymer is 96.3:0.7:1.5:1.2:0.3. In the liquid-retaining polymer, the mass ratio of polyethylene glycol with a number average molecular weight of 80, lithium polyethylene glycol with a number average molecular weight of 80, polyethylene glycol with a number average molecular weight of 200, lithium polyethylene glycol with a number average molecular weight of 200, polyethylene glycol with a number average molecular weight of 500, and lithium polyethylene glycol with a number average molecular weight of 500 is 1%:9%:4%:36%:5%:45%.

[0253] The other steps are the same as in Implementation 1. Please refer to Table 1 for specific parameters.

[0254] Example 10

[0255] Example 10 is basically the same as Example 9, except that in step S2, the mass ratios of polyethylene glycol with a number average molecular weight of 80, lithium polyethylene glycol with a number average molecular weight of 80, polyethylene glycol with a number average molecular weight of 200, lithium polyethylene glycol with a number average molecular weight of 200, polyethylene glycol with a number average molecular weight of 500, and lithium polyethylene glycol with a number average molecular weight of 500 in the liquid-retaining polymer are 1.4%, 12.9%, 1.4%, 12.9%, 7.1%, and 64.3%, respectively.

[0256] The other steps are the same as in Implementation 1. Please refer to Table 1 for specific parameters.

[0257] Example 11

[0258] Example 11 is basically the same as Example 10, except that in step S2, the mass ratio of the negative electrode active material graphite, the conductive agent acetylene black, styrene-butadiene latex, sodium carboxymethyl cellulose, and the liquid-retaining polymer is 96.3:0.7:1.5:1.2:0.3. In the liquid-retaining polymer, the mass ratios of polyethylene glycol with a number average molecular weight of 80, lithium polyethylene glycol with a number average molecular weight of 80, polyethylene glycol with a number average molecular weight of 200, lithium polyethylene glycol with a number average molecular weight of 200, polyethylene glycol with a number average molecular weight of 500, and lithium polyethylene glycol with a number average molecular weight of 500 are 5.0%, 7.5%, 12.5%, 12.5%, 18.8%, and 43.7%, respectively.

[0259] The other steps are the same as in Implementation 1. Please refer to Table 1 for specific parameters.

[0260] Example 12

[0261] Example 12 is basically the same as Example 9, except that in step S2, the mass ratio of the negative electrode active material graphite, the conductive agent acetylene black, styrene-butadiene latex, sodium carboxymethyl cellulose, and the liquid-retaining polymer is 96.8:0.7:1.5:0.5:0.5. In the liquid-retaining polymer, the mass percentages of polyethylene glycol with a number average molecular weight of 90, lithium polyethylene glycol with a number average molecular weight of 90, polyethylene glycol with a number average molecular weight of 250, lithium polyethylene glycol with a number average molecular weight of 250, polyethylene glycol with a number average molecular weight of 600, and lithium polyethylene glycol with a number average molecular weight of 600 are 4.0%, 6.0%, 20.0%, 20.0%, 15.0%, and 35.0%, respectively.

[0262] The other steps are the same as in Implementation 1. Please refer to Table 1 for specific parameters.

[0263] Example 13

[0264] Example 13 is basically the same as Example 9, except that in step S2, the mass ratio of the negative electrode active material graphite, the conductive agent acetylene black, styrene-butadiene latex, sodium carboxymethyl cellulose, and the liquid-retaining polymer is 96.8:0.7:1.5:0.5:0.5. In the liquid-retaining polymer, the mass percentages of polyvinyl alcohol with a number average molecular weight of 90, lithium polyvinyl alcohol with a number average molecular weight of 90, polyvinyl alcohol with a number average molecular weight of 250, lithium polyvinyl alcohol with a number average molecular weight of 250, polyvinyl alcohol with a number average molecular weight of 600, and lithium polyvinyl alcohol with a number average molecular weight of 600 are 4.0%, 6.0%, 20.0%, 20.0%, 15.0%, and 35.0%, respectively.

[0265] The other steps are the same as in Implementation 1. Please refer to Table 1 for specific parameters.

[0266] Example 14

[0267] Example 14 is basically the same as Example 9, except that in step S2, the mass ratio of the negative electrode active material graphite, the conductive agent acetylene black, styrene-butadiene latex, lithium carboxymethyl cellulose, and the liquid-retaining polymer is 96.8:0.7:1.5:0.5:0.5. In the liquid-retaining polymer, the mass percentages of polyacrylic acid with a number average molecular weight of 90, lithium polyacrylate with a number average molecular weight of 90, polyacrylic acid with a number average molecular weight of 250, lithium polyacrylate with a number average molecular weight of 250, polyacrylic acid with a number average molecular weight of 600, and lithium polyacrylate with a number average molecular weight of 600 are 4.0%, 6.0%, 20.0%, 20.0%, 15.0%, and 35.0%, respectively.

[0268] The other steps are the same as in Implementation 1. Please refer to Table 1 for specific parameters.

[0269] Example 15

[0270] Example 15 is basically the same as Example 10, except that in step S2, the mass ratio of the negative electrode active material graphite, the conductive agent acetylene black, styrene-butadiene latex, sodium carboxymethyl cellulose, and the liquid-retaining polymer is 96.3:0.7:1.5:1.2:0.3. In the liquid-retaining polymer, the mass percentages of polyethylene glycol with a number average molecular weight of 80, lithium polyethylene glycol with a number average molecular weight of 80, polyethylene glycol with a number average molecular weight of 200, lithium polyethylene glycol with a number average molecular weight of 200, polyethylene glycol with a number average molecular weight of 500, and lithium polyethylene glycol with a number average molecular weight of 500 are 4.0%, 6.0%, 15.0%, 15.0%, 18.0%, and 42.0%, respectively.

[0271] Comparative Example 1

[0272] Comparative Example 1 is basically the same as Example 1, except that in step S2, no liquid-retaining polymer is added to the negative electrode slurry, and the negative electrode active material graphite, conductive agent acetylene black, styrene-butadiene latex and sodium carboxymethyl cellulose are mixed in a mass ratio of 96.8:0.7:1.5:1.

[0273] The other steps are the same as in Implementation 1. Please refer to Table 1 for specific parameters.

[0274] Comparative Example 2

[0275] Comparative Example 2 is basically the same as Example 1, except that in step S2, the mass ratio of the negative electrode active material graphite, the conductive agent acetylene black, styrene-butadiene latex, sodium carboxymethyl cellulose, and the liquid-retaining polymer is 96.8:0.7:1.5:0.5:0.5, and the liquid-retaining polymer is polyethylene glycol with a number average molecular weight of 500.

[0276] The other steps are the same as in Implementation 1. Please refer to Table 1 for specific parameters.

[0277] Comparative Example 3

[0278] Comparative Example 3 is basically the same as Example 1, except that in step S2, the mass ratio of the negative electrode active material graphite, the conductive agent acetylene black, styrene-butadiene latex, sodium carboxymethyl cellulose, and the liquid-retaining polymer is 96.8:0.7:1.5:0.5:0.5, and the liquid-retaining polymer is polyethylene glycol with a number average molecular weight of 80.

[0279] The other steps are the same as in Implementation 1. Please refer to Table 1 for specific parameters.

[0280] The relevant parameters and performance test results of each embodiment and comparative example are shown in Table 1. The proportion of the liquid-retaining polymer in the active layer is denoted as H1, the total mass proportion of carboxymethyl cellulose binder and liquid-retaining polymer in the active layer is denoted as H2, the mass ratio of the first liquid-retaining polymer, the second liquid-retaining polymer and the third liquid-retaining polymer is Y1, and the mass proportion of lithium ions in the liquid-retaining polymer in the active layer is Y2.

[0281] Table 1

[0282]

[0283] " / " indicates that the substance or parameter does not exist.

[0284] Comparative analysis of the data from Comparative Examples 1-3 and Examples 1-13 using the scheme of this application in Table 1 shows that using the technical solution of this application, and combining liquid-retaining polymers with different molecular weights, can improve the cycle performance and charging rate of the battery. Comparative Example 2 uses high molecular weight liquid-retaining polymers, which can improve the liquid retention capacity, but at the same time, the swelling after liquid absorption will block the lithium-ion channels, resulting in a deterioration in charging capacity and cycle performance. Comparative Example 3 uses low molecular weight liquid-retaining polymers, which deteriorates the charging window and shows a significant deterioration in lithium plating.

[0285] Furthermore, comparative analysis of the data from Examples 1-7 and Examples 9-15 shows that adjusting the molecular weight and mass ratio of the liquid-retaining polymer at each level can further improve the cycle performance and rate capability of the battery.

[0286] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0287] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A negative electrode sheet, characterized in that, The negative electrode includes a current collector and an active layer disposed on the surface of the current collector, wherein the active layer comprises at least two liquid-retaining polymers with different molecular weights; The liquid-retaining polymer contains functional groups that can form hydrogen bonds with water.

2. The negative electrode sheet as described in claim 1, characterized in that, The gel chromatography elution curve of the liquid-retaining polymer in the active layer contains at least two peaks.

3. The negative electrode sheet as described in claim 2, characterized in that, In the gel chromatography elution curve, the number-average molecular weight corresponding to each peak is independently selected from 50 to 600.

4. The negative electrode sheet as described in claim 3, characterized in that, At least one peak corresponds to a number-average molecular weight of 50 to 100, and at least another peak corresponds to a number-average molecular weight of 300 to 600.

5. The negative electrode sheet as described in claim 3, characterized in that, The mass ratio of the liquid-retaining polymer with a number average molecular weight of 50-100 to the liquid-retaining polymer with a number average molecular weight of 300-600 is 1:(1-6).

6. The negative electrode sheet according to any one of claims 1 to 5, characterized in that, The gel chromatography elution curve of the liquid-retaining polymer in the active layer contains three peaks.

7. The negative electrode sheet according to any one of claims 1 to 5, characterized in that, The active layer includes a first liquid-retaining polymer with a number-average molecular weight of T1, a second liquid-retaining polymer with a number-average molecular weight of T2, and a third liquid-retaining polymer with a number-average molecular weight of T3. Among them, 50≤T1≤100, 100<T2≤250, and 250<T3≤600.

8. The negative electrode sheet as described in claim 7, characterized in that, 500≤T3≤600。 9. The negative electrode sheet as described in claim 7, characterized in that, The mass ratio of the first liquid-retaining polymer, the second liquid-retaining polymer, and the third liquid-retaining polymer is (1~2):(1~4):(3~6).

10. The negative electrode sheet as described in claim 9, characterized in that, The mass ratio of the first liquid-retaining polymer, the second liquid-retaining polymer and the third liquid-retaining polymer is 1:(1~4):(5~6).

11. The negative electrode sheet according to any one of claims 1 to 5, characterized in that, At least one liquid-retaining polymer contains lithium ions.

12. The negative electrode sheet as described in claim 11, characterized in that, Based on the mass of the liquid-retaining polymer, the mass percentage of lithium ions is 0.2% to 15%.

13. The negative electrode sheet according to any one of claims 1 to 5, characterized in that, At least one of the liquid-retaining polymers contains lithium ions on the side groups of its molecular chain.

14. The negative electrode sheet as described in claim 13, characterized in that, The mass ratio of the liquid-retaining polymer containing lithium ions to the liquid-retaining polymer without lithium ions is 10:(2~5).

15. The negative electrode sheet according to any one of claims 1 to 5, characterized in that, In the active layer, the total mass percentage of the liquid-retaining polymer is 0.3% to 0.8%.

16. The negative electrode sheet as described in claim 15, characterized in that, In the active layer, the total mass percentage of the liquid-retaining polymer is 0.3% to 0.5%.

17. The negative electrode sheet according to any one of claims 1 to 5, characterized in that, The liquid-retaining polymer satisfies at least one of the following conditions (Ⅰ) to (Ⅱ): (I) The functional group includes at least one of hydroxyl, carboxyl, carbonyl and ether groups; (II) Each of the liquid-retaining polymers has the same main chain structure.

18. The negative electrode sheet as described in claim 17, characterized in that, The liquid-retaining polymer satisfies at least one of the following conditions (Ⅰ) to (Ⅱ): (I) Each of the liquid-retaining polymers contains the same functional groups; (II) The main chain is selected from any one of polyethylene glycol main chain, polyvinyl alcohol main chain and polyacrylic acid main chain.

19. The negative electrode sheet according to any one of claims 1 to 5, characterized in that, The liquid-retaining polymer includes at least one of the following: lithium-free polyvinyl alcohol, lithium-containing polyvinyl alcohol, lithium-free polyethylene glycol, lithium-containing polyethylene glycol, lithium-free polyacrylic acid, lithium-containing polyacrylic acid, lithium-free polyvinyl alcohol-acrylic acid graft polymer, lithium-containing polyvinyl alcohol-acrylic acid graft polymer, lithium-free polyethylene glycol acrylate, lithium-containing polyethylene glycol acrylate, lithium-free polyethylene glycol diacrylate, lithium-containing polyethylene glycol diacrylate, lithium-free polyethylene glycol acrylate, and lithium-containing polyethylene glycol acrylate.

20. The negative electrode sheet according to any one of claims 1 to 5, characterized in that, The active layer also includes a binder.

21. The negative electrode sheet as described in claim 20, characterized in that, The adhesive includes a carboxymethyl cellulose adhesive, and in the active layer, the total mass ratio of the carboxymethyl cellulose adhesive to the liquid-retaining polymer is 1% to 2%.

22. The negative electrode sheet as described in claim 21, characterized in that, The total mass ratio of the carboxymethyl cellulose binder to the liquid-retaining polymer is 1% to 1.5%.

23. The negative electrode sheet as described in claim 20, characterized in that, The molecular weight of the adhesive is different from that of the liquid-retaining polymer.

24. The negative electrode sheet as described in claim 23, characterized in that, The number-average molecular weight of the adhesive is greater than the molecular weight of the liquid-retaining polymer.

25. The negative electrode sheet as described in claim 23, characterized in that, The number average molecular weight of the adhesive is ≥100,000.

26. A method for preparing a negative electrode sheet, characterized in that, Includes the following steps: A negative electrode sheet is prepared by forming an active layer on the surface of a current collector using an active slurry. The active slurry comprises at least two liquid-retaining polymers with different molecular weights; the liquid-retaining polymers contain functional groups that can form hydrogen bonds with water.

27. A battery, characterized in that, The battery includes a negative electrode sheet prepared by any one of claims 1 to 25 or by the method of preparing a negative electrode sheet as described in claim 26.

28. An electrical appliance, characterized in that, The electrical device includes the battery as described in claim 27.

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