Positive electrode sheet, lithium ion battery, and electric device

Abstract

The embodiment of the application discloses a positive electrode sheet, a lithium ion battery and an electric device. The positive electrode sheet comprises a current collector and a positive electrode film layer arranged on at least one side of the current collector. The positive electrode film layer comprises a metal salt, the metal salt comprises metal ions, the reduction potential of the metal ions is greater than the reduction potential of lithium ions, and the difference between the reduction potential of the metal ions and the reduction potential of lithium ions is less than or equal to 0.8 V. The application of the positive electrode sheet to the lithium ion battery can effectively inhibit lithium precipitation and help improve the cycle performance of the lithium ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, and more particularly, to a positive electrode sheet, a lithium ion battery and an electric device. BACKGROUND

[0002] In recent years, lithium ion batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc., thus getting great development. However, the limited reserves of lithium resources and uneven distribution have become a major problem restricting the development of lithium ion batteries.

[0003] During the cycle process of the lithium ion battery, due to the limitation of process, use environment and other factors, lithium precipitation occurs on the negative electrode sheet, which seriously leads to the growth of lithium dendrites, threatening the reversible capacity and cycle life of the lithium ion battery. Therefore, how to improve the lithium precipitation of the lithium ion battery has become a technical problem to be solved. SUMMARY

[0004] The present application is made in view of the above technical problems, and aims to provide a positive electrode sheet, a lithium ion battery and an electric device. The application of the positive electrode sheet to the lithium ion battery can effectively suppress lithium precipitation and help improve the cycle performance and coulomb efficiency of the lithium ion battery.

[0005] In a first aspect, a positive electrode sheet is provided, which includes: a current collector and a positive film layer arranged on at least one side of the current collector; the positive film layer includes a metal salt, the metal salt includes metal ions, the reduction potential of the metal ions is greater than the reduction potential of lithium ions, and the difference between the reduction potential of the metal ions and the reduction potential of the lithium ions is less than or equal to 0.8V.

[0006] In an embodiment of the present application, by introducing a metal salt into the positive electrode sheet, the metal salt can be dissolved or partially dissolved in the electrolyte, so that when the positive electrode sheet is applied to the lithium ion battery, there are free metal ions in the electrolyte. This part of the free metal ions can move freely to the position with lower potential on the negative electrode sheet, and the reduction potential is close to that of lithium ions (the difference is less than or equal to 0.8V), so as to form a local positive charge electrostatic field, thereby uniforming the current density on the negative electrode sheet and suppressing lithium precipitation. Thus, by using the positive electrode sheet provided by the present application, lithium precipitation can be effectively suppressed, side reactions in the cycle process of the lithium ion battery can be reduced, and the cycle performance and coulomb efficiency of the lithium ion battery can be improved.

[0007] In a possible implementation, the positive film layer includes a positive active material layer arranged on the current collector; and the positive active material layer includes the metal salt.

[0008] In a possible implementation, the positive electrode active material layer includes a positive electrode active material; and the average volume particle size Dv50 of the particles of the metal salt is equal to the average volume particle size Dv50 of the positive electrode active material.

[0009] After the metal salt is dissolved in the electrolyte, a pore is left in the positive electrode active material layer. In the embodiments of the present application, by selecting the particles of the metal salt with the average volume particle size equal to that of the positive electrode active material, a pore is left in the positive electrode active material layer, the contact area between the positive electrode active material and the electrolyte is increased, and the risk of structural instability of the positive electrode active material layer caused by the dissolution of the metal salt is reduced.

[0010] In a possible implementation, the average volume particle size Dv50 of the particles of the metal salt satisfies: 0.05 μm≤Dv50≤70 μm; and optionally, 0.5 μm≤Dv50≤60 μm.

[0011] In a possible implementation, the mass content a of the metal salt satisfies: 1%≤a≤50% in the total mass of the positive electrode active material layer; and optionally, 5%≤a≤40%.

[0012] In the embodiments of the present application, by controlling the mass content of the metal salt in the positive electrode active material layer within a proper range, the lithium precipitation is inhibited, and the influence of the metal salt on the energy density of the lithium ion battery is reduced.

[0013] In a possible implementation, the positive electrode film layer includes a positive electrode active material layer and a coating layer, the positive electrode active material layer is arranged on the current collector, and the coating layer is arranged on the positive electrode active material layer; and the coating layer includes the metal salt.

[0014] In a possible implementation, the thickness d of the coating layer satisfies: 0.05 μm≤d≤100 μm; and optionally, 0.1 μm≤d≤50 μm.

[0015] In a possible implementation, the mass content b of the metal salt satisfies: 1%≤b≤40% in the total mass of the positive electrode film layer; and optionally, 5%≤b≤30%.

[0016] In the embodiments of the present application, by controlling the mass content of the metal salt in the positive electrode film layer within a proper range, the lithium precipitation is inhibited, and the influence of the metal salt on the energy density of the lithium ion battery is reduced.

[0017] In a possible implementation, the metal salt includes at least one of a sodium salt, a potassium salt, a calcium salt, a magnesium salt, and a cesium salt.

[0018] In a possible implementation, the metal salt comprises anions, and the anions comprise one or more of fluorine, phosphorus, sulfur, and nitrogen.

[0019] In a possible implementation, the solubility S of the metal salt in the electrolyte satisfies: S≥0.005 g / mL.

[0020] In a possible implementation, the powder compaction density of the positive electrode film layer satisfies: p satisfies: 0.8 g / cm 3 ≤ p ≤ 4.0 g / cm 3 ; optionally, 1.0 g / cm 3 ≤ p ≤ 3.5 g / cm 3 .

[0021] In a second aspect, a method for manufacturing a positive electrode sheet is provided, the method comprising: disposing a positive electrode film layer on at least one side of a current collector to obtain the positive electrode sheet; the positive electrode film layer comprising a metal salt, the metal salt comprising metal ions, the reduction potential of the metal ions being greater than the reduction potential of lithium ions, and the difference between the reduction potential of the metal ions and the reduction potential of the lithium ions being less than or equal to 0.8 V.

[0022] In a possible implementation, the disposing of the positive electrode film layer on at least one side of the current collector comprises: disposing a positive electrode active material layer on at least one side of the current collector, the positive electrode active material layer comprising the metal salt.

[0023] In a possible implementation, the disposing of the positive electrode active material layer on at least one side of the current collector comprises: preparing a first slurry, the first slurry comprising a positive electrode active material and the metal salt; coating the first slurry on at least one side of the current collector; drying the first slurry to form a first coating layer on the current collector; and rolling the current collector and the first coating layer to obtain the positive electrode sheet.

[0024] In a possible implementation, the disposing of the positive electrode film layer on at least one side of the current collector comprises: disposing a positive electrode active material layer on at least one side of the current collector; and disposing a coating layer on the positive electrode active material layer, the coating layer comprising the metal salt.

[0025] In a possible implementation, the disposing of the positive electrode active material layer on at least one side of the current collector comprises: preparing a second slurry, the second slurry comprising a positive electrode active material; coating the second slurry on at least one side of the current collector; and drying the second slurry to form the positive electrode active material layer on the current collector.

[0026] In a possible implementation, the disposing the coating on the positive active material layer comprises: preparing a third slurry, the third slurry comprising the metal salt; coating the third slurry on the positive active material layer; drying the third slurry to form the coating on the positive active material layer; and rolling the dried current collector, the positive active material layer, and the coating to obtain the positive electrode sheet.

[0027] In a third aspect, a lithium ion battery is provided, comprising the positive electrode sheet of any possible implementation of the first aspect, and / or the positive electrode sheet prepared by the method of any possible implementation of the second aspect.

[0028] In a possible implementation, the lithium ion battery comprises an electrolyte, and the electrolyte comprises the metal ion.

[0029] In a possible implementation, the weight content c of the metal ion in the total weight of the electrolyte satisfies: 0.02%≤c≤30%; optionally, 0.03%≤c≤6%.

[0030] In a fourth aspect, a power utilization device is provided, comprising the lithium ion battery of any possible implementation of the third aspect. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of the drawings.

[0032] Figure 1 A schematic flow chart of a method for preparing a positive electrode sheet.

[0033] Figure 2 A schematic diagram of a battery cell of a lithium ion battery.

[0034] Figure 3 A schematic diagram of a battery module of a lithium ion battery.

[0035] Figure 4 A schematic diagram of a lithium ion battery.

[0036] Figure 5 Another schematic diagram of a lithium ion battery. DETAILED DESCRIPTION

[0037] Hereinafter, specific embodiments of the positive electrode sheet, the method of manufacturing the same, the lithium ion battery, and the electric device according to the present application will be described in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters known well, redundant repeated description of substantially identical configurations are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided to allow those skilled in the art to sufficiently understand the present application, and are not intended to limit the subject matter recited in the claims.

[0038] The ranges disclosed herein are defined by their lower and upper limits. Ranges created by the upper and lower limits are inclusive of the endpoints. Ranges created by the upper and lower limits are also inclusive of any and all sub-ranges subsumed therein. For example, a range of "60% to 120%" is inclusive of from 60% to 120%, as well as from 60% to 69%, from 60% to 70%, from 60% to 71%, from 60% to 72%, from 60% to 73%, from 60% to 74%, from 60% to 75%, from 60% to 76%, from 60% to 77%, from 60% to 78%, from 60% to 79%, from 60% to 80%, and so on, up to and including 120%. Similarly, a range of "80% to 110%" is inclusive of from 80% to 110%, as well as from 80% to 89%, from 80% to 90%, from 80% to 91%, from 80% to 92%, from 80% to 93%, from 80% to 94%, from 80% to 95%, from 80% to 96%, from 80% to 97%, from 80% to 98%, from 80% to 99%, and so on, up to and including 110%. Unless otherwise stated, the numerical values are indicative of any and all sub-ranges subsumed therein. For example, a range of 1-5 is indicative of any and all sub-ranges between and including the minimum value of 1 and the maximum value of 5, that is, all sub-ranges beginning with a minimum value of 1 or more and ending with a maximum value of 5 or less, as well as every number, whole or fraction, in between within this range. In this disclosure, unless otherwise indicated, the use of "or" means "and / or" and not the exclusive "or". Unless otherwise indicated, all numbers expressing quantities of aspects such as use percentages, levels, and ranges are to be understood as modified in all instances by the term "about". Accordingly, unless indicated to the contrary, it is intended that any and all parameters listed herein can be varied and / or combined for each instance. At the very least, therefore, the numerical parameters should serve as a guide as the values will typically fall within a range of values in the art, and can be expressed or perceived differently from this guide depending upon the context in which they are used. All numerical values of parameters are thus understood as modified in all instances by the term "about" unless otherwise indicated.

[0039] In the description of the present application, it is necessary to note that, unless otherwise specified, the meaning of "a plurality of" is more than two; the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", "inner", "outer" and the like is only for the purpose of facilitating the description of the present application and simplifying the description, and is not intended to indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third" and the like are only for the purpose of description and cannot be understood as indicating or implying relative importance.

[0040] If not specifically stated, the term "and / or" is inclusive in the present application. For example, the phrase "A and / or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A and / or B": 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).

[0041] If not specifically stated, all steps of the present application can be performed in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method is mentioned to further comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0042] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0043] If not specifically stated, the following terms have the following meanings. Any undefined term has its commonly accepted meaning in the art.

[0044] If mentioned, "reduction potential" refers to the electrode potential of a substance relative to the standard hydrogen electrode. Specifically, the reduction potential is the electrode potential of the substance measured by forming a primary cell with the standard hydrogen electrode.

[0045] If mentioned, "metal salt" refers to a compound composed of a metal cation and an anion.

[0046] Next, the embodiments of the present application are introduced.

[0047] In recent years, secondary batteries have been widely used in electric tools, electronic products, electric vehicles, aerospace and other fields due to their high energy density and long service life, and have made great progress. Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the charging and discharging process of the battery, active ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet. Among them, the electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, which prevents the positive and negative electrodes from short-circuiting while allowing active ions to pass through, so that the secondary battery can normally perform electrochemical reactions.

[0048] For example, a lithium ion battery is a typical secondary battery. Since the lithium ion battery relies on the chemical reaction of lithium ions deintercalating between the positive and negative electrodes to charge and discharge, the lithium ion battery is also called a rocking chair battery. During the charging process of the lithium ion battery, lithium ions are deintercalated from the positive active material, move to the negative electrode through the conduction of the electrolyte, and are intercalated into the negative active material. During the discharging process, lithium ions are deintercalated from the negative active material, move to the positive electrode through the conduction of the electrolyte, and are intercalated into the positive active material.

[0049] It should be understood that the "intercalation of lithium" and "intercalation" processes described in the present application refer to the process in which lithium ions are intercalated into the positive active material or the negative active material due to an electrochemical reaction. The "deintercalation" and "deintercalation of lithium" processes described in the present application refer to the process in which lithium ions are deintercalated from the positive active material or the negative active material due to an electrochemical reaction.

[0050] During the cycling process of the lithium ion battery, due to the limitations of the battery preparation process, battery aging and other factors, the intercalation of lithium ions into the negative active material is hindered, and lithium metal is easily precipitated on the surface of the negative electrode plate in the form of dendrites. As the precipitation of lithium further occurs, lithium dendrites grow, and in severe cases, the SEI (Solidelectrolyte interface) film is pierced, causing a side reaction with the electrolyte, consuming active lithium ions in the battery, and causing the reversible capacity of the battery to decay and the cycle life to decrease. Once the lithium dendrites pierce the separator, it will also cause serious safety problems.

[0051] Therefore, the embodiments of the present application provide a positive electrode plate and a preparation method thereof, a lithium ion battery and an electric device. The positive electrode plate comprises a current collector and a positive film layer arranged on at least one side of the current collector. The positive film layer comprises a metal salt, and the metal salt comprises metal ions. The reduction potential of the metal ions is greater than the reduction potential of lithium ions, and the difference between the reduction potential of the metal ions and the reduction potential of lithium ions is less than or equal to 0.8 V.

[0052] When the positive electrode plate is applied to a lithium ion battery, the metal salt can be dissolved or partially dissolved in the electrolyte, so that free metal ions exist in the electrolyte. This part of free metal ions has a potential similar to that of lithium ions, and since the metal salt can be regarded as an additive of the positive film layer, the concentration of this part of metal ions in the electrolyte is much smaller than that of lithium ions, so that the metal ions cannot be reduced to metal elements. Thus, the metal ions can freely move to the position with lower potential on the negative electrode plate, i.e., the position where lithium precipitation is easy to occur or has occurred, and form an electrostatic shield at this position, thereby uniformizing the current density on the negative electrode plate, inhibiting lithium precipitation, and reducing the side reaction during the cycling process of lithium ions. Thus, the cycling performance and coulombic efficiency of the lithium ion battery are improved.

[0053] Generally, a lithium ion battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. Next, the lithium ion battery provided by the present application and each part in the lithium ion battery will be introduced.

[0054] [Positive electrode sheet]

[0055] The present application first provides a positive electrode sheet, which includes a current collector and a positive film layer disposed on at least one side of the current collector.

[0056] It should be understood that the current collector in the positive electrode sheet is also called a positive current collector. As an example, the positive current collector has two opposite surfaces in the thickness direction of itself, and the positive film layer is disposed on any one or both of the two opposite surfaces of the positive current collector.

[0057] In one embodiment, the positive current collector can adopt a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be adopted. The composite current collector can 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 a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0058] In one embodiment, the positive film layer includes a positive active material layer disposed on the positive current collector; and the positive active material layer includes a metal salt.

[0059] Specifically, the metal salt can be introduced into the positive active material layer. For example, the positive active material and the metal salt can be mixed into a stable and uniform slurry in the process of preparing the positive active material layer, so as to introduce the metal salt into the positive film layer.

[0060] In one embodiment, the positive active material layer includes a positive active material; and the average volume particle size Dv50 of the particles of the metal salt is equal to the average volume particle size Dv50 of the positive active material.

[0061] It should be understood that "the average volume particle size Dv50 of the particles of the metal salt is equal to the average volume particle size Dv50 of the positive active material" can mean that the average volume particle size Dv50 of the particles of the metal salt is equal to the average volume particle size Dv50 of the positive active material, or that the average volume particle size Dv50 of the particles of the metal salt is close to the average volume particle size Dv50 of the positive active material. In the case where the average volume particle size Dv50 of the particles of the metal salt is close to the average volume particle size Dv50 of the positive active material, the absolute value of the difference between the average volume particle size of the particles of the metal salt and the average volume particle size of the positive active material is less than or equal to 2 μm.

[0062] When the positive electrode tab is applied to a lithium ion battery, the metal salt on the positive electrode tab will dissolve or partially dissolve in the electrolyte, and thus, the metal salt will leave pores in the positive active material layer. In this embodiment, by controlling the average volume particle size of the metal salt particles to be equal to or close to the average volume particle size of the positive active material, pores can be left in the positive active material layer, increasing the contact area between the positive active material and the electrolyte while reducing the risk of the pores being too large and the positive active material layer collapsing.

[0063] In one embodiment, the average volume particle size Dv50 of the particles of the metal salt satisfies: 0.05 μm≤Dv50≤70 μm; optionally, 0.5 μm≤Dv50≤60 μm.

[0064] Specifically, the average volume particle size Dv50 of the particles of the metal salt can be 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, or a value within a range obtained by combining any two of the above values.

[0065] In one embodiment, the mass content a of the metal salt satisfies: 1%≤a≤50%, in terms of the total mass of the positive active material layer; optionally, 5%≤a≤40%.

[0066] Specifically, a can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, or a value within a range obtained by combining any two of the above values.

[0067] On the one hand, if the content of the metal salt in the positive active material layer is too low, the amount of the metal salt that can dissolve in the electrolyte is limited, and thus, the inhibitory effect of the metal ions on lithium precipitation is limited. On the other hand, since the metal salt does not participate in the charge-discharge reaction of the lithium ion battery, a too high content of the metal salt in the positive active material layer will affect the energy density of the lithium ion battery.

[0068] In this embodiment, by controlling the mass content of the metal salt in the positive active material layer to be within a suitable range, the lithium precipitation can be inhibited while reducing the impact of the metal salt on the energy density of the lithium ion battery.

[0069] In one embodiment, the positive electrode film layer includes a positive electrode active material layer and a coating layer, the positive electrode active material layer is disposed on the positive electrode current collector, and the coating layer is disposed on the positive electrode active material layer; the coating layer includes the metal salt.

[0070] Specifically, in addition to the scheme of introducing the metal salt into the positive electrode active material layer, the metal salt can also be introduced into the coating layer of the positive electrode film layer. For example, after the positive electrode active material layer is prepared on the positive electrode current collector, a slurry containing the metal salt is coated on the positive electrode active material layer to form the coating layer. In this way, the metal salt is introduced into the positive electrode film layer.

[0071] In one embodiment, the thickness d of the coating layer satisfies: 0.05 μm≤d≤100 μm; optionally, 0.1 μm≤d≤50 μm.

[0072] Specifically, d can be 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, or a value within a range obtained by combining any two of the above values.

[0073] In one embodiment, the mass content b of the metal salt in the positive electrode film layer satisfies: 1%≤b≤40%; optionally, 5%≤b≤30%.

[0074] Specifically, b can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, or a value within a range obtained by combining any two of the above values.

[0075] In this embodiment, by controlling the thickness of the coating layer and the mass content of the metal salt in the positive electrode film layer within a suitable range, the lithium precipitation can be inhibited, and the influence of the metal salt on the energy density of the lithium ion battery can also be reduced.

[0076] In one embodiment, the metal salt includes at least one of a sodium salt, a potassium salt, a calcium salt, a magnesium salt, and a cesium salt.

[0077] In one embodiment, the metal salt comprises anions comprising one or more of fluorine element, phosphorus element, sulfur element, nitrogen element.

[0078] Specifically, after the metal salt is dissolved or partially dissolved in the electrolyte, free anions are also included in the electrolyte, and part of the free anions can participate in the formation of the SEI film. Therefore, by selecting anions comprising the above elements, it is beneficial to form a uniform and dense SEI film. In the case of lithium deposition on the negative electrode tab, a uniform and dense SEI film helps to induce uniform deposition of lithium ions, in other words, makes lithium deposition more uniform, thereby further inhibiting the formation or growth of lithium dendrites, and improving the cycle performance and coulombic efficiency of the lithium ion battery.

[0079] Illustratively, the anions comprising sulfur element means that the anions include but are not limited to sulfide ions, sulfate ions, sulfite ions, etc. In another example, the anions include acetate, fluorophosphate, nitrate, carbonate, bistrifluoromethylsulfonylimide, hexafluorophosphate.

[0080] In one embodiment, the solubility S of the metal salt in the electrolyte satisfies: S≥0.005 g / mL.

[0081] For example, S can be 0.005 g / mL, 0.01 g / mL, 0.05 g / mL, etc. a value greater than 0.005 g / mL.

[0082] The powder compaction density of the positive electrode film layer satisfies: p satisfies: 0.8 g / cm 3 ≤ p ≤ 4.0 g / cm 3 ; optionally, 1.0 g / cm 3 ≤ p ≤ 3.5 g / cm 3 .

[0083] Specifically, p can be 0.8 g / cm 3 , 0.85 g / cm 3 , 0.9 g / cm 3 , 0.95 g / cm 3 , 1.0 g / cm 3 , 1.1 g / cm 3 , 1.2 g / cm 3 , 1.3 g / cm 3 , 1.4 g / cm 3 , 1.5 g / cm 3 , 1.6 g / cm 3 , 1.7 g / cm 3 , 1.8 g / cm 3 , 1.9 g / cm 3 , 2.0 g / cm 3, 2.1 g / cm 3 , 2.2 g / cm 3 , 2.2 g / cm 3 , 2.3 g / cm 3 , 2.4 g / cm 3 , 2.5 g / cm 3 , 2.6 g / cm 3 , 2.7 g / cm 3 , 2.8 g / cm 3 , 2.9 g / cm 3 , 3.0 g / cm 3 , 3.1 g / cm 3 , 3.2 g / cm 3 , 3.3 g / cm 3 , 3.4 g / cm 3 , 3.5 g / cm 3 , 3.6 g / cm 3 , 3.7 g / cm 3 , 3.8 g / cm 3 , 3.9 g / cm 3 , 4.0 g / cm 3 , or a value within a range derived from any two of the above.

[0084] In one embodiment, the positive electrode active material can employ a positive electrode active material for a battery known in the art. As an example, the positive electrode active material can include at least one of a lithium-containing phosphate of olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material for a battery can also be used. These positive electrode active materials can be used alone only one or two or more can be used in combination. Among them, examples of the lithium transition metal oxide can include, but are not limited to, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(also referred to simply as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(also referred to simply as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2(also referred to simply as NCM211), LiNi 0.6 Co 0.2 Mn 0.2O2(also can be referred to as NCM622), lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.1 Mn 0.1 O2(also can be referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and modified compounds thereof. Examples of lithium-containing olivine-structured phosphates can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also can be referred to as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon. During the charging and discharging process of the battery, Li will be deintercalated and consumed, and the molar content of Li in the positive active material is different when the battery is discharged to different states. In the list of positive active materials in this application, the molar content of Li is the initial state of the material, i.e. the state before feeding, and the positive active material is applied to the battery system. After charging and discharging cycle, the molar content of Li will change. In the list of positive active materials in this application, the molar content of O is only the ideal state value, and the release of oxygen from the lattice will cause the molar content of O to change, and the actual molar content of O will fluctuate.

[0085] In one embodiment, the positive electrode film layer further includes a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0086] In one embodiment, the positive electrode film layer further includes a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0087] In one embodiment, the positive electrode sheet can be prepared by forming the above-mentioned components for preparing the positive electrode sheet into a positive electrode slurry, respectively. For example, the positive electrode active material, the conductive agent, the binder, and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry. Then, the positive electrode slurry is coated on the positive electrode current collector, and after processes such as drying and rolling, the positive electrode sheet is obtained.

[0088] [Negative electrode sheet]

[0089] The negative electrode sheet generally includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector.

[0090] As an example, the negative current collector has two surfaces opposite in the thickness direction thereof, and the negative film layer is disposed on either one or both of the two opposite surfaces of the negative current collector.

[0091] In one embodiment, the negative current collector can employ a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be employed. The composite current collector can 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 a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0092] In one embodiment, the negative active material can employ a negative active material for a battery known in the art. As an example, the negative active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can be selected from at least one of elemental tin, tin oxide compound, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative active material for a battery can also be used. These negative active materials can be used alone only one or in combination of two or more.

[0093] In one embodiment, the negative film layer further includes a binder. The binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0094] In one embodiment, the negative film layer further includes a conductive agent. The conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber.

[0095] In one embodiment, the negative active material layer further includes other auxiliary agents such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0096] In one embodiment, the negative electrode sheet can be prepared by forming the above-mentioned components for preparing the negative electrode sheet into a negative electrode slurry. For example, the negative electrode active material, the conductive agent, the binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a negative electrode slurry. The negative electrode slurry is then coated on the negative electrode current collector, and after processes such as drying and rolling, the negative electrode sheet is obtained.

[0097] [Electrolyte]

[0098] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The type of electrolyte is not particularly limited in the present application, and can be selected as needed. The electrolyte includes an electrolyte salt and a solvent.

[0099] In one embodiment, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro oxalato borate, lithium di oxalato borate, lithium difluoro di oxalato phosphate, and lithium tetrafluoro oxalato phosphate.

[0100] In one embodiment, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0101] In one embodiment, the electrolyte can further include an additive. The additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0102] [Separator]

[0103] In one embodiment, the battery further includes a separator. The type of separator is not particularly limited in the present application, and for example, any known porous structure separator film having good chemical stability and mechanical stability can be used.

[0104] In one embodiment, the material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0105] [Preparation method]

[0106] Next, the preparation method of the positive electrode tab in the foregoing embodiment is introduced.

[0107] The application also provides a method for preparing a positive electrode tab. Figure 1 A schematic flowchart of the method for preparing a positive electrode tab.

[0108] As shown in Figure 1 The method 100 includes:

[0109] S101, setting a positive electrode film layer on at least one side of the current collector to obtain a positive electrode tab.

[0110] The positive electrode film layer includes a metal salt, and the metal salt includes metal ions, and the difference between the reduction potential of the metal ions and the reduction potential of lithium ions is less than or equal to 0.8V.

[0111] It should be understood that the current collector mentioned in the method 100 is a positive electrode current collector.

[0112] Optionally, in S101, setting the positive electrode film layer on at least one side of the current collector includes: setting a positive electrode active material layer on at least one side of the current collector, the positive electrode active material layer including a metal salt.

[0113] Optionally, in S101, setting the positive electrode film layer on at least one side of the current collector includes: setting a positive electrode active material layer on at least one side of the current collector; and setting a coating layer on the positive electrode active material layer, the coating layer including a metal salt.

[0114] In other words, the positive electrode film layer including a metal salt can be that the positive electrode active material layer includes a metal salt, or that the coating layer on the positive electrode active material layer includes a metal salt.

[0115] Optionally, setting the positive electrode active material layer on at least one side of the current collector includes:

[0116] i) preparing a first slurry, the first slurry including a positive electrode active material and a metal salt.

[0117] ii) coating the first slurry on at least one side of the current collector.

[0118] iii) drying the first slurry to form a first coating layer on the separator film.

[0119] iv) rolling the current collector and the first coating layer to obtain a positive electrode tab.

[0120] Thus, in the positive electrode tab prepared by the above steps i)-iv), the positive electrode active material layer contains a metal salt.

[0121] Optionally, setting the positive electrode active material layer on at least one side of the current collector includes:

[0122] a) preparing a second slurry, the second slurry comprising a positive active material.

[0123] b) coating the second slurry on at least one side of the current collector.

[0124] c) drying the second slurry to form a positive active material layer on the separator film.

[0125] Optionally, the coating layer disposed on the positive active material layer comprises:

[0126] 1) preparing a third slurry, the third slurry comprising a metal salt.

[0127] 2) coating the third slurry on the positive active material layer.

[0128] 3) drying the third slurry to form a coating layer on the positive active material layer.

[0129] 4) roll-pressing the dried current collector, the positive active material layer and the coating layer to obtain a positive electrode sheet.

[0130] Thus, in the positive electrode sheet prepared by the above steps a)-c) and steps 1)-4), the positive active material layer contains the metal salt.

[0131] The present application also provides a lithium ion battery comprising the positive electrode sheet in any of the foregoing embodiments, and / or the positive electrode sheet prepared by the foregoing method 100.

[0132] In one embodiment, the lithium ion battery comprises an electrolyte, and the electrolyte comprises metal ions.

[0133] Specifically, after the foregoing positive electrode sheet is applied to the lithium ion battery, the metal salt will dissolve or partially dissolve in the electrolyte to form free metal ions, thereby causing the presence of metal ions in the electrolyte of the lithium ion battery.

[0134] In one embodiment, the weight content c of the metal ions satisfies: 0.02%≤c≤30%; optionally, 0.03%≤c≤6%, based on the total weight of the electrolyte.

[0135] Specifically, c can be 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, or a value within the range obtained by any two of the above values.

[0136] The application also provides a power utilization device, which comprises the lithium ion battery of any one of the foregoing embodiments.

[0137] In one embodiment, the negative electrode tab, the positive electrode tab, and the separator can be made into an electrode assembly through a rolling process or a stacking process.

[0138] In one embodiment, the battery cell can comprise an outer package. The outer package can be used to encapsulate the electrode assembly and the electrolyte as described above.

[0139] In one embodiment, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. can be listed.

[0140] The application does not have a particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, Figure 2 is a square structure battery cell 200 as an example.

[0141] It should be understood that the battery cell 200 can comprise the lithium ion battery of the foregoing embodiments.

[0142] Figure 3 is a battery module 300 as an example. Refer to Figure 3 In the battery module 300, a plurality of battery cells 200 can be arranged sequentially along the length direction of the battery module 300. Of course, they can also be arranged in any other manner. Further, the plurality of battery cells 200 can be fixed by fasteners. The plurality of battery cells 200 can be battery cells 200 of the same chemical system, or battery cells 200 of different chemical systems.

[0143] Optionally, in one embodiment, the battery module 300 can further comprise a housing having an accommodation space, and the plurality of battery cells 200 are accommodated in the accommodation space.

[0144] Optionally, in one embodiment, the battery module 300 as described above can also be assembled into a battery, and the number of battery modules 300 contained in the battery can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery.

[0145] Figure 4 and Figure 5 is a battery 400 as an example. Refer to Figure 4 and Figure 5In the battery 400, a battery case and a plurality of battery modules 300 disposed in the battery case can be included. The battery case includes an upper case 401 and a lower case 402, and the upper case 401 can be disposed on the lower case 402 to form an enclosed space for accommodating the battery modules 300. The plurality of battery modules 300 can be arranged in the battery case in any manner.

[0146] It should be understood that in other embodiments, the above-described battery 400 is also referred to as a battery pack. The battery cells 200 can be first assembled into the battery modules 300, and the battery 400 is assembled from the battery modules 300. The battery 400 can also be directly assembled from the battery cells 200, and the intermediate form of the battery module 300 is omitted.

[0147] In addition, the present application also provides a power utilization device, which includes the lithium ion battery in the foregoing embodiments.

[0148] In another embodiment, the power utilization device includes at least one of the battery cell 200, the battery module 300, or the battery 400 provided by the present application. The battery cell 200, the battery module 300, or the battery 400 can be used as a power supply of the power utilization device, or can be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device (such as a mobile phone, a notebook computer, 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, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0149] As the power utilization device, the battery cell 200, the battery module 300, or the battery 400 can be selected according to the use requirements thereof.

[0150] As an example of the power utilization device. The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of high power and high energy density of the secondary battery for the power utilization device, a battery pack or a battery module can be used.

[0151] As another example of the device can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and a secondary battery can be used as a power supply.

[0152] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. If the specific technology or condition is not indicated in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument used is not indicated by the manufacturer, it is a conventional product that can be obtained by market purchase.

[0153] [Examples 1-23 and Comparative Examples 1-2]

[0154] Example 1

[0155] (1) Preparation of the negative electrode tab

[0156] 1 kg of negative electrode active material artificial graphite, 10 g of conductive agent acetylene black, 30 g of binder styrene-butadiene rubber (SBR), and 20 g of thickening agent sodium carboxymethyl cellulose (CMC) were dissolved in 1 kg of deionized water to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on a negative electrode current collector copper foil. After rolling and slitting, a negative electrode tab was obtained.

[0157] (2) Preparation of the positive electrode tab

[0158] 1 kg of positive electrode active material LiNi5Co2Mn3O2, 20 g of metal salt potassium nitrate, 20 g of conductive agent carbon nanotube, and 20 g of binder polyvinylidene fluoride (PVDF) were dissolved in 1 kg of N-methyl pyrrolidone to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on a positive electrode current collector aluminum foil. After drying in an oven at 80°C, a positive electrode active material layer was obtained. After rolling and slitting, a positive electrode tab was obtained.

[0159] (3) Preparation of the lithium ion battery

[0160] The above-mentioned positive electrode tab, negative electrode tab, separator, and negative electrode tab were stacked in order, so that the separator was between the positive electrode tab and the negative electrode tab and could separate the positive electrode tab and the negative electrode tab. Then, the stacked components were wound and placed in a shell. After drying, a lithium ion battery was obtained by injecting a lithium hexafluorophosphate (LiPF6) electrolyte with a concentration of 1 mol / L and packaging.

[0161] In Example 1, the positive electrode active material layer includes a metal salt, the metal salt is potassium nitrate, the metal ion is potassium ion, the difference between the reduction potential of the metal ion and the reduction potential of lithium ion is 0.332 V, the thickness of the positive electrode active material layer is 65 μm, the average volume particle size Dv50 of the metal salt particles is 5 μm, the solubility S of the metal salt in the electrolyte is 0.032 g / mL, the mass content a of the metal salt in the positive electrode active material layer is 20%, the powder compaction density p of the positive electrode film layer is 2.8, and the mass content c of the metal ion in the electrolyte is 2.7%.

[0162] To verify the inhibitory effect of the positive electrode tab provided by the present application on lithium precipitation and lithium dendrite growth, the CB value of the lithium ion battery can be designed to be less than 1. Specifically, in Example 1, the CB value of the lithium ion battery is 0.95.

[0163] Example 2

[0164] Compared to example 1, the metal salt is magnesium nitrate, the metal ion is magnesium ion, the difference between the reduction potential of the metal ion and the reduction potential of lithium ion is 0.672 V, Dv50 = 5 pm, S = 0.054 g / mL, c = 4.7%.

[0165] Example 3

[0166] Compared to example 1, in the spacer of example 3, the metal salt is potassium nitrate and magnesium nitrate, the metal ion is potassium ion and magnesium ion, the difference between the reduction potential of the metal ion and the reduction potential of lithium ion is 0.332 V and 0.672 V respectively, S = 0.047 g / mL, Dv50 = 5 pm, c = 1.8% and 4.2%.

[0167] Example 4

[0168] Compared to example 1, in example 4, the metal salt is potassium hexafluorophosphate, Dv50 = 5 pm, S = 0.035 g / mL, c = 2.9%.

[0169] Example 5

[0170] Compared to example 1, in example 5, the metal salt is barium sulfate, the difference between the reduction potential of the metal ion and the reduction potential of lithium ion is 0.142 V, S = 0.005 g / mL, Dv50 = 5 pm, c = 0.41%.

[0171] Example 6

[0172] Compared to example 1, in example 6, the average volume particle size Dv50 of the metal salt particles is 0.05 pm.

[0173] Example 7

[0174] Compared to example 1, in example 7, the average volume particle size Dv50 of the metal salt particles is 70 pm.

[0175] Example 8

[0176] Compared to example 1, in example 8, a = 1%, c = 0.02%.

[0177] Example 9

[0178] Compared to example 1, in example 9, a = 50%, c = 3.2%.

[0179] Example 10

[0180] Compared with Example 1, in Example 10, the preparation process of the positive electrode plate is as follows: the positive electrode active material LiNi5Co2Mn3O2 1 kg, the conductive agent carbon nanotube 20 g, and the binder polyvinylidene fluoride (PVDF) 20 g are dissolved in 1 kg of N-methyl pyrrolidone to obtain a positive electrode slurry. Then the positive electrode slurry is uniformly coated on the positive electrode current collector aluminum foil. After drying in an oven at 80°C, a positive electrode active material layer is obtained. The metal salt potassium nitrate 20 g, PVDF 2 g, and 20 g of N-methyl pyrrolidone are mixed and stirred into a slurry, which is then coated on the positive electrode active material layer, and then rolled and cut to obtain the positive electrode plate.

[0181] In other words, in Example 10, the coating layer includes a metal salt, the thickness of the coating layer d = 0.05 μm, the thickness of the positive electrode active material layer is 65 μm, the mass content of the metal salt in the positive electrode film layer b = 1%, and c = 0.02%.

[0182] Example 11

[0183] Compared with Example 10, in Example 11, d = 0.1 μm, and c = 0.04%.

[0184] Example 12

[0185] Compared with Example 10, in Example 12, d = 50 μm, and c = 3.2%.

[0186] Example 13

[0187] Compared with Example 10, in Example 13, d = 100 μm, and c = 3.2%.

[0188] Example 14

[0189] Compared with Example 10, in Example 14, b = 5%, and c = 0.09%.

[0190] Example 15

[0191] Compared with Example 10, in Example 15, b = 30%, and c = 2.9%.

[0192] Example 16

[0193] Compared with Example 1, in Example 16, p = 0.8 g / cm 3 , and c = 2.76%.

[0194] Example 17

[0195] Compared with Example 1, in Example 17, p = 1.0 g / cm 3 , and c = 2.73%.

[0196] Example 18

[0197] In Example 18, ρ = 3.5 g / cm 3 , c = 2.64%.

[0198] Example 19

[0199] In Example 19, ρ = 4.0 g / cm 3 , c = 2.63%.

[0200] Example 20

[0201] In Example 20, a = 1%, c = 0.02%.

[0202] Example 21

[0203] In Example 21, a = 1.5%, c = 0.03%.

[0204] Example 22

[0205] In Example 22, the metal salt is sodium hexafluorophosphate, a = 10%, c = 6%.

[0206] Example 23

[0207] In Example 23, the metal salt is sodium bisfluorosulfonylimide, a = 40%, c = 30%.

[0208] Comparative Example 1

[0209] In Comparative Example 1, the positive electrode film layer does not contain a metal salt.

[0210] Comparative Example 2

[0211] In Comparative Example 2, the metal salt is manganese nitrate, the metal ion is manganese ion, and the difference between the reduction potential of the metal ion and the reduction potential of lithium ion is 1.86 V.

[0212] The product parameters of Examples 1-23 and Comparative Examples 1-2 are shown in Table 1.

[0213] Table 1: Product parameters of Examples 1-23 and Comparative Examples 1-2

[0214]

[0215]

[0216]

[0217] In Table 1, S represents the solubility of the metal salt in the electrolyte; Dv50 represents the average volume particle size of the metal salt particles; p represents the powder compaction density of the positive electrode film layer; d represents the thickness of the coating layer; a represents the mass content of the metal salt based on the total mass of the positive electrode active material layer; b represents the mass content of the metal salt based on the total mass of the positive electrode film layer; and c represents the mass content of the metal ion based on the total mass of the electrolyte.

[0218] The performance test results of the products of Examples 1-23 and Comparative Examples 1-2 are shown in Table 2.

[0219] Table 2: Performance data of Examples 1-23 and Comparative Examples 1-2

[0220]

[0221]

[0222] In Table 2, the "cycle number" represents the cycle number of the lithium ion battery when the SOH is less than or equal to 80%. "Whether lithium dendrites appear" represents whether obvious dendritic lithium precipitation appears on the negative electrode sheet obtained after the lithium ion battery is disassembled after the cycle is completed.

[0223] From the comparative analysis of Examples 1-23 and Comparative Examples 1-2, it can be seen that by introducing metal ions with a reduction potential difference of less than or equal to 0.8 V with respect to the reduction potential of lithium ions into the positive electrode sheet, the precipitation of lithium and the growth of lithium dendrites on the negative electrode sheet can be effectively inhibited, thereby improving the cycle performance and average coulomb efficiency of the lithium ion battery.

[0224] From the comparative analysis of Examples 1-4, it can be seen that the metal salt introduced into the positive electrode sheet can be potassium nitrate, magnesium nitrate, potassium nitrate and magnesium nitrate, and magnesium hexafluorophosphate, all of which can help improve the cycle performance and average coulomb efficiency of the lithium ion battery. Among them, in Example 4, the use of a metal salt containing fluorine helps the lithium ion battery to form a uniform and dense SEI film, thereby further improving the cycle performance and average coulomb efficiency of the lithium ion battery.

[0225] From the comparative analysis of Examples 8-9, it can be seen that the performance of Example 8 with a lower content of metal salt in the positive electrode active material layer is significantly inferior to that of Example 9 with a higher content of metal salt in the positive electrode active material layer, indicating that the higher the mass content of the metal salt in the positive electrode active material layer, the higher the content of metal ions in the electrolyte, and the better the inhibition of lithium precipitation and lithium dendrites. In addition, since the metal salt does not participate in the charge and discharge reaction of the lithium ion battery and does not contribute to the capacity, the mass content of the metal salt in the positive electrode active material layer cannot be increased indefinitely. Therefore, by controlling the mass content of the metal salt in the positive electrode active material layer within a suitable range, the precipitation of lithium can be effectively inhibited while reducing the impact of the metal salt on the energy density of the lithium ion battery.

[0226] Through comparative analysis of Examples 10-15, it can be seen that by providing a coating layer on the positive active material layer, metal salt can also be introduced into the positive electrode tab, thereby improving the lithium ion cycle performance. Under the same conditions, as the thickness of the coating layer increases, the mass content of the metal salt in the positive electrode tab increases, and the inhibition of lithium precipitation and lithium dendrite growth is enhanced.

[0227] The test methods of the physicochemical parameters and performance parameters involved in the examples of the present application are briefly introduced below. It should be understood that the following test methods are only examples, and other test methods known in the art can also be used for testing.

[0228] 1. Test method of reduction potential

[0229] Dissolve the test substance in a suitable solvent, then use a reference electrode (such as a standard hydrogen electrode) and a working electrode (such as a glassy carbon electrode) to form a battery, and test the cyclic voltammogram under different conditions (such as pH value, temperature, etc.). The reduction peak potential of the test substance is read to obtain the reduction potential of the test substance.

[0230] 2. Test method of solubility of metal salt in electrolyte

[0231] Dissolve the metal salt in 100 mL of lithium hexafluorophosphate electrolyte with a concentration of 1 mol / L until crystals are precipitated. Calculate the total amount of metal salt added m, and measure the total volume of the solution V at this time. The solubility S can be calculated by the following formula: S = m / V.

[0232] 3. Test method of average volume particle size

[0233] Laser particle size analyzer method: Laser particle size analyzer uses the principle of laser scattering to determine the particle size by measuring the scattering intensity of particles in the substance.

[0234] Exemplarily, the average volume particle size of the metal salt particles involved in the present application can be tested by ion beam polishing (CP) combined with scanning electron microscopy (SEM): after disassembling the lithium ion battery, the positive electrode tab is cleaned with a reagent same as the solvent of the electrolyte and dried. The dried positive electrode tab is ion beam polished and the inner diameter of the cavity (metal salt completely dissolved) or half-cavity (metal salt not completely dissolved) on the cross-section of the tab is observed by SEM. The average value of the inner diameters is repeatedly measured, which is approximately the average volume particle size Dv50 of the metal salt particles.

[0235] 4. Test method of powder compaction density

[0236] After disassembling the lithium ion battery, measure the total area P of the positive electrode sheet, cut a certain area P1 of the positive electrode sheet and weigh m1, and measure the thickness h1; after washing off the positive electrode film layer, weigh m2 and measure the thickness h2. Test the metal salt content in the electrolyte by ICP, and obtain the mass m3 of the metal salt dissolved on the positive electrode sheet with area d P1 through the proportional relationship of P and P1. The compaction density is (m1+m3-m2) / (P1x(h1-h2)).

[0237] 5. Test method of mass content

[0238] After disassembling the lithium ion battery, weigh the total mass m3 of the positive electrode sheet, scrape the positive electrode film layer on the surface of the positive electrode sheet, and test the mass m4 of the metal salt in the positive electrode film layer and the mass m5 of the metal salt in the electrolyte by ICP, and weigh the mass m6 of the remaining positive electrode sheet. The mass content of the metal salt is (m4+m5) / (m3+m5-m6).

[0239] 6. Test method of cycle number of lithium ion battery

[0240] After the lithium ion battery is subjected to formation aging, it is subjected to full charge and full discharge cycles at a current of 0.33C, and the cycle number of the battery when the SOH of the battery reaches 80% is counted.

[0241] 7. Test method of average coulomb efficiency of lithium ion battery

[0242] Divide the discharge capacity of each cycle in the lithium ion battery cycle charging and discharging process by the charging capacity to obtain the coulomb efficiency of each cycle, then add the coulomb efficiency of each cycle and divide by the number of cycles to obtain the average coulomb efficiency.

[0243] 8. Test method of whether lithium dendrites appear

[0244] After the lithium ion battery is cycled, it is disassembled to obtain the cycled negative electrode sheet, and whether dendrites appear on the negative electrode sheet can be directly observed.

[0245] Although the present application has been described with reference to the preferred embodiments, various modifications can be made to it without departing from the scope of the application, and equivalent parts can be substituted for the parts thereof. In particular, the technical features mentioned in each embodiment can be combined in any way as long as there is no structural conflict. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A positive electrode sheet, characterized by, The positive electrode plate comprises: a current collector and a positive electrode film layer arranged on at least one side of the current collector; the positive electrode film layer comprises a metal salt, the metal salt comprises metal ions, the reduction potential of the metal ions is greater than the reduction potential of lithium ions, and the difference between the reduction potential of the metal ions and the reduction potential of the lithium ions is less than or equal to 0.8 V; the metal salt comprises one or more of a sodium salt, a potassium salt, a calcium salt, a magnesium salt, and a cesium salt; the metal salt comprises anions, the anions comprise one or more of fluorine elements, phosphorus elements, sulfur elements, and nitrogen elements; the solubility S of the metal salt in the electrolyte satisfies: S≥0.005 g / mL.

2. The cathode electrode of claim 1, wherein, The positive electrode film layer comprises a positive electrode active material layer arranged on the current collector; the positive electrode active material layer comprises the metal salt.

3. The cathode electrode of claim 2, wherein, The positive electrode active material layer comprises a positive electrode active material; the average volume particle size Dv50 of the particles of the metal salt is equal to the average volume particle size Dv50 of the positive electrode active material.

4. The cathode electrode of claim 1, wherein The average volume particle size Dv50 of the particles of the metal salt satisfies: 0.05 μm≤Dv50≤70 μm.

5. The cathode electrode of claim 4, wherein, 0.5μm≤Dv50≤60 μm.

6. The cathode electrode of claim 2, wherein, The mass content a of the metal salt satisfies: 1%≤a≤50% based on the total mass of the positive electrode active material layer.

7. The cathode electrode of claim 6, wherein, 5%≤a≤40%。 8. The cathode sheet of claim 1, wherein, The positive electrode film layer comprises a positive electrode active material layer arranged on the current collector and a coating layer arranged on the positive electrode active material layer; the coating layer comprises the metal salt.

9. The cathode electrode plate of claim 8, wherein, The thickness d of the coating layer satisfies: 0.05μm≤d≤100 μm.

10. The cathode electrode of claim 9, wherein, 0.1 μm≤d≤50 μm.

11. The cathode electrode of claim 8, wherein, The mass content b of the metal salt satisfies: 1%≤b≤40% based on the total mass of the positive electrode film layer.

12. The cathode electrode of claim 11, wherein, 5%≤b≤30%。 13. The cathode sheet of any one of claims 1-12, wherein, The powder compaction density p of the positive electrode film layer satisfies: 0.8 g / cm 3 ≤ p ≤ 4.0 g / cm 3 .

14. The cathode electrode of claim 13, wherein, 1.0 g / cm 3 ≤ p ≤ 3.5 g / cm 3 .

15. A lithium-ion battery, characterized by, The lithium ion battery comprises the positive electrode plate according to any one of claims 1-14.

16. The lithium-ion battery of claim 15, wherein, The lithium ion battery comprises an electrolyte, and the electrolyte comprises the metal ions.

17. The lithium-ion battery of claim 16, wherein, The weight content c of the metal ions satisfies: 0.02%≤b≤30% based on the total weight of the electrolyte.

18. The lithium-ion battery of claim 17, wherein, 0.03%≤b≤6%。 19. An electrical device, comprising: The electric device comprises the lithium ion battery according to any one of claims 15-18.

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