Lithium ion secondary battery and electric equipment

Abstract

The invention relates to the technical field of batteries, in particular to a lithium ion secondary battery and electric equipment, and the lithium ion secondary battery comprises a positive pole piece, a negative pole piece and an electrolyte; the positive pole piece comprises a positive active material layer, the positive active material layer comprises a positive material, the positive material at least comprises a first positive active material and a second positive active material, and the charging cut-off voltage of the first positive active material is greater than that of the second positive active material; the lithium ion secondary battery further comprises additives, the additives comprise a first additive, the first additive comprises salt containing metal cations, the metal cations comprise one or a combination of more than two of alkali metal ions, alkaline earth metal ions and amphoteric metal ions, and the alkali metal ions comprise Na < + > and / or K < + >. When the charging cut-off voltage is relatively high, metal cations can be embedded into low reversible sites, so that the structural stability of the material can be enhanced, and the cycle and rate performance of the battery can be further improved.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to lithium-ion secondary batteries and electrical equipment. Background Technology

[0002] With the rapid development of electric vehicles, energy storage power stations, and other fields, developing high-energy-density lithium-ion batteries has become a top priority in the new energy sector. Increasing the charging cut-off voltage of cathode materials is one of the most effective methods to improve their energy density. Currently, at higher charging cut-off voltages, the cycle performance and rate performance of lithium-ion secondary batteries are poor. Therefore, how to improve the stability of the cathode material structure at high charging cut-off voltages, thereby improving the cycle performance and rate performance of lithium-ion batteries, remains a problem to be solved. Summary of the Invention

[0003] In view of this, the lithium-ion secondary battery and electrical equipment provided in this application can improve the stability of the positive electrode material structure under high charging cutoff voltage, thereby improving the cycle performance and rate performance of the lithium-ion battery.

[0004] The first aspect of this application provides a lithium-ion secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte; the positive electrode includes a positive active material layer, the positive active material layer includes a positive electrode material, the positive electrode material includes at least a first positive active material and a second positive active material, the charging cut-off voltage of the first positive active material is greater than the charging cut-off voltage of the second positive active material; the lithium-ion secondary battery further includes an additive, the additive including a first additive, the first additive including a salt containing a metal cation, the metal cation including one or more combinations of alkali metal ions, alkaline earth metal ions, and amphoteric metal ions, the alkali metal ions including Na + and / or K + .

[0005] In the technical solution of this application embodiment, when the second positive electrode active material with a high charging cutoff voltage and a low charging cutoff voltage in the mixed system undergoes lithium-ion over-intercalation / deintercalation, metal cations such as alkali metal ions, alkaline earth metal ions, and amphoteric metal ions can utilize entropy increase and trickle-flow to be directionally induced to intercalate into the low reversible sites formed by the lithium-ion over-intercalation / deintercalation. On the one hand, after the metal cations intercalate into the low reversible sites formed by the lithium-ion over-intercalation / deintercalation, they will not be extracted again. Therefore, the structural stability of the material can be enhanced, thereby improving the cycle performance and rate performance of the lithium-ion secondary battery. On the other hand, the intercalation of metal cations into the low reversible sites will not cause a capacity reduction problem in the lithium-ion secondary battery. The channel structure extended by these metal cations is also beneficial to improving the kinetic characteristics of the electrode, and the rate performance of the lithium-ion secondary battery is also enhanced. In addition, Na + K+ The radius of Li + The radius is large, Na + K + The expanded channels are more conducive to improving the kinetic performance of the electrodes, which in turn is more beneficial to improving the rate performance of lithium-ion secondary batteries. At the same time, Na and K are abundant and evenly distributed on Earth, thus reducing the cost of use.

[0006] In any embodiment, the alkaline earth metal ions include Mg 2+ Ca 2+ One or two of them. Mg 2+ Ca 2+ Low reversible sites embedded in cathode materials can not only improve the cycle performance and rate performance of lithium-ion secondary batteries, but also enhance their cycle stability and capacity retention. This is especially true under high charge cutoff voltage and long charge-discharge conditions, where Mg... 2+ Ca 2+ The doped positive electrode active material exhibits better cycle stability and capacity retention during charge and discharge processes. Additionally, Mg doping... 2+ Ca 2+ The resulting positive electrode active material also has high crystallinity and good electrochemical activity, which helps to improve the energy density and lifespan of lithium-ion secondary batteries.

[0007] In any embodiment, the amphoteric metal ion includes Zn. 2+ Al 3+ One or two of them. Zn 2+ Al 3+ Low reversible sites embedded in positive electrode active materials can not only improve the cycle performance and rate performance of lithium-ion secondary batteries, but also enhance the overall performance and lifespan of lithium-ion secondary batteries.

[0008] In any embodiment, the difference between the charging cutoff voltage of the first positive electrode active material and the second positive electrode active material is greater than or equal to 0.1V and less than or equal to 1.5V. When the difference in charging cutoff voltage is greater than 0.1V, the first positive electrode active material and the second positive electrode active material have a large potential difference. Under a high charging cutoff voltage, metal cations are directionally induced to insert into low reversible sites by trickle-flow.

[0009] In any embodiment, the first positive electrode active material includes one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-rich manganese-based materials; the second positive electrode active material includes one or two of lithium manganese iron phosphate and lithium iron phosphate. Lithium-rich manganese-based materials, with their high specific capacity and high charging cut-off voltage characteristics, have become an effective means to improve the energy density of lithium-ion secondary batteries. However, lithium-rich manganese-based materials suffer from voltage decay and deterioration in cycle and rate performance during long-term use. These problems can be effectively solved by doping the lithium-rich manganese-based material with one or more of ternary materials (lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide), lithium manganese iron phosphate, and lithium iron phosphate. The capacity advantage of lithium-rich manganese-based materials can only be realized at voltages above 4.5V; however, the charging cutoff voltage of lithium nickel cobalt manganese oxide does not exceed 4.35V, that of lithium nickel cobalt aluminum oxide does not exceed 4.3V, and that of lithium manganese iron phosphate and lithium iron phosphate does not exceed 4.15V. Excessively high charging cutoff voltages can lead to overcharging problems in ternary materials (lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide), lithium manganese iron phosphate, and lithium iron phosphate. In this application, this problem is solved by adding a salt containing metal cations. At high charging cutoff voltages, the low reversible sites formed by lithium-ion intercalation and deintercalation facilitate the intercalation of metal cations. During cycling at high charging cutoff voltages, metal cations can effectively and spontaneously intercalate into these low reversible sites, which helps stabilize the electrode structure in subsequent cycles and also limits the surface valence state of Mn in lithium manganese iron phosphate, thereby reducing the occurrence of side reactions.

[0010] In any embodiment, the additive is disposed in the electrolyte. The process of disposing of the additive in the electrolyte is simple, and the amount of additive is easy to control.

[0011] In any embodiment, the electrolyte further includes a second additive, the second additive comprising Li + The valence state of the metal cation is x, based on the Li in the electrolyte. +The molar amount of the metal cation is (0.1 / x)% to (2 / x)%. In this embodiment, an additive is introduced into the electrolyte. The metal cation in the additive can spontaneously and uniformly embed into the structure of the positive electrode active material. It can effectively stabilize the crystal structure of the positive electrode active material and reduce the occurrence of side reactions. It can effectively reduce the risk of overcharging of the second positive electrode active material under high charging cutoff voltage, thereby improving the cycle performance and rate performance of the lithium-ion secondary battery. In this embodiment, when the molar percentage of the metal cation is within the above range, the metal cation mainly occupies low reversible sites through diffusion. In this state, the metal cation also expands and stabilizes the lithium-ion transport channel, thereby enhancing the kinetic performance of the lithium-ion secondary battery and increasing the capacity of the lithium-ion secondary battery. The capacity increase caused by the expansion and stabilization of the lithium-ion transport channel by the metal cation is equal to the capacity loss caused by the metal cation occupying the active lithium sites. At the same time, when the molar percentage of the metal cation is within the above range, the lattice distortion caused by metal cation doping is small.

[0012] In any embodiment, the first additive is disposed in the positive electrode active material layer, and the first additive is attached to and / or coated on the first type of positive electrode active material. Disposing of the first additive on the first type of positive electrode active material is more conducive to the insertion of metal cations into low reversible sites, thereby improving the cycle performance and rate performance of the lithium-ion secondary battery.

[0013] In any embodiment, the first additive is disposed in the positive electrode active material layer, and the first additive is attached to or / and coated on the second positive electrode active material. Similarly, disposing of the first additive on the second positive electrode active material is more conducive to the insertion of metal cations into low reversible sites, thereby improving the cycle performance and rate performance of the lithium-ion secondary battery.

[0014] In any embodiment, the positive electrode sheet includes a positive current collector and an additive layer, wherein the additive layer is disposed on the surface of the positive active material layer opposite to the positive current collector; the first additive is disposed in the additive layer. Disposing of the first additive in the additive layer facilitates control of the additive dosage and simplifies the process.

[0015] In any embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, and the first additive is disposed in the negative electrode active material layer, wherein the first additive is soluble in the electrolyte. By disposing of the first additive in the negative electrode active material layer, the metal cations in the first additive diffusely intercalate into the low reversible sites in the positive electrode material, which not only improves the cycle performance and rate performance of the lithium-ion secondary battery, but also protects the negative electrode sheet, reduces the occurrence of side reactions, and thus improves the stability of the lithium-ion secondary battery.

[0016] In any embodiment, the first additive is disposed on the surface of the negative electrode active material layer opposite to the negative electrode current collector; wherein, the first additive is soluble in the electrolyte. Disposing of the first additive on the surface of the negative electrode active material layer opposite to the negative electrode current collector facilitates control of the additive dosage and simplifies the process.

[0017] In any embodiment, based on the total mass of the first positive electrode active material and the second positive electrode active material, the mass percentage of the first additive is 0.1% to 2%. When the mass percentage of the first additive is within the above range, the metal cations in the first additive mainly occupy low reversible sites through diffusion. In this state, the metal cations also expand and stabilize the lithium-ion transport channels, thereby enhancing the kinetic performance of the lithium-ion secondary battery and increasing its capacity. The capacity increase caused by the expansion and stabilization of lithium-ion transport channels by the metal cations is equal to the capacity loss caused by the metal cations occupying active lithium sites. Simultaneously, when the molar percentage of the metal cations is within the above range, the lattice distortion caused by metal cation doping is relatively small.

[0018] In any embodiment, the anion of the first additive includes PF6. - PO4 3- ClO4 - CO3 2- One or more combinations of PF6. - It has very high solubility, making it particularly suitable for electrolyte systems requiring high solubility. PO4 3- The performance of lithium-ion secondary batteries can be significantly improved by reducing the impedance of the battery, especially at low temperatures, thus solving the problem of lithium plating during charging with conventional additives at low temperatures. ClO4 - Adding CO3 to the electrolyte can give it better ion migration properties, enabling faster ion transport and thus improving the charge / discharge speed and efficiency of lithium-ion secondary batteries. 2- It can enhance the stability of the electrolyte, thereby extending the lifespan of lithium-ion secondary batteries.

[0019] A second aspect of this application provides an electrical device that includes the lithium-ion secondary battery of the first aspect of this application. In embodiments of this application, the electrical device possesses at least the same advantages as the lithium-ion secondary battery of the first aspect.

[0020] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Attached Figure Description

[0021] Figure 1 This is a structural schematic diagram of a vehicle according to one embodiment of this application.

[0022] Figure 2 This is an exploded structural diagram of a battery according to one embodiment of this application.

[0023] Figure 3 This is an exploded structural diagram of a battery cell according to one embodiment of this application.

[0024] Figure 4 These are X-ray photoelectron spectra of the positive electrode active material, the positive electrode active material after low-pressure cycling, and the positive electrode active material after high-pressure cycling in the lithium-ion secondary battery of Example 1 of this application.

[0025] Figure 5 This is a comparison curve of the cycle capacity retention rate of the lithium-ion secondary batteries prepared in Example 1 and Comparative Example 1 of this application.

[0026] Figure 6 This is a comparison curve of the rate capacity retention of the lithium-ion secondary batteries prepared in Example 1 and Comparative Example 1 of this application. Detailed Implementation

[0027] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the lithium-ion secondary battery and electrical device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0028] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0029] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0030] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0031] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0032] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0033] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0034] In hybrid systems composed of various cathode active materials with different charging cutoff voltages, the system voltage typically depends on the cathode active material with the lower charging cutoff voltage. Taking a hybrid cathode material system consisting of ternary materials, lithium manganese iron phosphate (LFP), and lithium-rich manganese-based materials as an example, at higher charging cutoff voltages, LFP is prone to side reactions. Furthermore, if a higher charging cutoff voltage is used in the hybrid system, the internal circulating current will cause LFP to maintain a consistently high voltage state, severely degrading its cycle performance. Simultaneously, lithium-ion over-intercalation / deintercalation can lead to localized structural collapse in ternary materials. Most solutions address this by lowering the upper limit of the hybrid system's operating voltage to mitigate the over-intercalation / deintercalation and side reactions of the cathode active material with the lower charging cutoff voltage. However, for systems containing lithium-rich manganese-based materials, their high capacity advantage is only realized within a charging cutoff voltage range above 4.5V. Lowering the charging cutoff voltage would severely limit the advantages of hybrid systems containing lithium-rich manganese-based materials. Alternatively, doping the cathode active material can improve its structural stability at high charging cutoff voltages. However, doping significantly increases the manufacturing cost and makes it difficult to control the uniformity of doping, which can easily lead to problems such as reduced capacity and poor cycle life of lithium-ion secondary batteries.

[0035] Based on this, the first aspect of this application provides a lithium-ion secondary battery, including a positive electrode, a negative electrode, and an electrolyte; the positive electrode includes a positive active material layer, the positive active material layer includes a positive electrode material, the positive electrode material includes at least a first positive active material and a second positive active material, the charging cut-off voltage of the first positive active material is greater than the charging cut-off voltage of the second positive active material; the lithium-ion secondary battery further includes an additive, the additive including a first additive, the first additive including a salt containing a metal cation, the metal cation including one or more combinations of alkali metal ions, alkaline earth metal ions, and amphoteric metal ions, the alkali metal ions including Na + and / or K + .

[0036] In the technical solution of this application embodiment, when the second positive electrode active material with a high charging cutoff voltage and a low charging cutoff voltage in the mixed system undergoes lithium-ion over-intercalation / deintercalation, metal cations such as alkali metal ions, alkaline earth metal ions, and amphoteric metal ions can utilize entropy increase and trickle-flow to be directionally induced to intercalate into the low reversible sites formed by the lithium-ion over-intercalation / deintercalation. On the one hand, after the metal cations intercalate into the low reversible sites formed by the lithium-ion over-intercalation / deintercalation, they will not be extracted again. Therefore, the structural stability of the material can be enhanced, thereby improving the cycle performance and rate performance of the lithium-ion secondary battery. On the other hand, the intercalation of metal cations into the low reversible sites will not lead to a reduction in the capacity of the lithium-ion secondary battery. The channel structure extended by these metal cations is also beneficial to improving the kinetic characteristics of the electrode, and the rate performance of the lithium-ion secondary battery is also enhanced. In addition, Na + K + The radius of Li + The radius is large, Na + K + The expanded channels are more conducive to improving the kinetic performance of the electrodes, which in turn is more conducive to improving the rate performance of lithium-ion secondary batteries. At the same time, Na and K are abundant and evenly distributed on Earth, thus reducing the cost of use.

[0037] Among them, amphoteric metal ions refer to metal ions that can react with both acids and bases.

[0038] The charging cutoff voltage refers to the charging voltage corresponding to the maximum charging capacity of the battery material.

[0039] In a hybrid system, positive electrode active materials with higher charging cut-off voltages can achieve greater capacity, thus having more sites to accommodate active ions, resulting in lower charging resistance and, at the same charging cut-off voltage, higher current. Conversely, positive electrode active materials with lower charging cut-off voltages have lower capacity, higher charging resistance, and lower current. Therefore, positive electrode active materials with different charging cut-off voltages exhibit different current distribution ratios, leading to the induced insertion of metal cations into low-reversibility sites formed by excessive lithium ion intercalation / deintercalation in positive electrode active materials with lower charging cut-off voltages.

[0040] It's important to note that excessive lithium-ion insertion / extraction increases the degree of ion arrangement order; this process is entropy reduction, and the system is in a high-energy state. Conversely, when metal cations insert into low-reversibility sites, the ion arrangement order decreases; this process is entropy increase, and the system energy decreases, resulting in a more stable system state.

[0041] It is worth noting that in a pure system (where the cathode material contains only one type of cathode active material), metal cations can only intercalate into active lithium sites. These cations replace the active lithium sites, leading to a decrease in the capacity of the lithium-ion secondary battery. Furthermore, the small amount of metal cation intercalation has a very limited effect on improving the stability of the cathode active material. However, the metal cations in this application can intercalate extensively into low-reversibility sites, preventing a decrease in the capacity of the lithium-ion secondary battery. Additionally, if metal cations are intercalated in a pure system, the large local current can directly cause structural damage to the cathode active material. The mixed system in this application, however, can effectively achieve uniform current distribution and spontaneously reduce current shunting, a characteristic highly beneficial for metal cation intercalation.

[0042] In any embodiment, the alkaline earth metal ions include Mg 2+ Ca 2+ One or two of them. Mg 2+ Ca 2+ Low reversible sites embedded in cathode materials can not only improve the cycle performance and rate performance of lithium-ion secondary batteries, but also enhance their cycle stability and capacity retention. This is especially true under high charge cutoff voltage and long charge-discharge conditions, where Mg... 2+ Ca 2+ The doped positive electrode active material exhibits better cycle stability and capacity retention during charge and discharge processes. Additionally, Mg doping... 2+ Ca 2+ The resulting positive electrode active material also has high crystallinity and good electrochemical activity, which helps to improve the energy density and lifespan of lithium-ion secondary batteries.

[0043] In any embodiment, the amphoteric metal ion includes Zn. 2+ Al 3+ One or two of them. Zn 2+ Al 3+ Low reversible sites embedded in positive electrode active materials can not only improve the cycle performance and rate performance of lithium-ion secondary batteries, but also enhance the overall performance and lifespan of lithium-ion secondary batteries.

[0044] In any embodiment, the difference between the charging cutoff voltage of the first positive electrode active material and the second positive electrode active material is greater than or equal to 0.1V and less than or equal to 1.5V. When the difference in charging cutoff voltage is greater than 0.1V, the first positive electrode active material and the second positive electrode active material have a large potential difference. Under a high charging cutoff voltage, metal cations are directionally induced to insert into low reversible sites by trickle-flow.

[0045] In any embodiment, the first positive electrode active material includes one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-rich manganese-based materials; the second positive electrode active material includes one or two of lithium manganese iron phosphate and lithium iron phosphate. The lithium nickel cobalt manganese oxide includes materials with the structural formula Li... a Ni b Co c Mn d M1 (1-b-c-d) O f The core material and the coating layer disposed on the surface of the core material; 0.9≤a≤1.2, 0.1≤b≤0.99, 0.02≤c≤0.1, 0.01<d≤0.06, 1.9≤f≤2.2, M1 includes one or more combinations of Al, Ti, Zr, W, Mo, Ba, and Nb. Lithium nickel cobalt aluminum oxide includes the structure with the formula Li a Ni b Co c Al d M1(1-bcd)O f The core material and the coating layer disposed on the surface of the core material; 0.9≤a≤1.2, 0.1≤b≤0.99, 0.02≤c≤0.1, 0.01<d≤0.06, 1.9≤f≤2.2, M1 includes one or more combinations of Ti, Zr, W, Mo, Ba, and Nb. Lithium-rich manganese-based materials include materials with the structural formula nLi2MnO3·(1-n)LiMO2, where 0.1≤n≤0.5, and M includes at least two combinations of Ni, Co, and Mn. Lithium manganese iron phosphate materials include Li x Fe y Mn 1-y PO4, where 0.05 ≤ x ≤ 1.2, 0.2 ≤ y ≤ 1, the surface of lithium iron phosphate may include a coating layer. Lithium iron phosphate materials include Li x Fe yPO4, where 0.05≤x≤1.2, 0.2≤y≤1, lithium iron phosphate can also be doped with other metal elements or have a surface coating. Lithium-rich manganese-based materials, with their high specific capacity and high charging cut-off voltage characteristics, have become an effective means to improve the energy density of lithium-ion secondary batteries. However, lithium-rich manganese-based materials suffer from voltage decay and deterioration in cycle and rate performance during long-term use. These problems can be effectively solved by doping lithium-rich manganese-based materials with ternary materials (lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide), and one or more of lithium manganese iron phosphate and lithium iron phosphate. The capacity advantage of lithium-rich manganese-based materials can only be realized at voltages above 4.5V. In one embodiment of this application, the charging cut-off voltage of the lithium-rich manganese-based material is 4.55V; while the charging cut-off voltage of lithium nickel cobalt manganese oxide does not exceed 4.35V. In one embodiment of this application, the charging cut-off voltage of lithium nickel cobalt manganese oxide is 4.35V. The charging cutoff voltage of lithium nickel cobalt aluminum oxide does not exceed 4.3V. In one embodiment of this application, the charging cutoff voltage of lithium nickel cobalt aluminum oxide is 4.3V. The charging cutoff voltage of lithium manganese iron phosphate and lithium iron phosphate does not exceed 4.15V. In one embodiment of this application, the charging cutoff voltage of lithium manganese iron phosphate and lithium iron phosphate is 4.15V. Excessively high charging cutoff voltages can cause overcharging problems for ternary materials (lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide), lithium manganese iron phosphate, and lithium iron phosphate. In this embodiment, this problem is solved by adding a salt containing metal cations. At high charging cutoff voltages, the low reversible sites formed by lithium ion intercalation and deintercalation are conducive to the intercalation of metal cations. During cycling at higher charging cutoff voltages, metal cations can effectively and spontaneously intercalate into these low reversible sites, which helps to stabilize the electrode structure in subsequent cycles. It can also limit the surface valence state of Mn in lithium manganese iron phosphate, thereby reducing the occurrence of side reactions.

[0046] In any embodiment, the additive is disposed in the electrolyte. The process of disposing of the additive in the electrolyte is simple, and the amount of additive is easy to control.

[0047] In any embodiment, the electrolyte further includes a second additive, the second additive comprising Li + The valence state of the metal cation is x, based on the Li in the electrolyte. +The molar amount of the metal cation is (0.1 / x)% to (2 / x)%. In this embodiment, an additive is introduced into the electrolyte. The metal cation in the additive can spontaneously and uniformly embed into the structure of the positive electrode active material. It can effectively stabilize the crystal structure of the positive electrode active material and reduce the occurrence of side reactions. It can effectively reduce the risk of overcharging of the second positive electrode active material under high charging cutoff voltage, thereby improving the cycle performance and rate performance of the lithium-ion secondary battery. In this embodiment, when the molar percentage of the metal cation is within the above range, the metal cation mainly occupies low reversible sites through diffusion. In this state, the metal cation also expands and stabilizes the lithium-ion transport channel, thereby enhancing the kinetic performance of the lithium-ion secondary battery and increasing the capacity of the lithium-ion secondary battery. The capacity increase caused by the expansion and stabilization of the lithium-ion transport channel by the metal cation is equal to the capacity loss caused by the metal cation occupying the active lithium sites. At the same time, when the molar percentage of the metal cation is within the above range, the lattice distortion caused by metal cation doping is small.

[0048] It should be noted here that the molar percentage of metal cations is related to the valence state of the metal cations, based on the Li in the electrolyte. + The molar amount of the metal cation is (0.1 / x)% to (2 / x)%. Based on the Li in the electrolyte + The molar amounts of the metal cations are (0.1 / x)%, (0.3 / x)%, (0.5 / x)%, (0.7 / x)%, (1 / x)%, (1.3 / x)%, (1.6 / x)%, (2 / x)%, etc., or a range of any two of the above values, such as (0.1 / x)%~(0.3 / x)%, (0.3 / x)%~(0.5 / x)%, (0.5 / x)%~(0.7 / x)%, (0.7 / x)%~(1 / x)%, (1 / x)%~(1.3 / x)%, (1.3 / x)%~(1.6 / x)%, (1.6 / x)%~(2 / x)%, etc. For example, when the metal cation is Na... + Because of Na + If the valence state is 1, then based on the Li in the electrolyte... + molar amount of Na + The molar percentage is 0.1% to 2%; when the metal cation is Mg 2+ At that time, due to Mg 2+ If the valence state is 2, then based on the Li in the electrolyte... + molar amount of Mg 2+ The molar percentage is 0.05% to 1%.

[0049] In practice, a corresponding amount of additive is added to the electrolyte. During the formation process (temperature 45℃~60℃), through multiple (2 to 4) high charging cutoff voltage discharges, metal cations can spontaneously embed into the material lattice and occupy stable sites.

[0050] In any embodiment, the first additive is disposed in the positive electrode active material layer, and the first additive is attached to or / and coated on the first type of positive electrode active material. Disposing of the first additive on the first type of positive electrode active material is more conducive to the insertion of metal cations into low reversible sites, thereby improving the cycle performance and rate performance of the lithium-ion secondary battery. Wherein, "the first additive is attached to the first type of positive electrode active material" means that the first additive, the first type of positive electrode active material, a positive electrode conductive agent, a positive electrode binder, etc., are mixed to form a positive electrode slurry, and then the positive electrode slurry is coated onto a positive electrode current collector to form a positive electrode active material layer, which is then cold-pressed and cut to obtain the positive electrode sheet. The first additive coating on the first positive electrode active material refers to the process of coating the first additive onto the surface of the first positive electrode active material using dry or wet coating methods to form a first positive electrode active material with the first additive coating. Then, the first positive electrode active material with the first additive coating is mixed with a positive electrode conductive agent, a positive electrode binder, etc., to form a positive electrode slurry. The positive electrode slurry is then coated onto a positive electrode current collector to form a positive electrode active material layer. After cold pressing and cutting, a positive electrode sheet is obtained. Dry coating is achieved through airflow carrier action and spraying methods, while wet coating is achieved through sulfonation treatment and sand milling treatment.

[0051] In any embodiment, the first additive is disposed in the positive electrode active material layer, and the first additive is attached to or / and coated on the second positive electrode active material. Similarly, disposing of the first additive on the second positive electrode active material is more conducive to the insertion of metal cations into low reversible sites, thereby improving the cycle performance and rate performance of the lithium-ion secondary battery.

[0052] It should be noted that the first additive can be simultaneously attached to the first positive electrode active material and the second positive electrode active material; the first additive can also be simultaneously coated on the first positive electrode active material and the second positive electrode active material; the first additive can also be attached to the first positive electrode active material and coated on the second positive electrode active material; the first additive can also be attached to the second positive electrode active material and coated on the first positive electrode active material, etc.

[0053] In any embodiment, the positive electrode sheet includes a positive current collector and an additive layer, wherein the additive layer is disposed on the surface of the positive active material layer opposite to the positive current collector; the first additive is disposed in the additive layer. Disposing of the first additive in the additive layer facilitates control of the additive dosage and simplifies the process.

[0054] In any embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, and the first additive is disposed in the negative electrode active material layer, wherein the first additive is soluble in the electrolyte. By disposing of the first additive in the negative electrode active material layer, the metal cations in the first additive diffusely intercalate into the low reversible sites in the positive electrode material, which not only improves the cycle performance and rate performance of the lithium-ion secondary battery, but also protects the negative electrode sheet, reduces the occurrence of side reactions, and thus improves the stability of the lithium-ion secondary battery.

[0055] In any embodiment, the first additive is disposed on the surface of the negative electrode active material layer opposite to the negative electrode current collector; wherein, the first additive is soluble in the electrolyte. Disposing of the first additive on the surface of the negative electrode active material layer opposite to the negative electrode current collector facilitates control of the additive dosage and simplifies the process.

[0056] In any embodiment, based on the total mass of the first positive electrode active material and the second positive electrode active material, the mass percentage of the first additive is 0.1% to 2%. When the mass percentage of the first additive is within the above range, the metal cations in the first additive mainly occupy low reversible sites through diffusion. In this state, the metal cations also expand and stabilize the lithium-ion transport channels, thereby enhancing the kinetic performance of the lithium-ion secondary battery and increasing its capacity. The capacity increase caused by the expansion and stabilization of lithium-ion transport channels by the metal cations is equal to the capacity loss caused by the metal cations occupying active lithium sites. Simultaneously, when the molar percentage of the metal cations is within the above range, the lattice distortion caused by metal cation doping is relatively small. Wherein, based on the total mass of the first type of positive electrode active material and the second type of positive electrode active material, the mass percentage of the first additive is 0.1%, 0.3%, 0.5%, 0.7%, 1%, 1.3%, 1.6%, 2%, etc., or a range of any two of the above values, such as 0.1% to 0.3%, 0.3% to 0.5%, 0.5% to 0.7%, 0.7% to 1%, 1% to 1.3%, 1.3% to 1.6%, 1.6% to 2%, etc.

[0057] In any embodiment, the anion of the first additive includes PF6. - PO4 3- ClO4 - CO3 2- One or more combinations of PF6. - It has very high solubility, making it particularly suitable for electrolyte systems requiring high solubility. PO4 3-The performance of lithium-ion secondary batteries can be significantly improved by reducing the impedance of the battery, especially at low temperatures, thus solving the problem of lithium plating during charging with conventional additives at low temperatures. ClO4 - Adding CO3 to the electrolyte can give it better ion migration properties, enabling faster ion transport and thus improving the charge / discharge speed and efficiency of lithium-ion secondary batteries. 2- This can enhance the stability of the electrolyte, thereby extending the lifespan of lithium-ion secondary batteries. Specifically, when the metal cation is Na... + At this time, the salt compounds can be NaPF6, NaFePO4, Na3V2(PO4)3, NaMnPO4, Na x MO4, NaCFSO3, NaPF6, NaClO4, BF4Na, CF3NaO3S, etc.

[0058] In the embodiments of this application, the electrolyte plays a role in conducting ions between the positive and negative electrode plates. This application does not specifically limit the type of electrolyte; it can be selected according to requirements.

[0059] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0060] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0061] In some embodiments, the solvent may 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, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0062] In some embodiments, the electrolyte may optionally include electrolyte additives. For example, electrolyte 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.

[0063] In some embodiments, the lithium-ion secondary battery further includes a separator membrane disposed between the positive and negative electrode plates. The separator membrane primarily serves to prevent short circuits between the positive and negative electrodes while allowing ions to pass through. This application does not impose any particular limitation on the type of separator membrane; any known porous structure separator membrane with good chemical and mechanical stability can be selected.

[0064] 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.

[0065] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0066] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0067] In some embodiments, the positive current collector 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 substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0068] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0069] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0070] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0071] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0072] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0073] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper 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 (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0074] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0075] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may 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).

[0076] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0077] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0078] In some embodiments, 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, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0079] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into a battery cell assembly using a winding or stacking process.

[0080] The second aspect of this application provides an electrical device including the lithium-ion secondary battery of the first aspect of this application. In embodiments of this application, the electrical device possesses at least the same advantages as the lithium-ion secondary battery of the first aspect. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

[0081] For ease of explanation, we will take a vehicle 1000 as an example of an electrical device.

[0082] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the structure of one embodiment of the vehicle 1000 of this application. The vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A battery 100 is disposed inside the vehicle 1000, and the battery 100 can be located at the bottom, front, or rear of the vehicle 1000. The battery 100 can be used to power the vehicle 1000; for example, the battery 100 can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to supply power to the motor 300, for example, to meet the power needs of the vehicle 1000 during starting, navigation, and driving.

[0083] In some embodiments of this application, the battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0084] Please refer to Figure 2 , Figure 2 This is an exploded structural diagram of an embodiment of the battery 100 of this application. The battery 100 includes a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10. The housing 10 provides a space for the battery cell 20 and can have various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other, jointly defining a space for accommodating the battery cell 20. The second portion 12 may be a hollow structure with one open end, and the first portion 11 may be a plate-like structure, covering the open side of the second portion 12 so that the first portion 11 and the second portion 12 jointly define the space; alternatively, the first portion 11 and the second portion 12 may both be hollow structures with one open side, with the open side of the first portion 11 covering the open side of the second portion 12. Of course, the housing 10 formed by the first portion 11 and the second portion 12 can have various shapes, such as a cylinder, a cuboid, etc.

[0085] In battery 100, there can be multiple battery cells 20. These multiple battery cells 20 can be connected in series, in parallel, or in a mixed manner. A mixed connection means that multiple battery cells 20 are connected in both series and parallel. Multiple battery cells 20 can be directly connected in series, in parallel, or in a mixed manner, and then the whole assembly of multiple battery cells 20 is housed in the housing 10. Alternatively, battery 100 can also be composed of multiple battery cells 20 first connected in series, in parallel, or in a mixed manner to form a battery module, and then multiple battery modules are connected in series, in parallel, or in a mixed manner to form a whole, which is then housed in the housing 10.

[0086] The battery cell 20 includes the lithium-ion secondary battery provided in this application. There can be multiple battery cells 20. Besides the lithium-ion secondary battery provided in this application, the battery cell 20 may also include lithium-sulfur batteries, sodium-ion batteries, or magnesium-ion batteries, but is not limited to these. The battery cell 20 may be cylindrical, flat, cuboid, or other shapes.

[0087] Please refer to Figure 3 , Figure 3 This is an exploded structural diagram of one embodiment of the battery cell 20 of this application. Figure 3In this context, X, Y, and Z represent the directions of the three-dimensional spatial coordinate axes. A battery cell 20 refers to the smallest unit that makes up the battery 100. The battery cell 20 includes an end cap 21, a casing 22, a cell assembly 23, and other functional components.

[0088] End cap 21 refers to a component that covers the opening of housing 22 to isolate the internal environment of battery cell 20 from the external environment. The shape of end cap 21 can be adapted to the shape of housing 22 to fit it. Optionally, end cap 21 can be made of a material with certain hardness and strength (such as aluminum alloy), so that end cap 21 is not easily deformed under pressure and impact, allowing battery cell 20 to have higher structural strength and improved safety performance. Functional components such as electrode terminals 21a can be provided on end cap 21. Electrode terminals 21a can be used for electrical connection with cell assembly 23 to output or input electrical energy to battery cell 20. In some embodiments, end cap 21 can also be provided with a pressure relief mechanism for releasing internal pressure when the internal pressure or temperature of battery cell 20 reaches a threshold. The material of end cap 21 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and this application embodiment does not impose special limitations on this. In some embodiments, an insulating element may be provided on the inner side of the end cap 21. The insulating element can be used to isolate the electrical connection components within the housing 22 from the end cap 21 to reduce the risk of short circuits. For example, the insulating element may be made of plastic, rubber, etc.

[0089] The housing 22 is a component used to cooperate with the end cap 21 to form the internal environment of the battery cell 20. This internal environment can accommodate the cell assembly 23, electrolyte, and other components. The housing 22 and the end cap 21 can be independent components. An opening can be provided on the housing 22, and the end cap 21 can be used to close the opening to form the internal environment of the battery cell 20. Alternatively, the end cap 21 and the housing 22 can be integrated. Specifically, the end cap 21 and the housing 22 can form a common connecting surface before other components are inserted into the housing. When it is necessary to encapsulate the interior of the housing 22, the end cap 21 closes the housing 22. The housing 22 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 22 can be determined according to the specific shape and size of the cell assembly 23. The material of the housing 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. This application embodiment does not impose any special limitations on this.

[0090] The cell assembly 23 is the component in the battery cell 20 where the electrochemical reaction occurs. The casing 22 may contain one or more cell assemblies 23. The cell assembly 23 is mainly formed by winding or stacking positive and negative electrode plates, and typically a separator is provided between the positive and negative electrode plates. The portions of the positive and negative electrode plates containing active material constitute the main body of the cell assembly, while the portions of the positive and negative electrode plates without active material each constitute a tab 23a. The positive and negative tabs may be located together at one end of the main body or separately at both ends of the main body. During the charging and discharging process of the battery 100, the positive and negative active materials react with the electrolyte, and the tabs 23a connect to the electrode terminals 21a to form a current loop.

[0091] The beneficial effects of this application are further illustrated below with reference to the embodiments.

[0092] To make the technical problems, technical solutions, and beneficial effects solved by the embodiments of this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0093] Example 1

[0094] 1) Preparation of lithium-ion secondary batteries

[0095] 1.1) Preparation of the positive electrode sheet

[0096] Lithium nickel cobalt manganese oxide (LiNi) with a mass ratio of 4:3:3 0.5 Co 0.2 Mn 0.3 O2), lithium manganese iron phosphate (LiFe) 0.4 Mn 0.6 PO4) and lithium-rich materials (0.3Li2MnO3·0.7LiNi) 0.3 Co 0.1 Mn 0.6 The positive electrode active material is obtained by mixing O2. The positive electrode active material, polyvinylidene fluoride (PVDF) and conductive carbon black (Super P) are mixed evenly at a mass ratio of 97:1:2 to obtain a positive electrode slurry. The positive electrode slurry is evenly coated on both sides of aluminum foil, and then cold-pressed and cut to obtain a positive electrode sheet.

[0097] 1.2) Preparation of negative electrode sheet

[0098] A negative electrode slurry is prepared by uniformly mixing graphite, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and conductive carbon black (Super P) in a mass ratio of 96:1:1:2. The negative electrode slurry is then coated on both sides of a copper foil, cold-pressed, and cut to obtain the negative electrode sheet.

[0099] 1.3) Separating membrane

[0100] A polyethylene diaphragm with a thickness of 13 μm was used as the separator.

[0101] 1.4) Electrolyte

[0102] Ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1. LiPF6 and NaPF6 were dissolved in the mixture to obtain an electrolyte. The concentration of LiPF6 in the electrolyte was 1 mol / L, and the concentration of NaPF6 was 0.003 mol / L.

[0103] 1.5) Assembly of lithium-ion secondary batteries

[0104] The electrodes are arranged in the order of "separator-negative electrode-separator-positive electrode". One end of the positive electrode, negative electrode, and two separators is fixed to the discharge roller, and the other end is stacked together and fixed to the winding shaft. The winding shaft is rotated by a motor to wind the positive electrode, negative electrode, and two separators to obtain a wound battery.

[0105] Example 2

[0106] The difference between Example 2 and Example 1 is that the concentration of NaPF6 in the electrolyte is 0.001 mol / L.

[0107] Example 3

[0108] The difference between Example 3 and Example 1 is that the concentration of NaPF6 in the electrolyte is 0.01 mol / L.

[0109] Example 4

[0110] The difference between Example 4 and Example 1 lies in the preparation method of the electrolyte.

[0111] In Example 4, NaPF6 was replaced with Mg(PF6)2, and the concentration of Mg(PF6)2 was 0.0015 mol / L.

[0112] Example 5

[0113] The difference between Example 5 and Example 1 lies in the preparation method of the electrolyte.

[0114] In Example 5, NaPF6 was replaced with Mg(PF6)2, and the concentration of Mg(PF6)2 was 0.0005 mol / L.

[0115] Example 6

[0116] The difference between Example 6 and Example 1 lies in the preparation method of the electrolyte.

[0117] In Example 6, NaPF6 was replaced with Mg(PF6)2, and the concentration of Mg(PF6)2 was 0.005 mol / L.

[0118] Example 7

[0119] The difference between Example 7 and Example 1 lies in the different preparation methods of the positive electrode and the electrolyte.

[0120] Lithium nickel cobalt manganese oxide (LiNi) with a mass ratio of 4:3:3:0.02 0.5 Co 0.2 Mn 0.3 O2), lithium manganese iron phosphate (LiFe) 0.4 Mn 0.6 PO4), lithium-rich materials (0.3Li2MnO3·0.7LiNi) 0.3 Co 0.1 Mn 0.6 The positive electrode active material is obtained by mixing O2 and NaPF6, wherein NaPF6 is attached to lithium nickel cobalt manganese oxide (LiNi). 0.5 Co 0.2 Mn 0.3 O2), lithium manganese iron phosphate (LiFe) 0.4 Mn 0.6 PO4), lithium-rich materials (0.3Li2MnO3·0.7LiNi) 0.3 Co 0.1 Mn 0.6 On O2). The positive electrode active material, polyvinylidene fluoride (PVDF) and conductive carbon black (Super P) are mixed evenly at a mass ratio of 97:1:2 to obtain a positive electrode slurry. The positive electrode slurry is evenly coated on both sides of an aluminum foil, and after cold pressing and cutting, a positive electrode sheet is obtained.

[0121] Ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1. LiPF6 was then dissolved in this solution to obtain the electrolyte. The concentration of LiPF6 in this electrolyte was 1 mol / L.

[0122] Example 8

[0123] The difference between Example 8 and Example 1 lies in the different preparation methods of the positive electrode and the electrolyte.

[0124] Lithium nickel cobalt manganese oxide (LiNi) with a mass ratio of 4:3:3:0.2 0.5 Co 0.2 Mn 0.3 O2), lithium manganese iron phosphate (LiFe) 0.4 Mn 0.6 PO4) and lithium-rich materials (0.3Li2MnO3·0.7LiNi) 0.3 Co 0.1 Mn 0.6 The positive electrode active material is obtained by mixing O2 and NaPF6, wherein NaPF6 is attached to lithium nickel cobalt manganese oxide (LiNi). 0.5 Co 0.2 Mn 0.3 O2), lithium manganese iron phosphate (LiFe) 0.4 Mn 0.6 PO4) and lithium-rich materials (0.3Li2MnO3·0.7LiNi) 0.3 Co 0.1 Mn 0.6 On O2). The positive electrode active material, polyvinylidene fluoride (PVDF) and conductive carbon black (Super P) are mixed evenly at a mass ratio of 97:1:2 to obtain a positive electrode slurry. The positive electrode slurry is evenly coated on both sides of an aluminum foil, and after cold pressing and cutting, a positive electrode sheet is obtained.

[0125] Ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1. LiPF6 was then dissolved in this solution to obtain the electrolyte. The concentration of LiPF6 in this electrolyte was 1 mol / L.

[0126] Example 9

[0127] The difference between Example 9 and Example 1 lies in the different preparation methods of the positive electrode and the electrolyte.

[0128] At 25°C, lithium nickel cobalt aluminum oxide (LiNi) with a mass ratio of 4:3:3 was used. 0.5 Co 0.2 Al 0.3 O2), lithium manganese iron phosphate (LiFe) 0.4 Mn 0.6 PO4), lithium-rich materials (0.3Li2MnO3·0.7LiNi) 0.3 Co 0.1 Mn 0.6After mixing with O2, a first intermediate product is formed. NaPF6 is dissolved in ethylene carbonate (EC) to form a second intermediate product with a concentration of 1 mol / L. 240 g of the first intermediate product is added to 1 L of the second intermediate product, and the first intermediate product is dispersed into a suspension by stirring. The temperature is raised to 130°C, and some EC volatilizes, causing NaPF6 to precipitate as a supersaturated solution. At this point, NaPF6 will precipitate on existing nucleation sites (i.e., dispersed lithium nickel cobalt aluminum oxide, lithium manganese iron phosphate, and lithium-rich material particles). The residual EC is then removed by chloroform washing, and finally dried to obtain the positive electrode active material. In this positive electrode active material, NaPF6 is coated on lithium nickel cobalt aluminum oxide, lithium manganese iron phosphate, and lithium-rich materials. Among them, lithium nickel cobalt aluminum oxide (LiNi) is based on lithium nickel cobalt aluminum oxide (LiNi) 0.5 Co 0.2 Al 0.3 O2), lithium manganese iron phosphate (LiFe) 0.4 Mn 0.6 PO4), lithium-rich materials (0.3Li2MnO3·0.7LiNi) 0.3 Co 0.1 Mn 0.6 Of the total mass of O2, NaPF6 accounts for 0.3%.

[0129] The positive electrode active material, polyvinylidene fluoride (PVDF), and conductive carbon black (Super P) are mixed evenly in a mass ratio of 97:1:2 to obtain a positive electrode slurry. The positive electrode slurry is evenly coated on both sides of an aluminum foil, and then cold-pressed and cut to obtain a positive electrode sheet.

[0130] Ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1. LiPF6 was then dissolved in this solution to obtain the electrolyte. The concentration of LiPF6 in this electrolyte was 1 mol / L.

[0131] Example 10

[0132] The difference between Example 10 and Example 1 lies in the different preparation methods of the positive electrode and the electrolyte.

[0133] At 25°C, lithium nickel cobalt aluminum oxide (LiNi) with a mass ratio of 4:3:3 was used. 0.5 Co 0.2 Al 0.3 O2), lithium manganese iron phosphate (LiFe) 0.4 Mn 0.6 PO4), lithium-rich materials (0.3Li2MnO3·0.7LiNi) 0.3 Co 0.1 Mn 0.6After mixing with O2, a first intermediate product is formed. NaPF6 is dissolved in ethylene carbonate (EC) to form a second intermediate product with a concentration of 1 mol / L. 1600 g of the first intermediate product is added to 1 L of the second intermediate product, and the first intermediate product is dispersed into a suspension by stirring. The temperature is raised to 130°C, and some EC volatilizes, causing NaPF6 to precipitate as a supersaturated solution. At this point, NaPF6 will precipitate on existing nucleation sites (i.e., dispersed lithium nickel cobalt aluminum oxide, lithium manganese iron phosphate, and lithium-rich material particles). The residual EC is then removed by chloroform washing, and finally dried to obtain the positive electrode active material. In this positive electrode active material, NaPF6 is coated on lithium nickel cobalt aluminum oxide, lithium manganese iron phosphate, and lithium-rich materials. Among them, lithium nickel cobalt aluminum oxide (LiNi) is based on lithium nickel cobalt aluminum oxide (LiNi) 0.5 Co 0.2 Al 0.3 O2), lithium manganese iron phosphate (LiFe) 0.4 Mn 0.6 PO4), lithium-rich materials (0.3Li2MnO3·0.7LiNi) 0.3 Co 0.1 Mn 0.6 Of the total mass of O2, NaPF6 accounts for 2% of the mass.

[0134] The positive electrode active material, polyvinylidene fluoride (PVDF), and conductive carbon black (Super P) are mixed evenly in a mass ratio of 97:1:2 to obtain a positive electrode slurry. The positive electrode slurry is evenly coated on both sides of an aluminum foil, and then cold-pressed and cut to obtain a positive electrode sheet.

[0135] Ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1. LiPF6 was then dissolved in this solution to obtain the electrolyte. The concentration of LiPF6 in this electrolyte was 1 mol / L.

[0136] Example 11

[0137] The difference between Example 11 and Example 1 lies in the different preparation methods of the negative electrode sheet and the electrolyte.

[0138] Graphite, NaPF6, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and conductive carbon black (Super P) were mixed uniformly in a mass ratio of 95.5:0.5:1:1:2 to obtain a negative electrode slurry. The negative electrode slurry was coated on both sides of a copper foil, cold-pressed, and cut to obtain the negative electrode sheet. Among these, lithium nickel cobalt manganese oxide (LiNi) was used. 0.5 Co 0.2 Mn 0.3 O2), lithium manganese iron phosphate (LiFe) 0.4 Mn 0.6PO4) and lithium-rich materials (0.3Li2MnO3·0.7LiNi) 0.3 Co 0.1 Mn 0.6 Of the total mass of O2, NaPF6 accounts for 0.3%.

[0139] Ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1. LiPF6 was then dissolved in this solution to obtain the electrolyte. The concentration of LiPF6 in this electrolyte was 1 mol / L.

[0140] Example 12

[0141] The difference between Example 12 and Example 1 lies in the different preparation methods of the negative electrode sheet and the electrolyte.

[0142] A negative electrode slurry was prepared by uniformly mixing graphite, NaPF6, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and conductive carbon black (Super P) in a mass ratio of 92:4:1:1:2. The negative electrode slurry was coated onto both sides of a copper foil, cold-pressed, and cut to obtain the negative electrode sheet. This negative electrode sheet is based on lithium nickel cobalt manganese oxide (LiNi). 0.5 Co 0.2 Mn 0.3 O2), lithium manganese iron phosphate (LiFe) 0.4 Mn 0.6 PO4) and lithium-rich materials (0.3Li2MnO3·0.7LiNi) 0.3 Co 0.1 Mn 0.6 Of the total mass of O2, NaPF6 accounts for 2% of the mass.

[0143] Ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1. LiPF6 was then dissolved in this solution to obtain the electrolyte. The concentration of LiPF6 in this electrolyte was 1 mol / L.

[0144] Example 13

[0145] The difference between Comparative Example 13 and Example 1 is that the concentration of NaPF6 in the electrolyte is 0.0005 mol / L.

[0146] Example 14

[0147] The difference between Comparative Example 14 and Example 1 is that the concentration of NaPF6 in the electrolyte is 0.02 mol / L.

[0148] Example 15

[0149] The difference between Example 15 and Example 1 lies in the different preparation methods of the positive electrode and the electrolyte.

[0150] Lithium nickel cobalt aluminum oxide (LiNi) with a mass ratio of 4:3 0.5 Co 0.2 Al 0.3 O2), lithium manganese iron phosphate (LiFe) 0.4 Mn 0.6 The positive electrode active material is obtained by mixing NaFePO4, polyvinylidene fluoride (PVDF), and conductive carbon black (Super P) at a mass ratio of 90:5:5. The positive electrode slurry is then uniformly coated onto both sides of an aluminum foil to obtain the positive electrode active material layer. An additive slurry is obtained by uniformly mixing NaFePO4, PVDF, and N-methyl-2-pyrrolidone (NMP). This additive slurry is coated onto the positive electrode active material layer to obtain the additive layer. After cold pressing and cutting, the positive electrode sheet is obtained. The mass ratio of NaFePO4 to PVDF is 80:20. (Note: The last sentence appears to be incomplete and possibly refers to a different process based on LiNi.) 0.5 Co 0.2 Mn 0.3 The total mass of O2 and lithium iron manganese phosphate contains 0.2% NaPF6.

[0151] Ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1. LiPF6 was then dissolved in this solution to obtain the electrolyte. The concentration of LiPF6 in this electrolyte was 1 mol / L.

[0152] Example 16

[0153] The difference between Example 16 and Example 1 lies in the different preparation methods of the negative electrode sheet and the electrolyte.

[0154] Graphite, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and conductive carbon black (Super P) were mixed uniformly in a mass ratio of 96:1:1:2 to obtain a negative electrode slurry. The negative electrode slurry was coated onto both sides of a copper foil to obtain a negative electrode active material layer. KPF6 was mixed uniformly with polyvinylidene fluoride (PVDF) and N-methyl-2-pyrrolidone (NMP) to obtain an additive slurry. This additive slurry was coated onto the negative electrode active material layer, and after cold pressing and cutting, a negative electrode sheet was obtained. The mass ratio of KPF6 to PVDF was 80:20. (Note: The last sentence appears to be incomplete and possibly refers to a different topic.) 0.5 Co 0.2 Mn 0.3 The total mass of O2, lithium manganese iron phosphate, and lithium-rich materials, with NaPF6 accounting for 0.2% of the total mass.

[0155] Ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1. LiPF6 was then dissolved in this solution to obtain the electrolyte. The concentration of LiPF6 in this electrolyte was 1 mol / L.

[0156] Example 17

[0157] The difference between Comparative Example 17 and Example 1 is that the concentration of NaPF6 in the electrolyte is 5 mol / L.

[0158] Example 18

[0159] The difference between Comparative Example 18 and Example 1 lies in the different methods of preparing the positive electrode sheet.

[0160] Lithium nickel cobalt manganese oxide (LiNi) with a mass ratio of 4:3:3 0.5 Co 0.2 Mn 0.3 O2), lithium iron phosphate (LiFePO4), and lithium-rich materials (0.3Li2MnO3·0.7LiNi). 0.3 Co 0.1 Mn 0.6 The positive electrode active material is obtained by mixing O2. The positive electrode active material, polyvinylidene fluoride (PVDF) and conductive carbon black (Super P) are mixed evenly at a mass ratio of 97:1:2 to obtain a positive electrode slurry. The positive electrode slurry is evenly coated on both sides of aluminum foil, and then cold-pressed and cut to obtain a positive electrode sheet.

[0161] Comparative Example 1

[0162] The difference between Comparative Example 1 and Example 1 is that the electrolyte is different.

[0163] In Comparative Example 1, ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1, and LiPF6 was dissolved in the mixture to obtain an electrolyte. The concentration of LiPF6 in this electrolyte was 1 mol / L.

[0164] The specific testing methods for the relevant parameters are as follows:

[0165] 1) X-ray photoelectron spectroscopy (XPS) test

[0166] The positive electrode active material of the example was tested using an X-ray photoelectron spectroscopy spectrometer (Thermo Scientific ESCALAB Xi+) in accordance with the general rules of X-ray photoelectron spectroscopy analysis method GB / T19500-2004.

[0167] 2) Testing of the amount of metal cations inserted into the cathode material and the insertion sites.

[0168] The initial lithium-ion content m in the cathode material was measured using an inductively coupled plasma optical generator (ICP7400).

[0169] Without adding any additives, the lithium-ion content q in the cathode material after testing the charging cutoff voltage;

[0170] After adding additives, the lithium-ion content n1 and the metal cation content n2 were tested after the charging cutoff voltage was tested.

[0171] By comparing m, q, n1, and n2, we can infer the number of low reversible sites in the cathode material and the types of sites occupied by metal cations.

[0172] 3) Electrochemical performance testing.

[0173] 3.1) Cyclic capacity retention test.

[0174] Under constant temperature conditions of 25℃, the battery was charged to 4.5V at 0.5C, then charged at 4.5V with a constant voltage until the current ≤0.05mA, allowed to stand for 5 minutes, and then discharged to 2.5V at 0.5C. The resulting capacity was recorded as the initial capacity C0. The battery was then cycled under the same conditions, and the discharge capacity Cn was recorded after n cycles. The cycle capacity retention rate of the battery after each cycle was calculated using the following formula: P n =(C n / C0)×100%.

[0175] The number of cycles is plotted on the x-axis, and the battery's cycle capacity retention rate after the corresponding number of cycles is plotted on the y-axis.

[0176] 3.2) Ratio capacity retention test.

[0177] At 25℃, the battery is charged at a constant current of 1 / 3C to 4.5V, then charged at a constant voltage of 4.5V to a current of 0.05C, rested for 5 minutes, and then discharged at 0.1C to 2.5V. The average capacity obtained after 5 cycles is recorded as the initial capacity D0. Then, the battery is charged under the same conditions as above, discharged at 1C, and the average capacity obtained after 5 cycles is recorded as the initial capacity D1. The rate capacity retention rate Q1 of the battery is calculated according to the following formula: Q1=(D1 / D0)×100%.

[0178] Similarly, the rate capacity retention rate (Q2) of the battery is measured. Specifically, at 25°C, the battery is charged at a constant current of 1 / 3C to 4.5V, then charged at a constant voltage of 4.5V to a current of 0.05C, rested for 5 minutes, and then discharged at 0.1C to 2.5V. The average capacity obtained after 5 cycles is recorded as the initial capacity (D0). Then, the battery is charged under the same conditions as above, discharged at 2C, and the average capacity obtained after 5 cycles is recorded as the initial capacity (D2). The rate capacity retention rate (Q2) of the battery is calculated according to the following formula: Q2 = (D2 / D0) × 100%.

[0179] Similarly, the rate capacity retention rate (Q3) of the battery is measured. Specifically, at 25°C, the battery is charged at a constant current of 1 / 3C to 4.5V, then charged at a constant voltage of 4.5V to a current of 0.05C, rested for 5 minutes, and then discharged at 0.1C to 2.5V. The average capacity obtained after 5 cycles is recorded as the initial capacity (D0). Then, the battery is charged under the same conditions as above, discharged at 3C, and the average capacity obtained after 5 cycles is recorded as the initial capacity (D3). The rate capacity retention rate (Q3) of the battery is calculated according to the following formula: Q3 = (D3 / D0) × 100%.

[0180] 3.3) Test method for charging cut-off voltage.

[0181] First, test the battery's capacity after 5 cycles at an initial voltage (e.g., 2.0V to 4.0V). Then, increase the voltage by 50mV and continue testing the battery's capacity after 5 cycles at the current voltage. Compare the current capacity with the capacity at the previous voltage. If the current capacity is less than the capacity at the previous voltage, the charging cutoff voltage is the previous voltage value. If the current capacity is greater than the capacity at the previous voltage, continue increasing the voltage by 50mV until the current capacity is less than the capacity at the previous voltage. In this case, the charging cutoff voltage is the previous voltage value.

[0182]

[0183]

[0184]

[0185]

[0186]

[0187]

[0188]

[0189] 1) Compared to Comparative Example 1, in Examples 1 to 18, the addition of an additive containing a metal cation to the mixed system improved the cycle performance and rate performance of the lithium-ion secondary battery. This is because the metal cations in the additive, after intercalating into the low reversible sites formed by the excessive intercalation and deintercalation of lithium ions, will not be extracted again. Therefore, the structural stability of the positive electrode active material can be enhanced, thereby improving the cycle performance and rate performance of the lithium-ion secondary battery. The intercalation of the metal cations in the additive into the low reversible sites does not lead to a decrease in the capacity of the lithium-ion secondary battery. At the same time, the expanded channel structure of the metal cations in the additive is also beneficial to improving the kinetic characteristics of the electrode, and the rate performance of the lithium-ion secondary battery is also enhanced.

[0190] 2) Figure 4 The figures show the X-ray photoelectron spectra of the positive electrode active material, the positive electrode active material after low-voltage cycling, and the positive electrode active material after high-voltage cycling in the lithium-ion secondary battery of Example 1. The curve corresponding to "fresh" represents the X-ray photoelectron spectrum of the Na 1s orbital of the positive electrode active material before formation of the assembled lithium-ion secondary battery. The curve corresponding to "low-voltage cycling" represents the X-ray photoelectron spectrum of the Na 1s orbital of the positive electrode active material after 10 cycles at 2.0V-4.0V. The curve corresponding to "high-voltage cycling" represents the X-ray photoelectron spectrum of the Na 1s orbital of the positive electrode active material after 10 cycles at 2.0V-4.8V. As can be seen from the figures, the curve corresponding to "fresh" has a weak peak at 1071 eV, indicating trace amounts of Na from the electrolyte on its surface. + Residual Na remains in the positive electrode active material; the curve corresponding to low-voltage cycling has a small peak at 1071 eV, and some Na remains on the surface as cycling progresses. + The material is embedded into the positive electrode active material; the curve corresponding to high-voltage cycling shows a strong peak at 1071.5 eV, indicating that under high-voltage cycling conditions, Na… + The number of low-reversibility sites formed by lithium-ion insertion and extraction increases. This is due to the increased number of metal cations (Na+) under high-voltage cycling. + It can utilize entropy increase and trickle flow to be directionally induced to insert into low reversible sites formed by excessive lithium ion intercalation and deintercalation.

[0191] Figure 5This is a comparison curve of the cycle capacity retention of the lithium-ion secondary batteries prepared in Example 1 and Comparative Example 1 at 0.5C. When the number of cycles is the same (e.g., 150 cycles), the cycle capacity retention of the lithium-ion secondary battery prepared in Example 1 is greater than that of the lithium-ion secondary battery prepared in Comparative Example 1. When the cycle capacity retention reaches 80%, the number of cycles of the lithium-ion secondary battery prepared in Example 1 is greater than that of the lithium-ion secondary battery prepared in Comparative Example 1. This is due to the metal cation (Na₂O₃)... + Once the low reversible sites formed by the excessive insertion and extraction of lithium ions are inserted, they will not be extracted again. Therefore, the structural stability of the positive electrode active material can be enhanced, thereby improving the cycle performance of lithium-ion secondary batteries.

[0192] Figure 6 This is a comparison curve of the rate capacity retention of the lithium-ion secondary batteries prepared in Example 1 and Comparative Example 1. At the same charge / discharge rate, the rate capacity retention of the lithium-ion secondary battery prepared in Example 1 is greater than that of the lithium-ion secondary battery prepared in the Comparative Example. This is because the metal cation (Na₂O₃)... + Once the low reversible sites formed by excessive insertion and extraction of lithium ions are formed, they will not be extracted again. Therefore, the structural stability of the positive electrode active material can be enhanced, thereby improving the cycle performance and rate performance of lithium-ion secondary batteries. Additionally, the metal cation (Na₂O₃) + The extended channel structure also helps to improve the kinetic characteristics of the electrode, thereby improving the rate performance of lithium-ion secondary batteries.

[0193] 3) As can be seen from Examples 1 to 3, 13, 14 and 17, based on the Li in the electrolyte... + The molar percentage of metal cations in the additives of Examples 1-3 and Example 14 is in the range of (0.1 / x)% to (2 / x)% (where x is the valence state of the metal cation, i.e., 0.1% to 2%), resulting in better cycle performance and rate performance of lithium-ion secondary batteries. This is because the molar content of metal cations in the additives of Examples 1-3 and Example 14 of this application is optimal, allowing for a greater degree of insertion into low reversible sites formed by excessive lithium-ion insertion / extraction, thus improving the stability of the positive electrode active material.

[0194] The metal cation (Na) of the additive in Example 13 +The molar percentage of ) is 0.005%, which is less than 0.1%. It can occupy some low reversible sites. The amount of low reversible sites occupied is small, so it can improve the structural stability of the local area of ​​the positive electrode active material. However, the structure of another part of the positive electrode active material may be damaged, which leads to an improvement in the cycle performance and rate performance of the lithium-ion secondary battery. However, the improvement effect is less than that of Examples 1 to 3 and Example 14.

[0195] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A lithium-ion secondary battery, characterized in that, It includes positive electrode, negative electrode, and electrolyte; The positive electrode sheet includes a positive active material layer, the positive active material layer includes a positive electrode material, and the positive electrode material includes at least a first positive active material and a second positive active material, wherein the charging cut-off voltage of the first positive active material is greater than the charging cut-off voltage of the second positive active material; Lithium-ion secondary batteries also include additives, including a first additive comprising a salt containing a metal cation. The metal cation comprises one or more of alkali metal ions, alkaline earth metal ions, and amphoteric metal ions. The alkali metal ion includes Na. + And / or K+.

2. The lithium-ion secondary battery according to claim 1, characterized in that, The alkaline earth metal ions include Mg 2+ Ca 2+ One or two of them.

3. The lithium-ion secondary battery according to claim 1 or 2, characterized in that, The amphoteric metal ions include Zn. 2 + Al 3+ One or two of them.

4. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized in that, The difference between the charging cutoff voltage of the first positive electrode active material and the second positive electrode active material is greater than or equal to 0.1V and less than or equal to 1.5V.

5. The lithium-ion secondary battery according to any one of claims 1 to 4, characterized in that, The first type of positive electrode active material includes one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-rich manganese-based materials; the second type of positive electrode active material includes one or two of lithium manganese iron phosphate and lithium iron phosphate.

6. The lithium-ion secondary battery according to any one of claims 1 to 5, characterized in that, The additive is incorporated into the electrolyte.

7. The lithium-ion secondary battery according to claim 6, characterized in that, The electrolyte also includes a second additive, the second additive comprising Li + The valence state of the metal cation is x, based on the Li in the electrolyte. + The molar amount of the metal cation is (0.1 / x)% to (2 / x)%.

8. The lithium-ion secondary battery according to any one of claims 1 to 7, characterized in that, The first additive is disposed in the positive electrode active material layer, and the first additive is attached to and / or coated on the first positive electrode active material; or / and, The first additive is attached to and / or coated on the second positive electrode active material.

9. The lithium-ion secondary battery according to any one of claims 1 to 8, characterized in that, The positive electrode includes a positive current collector and an additive layer, wherein the additive layer is disposed on the surface of the positive active material layer opposite to the positive current collector; the first additive is disposed in the additive layer.

10. The lithium-ion secondary battery according to any one of claims 1 to 9, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, and the first additive is disposed in the negative electrode active material layer; or / and, The first additive is disposed on the surface of the negative electrode active material layer away from the negative electrode current collector; wherein the first additive is soluble in the electrolyte.

11. The lithium-ion secondary battery according to any one of claims 7 to 10, characterized in that, Based on the total mass of the first type of positive electrode active material and the second type of positive electrode active material, the mass percentage of the first additive is 0.1% to 2%.

12. The lithium-ion secondary battery according to any one of claims 1 to 11, characterized in that, The anion of the first additive includes PF6. - PO4 3- ClO4 - CO3 2- One or more combinations of the above.

13. An electrical appliance, characterized in that, Includes the lithium-ion secondary battery as described in any one of claims 1 to 12.

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