Positive electrode plate, secondary battery, battery module, battery pack, power consumption device, and method for equalizing internal voltage difference of battery

Abstract

The present application provides a positive plate, the positive plate having at least one of the formula LiFe 1-x Mn x The present application further provides a secondary battery including a positive electrode plate, a lithium iron phosphate-based material, a lithium nickel oxide, a lithium manganese oxide, a lithium cobalt oxide, a lithium nickel cobalt manganese oxide, a lithium nickel cobalt aluminate, a lithium rich manganese oxide, and a lithium vanadium phosphate, the amount of the second active material being 10-70%, optionally 10-30%, and optionally 15-20% of the total mass of the first active material and the second active material. The present application further provides a secondary battery including the positive electrode plate, and a battery module, a battery pack, and a power consumption device related thereto. The present application further provides a method for balancing an internal voltage difference of a secondary battery.

Description

[Technical Field]

[0001] The present application relates to the field of lithium battery technology, in particular to a positive electrode plate and related secondary batteries, battery modules, battery packs and power consumption devices, and the present application further relates to a method for balancing internal voltage differences in secondary batteries. [Background technology]

[0002] In recent years, the range of applications of lithium-ion batteries has become increasingly broad. Lithium-ion batteries are widely used in energy storage power systems, such as hydroelectric, thermal, wind, and solar power plants, as well as in various fields, including power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Lithium iron phosphate batteries have attracted attention due to their large capacity, high safety, long life, and low price. However, lithium iron phosphate batteries often suffer from inaccurate battery level indication and rapid capacity decay during use, which seriously impacts user experience. Therefore, it is highly desirable to provide a secondary battery with excellent capacity retention and the ability to accurately indicate the remaining battery level. Summary of the Invention

[0003] The present application has been made in view of the above-mentioned problems, and its purpose is to provide a positive plate that allows a secondary battery to which the positive plate is applied to have good capacity retention, and that allows a secondary battery to which the positive plate is applied to accurately display the remaining battery capacity of the secondary battery, thereby improving the user experience.

[0004] To achieve the above object, the present application provides a positive electrode plate, a secondary battery including the same, a battery module, a battery pack, and a power consumption device, and further provides a method for balancing the internal voltage difference of a secondary battery.

[0005] A first aspect of the present application provides a positive electrode plate, the positive electrode plate comprising at least: Formula LiFe 1-x Mn xA first active material selected from a lithium iron phosphate material of PO4, where x ranges from 0 to 0.8, optionally from 0 to 0.5, and further optionally from 0 to 0.25, and A second active material selected from one or more of lithium nickelate, lithium manganate, lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium-rich manganese-based, and lithium vanadium phosphate, and Here, with respect to the total mass of the first active material and the second active material, the usage amount of the second active material is 10 to 70%, optionally 10 to 30%, and further optionally 15 to 20%.

[0006] The secondary battery applying the positive electrode plate described in this application has good voltage self-balancing performance, thereby having improved capacity retention, accurately displaying the remaining battery amount of the secondary battery, and improving the user experience.

[0007] In any embodiment, optionally, with respect to the total mass of the first active material and the second active material, the usage amount of the first active material is 30 to 90%, optionally 70 to 90%, and further optionally 80 to 85%.

[0008] In any embodiment, optionally, the mass ratio of the first active material to the second active material is 3:7 to 9:1, optionally 7:3 to 9:1, and further optionally 80:20 to 85:15.

[0009] When the mass ratio of the first active material to the second active material is within the above range, it is advantageous for improving the voltage self-balancing performance of the secondary battery applying the positive electrode plate of this application.

[0010] In any embodiment, optionally, the first active material is lithium iron phosphate or lithium manganese iron phosphate or a mixture of lithium iron phosphate and lithium manganese iron phosphate.

[0011] In any embodiment, optionally, the second active material comprises at least one of lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminate.

[0012] In any embodiment, optionally, in the thickness direction of the positive electrode plate, the geometric center at which the first active material is distributed is not higher than the geometric center at which the second active material is distributed.

[0013] When the distribution of the geometric center of the first active material and the geometric center of the second active material meets the above conditions, the charge polarization of a secondary battery using the positive electrode plate of the present application can be reduced, thereby reducing the heat generation and temperature rise of the secondary battery and further improving the safety performance and lifespan of the battery.

[0014] In any embodiment, optionally, in the thickness direction of the positive electrode plate, the geometric center in which the first active material is distributed overlaps with the geometric center in which the second active material is distributed, or the geometric center in which the first active material is distributed is lower than the geometric center in which the second active material is distributed.

[0015] A second aspect of the present application provides a method for balancing an internal voltage difference in a secondary battery, wherein a positive electrode plate is used, the positive electrode plate comprising at least: Formula LiFe 1-x Mn x a first active material selected from lithium iron phosphate based materials of PO4, where x is between 0 and 0.8, optionally between 0 and 0.5, and further optionally between 0 and 0.25; a second active material selected from one or more of lithium nickel oxide, lithium manganese oxide, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium-rich manganese-based, and lithium vanadium phosphate; Here, the amount of the second active material used is 10 to 70%, optionally 10 to 30%, and further optionally 15 to 20% based on the total mass of the first active material and the second active material.

[0016] The third aspect of the present application provides a secondary battery including the positive electrode plate of the first aspect of the present application. The secondary battery can be manufactured by a secondary battery manufacturing method generally used in the art.

[0017] In any embodiment, optionally, in the charging voltage curve of the secondary battery, the voltage value V1 at the position corresponding to 85% state of charge and the voltage value V2 at the position corresponding to 60% state of charge satisfy V1 - V2 ≥ 0.15V.

[0018] When V1 and V2 satisfy the above relationship, by ensuring good voltage self - balancing performance of the secondary battery, it is advantageous to improve the capacity retention of the secondary battery and accurately display the remaining battery level of the secondary battery.

[0019] The fourth aspect of the present application provides a battery module including the secondary battery of the third aspect of the present application. The battery module can be manufactured by a battery module manufacturing method generally used in the art.

[0020] The fifth aspect of the present application provides a battery pack including the battery module of the fourth aspect of the present application. The battery pack can be manufactured by a battery pack manufacturing method generally used in the art.

[0021] The sixth aspect of the present application provides a power consumption device including at least one of the secondary battery of the third aspect of the present application, the battery module of the fourth aspect of the present application, or the battery pack of the fifth aspect of the present application.

[0022] [Beneficial Effects] In the secondary battery of this application, the positive electrode plate includes a first active material and a second active material. Due to the organic bonding of the two active materials, the secondary battery has good voltage self-balancing performance. By adjusting the difference in the SOC (State of Charge) state inside the electrode plate by itself, the capacity retention of the secondary battery can be improved. Moreover, since the voltage and SOC correspond well one-to-one, when monitoring the battery remaining capacity by voltage, the battery remaining capacity can be accurately displayed, improving the user experience.

[0023] The battery module, battery pack, and power consumption device of this application include the secondary battery according to this application, so they have at least the same advantages as the secondary battery.

Brief Description of the Drawings

[0024] [Figure 1] It is a schematic diagram when the geometric center A of the first active material overlaps with the geometric center B of the second active material (Figure 1-1), and when the geometric center A is lower than the geometric center B (Figure 1-2). [Diagram 2] They are the charge curves of LFP (lithium iron phosphate) (Figure 2-1) and the charge curves of NCM (lithium nickel cobalt manganese oxide) (Figure 2-2). The charge curve of LFP is gentle, and the charge curve of NCM is steep, and the voltage and SOC correspond well one-to-one. [Figure 3] It is a schematic diagram in which unit cell 1 and unit cell 2 are connected in parallel. [Figure 4] It is a graph in which the SOC difference between unit cell 1 and unit cell 2 corresponding to the LFP system (the left column graph) and the NCM523 system (i.e., LiNi0.5Co0.2Mn0.3O2) (the right column graph) increases with the increase of SOC. [Figure 5] It is a schematic diagram of the secondary battery according to an embodiment of this application. [Figure 6] It is an exploded view of the secondary battery according to an embodiment of this application shown in Figure 5. [Figure 7] It is a schematic diagram of the battery module according to an embodiment of this application. [Figure 8]It is a schematic diagram of a battery pack according to an embodiment of the present application. [Figure 9] It is an exploded view of a battery pack according to an embodiment of the present application shown in FIG. 8. [Figure 10] It is a schematic diagram of a power consumption device in which a secondary battery according to an embodiment of the present application is used as a power source.

Mode for Carrying Out the Invention

[0025] The following will specifically disclose embodiments of the positive electrode plate of the present application, its manufacturing method, secondary battery, battery module, battery pack, and power consumption device in detail with appropriate reference to the drawings. However, detailed descriptions that are not necessary may be omitted. For example, detailed descriptions of well-known matters and duplicate descriptions of structures that are actually the same may be omitted. This is to avoid the following description from becoming unnecessarily long and to make it easily understandable to those skilled in the art. Note that the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0026] The "ranges" disclosed in this application are defined in the form of lower and upper limits, and a given range is defined by selecting one lower limit and one upper limit that define the boundaries of the particular range. Such defined ranges may or may not include the end values and may be arbitrarily combined, i.e., any lower limit and any upper limit may be combined to form a single range. For example, if ranges of 60 to 120 and 80 to 110 are recited for a particular parameter, it is understood that the ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if minimum range values of 1 and 2 and maximum range values of 3, 4, and 5 are recited, the following ranges are also contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" is a shorthand expression representing all combinations of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed herein, and "0-5" is merely a shorthand notation for combinations of these numbers. Also, describing a parameter as an integer ≧2 is equivalent to disclosing that this parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0027] Unless otherwise stated, all embodiments and optional embodiments in the present application may be combined with each other to form a new technical solution.

[0028] Unless otherwise stated, all technical features and optional technical features in the present application may be combined with each other to form a new technical solution.

[0029] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, and preferably, they are performed sequentially. For example, the fact that the method includes steps (a) and (b) means that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the fact that the method mentioned above further includes step (c) means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), steps (a), (c) and (b), steps (c), (a) and (b), etc.

[0030] Unless otherwise specified, the terms "comprise" and "include" mentioned in this application represent an open type and may also be a closed type. For example, the above "comprise" and "include" may further comprise or include other components not listed, or may comprise or include only the listed components.

[0031] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" represents "A, B, or both A and B". More specifically, any one of the following conditions satisfies the condition of "A or B". A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), or both A and B are true (or exist).

[0032] It should be noted that, as understood by those skilled in the art, the term "lithium-rich manganese-based" used in this specification means a lithium-rich manganese-based material commonly used in the art, which includes two components of Li2MnO3 and LiMnO2, and the chemical formula may be abbreviated as xLiMO2·(1-x)Li2MnO3, where 0 < x < 1.

[0033] It should be noted that in this application, the term "voltage self-balancing" refers to the ability of a manufactured secondary battery to self-balance the voltage difference that occurs at different regions of the electrode assembly inside the cell due to differences in charge state distribution during use. Good "voltage self-balancing" performance is advantageous for improving the capacity retention, safety, and lifespan of the secondary battery.

[0034] For clarity, in this application, the term "geometric center" refers to the geometric center of the location where the active materials are distributed in the thickness direction of the electrode plate. For example, the geometric center of the location where the first active material is distributed in the thickness direction of the electrode plate is geometric center A, and the geometric center of the location where the second active material is distributed in the thickness direction of the electrode plate is geometric center B.

[0035] The inventors of the present application have found that in actual use, lithium iron phosphate secondary batteries frequently encounter problems such as inaccurate battery level indication and rapid capacity decay during use, which seriously affect the user experience. Surprisingly, after many attempts, the inventors have found that the above problems can be effectively improved by adding a second active material to the lithium iron phosphate positive electrode plate.

[0036] [Positive electrode] A first aspect of the present application provides a positive electrode plate, the positive electrode plate comprising at least: Formula LiFe 1-x Mn x a first active material selected from lithium iron phosphate based materials of PO4, where x is between 0 and 0.8, optionally between 0 and 0.5, and further optionally between 0 and 0.25; a second active material selected from one or more of lithium nickel oxide, lithium manganese oxide, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium-rich manganese-based, and lithium vanadium phosphate; Here, the amount of the second active material used is 10 to 70%, optionally 10 to 30%, and further optionally 15 to 20% based on the total mass of the first active material and the second active material.

[0037] The positive electrode plate of the present application includes a first active material and a second active material, and the organic bonding of the two active materials allows the secondary battery to have good voltage self-balancing performance and to automatically adjust for differences in SOC state within the electrode plate, thereby improving the capacity maintenance of the secondary battery. At the same time, since there is a good one-to-one correspondence between voltage and SOC, when monitoring the remaining battery capacity by voltage, the remaining battery capacity can be accurately displayed, improving the user experience.

[0038] In the positive plate of the present application, the first active material has the formula LiFe 1-x Mn x PO4, where x is between 0 and 0.8, optionally between 0 and 0.5, and further optionally between 0 and 0.25. For example, x may be selected from 0, 0.1, 0.2, 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, etc.

[0039] In the positive electrode plate of the present application, the second active material is selected from one or more of lithium nickel oxide, lithium manganese oxide, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium-rich manganese, and lithium vanadium phosphate. For example, the second active material may be lithium nickel cobalt manganese oxide, a mixture of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminate, or a mixture of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, and lithium vanadium phosphate.

[0040] In the positive electrode plate of the present application, the amount of the second active material used is 10 to 70%, optionally 10 to 30%, and further optionally 15 to 20% of the total mass of the first active material and the second active material. For example, the amount of the second active material used may be 10%, 15%, 20%, 30%, 40%, 50%, 60%, or 70%, and optionally 15% or 20%.

[0041] When the amount of the second active material is within the above range, good voltage self-balancing performance of the manufactured positive electrode plate can be ensured, the capacity retention of the secondary battery applying the positive electrode plate of the present application can be improved, and the remaining battery level can be accurately displayed.

[0042] Note that although the first active material has a low energy density, it has excellent high-temperature safety. On the other hand, the second active material may have low high-temperature safety. Therefore, if the amount of the second active material used is too large, the high-temperature safety of the secondary battery may be impaired. Conversely, if the amount of the second active material used is too small, the energy density of the secondary battery may be low.

[0043] In some embodiments, optionally, when lithium nickel cobalt manganate is included in the second active material, on the premise that the total amount of the second active material used is within the range defined in the present application, the minimum content of lithium nickel cobalt manganate is 5% with respect to the total mass of the first active material and the second active material.

[0044] In some embodiments, optionally, when lithium nickel cobalt aluminate is included in the second active material, on the premise that the total amount of the second active material used is within the range defined in the present application, the minimum content of lithium nickel cobalt aluminate is 5% with respect to the total mass of the first active material and the second active material.

[0045] In some embodiments, optionally, the amount of the first active material used is 30-90%, optionally 70-90%, and further optionally 80-85% with respect to the total mass of the first active material and the second active material.

[0046] If the amount of the first active material used is higher than the above range, the energy density of the positive electrode plate may be low. If the amount of the first active material used is lower than the above range, the high-temperature safety of the secondary battery applying the positive electrode plate may be low.

[0047] In some embodiments, optionally, the mass ratio of the first active material to the second active material is from 3:7 to 9:1, optionally from 7:3 to 9:1, and further optionally from 80:20 to 85:15.

[0048] By organically combining the first active material and the second active material in the above mass ratio, good voltage self - balancing performance can be imparted to a secondary battery using the positive electrode plate. Note that the positive electrode plate containing the first active material and the second active material in the above mass ratio has a high energy density, and the secondary battery using the positive electrode plate further has excellent high - temperature performance.

[0049] In some embodiments, optionally, the first active material is lithium iron phosphate or lithium manganese iron phosphate or a mixture of lithium iron phosphate and lithium manganese iron phosphate.

[0050] In some embodiments, optionally, the second active material contains at least one of lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminate.

[0051] In some embodiments, optionally, in the thickness direction of the positive electrode plate, the geometric center where the first active material is distributed is not higher than the geometric center where the second active material is distributed.

[0052] In some embodiments, optionally, as shown in FIG. 1 - 1, in the thickness direction of the positive electrode plate, the geometric center A where the first active material is distributed overlaps with the geometric center B where the second active material is distributed.

[0053] In some embodiments, optionally, as shown in FIG. 1 - 2, in the thickness direction of the positive electrode plate, the geometric center A where the first active material is distributed is lower than the geometric center B where the second active material is distributed.

[0054] As will be understood by those skilled in the art, the spatial structure design at the electrode plate level, especially the design of an electrode plate containing two or more active materials, also has a significant impact on the performance of a lithium secondary battery. The spatial structure design of the electrode plate can further improve battery performance. In the present application, when the distribution of the geometric centers of the first active material and the second active material meets the above-mentioned conditions, particularly when the geometric center A where the first active material is distributed is lower than the geometric center B where the second active material is distributed, the charge polarization of a secondary battery using the positive electrode plate of the present application can be reduced, thereby reducing the heat generation and temperature rise of the secondary battery and further improving the safety performance and lifespan of the secondary battery.

[0055] The above-mentioned improvement effect can be understood as follows: if the first active material, for example, lithium iron phosphate, is less affected by diffusion and is placed closer to the current collector, the distance to the current collector can be shortened and ohmic polarization during the charging process can be reduced. On the other hand, if the second active material, for example, lithium nickel cobalt manganese oxide, is more affected by diffusion and is placed farther from the current collector, the lithium ion transmission path can be shortened and concentration polarization during the charging process can be reduced.

[0056] For example, if the first active material is lithium iron phosphate and the second active material is lithium nickel cobalt manganese oxide, and the lithium iron phosphate and the lithium nickel cobalt manganese oxide are directly and physically mixed and distributed, the geometric center A of the lithium iron phosphate and the geometric center B of the lithium nickel cobalt manganese oxide will overlap. Also, if two layers of lithium iron phosphate and lithium nickel cobalt manganese oxide are applied, and the lithium iron phosphate is located closer to the current collector and the lithium nickel cobalt manganese oxide is located farther from the current collector, the position of the geometric center A will be lower than the position of the geometric center B.

[0057] As will be understood by those skilled in the art, in the present application, the positive electrode plate further includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0058] In this application, the relative positions of the geometric centers can be determined by common methods known to those skilled in the art. For example, by analyzing the cross-sectional morphology of the polar plate using a scanning electron microscope and identifying the height range where the first active material is distributed based on the particle size, the geometric center A can be determined. By determining the geometric center B in the height range where the second active material is distributed, the relative positional relationship between the geometric centers A and B can be confirmed. Also, for example, surface element analysis can be performed on the positive electrode plate to form a distribution diagram of the characteristic elements of the active material in the cross-section, and by confirming the height range where the first active material is distributed and the height range where the second active material is distributed, the relative positional relationship between the geometric centers A and B can also be confirmed.

[0059] In this application, the positive electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode film layer is installed on either one or both of the two opposing surfaces of the positive electrode current collector.

[0060] In some embodiments, the positive electrode current collector may employ a metal foil sheet or a composite current collector. For example, as the metal foil sheet, aluminum foil may be employed. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as substrates like polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0061] In some embodiments, the positive electrode film layer may optionally further include an adhesive. As an example, the adhesive may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0062] In some embodiments, the positive electrode film layer may optionally further include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0063] In some embodiments, the mass ratio of the total mass of the first active material and the second active material in the positive electrode plate film layer is 80% or more, optionally 90% or more, and further optionally 95% or more.

[0064] In some embodiments, the positive electrode plate can be manufactured in the following manner. The above components for manufacturing the positive electrode plate, for example, any other components such as the positive electrode active material, the conductive agent, and the adhesive, are dispersed in a solvent (for example, N-methylpyrrolidone) to form a positive electrode slurry. The positive electrode slurry is coated on the positive electrode current collector, and after processes such as drying and cold pressing, a positive electrode plate is obtained.

[0065] In some embodiments, the positive electrode slurry of the first active material and the positive electrode slurry of the second active material may be manufactured respectively. The positive electrode slurry of the first active material may be coated on the side closer to the current collector, and the positive electrode slurry of the second active material may be coated on the side farther from the current collector.

[0066] [Method] As described above, according to the inventor's research, lithium iron phosphate secondary batteries are prone to problems such as attenuation of battery capacity and inaccurate display of power during use. Surprisingly, by adding a second active material to the first active material, the above problems can be well solved. It is considered that the secondary battery obtained by adding the second active material to the first active material has good voltage self-balancing performance and can well balance the voltage difference inside the secondary battery.

[0067] Therefore, the second aspect of the present application provides a method for balancing the internal voltage difference of a secondary battery. Here, a positive electrode plate is used, and the positive electrode plate includes at least the formula LiFe 1-x Mn x a first active material selected from lithium iron phosphate-based materials of PO4, where x is 0 to 0.8, optionally 0 to 0.5, and further optionally 0 to 0.25, and a second active material selected from one or more of lithium nickelate, lithium manganate, lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium-rich manganese-based, and lithium vanadium phosphate, and here, with respect to the total mass of the first active material and the second active material, the usage amount of the second active material is 10 to 70%, optionally 10 to 30%, and further optionally 15 to 20%.

[0068] As will be understood by those skilled in the art, in the method described in the second aspect of the present application, the first active material and the second active material may have the meanings described for the part related to the positive electrode plate.

[0069] The inventors simulated the method described in this application using a mathematical physics model. A lithium secondary battery may be regarded as a parallel connection of innumerable small unit cells. When charging a lithium secondary battery, different unit cells have different spatial positions where they are located, and environmental factors that affect the dynamics such as temperature / stress / electrolyte infiltration are different. Therefore, the dynamics during charging are different, the charging rates are different, and an SOC deviation is formed in the unit cells at different positions.

[0070] As shown in FIG. 3, in the model, unit cell 1 and unit cell 2 are connected in parallel. The temperature at the position of unit cell 1 is set to 30 °C, and the temperature at the position of unit cell 2 is set to be higher than the temperature at the position of unit cell 1 (for example, 5 °C higher or 10 °C higher), and they are charged at different rates (for example, charging rates of 1C, 2C, 4C). Calculate the SOC difference between unit cell 1 and unit cell 2.

[0071] As shown in FIG. 4, in a lithium iron phosphate battery, with the increase in the temperature difference and the charging rate, the SOC difference between unit cell 1 and unit cell 2 continuously increases, and until the average SOC of charging reaches 80% SOC or more, there is no inflection point in the SOC difference between unit cell 1 and unit cell 2, indicating that the voltage self-balancing performance of the unit cell is poor and the generated voltage difference is insufficient to adjust the difference in the SOC state. In contrast, in a lithium nickel cobalt manganese oxide battery, when the average SOC of charging reaches about 50% SOC, the SOC difference decreases with the increase in the average SOC, and an internal self-balance is formed in the voltage difference between unit cell 1 and unit cell 2, indicating that the unit cell can adjust the difference in the SOC state by itself under the action of the voltage difference. As can be seen from this, by adding a second active material such as lithium nickel cobalt manganese oxide to a first active material such as lithium iron phosphate, the voltage self-balancing performance of the secondary battery can be effectively improved.

[0072] [Secondary battery] The third aspect of this application provides a secondary battery including the positive electrode plate described in the first aspect of this application. The secondary battery can be manufactured by a method generally used in the art.

[0073] A typical secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During the charge and discharge process, active ions travel back and forth between the positive and negative electrodes, intercalating and deintercalating. The electrolyte serves to conduct ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short-circuiting between the positive and negative electrodes and allows ions to pass through.

[0074] In some embodiments, optionally, in the charging voltage curve of the secondary battery of the present application, a voltage value V1 at a position corresponding to an 85% charge state and a voltage value V2 at a position corresponding to a 60% charge state satisfy V1-V2≧0.15V.

[0075] When V1 and V2 satisfy the above relationship, the secondary battery has good voltage self-balancing performance, which is advantageous for improving the capacity maintenance of the secondary battery and accurately displaying the remaining battery capacity of the secondary battery.

[0076] Other components of the secondary battery, such as the negative plate, electrolyte, and separator, are described below.

[0077] [Negative electrode] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0078] For example, the negative electrode current collector has two surfaces that face each other in the thickness direction thereof, and the negative electrode film layer is disposed on one or both of the two facing surfaces of the negative electrode current collector.

[0079] In some embodiments, the negative electrode current collector may employ a metal foil sheet or a composite current collector. For example, a copper foil may be employed as the metal foil sheet. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer material substrate (such as substrates of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0080] In some embodiments, the negative electrode active material may employ a negative electrode active material for batteries well known in the art. As an example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from at least one of silicon alone, silicon oxide, silicon carbon composite, silicon nitride composite, and silicon alloy. The tin-based material may be selected from at least one of tin alone, tin oxide, and tin alloy. However, in this application, it is not limited to these materials, and other conventional materials that can be used as the negative electrode active material of the battery may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0081] In some embodiments, the negative electrode film layer may optionally further include an adhesive. The adhesive 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).

[0082] In some embodiments, the negative electrode film layer optionally further contains 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.

[0083] In some embodiments, the negative electrode film layer optionally further contains other auxiliaries, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)), etc.

[0084] In some embodiments, the negative electrode plate can be manufactured in the following manner. The above components for manufacturing the negative electrode plate, such as the negative electrode active material, conductive agent, adhesive, and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry. The negative electrode slurry is coated on the negative electrode current collector, and after processes such as drying and cold pressing, a negative electrode plate is obtained.

[0085] [Electrolyte] The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. This application does not specifically limit the type of electrolyte, and it can be selected according to demand. For example, the electrolyte may be liquid, gel-like, or all-solid.

[0086] In some embodiments, the electrolyte employs an electrolytic solution. The electrolytic solution contains an electrolyte salt and a solvent.

[0087] 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 difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, and lithium tetrafluoro(oxalato)phosphate.

[0088] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, ethyl methyl sulfone, and diethyl sulfone.

[0089] In some embodiments, the electrolyte may optionally further contain an additive. For example, the additive may include a negative electrode film-forming additive and a positive electrode film-forming additive, or may further include an additive that can improve some performances of the battery, such as an additive that improves the overcharge performance of the battery, an additive that improves the high-temperature or low-temperature performance of the battery, and the like.

[0090] [Separator] In some embodiments, the secondary battery further includes a separator. In the present application, there is no particular limitation on the type of the separator, and any separator having a porous structure with good chemical stability and mechanical stability, which is well known, may be selected.

[0091] In some embodiments, the material of the separator may be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and vinylidene fluoride. The separator may be a single-layer thin film or a multi-layer composite thin film, and there is no particular limitation. When the separator is a multi-layer composite thin film, the materials of each layer may be the same or different, and there is no particular limitation.

[0092] In some embodiments, the positive electrode plate, the negative electrode plate, and the separator may be used to manufacture an electrode assembly by a winding process or a lamination process.

[0093] In some embodiments, the secondary battery may include an outer casing, which may be used to package the electrode assembly and electrolyte.

[0094] In some embodiments, the exterior of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The exterior of the secondary battery may be a flexible package, such as a bag-type flexible package. The flexible package may be made of plastic, such as polypropylene, polybutylene terephthalate, or polybutylene succinate.

[0095] A fourth aspect of the present application provides a battery module including the secondary battery according to the third aspect of the present application.

[0096] A fifth aspect of the present application provides a battery pack including the battery module according to the fourth aspect of the present application.

[0097] A sixth aspect of the present application provides a power consuming device including at least one of the secondary battery of the third aspect, the battery module of the fourth aspect, or the battery pack of the fifth aspect of the present application. The secondary battery, battery module, or battery pack may be used as a power source for the power consuming device or as an energy storage unit for the power consuming device. The power consuming device may include, but is not limited to, mobile equipment (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.

[0098] The power consumption device may be a secondary battery, a battery module, or a battery pack, depending on the requirements of the use.

[0099] The secondary battery, battery module, battery pack, and power consumption device of the present application will be described below with appropriate reference to the drawings.

[0100] In the present application, there is no particular limitation on the shape of the secondary battery, which may be cylindrical, rectangular, or any other shape. For example, Fig. 5 shows a secondary battery 5 having a rectangular structure as an example.

[0101] In some embodiments, referring to FIG. 6 , the exterior may include a housing 51 and a cover plate 53. Here, the housing 51 may include a bottom plate and side plates connected to the bottom plate, which together form a surrounding accommodating cavity. The housing 51 has an opening communicating with the accommodating cavity, and the cover plate 53 can be provided to cover the opening and close the accommodating cavity. The positive electrode plate, the negative electrode plate, and the separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged in the accommodating cavity. An electrolyte permeates the electrode assembly 52. The secondary battery 5 may include one or more electrode assemblies 52, which can be selected by those skilled in the art according to actual specific needs.

[0102] In some embodiments, the secondary batteries may be assembled into a battery module, and the number of secondary batteries included in the battery module may be one or more, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0103] FIG. 7 shows an example of a battery module 4. Referring to FIG. 7, in the battery module 4, a plurality of secondary batteries 5 may be arranged in order along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fastened with fasteners.

[0104] Optionally, the battery module 4 may further include a housing having a storage space for storing a plurality of secondary batteries 5.

[0105] In some embodiments, the battery module may be further assembled into a battery pack. The number of battery modules included in the battery pack may be one or more, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0106] FIGS. 8 and 9 show a battery pack 1 as an example. Referring to FIGS. 8 and 9, the battery pack 1 may include a battery case and a plurality of battery modules 4 installed in the battery case. The battery case includes an upper case 2 and a lower case 3. The upper case 2 is provided to cover the lower case 3 and can form a sealed space for accommodating the battery module 4. The plurality of battery modules 4 may be arranged in the battery case according to any method.

[0107] FIG. 10 shows a power consumption device as an example. This power consumption device is, for example, a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the requirements for high output and high energy density for the secondary battery, a battery pack or a battery module can be used.

[0108] Another example of the device may be a mobile phone, a tablet computer, a notebook computer, etc. This device generally requires weight reduction and can adopt a secondary battery as a power source.

[0109] Examples Hereinafter, examples of the present application will be described. The examples described below are illustrative and are only used to interpret the present application and should not be understood as limiting the present application. For those where specific technologies or conditions are not specified in the examples, they are implemented according to the technologies or conditions described in the literature of the technical field or the product description. For the reagents or equipment used, those for which the manufacturer is not specified are all common products that can be purchased commercially.

[0110] The positive electrode active material according to the examples of the present application is as shown in Table 1 below.

[0111]

Table 1

[0112] Example 1 Manufacture of the positive electrode plate Lithium iron phosphate (based on LiFePO4) of the first active material, lithium nickel cobalt manganate (NCM523 i.e., LiNi 0.5 Co 0.2 Mn 0.3 O2) of the second active material, polyvinylidene fluoride as the binder, and acetylene black as the conductive agent were mixed at a weight ratio of 28.8:67.2:2:2, and N-methylpyrrolidone (NMP) was added as a solvent. The mixture was stirred by the action of a vacuum mixer until the system became uniform, and a positive electrode slurry with a solid content of 75 wt% was obtained. The positive electrode slurry was uniformly coated on an aluminum foil with a thickness of 13 μm at a coating density of 19.6 mg / cm 2 After coating on one side, drying, cold pressing, and slitting were carried out to obtain the positive electrode plate of Example 1.

[0113] Manufacture of the negative electrode plate Artificial graphite as the negative electrode active material, acetylene black as the conductive agent, styrene-butadiene rubber (SBR) as the binder, and sodium carboxymethyl cellulose (CMC-Na) as the thickener were dissolved in deionized water as the solvent at a weight ratio of 96:1:2:1, and after stirring and uniformly mixing, a negative electrode slurry was manufactured. The negative electrode slurry was uniformly coated on a copper foil of the negative electrode current collector at a coating density of 9.7 mg / cm 2 After drying, cold pressing, and slitting, a negative electrode plate was obtained.

[0114] Electrolyte In a glove box under an argon atmosphere (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC) / ethyl methyl carbonate (EMC) of the organic solvent was uniformly mixed at a volume ratio of 3 / 7, and 12.5 wt% (based on the weight of the ethylene carbonate / ethyl methyl carbonate solvent) of LiPF6 was added and dissolved in the above organic solvent, and uniformly stirred to obtain an electrolyte.

[0115] Separator A commercially available PP-PE polymer microporous thin film (Model No. 20, from Zhuoga Electronics Technology Co., Ltd.) with a thickness of 20 μm and an average pore size of 80 nm was used.

[0116] secondary battery The positive electrode plate, separator, and negative electrode plate are stacked in this order, with the separator acting as an insulator between the positive and negative electrodes, and then wound up to obtain a bare cell. The bare cell is then placed in a case, the electrolyte is injected, and the cell is packaged to obtain a secondary battery.

[0117] Examples 2 to 8 In the process of manufacturing the positive electrode plate, the first positive electrode active material is lithium iron phosphate (based on LiFePO4), the second positive electrode active material is lithium nickel cobalt manganese oxide (NCM523, i.e., LiNi 0.5 Co 0.2 Mn 0.3 The weight ratios of O2), polyvinylidene fluoride adhesive, and acetylene black conductive agent were 38.4:57.6:2:2, 48:48:2:2, 57.6:38.4:2:2, 67.2:28.8:2:2, 76.8:19.2:2:2, 81.6:14.4:2:2, and 86.4:9.6:2:2, respectively, and the coating density was 19.9 mg / cm. 2 , 20.1 mg / cm 2 , 20.4 mg / cm 2 , 20.7 mg / cm 2 , 20.9 mg / cm 2 , 21.1 mg / cm 2 and 21.2 mg / cm 2 Other than this, the other conditions of Examples 2 to 8 are the same as those of Example 1.

[0118] Example 9 The second positive electrode active material is lithium nickel cobalt manganese oxide (NCM523, i.e., LiNi 0.5 Co 0.2 Mn 0.3 O2) into an NCA of equal mass (i.e., LiNi 0.8 Co 0.15 Al 0.05Except for replacing it with O2), other conditions of Example 9 are the same as those of Example 6.

[0119] Comparative Examples 1 - 2 In the process of manufacturing the positive electrode plate, the weight ratios of lithium iron phosphate (based on LiFePO4) of the first positive electrode active material, lithium nickel cobalt manganese oxide (NCM523 i.e., LiNi 0.5 Co 0.2 Mn 0.3 O2), polyvinylidene fluoride as the binder, and acetylene black as the conductive agent are 91.2:4.8:2:2 and 96:0:2:2 respectively, and the coating densities are 21.4 mg / cm 2 and 21.5 mg / cm 2 respectively. Except for this, other conditions of Comparative Examples 1 - 2 are the same as those of Example 1.

[0120] Test Methods for Related Parameters 1. Test of the Geometric Centers of the First and Second Active Materials An appropriate amount of positive electrode plate sample was taken, and surface element analysis was performed by a scanning electron microscope to form a distribution diagram of the characteristic elements of the active material in the cross-section. By confirming the height interval where the first active material is distributed and the height interval where the second active material is distributed, the relative positions of the geometric center where the first active material is distributed and the geometric center where the second active material is distributed were confirmed.

[0121] 2. Voltage Curve Test of the Secondary Battery Suppose the upper and lower limits of the corresponding operating voltage of the secondary battery to be tested at 25°C are Vmax and Vmin respectively, and the nominal capacity is C0 Ah. Then the test method is as follows. The secondary battery to be tested was placed in a constant temperature test environment of 25°C and left standing for 2 hours. It was discharged at a constant current of 0.33C0 until the lower limit voltage Vmin, left standing for 30 minutes, charged at a constant current of 1C0 until the upper limit voltage Vmax, and then charged at a constant voltage until the current decreased to 0.05C0. All the capacities charged during this charging process corresponded to the capacities from 0% SOC to 100% SOC. By plotting SOC% on the horizontal axis and the corresponding voltage during the constant current charging process on the vertical axis, the voltage curve of the secondary battery was obtained.

[0122] In the obtained voltage curve, in the section from 15 to 97% SOC, when the SOC increases by 5% and the voltage increases by >0.2 V, the corresponding minimum onset SOC position is the voltage increase position.

[0123] 3. Fast charge cycle life / number of cycles at 25°C In this application, the capacity retention of the secondary battery was evaluated by the rapid charge cycle life / number of cycles at 25°C.

[0124] At 25°C, the lithium ion batteries manufactured in the examples and comparative examples were charged at a rate of 2C and discharged at a rate of 1C. Continuous cycle tests were performed in the SOC range of 3% to 97% until the capacity of the lithium ion batteries became less than 80% of the initial capacity, and the number of cycles was recorded, which was recorded as cycle performance.

[0125] The relevant parameters and test results for the above Examples 1 to 9 and Comparative Examples 1 and 2 are as shown in Table 2 below.

[0126] [Table 2]

[0127] As shown in Table 2, the secondary battery prepared by adding the second active material has a better fast charge cycle life / number of cycles at 25°C than Comparative Example 2, which uses only the first active material. In addition, by further adjusting the amounts of the first and second active materials used and their mass ratio, the self-balancing performance of the corresponding battery can be further improved, thereby improving capacity retention.

[0128] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any embodiment that has substantially the same configuration as the technical idea and achieves similar functions and effects within the scope of the technical solution of the present application is considered to be within the technical scope of the present application. Furthermore, various modifications that a person skilled in the art may make to the embodiments without departing from the spirit of the present application, and other forms constructed by combining some of the components of the embodiments are also considered to be within the scope of the present application. [Explanation of symbols]

[0129] 1 battery pack, 2 upper case, 3 lower case, 4 battery module, 5 secondary battery, 51 housing, 52 electrode assembly, 53 cover plate

Claims

1. A positive electrode plate, comprising at least Formula LiFe １－ｘ Mn ｘ P.O. ４ a first active material selected from the lithium iron phosphate-based materials, wherein x is 0 to 0.8; a second active material comprising at least one of lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminate; Here, the amount of the second active material used is 15 to 20% of the total mass of the first active material and the second active material.

2. 2. The positive electrode plate according to claim 1, wherein the amount of the first active material used is 80 to 85% of the total mass of the first active material and the second active material.

3. 3. The positive electrode plate according to claim 1, wherein the first active material is lithium iron phosphate, lithium manganese iron phosphate, or a mixture of lithium iron phosphate and lithium manganese iron phosphate.

4. In the thickness direction of the positive electrode plate, the geometric center at which the first active material is distributed along the side closer to the current collector to the side farther from the current collector is not higher than the geometric center at which the second active material is distributed. The positive electrode plate according to any one of claims 1 to 3.

5. In the thickness direction of the positive electrode plate, A geometric center of distribution of the first active material overlaps with a geometric center of distribution of the second active material along a direction from a side closer to the current collector to a side farther from the current collector, or The geometric center at which the first active material is distributed along the side closer to the current collector to the side farther from the current collector is lower than the geometric center at which the second active material is distributed. The positive electrode plate according to any one of claims 1 to 4.

6. A method for balancing an internal voltage difference of a secondary battery, comprising using a positive electrode plate, the positive electrode plate comprising at least: Formula LiFe １－ｘ Mn ｘ PO ４ A first active material selected from a lithium iron phosphate-based material of, wherein x is from 0 to 0.8, and a second active material comprising at least one of lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminate; The method for balancing the internal voltage difference of a secondary battery, wherein the amount of the second active material used is 15 to 20% of the total mass of the first active material and the second active material.

7. A secondary battery comprising the positive electrode plate according to any one of claims 1 to 5.

8. 8. The secondary battery according to claim 7, wherein in a charging voltage curve of the secondary battery, a voltage value V1 at a position corresponding to an 85% charge state and a voltage value V2 at a position corresponding to a 60% charge state satisfy V1-V2≧0.15V.

9. A battery module comprising the secondary battery according to claim 7 or 8.

10. A battery pack comprising the battery module according to claim 9.

11. A power consumption device including at least one of the secondary battery according to claim 7 or 8, the battery module according to claim 9, or the battery pack according to claim 10.

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