Battery cell combination, battery and power utilization device

Abstract

The invention discloses a battery core combination, a battery and an electric device. The battery core combination comprises first battery cores and second battery cores, the number of the first battery cores is greater than or equal to that of the second battery cores, and each of the first battery cores and the second battery cores comprises a positive pole piece and a negative pole piece; the battery core combination meets the following conditions: 0.7 < = NPA1 < = 1.05 NPB1 and NPA1 < 1, or 0.75 < = NPA2 < = 1.05 NPB2 and NPA2 < 1.2; and when the state of charge of the single-cell battery comprising the second cell is in a range of 95% to 100%, the voltage change of the second cell is correspondingly greater than 5mV every time the state of charge of the single-cell battery changes by 1%.

Description

Battery cell assembly, battery and electrical device Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a battery cell assembly, a battery, and an electrical device. Background Art

[0002] In recent years, the application of secondary batteries has become increasingly widespread. They are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As secondary batteries have achieved great development, higher requirements have been placed on cycle performance and safety performance.

[0003] Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a battery cell combination, a battery and an electrical device. The use of the battery cell combination of the application is conducive to reducing the occurrence of battery overcharging, improving the safety performance of the battery and extending the cycle life of the battery.

[0005] In order to achieve the above-mentioned object, the first aspect of the present application provides a battery cell combination, including a first battery cell and a second battery cell, the number of the first battery cells is greater than or equal to the number of the second battery cells, and the first battery cell and the second battery cell both include a positive electrode sheet and a negative electrode sheet;

[0006] Furthermore, the battery cell combination satisfies:

[0007] 0.7≤NP A1 ≤1.05NP B1 And NP A1 <1, or 0.75≤NP A2 ≤1.05NP B2 And NP A2 <1.2;

[0008] Among them, NP A1 NP is the ratio of the initial lithium insertion capacity of the negative electrode to the initial lithium removal capacity of the positive electrode in the first cell. B1 NP is the ratio of the first lithium insertion capacity of the negative electrode to the first lithium removal capacity of the positive electrode in the second cell. A2 NP is the ratio of the non-first lithium insertion capacity of the negative electrode to the non-first lithium removal capacity of the positive electrode in the first cell. B2 is the ratio of the non-first lithium insertion capacity of the negative electrode plate to the non-first lithium removal capacity of the positive electrode plate in the second battery cell;

[0009] When the state of charge of the single-cell battery including the second cell is in the range of 95% to 100%, the voltage of the second cell changes by more than 5 mV for every 1% change in the state of charge of the single-cell battery.

[0010] Designing the battery cell's NP to a limit of less than 1 is beneficial for reducing the amount of negative electrode active materials used and lowering costs. At the same time, the space saved can further increase capacity. However, this will cause the state of charge (SOC) of the single-cell battery to approach saturation. For every 1% change in the SOC of the single-cell battery, the corresponding battery cell voltage change is very small, which can easily lead to overcharging of the single-cell battery and pose a safety hazard.

[0011] The present application makes the number of first cells greater than or equal to the number of second cells by combining cells, and limits the voltage change of the second cell to more than 5mV for every 1% change in the SOC of the single cell battery when the SOC of the second cell is close to saturation, and limits the NP A1 Numerical Values ​​and NP B1 relationship, or restrict NP A2 Numerical Values ​​and NP B2 This helps reduce the occurrence of battery overcharge, improves battery safety performance, and extends the battery cycle life.

[0012] In any embodiment, when the state of charge of the single-cell battery including the first cell is in the range of 95% to 100%, for every 1% change in the state of charge of the single-cell battery, the voltage of the first cell changes by less than or equal to 5 mV.

[0013] When the first battery cell reaches its design limit, the first battery cell satisfies the above-mentioned voltage variation characteristics.

[0014] In any embodiment, the battery cell combination satisfies: 0.08≤(1.1-NP A1 ) / (NP B1 -1)≤20;

[0015] Preferably, 0.1≤(1.1-NP A1 ) / (NP B1 -1)≤15.

[0016] Therefore, when the above relationship is met, while meeting the battery capacity requirements, the initial voltage of the battery is limited, so that the battery can form a stable and dense SEI film in a lower voltage range, thereby extending the cycle life of the battery.

[0017] In any embodiment, the battery cell combination satisfies:

[0018] 0.95≤C B / C A≤1.4, optional 1.0≤C B / C A ≤1.3;

[0019] Among them, C A The widest voltage range capacity of the first battery cell during its entire life cycle, C B The second battery cell has the widest voltage range capacity for its entire life cycle.

[0020] Therefore, the present application satisfies the life matching of the battery throughout its entire life cycle by matching the capacity designs of the first battery cell and the second battery cell, thereby extending the cycle life of the battery and improving the safety performance of the battery throughout its entire life cycle.

[0021] In any embodiment, the positive electrode sheet in the first battery cell includes a first positive electrode active material, and the first positive electrode active material includes a compound Li a A x Mn 1-y B y P 1-z C z O 4-n D n ;

[0022] Wherein, A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W; B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge; C includes one or more elements selected from B (boron), S, Si and N; D includes one or more elements selected from S, F, Cl and Br; a is 0.85-1.15; x is 0-0.1; y is 0.001-1; z is 0-0.5; and n is 0-0.5.

[0023] In any embodiment, the first positive electrode active material comprises a core and a coating layer coating the core; wherein the core comprises the compound Li a A x Mn 1-y B y P 1-z C z O 4-n D n , the coating layer contains carbon element.

[0024] Therefore, the present application adopts the above-mentioned first positive electrode active material to achieve the NP limit design of the first battery cell, which is beneficial to improving the energy density of the first battery cell.

[0025] In any embodiment, the positive electrode plate in the second battery cell includes a second positive electrode active material; the second positive electrode active material includes a compound LiNi b Co d Mn e M f O2;

[0026] Wherein, the M includes one or more elements selected from the group consisting of Mn, Al, Mg, Ca, Na, Ti, W, Zr, Sr, Cr, Zn, Ba, B, S and Y, and may optionally include Mg and / or Al elements; the b value is 0.314-0.970; the d value is 0-0.320, and may optionally be 0.047-0.320; and the e value is 0.006-0.390; and the sum of b, d, e and f is 1, and f is greater than 0.

[0027] In any embodiment, the positive electrode sheet in the second battery cell further includes a third positive electrode active material; the third positive electrode active material includes a core and a shell covering the core, the shell including a first coating layer covering the core, a second coating layer covering the first coating layer, and a third coating layer covering the second coating layer; the core includes the compound Li 1+g Mn 1-h E h P 1-i R i O4, the first coating layer contains crystalline pyrophosphate Li j GP2O7 and / or G k (P2O7) r The second coating layer comprises crystalline phosphate X t PO4, the third coating layer contains carbon element;

[0028] Wherein, the E includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and may optionally include one or more elements selected from Fe, V, Ni and Co; the R includes one or more elements selected from B, Si, N and S, and may optionally include one or more elements selected from Si, N and S; the crystalline pyrophosphate Li j GP2O7 and G k (P2O7) rwherein G independently includes one or more elements selected from the group consisting of Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al, and may optionally include one or more elements selected from the group consisting of Fe, Co, Ti, and Al; wherein X includes one or more elements selected from the group consisting of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al, and may optionally include one or more elements selected from the group consisting of Li, Fe, Ag, and Al; wherein g is -0.100-0.100; h is 0.001-0.600; i is 0.001-0.100; j is greater than 0 and less than or equal to 2; k is 1-4; r is 1-3; and t is greater than 0 and less than or equal to 2.

[0029] Therefore, the second battery cell of the present application adopts the above-mentioned second positive electrode active material and the optional third positive electrode active material, which increases the compaction density of the second battery cell, improves the thermal stability of the battery, and extends the cycle life of the battery.

[0030] In any embodiment, in the positive electrode sheet of the second battery cell, the mass of the second positive electrode active material accounts for 5%-100% of the total mass of the second positive electrode active material and the third positive electrode active material, and can be optionally 5%-95%.

[0031] As a result, the compaction density of the second battery cell is further increased, the thermal stability of the battery is further improved, and the cycle life of the battery is further extended.

[0032] A second aspect of the present application provides a battery, comprising the battery cell combination of the first aspect of the present application.

[0033] In any embodiment, the upper limit voltage of the second battery cell during the 90th to 110th cycle of charge and discharge of the battery is greater than the upper limit voltage of the second battery cell during the first cycle of charge and discharge of the battery.

[0034] Therefore, while meeting the battery capacity requirements, the lower initial upper limit voltage of the second battery cell limits the initial voltage of the battery, allowing the battery to form a stable and dense SEI film in a lower voltage range, thereby extending the battery's cycle life after later expansion.

[0035] The second aspect of the present application further provides an electrical device comprising the battery of the first aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0037] FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 1 .

[0038] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0039] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0040] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application.

[0041] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0042] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0043] Below, the embodiments of the battery cell combination, secondary battery, battery module, battery pack and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0044] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0045] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0046] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0047] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may further include step (c), which indicates that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0048] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may indicate that other components not listed may also be included or that only the listed components are included.

[0049] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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).

[0050] [Secondary battery]

[0051] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged to activate the active materials after discharge and continue to be used.

[0052] Typically, a secondary battery includes a cell or cell combination, which includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During the charge and discharge process of the battery, active ions (such as lithium ions) are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing active ions to pass through. The electrolyte is between the positive electrode sheet and the negative electrode sheet, mainly to conduct active ions.

[0053] [Battery cell combination]

[0054] An embodiment of the present application provides a battery cell combination, comprising a first battery cell and a second battery cell, wherein the number of the first battery cells is greater than or equal to the number of the second battery cells, and the first battery cell and the second battery cell both comprise a positive electrode sheet and a negative electrode sheet;

[0055] Furthermore, the battery cell combination satisfies:

[0056] 0.7≤NP A1 ≤1.05NP B1 And NP A1 <1, or 0.75≤NP A2 ≤1.05NP B2 And NP A2 <1.2;

[0057] Among them, NP A1 NP is the ratio of the initial lithium insertion capacity of the negative electrode to the initial lithium removal capacity of the positive electrode in the first cell. B1 NP is the ratio of the first lithium insertion capacity of the negative electrode to the first lithium removal capacity of the positive electrode in the second cell. A2 NP is the ratio of the non-first lithium insertion capacity of the negative electrode to the non-first lithium removal capacity of the positive electrode in the first cell. B2 is the ratio of the non-first lithium insertion capacity of the negative electrode plate to the non-first lithium removal capacity of the positive electrode plate in the second battery cell;

[0058] When the state of charge of the single-cell battery including the second cell is in the range of 95% to 100%, the voltage of the second cell changes by more than 5 mV for every 1% change in the state of charge of the single-cell battery.

[0059] Designing the battery cell's NP to a limit of less than 1 is beneficial for reducing the amount of negative electrode active materials used and lowering costs. At the same time, the space saved can further increase capacity. However, this will cause the state of charge (SOC) of the single-cell battery to approach saturation. For every 1% change in the SOC of the single-cell battery, the corresponding battery cell voltage change is very small, which can easily lead to overcharging of the single-cell battery and pose a safety hazard.

[0060] Although the mechanism is not clear, the applicant unexpectedly found that: the present application makes the number of first cells greater than or equal to the number of second cells by combining the cells, and limits the second cell's single cell battery SOC to be close to saturation, and the corresponding second cell voltage change is greater than 5mV for every 1% change in the single cell battery SOC, and limits the NP A1 Numerical Values ​​and NP B1 relationship, or restrict NP A2 Numerical Values ​​and NP B2 This helps reduce the occurrence of battery overcharge, improves battery safety performance, and extends the cycle life of the battery.

[0061] In some embodiments, when the state of charge of the single-cell battery including the first cell is in the range of 95% to 100%, for every 1% change in the state of charge of the single-cell battery, the voltage of the first cell changes by less than or equal to 5 mV.

[0062] When the first battery cell reaches its design limit, the first battery cell satisfies the above-mentioned voltage variation characteristics.

[0063] In some embodiments, when the state of charge (SOC) of a single-cell battery is in the range of 95% to 100%, the voltage change value of the first cell or the second cell is determined using conventional methods in the art for every 1% change in the state of charge (SOC) of the single-cell battery; for example, the specific method is: assembling the first cell or the second cell into a single-cell battery according to a conventional method. In a constant temperature environment of 25°C, the battery is allowed to stand for 10 minutes and then discharged at a constant current of 0.1C to the cut-off voltage. It is allowed to stand for 10 minutes and then charged to the target voltage at a constant current of 0.04C. It is allowed to stand for 10 minutes and then discharged to the cut-off voltage at a constant current of 0.04C. It is allowed to stand for 10 minutes and then charged to the target voltage at a constant current of 0.04C. The charging capacity at this time is recorded as 100% SOC. It is allowed to stand for 10 minutes and then discharged to the cut-off voltage at a constant current of 0.04C. A graph is drawn with the charging capacity of the last charging process as the y-axis and the voltage as the x-axis. The voltage Vm corresponding to 95% SOC and the voltage Vn corresponding to 100% SOC are obtained from the graph. When the state of charge of the battery is in the range of 95% to 100%, the voltage change value of the first cell or the second cell is (Vn-Vm) / 5 for every 1% change in the state of charge of the battery.

[0064] In some embodiments, the first lithium insertion gram capacity and non-first lithium insertion gram capacity of the negative electrode sheet and the first lithium removal gram capacity and non-first lithium insertion gram capacity of the positive electrode sheet are determined by conventional methods in the art. For example, the method for determining the first lithium removal gram capacity and non-first lithium insertion gram capacity of the positive electrode sheet is as follows: the positive electrode sheet and the counter electrode lithium sheet are made into a button battery. In a constant temperature environment of 25°C, charge to 4.35V at a constant current of 0.1C, and then discharge to 2.8V at 0.1C, record the discharge capacity of the first cycle, divide the discharge capacity of the first cycle by the mass of the positive active material in the positive electrode sheet to obtain the first lithium removal gram capacity of the positive electrode sheet; the button battery continues to charge and discharge in the above manner for 2 times, for a total of 3 times, record the second charge and discharge capacity as the non-first cycle discharge capacity, divide the non-first cycle discharge capacity by the mass of the positive active material in the positive electrode sheet to obtain the non-first lithium removal gram capacity of the positive electrode sheet. For example, the method for determining the first lithium insertion gram capacity and non-first lithium insertion gram capacity of the negative electrode sheet is as follows: the negative electrode sheet and the counter electrode lithium sheet are made into a button battery. In a constant temperature environment of 25°C, the battery is charged to 2.0V at a constant current of 0.1C, and then discharged to 0V at 0.1C. The discharge capacity of the first cycle is recorded, and the discharge capacity of the first cycle is divided by the mass of the negative electrode active material in the negative electrode sheet to obtain the first lithium insertion gram capacity of the negative electrode sheet; the button battery is charged and discharged twice in the above manner, for a total of three times, and the second charge and discharge capacity is recorded as the non-first cycle discharge capacity. The discharge capacity of the non-first cycle is divided by the mass of the negative electrode active material in the negative electrode sheet to obtain the non-first lithium insertion gram capacity of the negative electrode sheet.

[0065] In some embodiments, the battery cell combination satisfies: 0.08≤(1.1-NP A1 ) / (NP B1 -1)≤20;

[0066] Preferably, 0.1≤(1.1-NP A1 ) / (NP B1 -1)≤15; for example (1.1-NP A1 ) / (NP B1 -1) is 0.2, 0.3, 0.6, 0.8, 1, 2, 3, 5, 7, 8, 10, 12, 14, 16, 17, 18, 19, or any range consisting of the above values.

[0067] Therefore, when the above relationship is met, while meeting the battery capacity requirements, the initial voltage of the battery is limited, so that the battery can form a stable and dense SEI film in a lower voltage range, thereby extending the cycle life of the battery.

[0068] In some embodiments, the battery cell combination satisfies: 0.95≤C B / C A ≤1.4;

[0069] Optional: 1.0≤C B / C A ≤1.3, for example, C B / C A The range is 1.1, 1.2, 1.25 and any of the above values;

[0070] Among them, C A The widest voltage range capacity of the first battery cell during its entire life cycle, C B The second battery cell has the widest voltage range capacity for its entire life cycle.

[0071] Therefore, the present application satisfies the life matching of the battery throughout its entire life cycle by matching the capacity designs of the first battery cell and the second battery cell, thereby extending the cycle life of the battery and improving the safety performance of the battery throughout its entire life cycle.

[0072] In some embodiments, the positive electrode sheet in the first battery cell includes a first positive electrode active material, and the first positive electrode active material includes a compound Li a A x Mn 1-y B y P 1-z C z O 4-n D n ;

[0073] Wherein, A comprises one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W; B comprises one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, and optionally comprises Ti and / or Fe; C comprises one or more elements selected from B (boron), S, Si and N; D comprises one or more elements selected from S, F, Cl and Br; a is 0.85-1.15, for example, 0.85, 0.90, 0.95, 1.00, 1.05, 1.10, 1.15 and the range consisting of any of the above values; x is 0-0.1, and can be 0, for example, 0, 0. 0.1, 0.2, 0.3, 0.4, 0.5, and a range consisting of the above values; the n is 0-0.5, for example, 0, 0.1, 0.2, 0.3, 0.4, 0.5, and a range consisting of the above values; the y is 0.001-1, for example, 0.005, 0.008, 0.01, 0.03, 0.05, 0.08, 0.1, 0.3, 0.5, 0.7, 0.8, 0.9, 0.95, 1, and a range consisting of the above values; the z is 0-0.5, for example, 0, 0.1, 0.2, 0.3, 0.4, 0.5, and a range consisting of the above values; the n is 0-0.5, for example, 0, 0.1, 0.2, 0.3, 0.4, 0.5, and a range consisting of the above values.

[0074] In some embodiments, the first positive electrode active material comprises a core and a coating layer coating the core; wherein the core comprises the compound Li a A x Mn 1-y B y P 1-z C z O 4-n D n , the coating layer contains carbon element.

[0075] Therefore, the present application adopts the above-mentioned first positive electrode active material to achieve the NP limit design of the first battery cell, which is beneficial to improving the energy density of the first battery cell.

[0076] In some embodiments, the positive electrode plate in the second battery cell includes a second positive electrode active material; the second positive electrode active material includes a compound LiNi b Co d Mn e M f O2;

[0077] Wherein, the M includes one or more elements selected from the group consisting of Mn, Al, Mg, Ca, Na, Ti, W, Zr, Sr, Cr, Zn, Ba, B, S and Y, and may optionally include Mg and / or Al; the b is 0.314-0.970, such as 0.4, 0.5, 0.55, 0.6, 0.7, 0.8, 0.9 and any range thereof; the d is 0-0.320, and may optionally be 0.047-0.320, such as 0.050, 0.060, 0.080, 0.100, 0.120, 0.141, 0.160, 0. .180, 0.200, 0.250, 0.270, 0.300, 0.310 and the range consisting of any of the above values; the e is 0.006-0.390, for example, 0.010, 0.020, 0.050, 0.080, 0.100, 0.130, 0.170, 0.200, 0.220, 0.230, 0.249, 0.260, 0.280, 0.300, 0.320, 0.350, 0.370, 0.380 and the range consisting of any of the above values; and the sum of b, d, e and f is 1 and f is greater than 0.

[0078] In some embodiments, the positive electrode sheet in the second battery cell further includes a third positive electrode active material; the third positive electrode active material includes a core and a shell covering the core, the shell including a first coating layer covering the core, a second coating layer covering the first coating layer, and a third coating layer covering the second coating layer; the core includes a compound Li 1+gMn 1-h E h P 1-i R i O4, the first coating layer contains crystalline pyrophosphate Li j GP2O7 and / or G k (P2O7) r The second coating layer comprises crystalline phosphate X t PO4, the third coating layer contains carbon element;

[0079] Wherein, the E includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and may optionally include one or more elements selected from Fe, V, Ni and Co, and may more optionally include one or more elements selected from Fe, V and Co; the R includes one or more elements selected from B, Si, N and S, and may optionally include one or more elements selected from Si, N and S, and may more optionally include Si; the crystalline pyrophosphate Li j GP2O7 and G k (P2O7) r wherein G independently comprises one or more elements selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al, and may be selected from one or more elements selected from Fe, Co, Ti and Al, and may be selected from Fe; wherein X comprises one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al, and may be selected from one or more elements selected from Li, Fe, Ag and Al, and may be selected from Li and / or Fe; wherein g is -0.100-0.100, For example, it is -0.05, -0.01, 0, 0.001, 0.005, 0.01, 0.02, 0.05, 0.07, 0.08, 0.09 and the range consisting of any of the above values; the h is 0.001-0.600, for example, 0.005, 0.01, 0.03, 0.05, 0.07, 0.1, 0.2, 0.3, 0.4, 0.5 and the range consisting of any of the above values; the i is 0.001-0.100, for example, 0.001, 0.003, 0.007, 0.01, 0.04, 0.06, 0.08, 0.1 and the range consisting of any of the above values; the j is greater than 0 and less than or equal to 2; the k is 1-4; the r is 1-3; and the t is greater than 0 and less than or equal to 2.

[0080] Therefore, the second battery cell of the present application adopts the above-mentioned second positive electrode active material and the optional third positive electrode active material, which increases the compaction density of the second battery cell, improves the thermal stability of the battery, and extends the cycle life of the battery.

[0081] In some embodiments, Li a A x Mn 1-y B y P 1-z C z O 4-n D n 、LiNi b Co d Mn e M f O2、Li 1+g Mn 1- h E h P 1-i R i O4、Li j GP2O7, G k (P2O7) r and X t PO4 is electrically neutral.

[0082] In some embodiments, in the positive electrode sheet of the second battery cell, the mass of the second positive electrode active material accounts for 5%-100% of the total mass of the second positive electrode active material and the third positive electrode active material, and can be optionally 5%-95%, for example, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and the range consisting of any of the above values.

[0083] As a result, the compaction density of the second battery cell is further increased, the thermal stability of the battery is further improved, and the cycle life of the battery is further extended.

[0084] In some embodiments, the method for preparing the first positive electrode active material of the present application comprises the following steps:

[0085] (1) dissolving a manganese source, a source of element B, and an acid in a solvent and stirring to generate a suspension of a manganese salt doped with element B, filtering the suspension and drying the filter cake to obtain a manganese salt doped with element B;

[0086] (2) adding a lithium source, a phosphorus source, a source of element A, a source of element C, a source of element D, a solvent, and the manganese salt doped with element B obtained in step (1) into a reaction container, grinding and mixing to obtain a slurry;

[0087] (3) transferring the slurry obtained in step (2) to a spray drying device for spray drying and granulation to obtain granules;

[0088] (4) Sintering the particles obtained in step (3).

[0089] In some embodiments, the source of element A is selected from at least one of a simple substance, oxide, phosphate, oxalate, carbonate, and sulfate of element A; the source of element B is selected from at least one of a simple substance, oxide, phosphate, oxalate, carbonate, and sulfate of element B; the source of element C is selected from at least one of a sulfate, borate, nitrate, and silicate of element C; and the source of element D is selected from at least one of a simple substance and an ammonium salt of element D. By selecting the source of each doping element, the uniformity of the distribution of the doping element can be improved, thereby improving the performance of the material.

[0090] In some embodiments, the acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and organic acids such as oxalic acid, for example, oxalic acid. In some embodiments, the acid is a dilute acid with a concentration of 60% by weight or less.

[0091] In some embodiments, the manganese source may be a manganese-containing substance known in the art that can be used to prepare lithium manganese phosphate. For example, the manganese source may be selected from elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, manganese carbonate, or a combination thereof.

[0092] In some embodiments, the lithium source may be a lithium-containing material known in the art that can be used to prepare lithium manganese phosphate. For example, the lithium source may be selected from lithium carbonate, lithium hydroxide, lithium phosphate, lithium dihydrogen phosphate, or a combination thereof.

[0093] In some embodiments, the phosphorus source may be a phosphorus-containing substance known in the art that can be used to prepare lithium manganese phosphate. For example, the phosphorus source may be selected from diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid, or a combination thereof.

[0094] The amount of each source of elements A, B, C, and D added depends on the target doping amount, and the ratio of the amount of lithium source, manganese source, and phosphorus source used conforms to the stoichiometric ratio.

[0095] In some embodiments, the solvents in step (1) and step (2) can each independently be a solvent conventionally used by those skilled in the art in the preparation of manganese salts and lithium manganese phosphate, for example, they can each independently be selected from at least one of ethanol and water (e.g., deionized water).

[0096] In some embodiments, the method for preparing the third positive electrode active material comprises the following steps:

[0097] Step of providing a core material: the core chemical formula is Li 1+g Mn 1-h E h P 1-i R i O4, wherein the definitions of E, R, g, h, and i are as described above;

[0098] First coating step: dissolving a source of element G, a phosphorus source, an acid, and optionally a lithium source in a solvent to obtain a first coating layer suspension; thoroughly mixing the core obtained in the core step with the first coating layer suspension obtained in the first coating step, drying, and then sintering to obtain a material coated with the first coating layer;

[0099] Second coating step: dissolving the source of element X, the phosphorus source and the acid in a solvent to obtain a second coating layer suspension; fully mixing the first coating layer material obtained in the first coating step with the second coating layer suspension obtained in the second coating step, drying, and then sintering to obtain a material coated with two coating layers;

[0100] The third coating step: dissolving the carbon source in a solvent and fully dissolving it to obtain a third coating layer solution; then adding the two-layer coating material obtained in the second coating step to the third coating layer solution, mixing evenly, drying, and then sintering to obtain a three-layer coating material.

[0101] One embodiment of the present application provides a secondary battery, including the battery cell combination described above.

[0102] In some embodiments, the upper limit voltage of the second battery cell at the 90th to 110th cycle (e.g., 92nd, 95th, 96th, 97th, 98th, 100th cycle and a range consisting of any of the above values) of the battery charge and discharge cycle is greater than the upper limit voltage of the second battery cell at the first cycle of charge and discharge of the battery.

[0103] Therefore, while meeting the battery capacity requirements, the lower initial upper limit voltage of the second battery cell limits the initial voltage of the battery, allowing the battery to form a stable and dense SEI film in a lower voltage range, thereby extending the battery's cycle life after later expansion.

[0104] [Positive electrode]

[0105] The positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0106] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0107] In some embodiments, the positive electrode 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 material base and a metal layer formed on at least one surface of the polymer material base. 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0108] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0109] In some embodiments, the positive electrode film layer may further include a conductive agent. For 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.

[0110] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0111] [Negative electrode]

[0112] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0113] As an example, the negative electrode current collector has two surfaces opposite to each other in its 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.

[0114] 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 base layer and a metal layer formed on at least one surface of the polymer base material. 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 base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0115] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. 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. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional 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.

[0116] In some embodiments, the negative electrode film layer may further include a binder. For example, 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).

[0117] In some embodiments, the negative electrode film layer may further include a conductive agent. For example, 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.

[0118] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0119] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0120] [Electrolytes]

[0121] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0122] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0123] 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0124] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl 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, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0125] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0126] [Isolation film]

[0127] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0128] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven 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.

[0129] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0130] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0131] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0132] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 5 with a square structure as an example.

[0133] In some embodiments, referring to FIG2 , the outer package may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0134] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0135] Figure 3 shows an example battery module 4. Referring to Figure 3 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0136] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0137] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0138] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0139] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0140] As an electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0141] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0142] [Example]

[0143] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0144] Example 1

[0145] (1) Preparation of the first battery cell

[0146] (1) Preparation of the first positive electrode active material:

[0147] With iron phosphate, lithium carbonate and titanium oxide as raw materials, according to the stoichiometric ratio of FePO4:Li2CO3:TiO2=0.996:0.498:0.004, iron phosphate, lithium carbonate and titanium oxide are mixed, and glucose and polyethylene glycol as carbon sources and reducing agents are added (the mass ratio of glucose and polyethylene glycol is 1:1, and the carbon source feed amount accounts for 6% of the total mass of the raw materials), and then solvent water is added for wet grinding to obtain a mixed slurry; the obtained slurry is spray-dried, and then the dried product is placed in a roller furnace and sintered at 500°C in an air-tight state for 20 hours, and then naturally cooled to a material temperature of less than 80°C and discharged to obtain a calcined material; the calcined material is crushed, sieved and demagnetized to obtain a lithium iron phosphate substrate LiFe 0.998 Ti 0.002PO 4, which is doped with about 0.3% carbon. The above substrate is placed in a roller furnace with a nitrogen atmosphere and sintered, and acetone solution is sprayed at the same time. The substrate is sintered at a constant temperature of 600℃ for 10 hours. The material is discharged after it is naturally cooled to a temperature of less than 80℃. After crushing and screening, the material is placed in a roller furnace again and acetone solution is sprayed again. The substrate is sintered at a constant temperature of 780℃ for 10 hours. The material is discharged after it is naturally cooled to a temperature of less than 80℃. The product of the second sintering is pulverized by air flow to obtain carbon-coated LiFe 0.998 Ti 0.002 PO4.

[0148] (2) Preparation of positive electrode sheet:

[0149] The first positive electrode active material, binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black are dissolved in solvent N-methylpyrrolidone (NMP) in a mass ratio of 96:2:2, and are fully stirred and mixed to prepare a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and then dried, cold pressed, and cut to obtain a positive electrode sheet.

[0150] (3) Preparation of negative electrode sheet:

[0151] The negative electrode active material artificial graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC-Na) were dissolved in deionized water in a mass ratio of 96:2:1:1, and the mixture was thoroughly stirred and mixed to prepare a negative electrode slurry; the negative electrode slurry was coated on the negative electrode current collector copper foil, and then dried, cold pressed, and cut to obtain the negative electrode sheet.

[0152] (4) Isolation film: Polypropylene film is used.

[0153] (5) Preparation of the first battery cell:

[0154] The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in order to obtain a first battery cell. The first battery cell has a capacity C in the widest voltage range of its entire life cycle. A Designed for 100Ah.

[0155] (2) Preparation of the second battery cell

[0156] (1) Preparation of the second positive electrode active material:

[0157] NiSO4, CoSO4 and MnSO4 were added to water in a molar ratio of 0.55:0.141:0.249 to prepare a mixed solution, wherein the concentration of NiSO4 in the mixed solution was 2 mol / L; 5 mol / L NaOH solution was prepared;

[0158] 50L of the mixed solution was introduced into the reactor, and then 50L of NaOH solution and an appropriate amount of 0.5mol / L ammonia solution were introduced into the reactor to adjust the pH value in the reactor to 9.0-12.0, the reaction temperature to 40°C-80°C, and the reaction was carried out under stirring for 60h at a stirring speed of 300-1000r / min. After completion, the precipitate was filtered out and washed, and the washed precipitate was vacuum dried at 120°C for 24h to obtain a precursor;

[0159] Li2CO3, a precursor, Al2O3 and MgO are mixed, wherein the molar ratio of Li2CO3 (measured in terms of the molar amount of the Li element), the precursor (measured in terms of the total molar amount of the three elements Ni, Co and Mn in the mixed solution), the Al2O3 (measured in terms of the molar amount of the Al element) and the MgO is 1.05:0.94:0.04:0.02. After mixing, the mixture is placed in a ball mill and ball milled at a speed of 300r / s for 2h, and then placed in a box furnace, and heated to 950℃ and kept warm for 12h in an air atmosphere of 0.2MPa for pre-sintering at a heating rate of 1℃ / min, and then cooled to 600℃ at a rate of 1℃ / min and kept warm for 8h for sintering. After sintering, the mixture is cooled to 300℃ at a rate of 1℃ / min, and then naturally cooled to room temperature, and then pulverized by a jet mill at a speed of 3000r / min and 500m 3 / h of air volume for crushing, crushing for 0.5h, and then sifting through a 500-mesh filter to obtain the second positive electrode active material LiNi 0.55 Co 0.141 Mn 0.249 Al 0.04 Mg 0.02 O2.

[0160] (2) Preparation of positive electrode sheet:

[0161] The second positive electrode active material, binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black are dissolved in solvent N-methylpyrrolidone (NMP) in a mass ratio of 96:2:2, and are fully stirred and mixed to prepare a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and then dried, cold pressed, and cut to obtain a positive electrode sheet.

[0162] (3) Preparation of negative electrode sheet:

[0163] The negative electrode active material artificial graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC-Na) were dissolved in deionized water in a mass ratio of 96:2:1:1, and the mixture was thoroughly stirred and mixed to prepare a negative electrode slurry; the negative electrode slurry was coated on the negative electrode current collector copper foil, and then dried, cold pressed, and cut to obtain the negative electrode sheet.

[0164] (4) Isolation film: Polypropylene film is used.

[0165] (5) Preparation of the second battery cell:

[0166] The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in order to obtain a second battery cell. The second battery cell has a widest voltage range capacity C over its entire life cycle. B Designed for 100Ah.

[0167] (3) Preparation of electrolyte:

[0168] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and then LiPF6 was uniformly dissolved in the above solution to obtain an electrolyte solution. The concentration of LiPF6 in the electrolyte solution was 1 mol / L.

[0169] (IV) Preparation of secondary batteries:

[0170] The three first battery cells and the two second battery cells are assembled into an electrode assembly; the electrode assembly is placed in a shell, and the above-prepared electrolyte is added. After packaging, standing, forming, aging and other processes, a secondary battery is obtained.

[0171] The secondary battery preparation methods of Examples 2-24 and Comparative Examples 1-3 are similar to those of Example 1, and the different product parameters are detailed in Table 1.

[0172] The NP content is adjusted by adjusting the ratio of the coating mass of the positive electrode slurry on the positive electrode collector to the coating mass of the negative electrode slurry on the negative electrode collector in the first cell. A1 and NP A2 .

[0173] The NP content is adjusted by adjusting the ratio of the coating mass of the positive electrode slurry on the positive electrode collector to the coating mass of the negative electrode slurry on the negative electrode collector in the second cell. B1 and NP B2 .

[0174] By using shells of different sizes, the widest voltage range capacity C of the first or second battery cell can be achieved throughout its entire life cycle. A or C B design requirements.

[0175] Five first battery cells were used in Comparative Example 3. The first positive electrode active materials of Examples 2-24 and Comparative Examples 1-3 were all carbon-coated core materials.

[0176] Preparation Method of the First Positive Electrode Active Material of Example 24

[0177] Step S1: Preparation of co-doped manganese oxalate

[0178] 689.6g of manganese carbonate, 455.3g of ferrous carbonate, 4.7g of cobalt sulfate, and 4.7g of vanadium dichloride were added to a mixer and thoroughly mixed for 6 hours. The resulting mixture was then transferred to a reactor, and 5L of deionized water and 1260.6g of oxalic acid dihydrate were added. The mixture was heated to 80°C and stirred at 500 rpm for 6 hours, mixing until the reaction terminated and no bubbles were generated, resulting in a manganese oxalate suspension co-doped with Fe, Co, and V. The suspension was then filtered, dried at 120°C, and sand-milled to obtain manganese oxalate particles with a particle size of 100nm.

[0179] Step S2: Prepare the core

[0180] Take 1793.1g of prepared manganese oxalate, 369.8g of lithium carbonate, 1148.9g of ammonium dihydrogen phosphate and 0.8g of silicic acid, add them to 20L of deionized water, stir them thoroughly, and mix them evenly at 80°C for 10h to obtain a slurry. The slurry is transferred to a spray drying equipment for spray drying and granulation, and dried at a temperature of 250°C to obtain a powder. In a protective atmosphere (90% nitrogen and 10% hydrogen), the powder is sintered in a roller kiln at 700°C for 4h to obtain carbon-coated Li 1.001 Mn 0.60 Fe 0.393 V 0.004 Co 0.003 P 0.999 Si 0.001 O4.

[0181] Preparation method of the third positive electrode active material of Examples 8-12 and 21

[0182] Step S1: Preparation of Fe, Co, V and S co-doped manganese oxalate

[0183] 689.6g of manganese carbonate, 455.3g of ferrous carbonate, 4.7g of cobalt sulfate, and 4.9g of vanadium dichloride were added to a mixer and thoroughly mixed for 6 hours. The resulting mixture was then transferred to a reactor, and 5L of deionized water and 1260.6g of oxalic acid dihydrate were added. The mixture was heated to 80°C and stirred at 500 rpm for 6 hours, mixing until the reaction terminated and no bubbles were generated, resulting in a manganese oxalate suspension co-doped with Fe, Co, and V. The suspension was then filtered, dried at 120°C, and sand-milled to obtain manganese oxalate particles with a particle size of 100nm.

[0184] Step S2: Prepare the core

[0185] Take 1793.1g of manganese oxalate prepared in (1), 369.8g of lithium carbonate, 1148.9g of ammonium dihydrogen phosphate and 0.8g of silicic acid, add them to 20L of deionized water, stir them thoroughly, and evenly mix and react at 80°C for 10 hours to obtain a slurry. The slurry is transferred to a spray drying equipment for spray drying and granulation, and dried at a temperature of 250°C to obtain a powder. In a protective atmosphere (90% nitrogen and 10% hydrogen), the powder is sintered in a roller kiln at 700°C for 4 hours to obtain a core material. The element content of the core material is detected by inductively coupled plasma emission spectroscopy (ICP) to obtain a core.

[0186] Step S3: Preparation of the first coating layer suspension

[0187] Preparation of Li2FeP2O7 solution: 7.4 g of lithium carbonate, 11.6 g of ferrous carbonate, 23.0 g of ammonium dihydrogen phosphate and 12.6 g of oxalic acid dihydrate were dissolved in 500 mL of deionized water, the pH was controlled to 5, and then stirred and reacted at room temperature for 2 h to obtain a solution. The solution was then heated to 80°C and maintained at this temperature for 4 h to obtain a first coating layer suspension.

[0188] Step S4: coating of the first coating layer

[0189] 1571.9 g of the doped lithium manganese phosphate core material obtained in step S2 was added to the first coating layer suspension (coating material content of 15.7 g) obtained in step S3, and the mixture was stirred and mixed for 6 h. After mixing evenly, it was transferred to a 120 ° C oven and dried for 6 h, and then sintered at 650 ° C for 6 h to obtain the pyrophosphate-coated material.

[0190] Step S5: Preparation of the second coating layer suspension

[0191] 3.7 g of lithium carbonate, 11.6 g of ferrous carbonate, 11.5 g of ammonium dihydrogen phosphate and 12.6 g of oxalic acid dihydrate were dissolved in 1500 mL of deionized water, and then stirred and reacted for 6 hours to obtain a solution. The solution was then heated to 120° C. and maintained at this temperature for 6 hours to obtain a second coating layer suspension.

[0192] Step S6: coating with the second coating layer

[0193] 1586.8 g of the pyrophosphate-coated material obtained in step S4 was added to the second coating layer suspension (coating material content of 47.1 g) obtained in step S5, and the mixture was stirred and mixed for 6 h. After mixing evenly, it was transferred to a 120°C oven and dried for 6 h, and then sintered at 700°C for 8 h to obtain a two-layer coated material.

[0194] Step S7: Preparation of the third coating layer aqueous solution

[0195] 37.3 g of sucrose was dissolved in 500 g of deionized water, and then stirred and fully dissolved to obtain a sucrose aqueous solution.

[0196] Step S8: coating with the third coating layer

[0197] 1633.9 g of the two-layer coated material obtained in step S6 was added to the sucrose solution obtained in step S7, and stirred and mixed together for 6 hours. After mixing evenly, it was transferred to a 150°C oven and dried for 6 hours, and then sintered at 700°C for 10 hours to obtain a three-layer coated third positive electrode active material.

[0198] Battery Test

[0199] (1) When the state of charge (SOC) of a single-cell battery is in the range of 95% to 100%, the voltage change value of the first cell or the second cell is tested for each 1% change in the state of charge (SOC) of the single-cell battery:

[0200] Assemble the first battery cell or the second battery cell into a single-cell battery according to item (4) above.

[0201] Single-cell battery test of the first cell: in a constant temperature environment of 25°C, the battery was allowed to stand for 10 minutes, then discharged at a constant current of 0.1C to a cut-off voltage of 2.8V, allowed to stand for 10 minutes, and charged at a constant current of 0.04C to a target voltage of 3.65V, allowed to stand for 10 minutes, discharged at a constant current of 0.04C to a cut-off voltage of 2.8V, allowed to stand for 10 minutes, and charged at a constant current of 0.04C to a target voltage of 3.65V, and the charging capacity at this time was recorded as 100% SOC, allowed to stand for 10 minutes, and discharged at a constant current of 0.04C to a cut-off voltage of 2.8V; a graph was drawn with the charging capacity of the last charging process as the y-axis and the voltage as the x-axis, and the voltage Vm corresponding to 95% SOC and the voltage Vn corresponding to 100% SOC were obtained from the graph. When the state of charge of the battery is in the range of 95% to 100%, the voltage change value of the first cell is (Vn1-Vm1) / 5 for every 1% change in the state of charge of the battery. The target voltage used for the first battery cell of Example 24 is 4.25V.

[0202] Single-cell battery test of the second cell: in a constant temperature environment of 25°C, the battery was allowed to stand for 10 minutes, then discharged at a constant current of 0.1C to a cut-off voltage of 2.8V, allowed to stand for 10 minutes, and charged at a constant current of 0.04C to a target voltage of 4.25V, allowed to stand for 10 minutes, discharged at a constant current of 0.04C to a cut-off voltage of 2.8V, allowed to stand for 10 minutes, and charged at a constant current of 0.04C to a target voltage of 4.25V, and the charging capacity at this time was recorded as 100% SOC. After standing for 10 minutes, it was discharged at a constant current of 0.04C to a cut-off voltage of 2.8V; a graph was drawn with the charging capacity of the last charging process as the y-axis and the voltage as the x-axis, and the voltage Vm corresponding to 95% SOC and the voltage Vn corresponding to 100% SOC were obtained from the graph. When the state of charge of the battery is in the range of 95% to 100%, the voltage change value of the second cell is (Vn2-Vm2) / 5 for every 1% change in the state of charge of the battery.

[0203] (2) Testing of the lithium-free capacity of the positive electrode and the lithium-embedded capacity of the negative electrode:

[0204] The positive electrode sheet, the negative electrode sheet and the counter electrode lithium sheet are respectively made into button batteries.

[0205] Test of button battery with positive electrode: in a constant temperature environment of 25℃, charge to 4.35V at a constant current of 0.1C, and then discharge to 2.8V at 0.1C, record the discharge capacity of the first cycle, and divide the discharge capacity of the first cycle by the mass of the positive active material in the positive electrode sheet to obtain the first lithium-free gram capacity of the positive electrode sheet; the button battery continues to be charged and discharged in the above manner for 2 times, for a total of 3 times, and record the second charge and discharge capacity as the non-first cycle discharge capacity, and divide the non-first cycle discharge capacity by the mass of the positive active material in the positive electrode sheet to obtain the non-first lithium-free gram capacity of the positive electrode sheet.

[0206] Test of button battery with negative electrode: in a constant temperature environment of 25℃, charge to 2.0V at a constant current of 0.1C, and then discharge to 0V at 0.1C, record the discharge capacity of the first cycle, and divide the discharge capacity of the first cycle by the mass of the negative active material in the negative electrode sheet to obtain the first lithium embedded capacity of the negative electrode sheet; the button battery continues to charge and discharge twice in the above manner, for a total of 3 times, and record the second charge and discharge capacity as the non-first cycle discharge capacity, and divide the non-first cycle discharge capacity by the mass of the negative active material in the negative electrode sheet to obtain the non-first lithium embedded capacity of the negative electrode sheet.

[0207] (3) Determine whether the upper limit voltage of the second battery cell increases:

[0208] In a constant temperature environment of 25°C, the battery is discharged at 0.33C to the lower limit of the cut-off voltage of 2.8V, left to stand for 10 minutes, and then charged at a constant current of 0.33C to the upper limit of the cut-off voltage of 5V. Constant voltage charging is performed to ≤0.05C, and the charging capacity is recorded as the nominal capacity. During the charging process, the voltage data of the second battery cell is monitored to obtain the upper limit voltage of the second battery cell corresponding to the nominal capacity. The battery is discharged and charged 100 times in a cycle according to the above method. During the last cycle of charging, the voltage data of the second battery cell is monitored to obtain the upper limit voltage of the second battery cell in the last cycle. If the upper limit voltage of the second battery cell in the last cycle minus the upper limit voltage of the second battery cell corresponding to the nominal capacity is greater than 0.05V, it is determined that the upper limit voltage of the second battery cell has increased; otherwise, its upper limit voltage has not increased.

[0209] (4) Overcharge protection test:

[0210] In a constant temperature environment of 25°C, the battery is charged at 0.1C to the upper limit of the cut-off voltage, and then discharged at 0.33C to the lower limit of the cut-off voltage. The values ​​of the upper and lower cut-off voltages are shown in Table 2. The battery is charged and discharged 200 times in the above manner. The battery is disassembled. If the lithium deposition area on the negative electrode (excluding the corner position) accounts for more than 1 / 5 of the total area of ​​the negative electrode, it is considered to have failed the overcharge protection test and is recorded as NG. Otherwise, it is considered to have passed the overcharge protection test and is recorded as OK.

[0211] (5) Cycle life test:

[0212] In a constant temperature environment of 25℃, let the battery stand for 10 minutes and then discharge it at 0.33C to 2.8V; let it stand for 10 minutes, then charge it at 0.1C constant current to 4.3V, charge it at constant voltage until the current is ≤0.05C, let it stand for 10 minutes and then discharge it at 0.33C to 2.8V. Record the discharge capacity of the battery in the first cycle as D1. Repeat the above charging and discharging operations, and record the discharge capacity of each cycle as D n (n=2, 3...); calculate the degradation degree of the battery cell (State of health SOH) according to the following formula, and record the number of cycles n when the degradation degree reaches 90% SOH.

[0213] Battery cell attenuation = 100% × D n / D3.

[0214] Table 2: Performance test results of Examples 1-24 and Comparative Examples 1-3

[0215] According to the above results, we can know that:

[0216] Compared with comparative examples 1-3, the batteries of examples 1-24 of the present application have higher safety and longer cycle life.

[0217] Compared with Examples 5-7, 17, and 19-22, the cycle life of the batteries of Examples 1-4, 8-16, and 23-24 of the present application is longer.

[0218] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present application, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present application. In addition, without departing from the scope of the subject matter of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A battery cell combination, comprising a first battery cell and a second battery cell, wherein the number of the first battery cells is greater than or equal to the number of the second battery cells, and the first battery cell and the second battery cell both comprise a positive electrode sheet and a negative electrode sheet; Furthermore, the battery cell combination satisfies: 0.7≤NP A1 ≤1.05NP B1 And NP A1 <1, or, 0.75≤NP A2 ≤1.05NP B2 And NP A2 <1.2; in, NP A1 is the ratio of the initial lithium insertion capacity of the negative electrode to the initial lithium removal capacity of the positive electrode in the first battery cell, NP B1 is the ratio of the first lithium insertion capacity of the negative electrode plate to the first lithium removal capacity of the positive electrode plate in the second battery cell, NP A2 NP is the ratio of the non-first lithium insertion capacity of the negative electrode plate to the non-first lithium removal capacity of the positive electrode plate in the first battery cell. B2 is the ratio of the non-first lithium insertion gram capacity of the negative electrode plate in the second battery cell to the non-first lithium removal gram capacity of the positive electrode plate; When the state of charge of the single-cell battery including the second cell is in the range of 95% to 100%, for every 1% change in the state of charge of the single-cell battery, the voltage of the second cell changes by more than 5 mV accordingly.

2. The battery cell assembly according to claim 1, wherein: When the state of charge of the single-cell battery including the first cell is in the range of 95% to 100%, for every 1% change in the state of charge of the single-cell battery, the voltage of the first cell changes by less than or equal to 5 mV.

3. The battery cell assembly according to claim 1 or 2, which satisfies: 0.08≤(1.1-NP A1 ) / (NP B1 -1)≤20; Preferably, 0.1≤(1.1-NP A1 ) / (NP B1 -1)≤15.

4. The battery cell assembly according to any one of claims 1 to 3, which satisfies: 0.95≤C B / C A ≤1.4, optional 1.0≤C B / C A ≤1.3; in, C A The widest voltage range capacity of the first battery cell in its entire life cycle, C B The widest voltage range capacity for the entire life cycle of the second battery cell.

5. The battery cell assembly according to any one of claims 1 to 4, wherein: The positive electrode sheet in the first battery cell includes a first positive electrode active material, and the first positive electrode active material includes a compound Li a A x Mn 1-y B y P 1-z C z O 4-n D n ; Wherein, A includes one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo and W; B includes one or more elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge; C includes one or more elements selected from the group consisting of B (boron), S, Si and N; D includes one or more elements selected from the group consisting of S, F, Cl and Br; a is 0.85-1.15; x is 0-0.1; y is 0.001-1; z is 0-0.5; and n is 0-0.

5.

6. The battery cell assembly according to claim 5, wherein: The first positive electrode active material comprises a core and a coating layer coating the core; wherein the core comprises the compound Li a A x Mn 1- y B y P 1-z C z O 4-n D n , the coating layer contains carbon element.

7. The battery cell assembly according to any one of claims 1 to 6, wherein: The positive electrode sheet in the second battery cell includes a second positive electrode active material; the second positive electrode active material includes a compound LiNi b Co d Mn e M f O2; Wherein, M includes one or more elements of Mn, Al, Mg, Ca, Na, Ti, W, Zr, Sr, Cr, Zn, Ba, B, S and Y, and can be optionally Mg and / or Al; b is 0.314-0.970; d is 0-0.320, and can be optionally 0.047-0.320; e is 0.006-0.390; and the sum of b, d, e and f is 1 and f is greater than 0.

8. The battery cell assembly according to claim 7, wherein: The positive electrode sheet in the second battery cell further includes a third positive electrode active material; the third positive electrode active material includes a core and a shell covering the core, the shell includes a first coating layer covering the core, a second coating layer covering the first coating layer, and a third coating layer covering the second coating layer; the core includes a compound Li 1+g Mn 1-h E h P 1-i R i O4, the first coating layer comprises crystalline pyrophosphate Li j GP2O7 and / or G k (P2O7) r The second coating layer comprises crystalline phosphate X t PO4, the third coating layer comprises carbon element; Wherein, the E includes one or more elements of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and may be one or more elements of Fe, V, Ni and Co; the R includes one or more elements of B, Si, N and S, and may be one or more elements of Si, N and S; the crystalline pyrophosphate Li j GP2O7 and G k (P2O7) r The Gs in each independently include Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, One or more elements of Nb and Al may be selected from Fe, Co, Ti and Al; X may be selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al, and may be selected from Li, Fe, Ag and Al; g is -0.100-0.100; h is 0.001-0.600; i is 0.001-0.100; j is greater than 0 and less than or equal to 2; k is 1-4; r is 1-3; t is greater than 0 and less than or equal to 2.

9. The battery cell assembly according to claim 7 or 8, wherein: In the positive electrode sheet of the second battery cell, the mass of the second positive electrode active material accounts for 5%-100% of the total mass of the second positive electrode active material and the third positive electrode active material, and can be optionally 5%-95%.

10. A battery comprising the battery cell combination according to any one of claims 1 to 9.

11. The battery according to claim 10, wherein The upper limit voltage of the second battery cell during the 90th to 110th cycle of charge and discharge of the battery is greater than the upper limit voltage of the second battery cell during the first cycle of charge and discharge of the battery.

12. An electrical device comprising the battery according to claim 10 or 11.

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