Battery cell assembly, battery, and electric device

Abstract

An electric cell assembly, a battery and a power utilization device. The electric cell assembly comprises a first electric cell and a second electric cell, the number of the first electric cells is greater than or equal to the number of the second electric cells, the first electric cells and the second electric cells each comprise a positive electrode sheet and a negative electrode sheet; and the electric cell assembly satisfies: 0.7≤NPA1≤1.05NPB1 and NPA1<1, or 0.75≤NPA2≤1.05NPB2 and NPA2<1.2; when the state of charge of a single-cell battery comprising the second electric cell is in the range of 95% to 100%, the voltage of the second electric cell changes more than 5mV accordingly when the state of charge of the single-cell battery changes 1%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a battery cell combination, a battery and a power utilization device. BACKGROUND

[0002] In recent years, with the increasingly wide application of secondary batteries, secondary batteries are widely used in energy storage power supply systems such as hydraulic, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. Due to the great development of secondary batteries, higher requirements are put forward for the cycle performance and safety performance. SUMMARY

[0003] The present application is made in view of the above-mentioned problems, and aims to provide a battery cell combination, a battery and a power utilization device. The battery cell combination of the present application is advantageous in reducing the occurrence of overcharging of the battery, improving the safety performance of the battery and prolonging the cycle life of the battery.

[0004] To achieve the above-mentioned purpose, the first aspect of the present application provides a battery cell combination, comprising a first battery cell and a second battery cell, the number of the first battery cell is greater than or equal to the number of the second battery cell, and the first battery cell and the second battery cell each comprise a positive electrode sheet and a negative electrode sheet.

[0005] And the battery cell combination satisfies:

[0006] 0.7≤NP A1 ≤1.05NP B1 and NP A1 <1, or 0.75≤NP A2 ≤1.05NP B2 and NP A2 <1.2.

[0007] Wherein, NP A1 is the ratio of the first lithium intercalation capacity of the negative electrode sheet to the first lithium extraction capacity of the positive electrode sheet in the first battery cell, NP B1 is the ratio of the first lithium intercalation capacity of the negative electrode sheet to the first lithium extraction capacity of the positive electrode sheet in the second battery cell, NP A2 is the ratio of the non-first lithium intercalation capacity of the negative electrode sheet to the non-first lithium extraction capacity of the positive electrode sheet in the first battery cell, NP B2 is the ratio of the non-first lithium intercalation capacity of the negative electrode sheet to the non-first lithium extraction capacity of the positive electrode sheet in the second battery cell.

[0008] 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 more than 5mV per 1% change of the state of charge of the single-cell battery.

[0009] The limit design of the NP of the cell to less than 1 is beneficial to reduce the amount of negative active material, reduce the cost, and the saved space can further improve the capacity, but it will make the state of charge (SOC) of the single-cell battery close to saturation, and the voltage of the cell changes very small per 1% change of the SOC of the single-cell battery, which is easy to cause the problem of overcharging of the single-cell battery, and there is a safety hazard.

[0010] The present application limits the voltage of the second cell to change more than 5mV per 1% change of the SOC of the single-cell battery when the SOC of the single-cell battery including the second cell is close to saturation, and limits the NP A1 The value and its relationship with NP B1 , or limits the NP A2 The value and its relationship with NP B2 The value and its relationship with NP B2 , which is beneficial to reduce the occurrence of battery overcharging, improve the safety performance of the battery, and prolong the cycle life of the battery.

[0011] 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%, the voltage of the first cell changes less than or equal to 5mV per 1% change of the state of charge of the single-cell battery.

[0012] When the first cell reaches the limit design, the first cell satisfies the above voltage change characteristics.

[0013] In any embodiment, the cell combination satisfies:

[0014] 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, the initial voltage of the battery is limited while meeting the capacity demand of the battery, so that the battery can form a stable and dense SEI film in a lower voltage range, thereby prolonging the cycle life of the battery.

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

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

[0019] wherein C A is the full life cycle applied widest voltage interval capacity of the first battery cell, C B is the full life cycle applied widest voltage interval capacity of the second battery cell.

[0020] Thus, the present application meets the life matching of the full life cycle of the battery by matching the capacity design of the first battery cell and the second battery cell, thereby prolonging the cycle life of the battery and improving the safety performance of the full life cycle of the battery.

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

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

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

[0025] In any embodiment, the positive electrode tab in the second electric core comprises a second positive electrode active material; the second positive electrode active material comprises a compound LiNi b Co d Mn e M f O2;

[0026] wherein the M comprises one or more elements selected from Mn, Al, Mg, Ca, Na, Ti, W, Zr, Sr, Cr, Zn, Ba, B, S and Y, and optionally comprises Mg and / or Al; the b is 0.314-0.970; the d is 0-0.320, and optionally 0.047-0.320; the e 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 tab in the second electric core further comprises a third positive electrode active material; the third positive electrode active material comprises a core and a shell covering the core, the shell comprises a first shell layer covering the core, a second shell layer covering the first shell layer, and a third shell layer covering the second shell layer; the core comprises a compound Li 1+g Mn 1-h E h P 1-i R i O4, the first shell layer comprises a crystalline pyrophosphate Li j GP2O7 and / or G k (P2O7) r , the second shell layer comprises a crystalline phosphate X t PO4, and the third shell layer comprises a carbon element.

[0028] wherein the E comprises 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 optionally comprises one or more elements selected from Fe, V, Ni and Co; the R comprises one or more elements selected from B, Si, N and S, and optionally comprises one or more elements selected from Si, N and S; the crystalline pyrophosphate Li j GP2O7 and G k (P2O7) reach of G independently comprises one or more elements selected from the group consisting of Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al, and optionally comprises one or more elements selected from the group consisting of Fe, Co, Ti, and Al; X comprises one or more elements selected from the group consisting of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al, and optionally comprises one or more elements selected from the group consisting of 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; and t is greater than 0 and less than or equal to 2.

[0029] Thus, the second electrode core of the present application uses the second positive electrode active material and the optional third positive electrode active material described above, which improves the compaction density of the second electrode core, improves the thermal stability of the battery, and prolongs the cycle life of the battery.

[0030] In any embodiment, in the positive electrode sheet of the second electrode core, the mass ratio of the second positive electrode active material in the total mass of the second positive electrode active material and the third positive electrode active material is 5%-100%, and optionally 5%-95%.

[0031] Thus, the compaction density of the second electrode core is further improved, the thermal stability of the battery is further improved, and the cycle life of the battery is further prolonged.

[0032] The second aspect of the present application provides a battery comprising the electrode core combination of the first aspect of the present application.

[0033] In any embodiment, the upper limit voltage of the second electrode core when the battery is cycled for 90-110 times is greater than the upper limit voltage of the second electrode core when the battery is cycled for the first time.

[0034] Thus, while meeting the capacity demand of the battery, the lower initial upper limit voltage of the second electrode core limits the initial voltage of the battery, allowing the battery to form a stable and dense SEI film in a lower voltage range, thereby prolonging the cycle life of the battery in the later stage.

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

[0036] Figure 1 is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0037] Figure 2 is a schematic diagram of a secondary battery according to an embodiment of the present application. Figure 1 is an exploded view of a secondary battery according to an embodiment of the present application.

[0038] Figure 3 is a schematic view of a battery module according to an embodiment of the present application.

[0039] Figure 4 is a schematic view of a battery pack according to an embodiment of the present application.

[0040] Figure 5 is Figure 4 is an exploded view of a battery pack according to an embodiment of the present application.

[0041] Figure 6 is a schematic view 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:

[0043] 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 case; 52 electrode assembly; 53 top cap assembly. DETAILED DESCRIPTION

[0044] Hereinafter, embodiments of the battery cell assembly, the secondary battery, the battery module, the battery pack, and the electric device according to the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there can be cases where unnecessary detailed description is omitted. For example, there can be cases where detailed description of matters that are well known, repeated description of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0045] The ranges disclosed herein are meant to be inclusive of the endpoints and include the end values in the range. Ranges can be combined to form new ranges, e.g., a range of "60-120 and 80-110" is understood to include 60-110 and 80-120. Further, if a minimum range value is listed as 1 and a maximum range value is listed as 3, 4, and 5, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise indicated, a numerical range "a-b" means a range of any combination of the numbers a and b, wherein both a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between 0 and 5 have been listed herein, and "0-5" is merely a shorthand for listing all of those numbers. Also, when a parameter is stated to be an integer > 2, it is equivalent to state that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0046] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0047] All technical features and optional technical features of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0048] All steps of the present application can be performed in sequence or randomly, preferably in sequence, unless otherwise specified. For example, a method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, it is mentioned that the method can further comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0049] Unless otherwise specified, "including" and "comprising" mentioned in the present application means open-ended, and can also be closed-ended. For example, "including" and "comprising" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0050] If not specifically stated, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true (or present) and B is false (or not present); A is false (or not present) and B is true (or present); or both A and B are true (or present).

[0051] [Secondary battery]

[0052] A secondary battery, also known as a rechargeable battery or a storage battery, refers to a battery that can continue to be used by activating active materials through charging after the battery is discharged.

[0053] Generally, a secondary battery includes a cell or a cell combination, which includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During the charging and discharging process of the battery, active ions (e.g., lithium ions) are inserted and extracted 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 short circuiting of the positive and negative electrodes, while allowing the active ions to pass through. The electrolyte is between the positive electrode sheet and the negative electrode sheet, mainly to conduct the active ions.

[0054] [Cell combination]

[0055] Embodiments of the present application provide a cell combination, including a first cell and a second cell, the number of the first cell is greater than or equal to the number of the second cell, the first cell and the second cell both include a positive electrode sheet and a negative electrode sheet;

[0056] And the cell combination satisfies:

[0057] 0.7≤NP A1 ≤1.05NP B1 and NP A1 <1, or 0.75≤NP A2 ≤1.05NP B2 and NP A2 <1.2;

[0058] wherein NP A1 is a ratio of the first lithium intercalation capacity of the negative electrode sheet to the first lithium extraction capacity of the positive electrode sheet in the first cell, NP B1 is a ratio of the first lithium intercalation capacity of the negative electrode sheet to the first lithium extraction capacity of the positive electrode sheet in the second cell, NP A2 is a ratio of the non-first lithium intercalation capacity of the negative electrode sheet to the non-first lithium extraction capacity of the positive electrode sheet in the first cell, NP B2 is a ratio of the non-first lithium intercalation capacity of the negative electrode sheet to the non-first lithium extraction capacity of the positive electrode sheet in the second cell;

[0059] 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 more than 5mV for each 1% change in the state of charge of the single-cell battery.

[0060] The limit design of the NP of the cell reaching less than 1 is beneficial to reduce the amount of negative active material, reduce the cost, and the saved space can further improve the capacity, but it will make the state of charge (SOC) of the single-cell battery close to saturation, and the voltage of the corresponding cell changes very small for each 1% change in the SOC of the single-cell battery, which is easy to cause the problem of overcharging of the single-cell battery, and there is a safety hazard.

[0061] Although the mechanism is not clear, the applicant accidentally found that the application limits the voltage of the second cell to change more than 5mV for each 1% change in the SOC of the single-cell battery when the SOC of the single-cell battery including the second cell is close to saturation, and limits the NP of the second cell to be greater than or equal to 1, by means of the cell combination that the number of the first cell is greater than or equal to the number of the second cell. A1 The value of NP and its relationship with NP B1 , or limiting the value of NP A2 and its relationship with NP B2 , which is beneficial to reduce the occurrence of battery overcharging, improve the safety performance of the battery, and prolong the cycle life of the battery.

[0062] 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%, the voltage of the first cell changes less than or equal to 5mV for each 1% change in the state of charge of the single-cell battery.

[0063] When the first cell reaches the limit design, the first cell meets the above voltage change characteristics.

[0064] In some embodiments, when the state of charge (SOC) of the single-cell battery is in the range of 95% to 100%, the voltage change value of the first cell or the second cell per 1% change in the state of charge (SOC) of the single-cell battery is determined by a method conventional in the art; for example, the specific method is as follows: the first cell or the second cell is assembled into a single-cell battery according to a conventional method. In a constant temperature environment of 25°C, the battery is rested for 10 min, then discharged at 0.1C constant current to the cut-off voltage, rested for 10 min, charged at 0.04C constant current to the target voltage, rested for 10 min, discharged at 0.04C constant current to the cut-off voltage, rested for 10 min, charged at 0.04C constant current to the target voltage, and the charging capacity at this time is recorded as 100% SOC, then discharged at 0.04C constant current to the cut-off voltage; the charging capacity of the last charging process is taken as the y-axis, and the voltage is taken as the x-axis to plot a graph, and the voltage Vm corresponding to 95% SOC and the voltage Vn corresponding to 100% SOC are obtained from the graph, then 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 per 1% change in the state of charge of the battery is (Vn-Vm) / 5.

[0065] In some embodiments, the first lithium intercalation capacity and the non-first lithium intercalation capacity of the negative electrode tab and the first lithium extraction capacity and the non-first lithium intercalation capacity of the positive electrode tab are determined by a method conventional in the art. For example, the first lithium extraction capacity and the non-first lithium intercalation capacity of the positive electrode tab are determined by the following method: the positive electrode tab and a counter electrode lithium sheet are made into a button cell. In a constant temperature environment of 25°C, the button cell is charged at 0.1C constant current to 4.35V, then discharged at 0.1C to 2.8V, the discharge capacity of the first cycle is recorded, and the first lithium extraction capacity of the positive electrode tab is obtained by dividing the discharge capacity of the first cycle by the mass of the positive electrode active material in the positive electrode tab; the button cell is further charged and discharged according to the above method for 2 times, and the total charging and discharging is 3 times, the discharge capacity of the 2nd charging and discharging is recorded as the discharge capacity of the non-first cycle, and the non-first lithium extraction capacity of the positive electrode tab is obtained by dividing the discharge capacity of the non-first cycle by the mass of the positive electrode active material in the positive electrode tab. For example, the first lithium intercalation capacity and the non-first lithium intercalation capacity of the negative electrode tab are determined by the following method: the negative electrode tab and a counter electrode lithium sheet are made into a button cell. In a constant temperature environment of 25°C, the button cell is charged at 0.1C constant current to 2.0V, then discharged at 0.1C to 0V, the discharge capacity of the first cycle is recorded, and the first lithium intercalation capacity of the negative electrode tab is obtained by dividing the discharge capacity of the first cycle by the mass of the negative electrode active material in the negative electrode tab; the button cell is further charged and discharged according to the above method for 2 times, and the total charging and discharging is 3 times, the discharge capacity of the 2nd charging and discharging is recorded as the discharge capacity of the non-first cycle, and the non-first lithium intercalation capacity of the negative electrode tab is obtained by dividing the discharge capacity of the non-first cycle by the mass of the negative electrode active material in the negative electrode tab.

[0066] In some embodiments, the combination of the cells satisfies:

[0067] 0.08≤(1.1-NP A1 ) / (NP B1 -1)≤20;

[0068] 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, and a range consisting of any of the aforementioned values.

[0069] Thus, when the above relationship is met, the initial voltage of the battery is limited while meeting the battery capacity requirement, so that the battery can form a stable and dense SEI film in a lower voltage range, thereby prolonging the cycle life of the battery.

[0070] In some embodiments, the combination of the battery cells satisfies:

[0071] 0.95≤C B / C A ≤1.4;

[0072] Optionally, 1.0≤C B / C A ≤1.3, for example, C B / C A is 1.1, 1.2, 1.25, and a range consisting of any of the aforementioned values.

[0073] wherein C A is the full-life application widest voltage range capacity of the first battery cell, and C B is the full-life application widest voltage range capacity of the second battery cell.

[0074] Thus, the present application matches the capacity design of the first battery cell and the second battery cell, meets the life matching of the full-life of the battery, thereby prolonging the cycle life of the battery and improving the safety performance of the full-life of the battery.

[0075] In some embodiments, the positive electrode sheet in the first battery cell comprises a first positive electrode active material, and the first positive electrode active material comprises a compound Li a A x Mn 1-y B y P 1-z C z O 4-n D n ;

[0076] 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 ranges formed by any of the above values; x is 0-0.1, and is optionally 0, for example 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08, 0.09, 0.1 and ranges formed by any of the above values; 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 ranges formed by any of the above values; z is 0-0.5, for example 0, 0.1, 0.2, 0.3, 0.4, 0.5 and ranges formed by any of the above values; n is 0-0.5, for example 0, 0.1, 0.2, 0.3, 0.4, 0.5 and ranges formed by any of the above values.

[0077] In some embodiments, the first positive active material comprises an inner core and a coating layer coating the inner core; wherein the inner core comprises the compound Li a A x Mn 1-y B y P 1-z C z O 4-n D n , and the coating layer comprises carbon elements.

[0078] Thus, the first positive active material described above is used to reach the limit design of the NP of the first battery cell, which is beneficial to improve the energy density of the first battery cell.

[0079] In some embodiments, the positive electrode sheet in the second battery cell comprises a second positive active material; the second positive active material comprises the compound LiNi b Co d Mn e M f O2;

[0080] M comprises one or more elements selected from Mn, Al, Mg, Ca, Na, Ti, W, Zr, Sr, Cr, Zn, Ba, B, S and Y, and optionally comprises Mg and / or Al; b is 0.314-0.970, for example 0.4, 0.5, 0.55, 0.6, 0.7, 0.8, 0.9, and ranges formed by any of the above values; d is 0-0.320, and optionally 0.047-0.320, for example 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 ranges formed by any of the above values; 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 ranges formed by any of the above values; and the sum of b, d, e and f is 1 and f is greater than 0.

[0081] In some embodiments, the positive electrode tab in the second battery cell further comprises a third positive active material; the third positive active material comprises a core and a shell covering the core, the shell comprising 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 comprises a compound Li 1+g Mn 1-h E h P 1-i R i O4, the first coating layer comprises a crystalline pyrophosphate Li j GP2O7 and / or G k (P2O7) r , the second coating layer comprises a crystalline phosphate X t PO4, and the third coating layer comprises a carbon element.

[0082] E comprises 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 optionally comprises one or more elements selected from Fe, V, Ni and Co, and more optionally comprises one or more elements selected from Fe, V and Co; R comprises one or more elements selected from B, Si, N and S, and optionally comprises one or more elements selected from Si, N and S, and more optionally comprises Si; the crystalline pyrophosphate Li j GP2O7 and G k (P2O7)r each G independently comprises one or more elements selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al, optionally comprises one or more elements selected from Fe, Co, Ti and Al, more optionally comprises Fe element; X comprises one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al, optionally comprises one or more elements selected from Li, Fe, Ag and Al, more optionally comprises Li element and / or Fe element; g is -0.100-0.100, for example -0.05, -0.01, 0, 0.001, 0.005, 0.01, 0.02, 0.05, 0.07, 0.08, 0.09 and a range formed by any of the above values; 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 a range formed by any of the above values; 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 a range formed by any of the above values; 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.

[0083] Therefore, the second electrode core of the application adopts the second positive electrode active material and the optional third positive electrode active material, which improves the compaction density of the second electrode core, improves the thermal stability of the battery and prolongs the cycle life of the battery.

[0084] 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 are all electrically neutral.

[0085] 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, which can be 5%-95%, for example, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and a range consisting of any of the above values.

[0086] Thus, the compaction density of the second battery cell is further improved, the thermal stability of the battery is further improved, and the cycle life of the battery is further prolonged.

[0087] In some embodiments, the preparation method of the first positive electrode active material of the present application comprises the following steps:

[0088] (1) Dissolve and stir a manganese source, a source of element B, and an acid in a solvent to generate a suspension of manganese salt doped with element B, filter the suspension, and dry the filter cake to obtain manganese salt doped with element B;

[0089] (2) Put 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 from step (1) into a reaction container, grind and mix to obtain a slurry;

[0090] (3) Transfer the slurry obtained from step (2) to a spray drying device for spray drying granulation to obtain granules;

[0091] (4) Sinter the granules obtained from step (3).

[0092] In some embodiments, the source of element A is selected from at least one of the elemental substance, oxide, phosphate, oxalate, carbonate, and sulfate of element A, the source of element B is selected from at least one of the elemental substance, oxide, phosphate, oxalate, carbonate, and sulfate of element B, the source of element C is selected from at least one of the sulfate, borate, nitrate, and silicate of element C, and the source of element D is selected from at least one of the elemental substance and ammonium salt of element D. By selecting the source of each doping element, the uniformity of the distribution of the doping elements can be improved, thereby improving the performance of the material.

[0093] 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, etc., which can be oxalic acid. In some embodiments, the acid is a dilute acid with a concentration of 60% by weight or less.

[0094] In some embodiments, the manganese source can be a manganese-containing substance known in the art that can be used to prepare lithium manganese phosphate, for example, the manganese source can be selected from one or a combination of elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, and manganese carbonate.

[0095] In some embodiments, the lithium source can be a lithium-containing substance known in the art that can be used to prepare lithium manganese phosphate, for example, the lithium source can be selected from one or a combination of lithium carbonate, lithium hydroxide, lithium phosphate, lithium dihydrogen phosphate.

[0096] In some embodiments, the phosphorus source can be a phosphorus-containing substance known in the art that can be used to prepare lithium manganese phosphate, for example, the phosphorus source can be selected from one or a combination of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid.

[0097] The amount of each source of elements A, B, C, D added depends on the target doping amount, and the amount ratio of the lithium source, the manganese source, and the phosphorus source conforms to the stoichiometric ratio.

[0098] In some embodiments, the solvent 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, it can each independently be selected from at least one of ethanol, water (e.g., deionized water), etc.

[0099] In some embodiments, the preparation method of the third positive electrode active material comprises the following steps:

[0100] The step of providing a core material: the chemical formula of the core material 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.

[0101] The first coating step: dissolving a source of element G, a phosphorus source, and 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 a first coating layer;

[0102] The second coating step: dissolving a source of element X, a phosphorus source, and an acid in a solvent to obtain a second coating layer suspension; thoroughly mixing the material coated with a first coating layer 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 layers of coating layers;

[0103] The third coating step: dissolving a carbon source in a solvent to obtain a third coating layer solution; then adding the material coated with two layers of coating layers obtained in the second coating step to the third coating layer solution, mixing uniformly, drying, and then sintering to obtain a material coated with three layers of coating layers.

[0104] One embodiment of the present application provides a secondary battery comprising the cell combination described above.

[0105] In some embodiments, the upper limit voltage of the second cell after 90-110 cycles (e.g., 92, 95, 96, 97, 98, 100 cycles, and any range consisting of any of the foregoing) of charge-discharge is greater than the upper limit voltage of the second cell after the first cycle of charge-discharge.

[0106] Thus, while meeting the battery capacity requirement, the low initial upper limit voltage of the second 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 cycle life of the battery in the later stage.

[0107] [Positive electrode sheet]

[0108] 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, the positive electrode film layer including a positive electrode active material.

[0109] By way of example, the positive electrode current collector has two opposing surfaces in the thickness direction thereof, and the positive electrode film layer is disposed on either one or both of the two opposing surfaces of the positive electrode current collector.

[0110] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0111] In some embodiments, the positive electrode film layer can further optionally include a binder. By way of example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0112] In some embodiments, the positive electrode film layer can further optionally include a conductive agent. By way of example, the conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0113] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector; and subjecting the positive electrode current collector to drying, cold pressing, and the like to obtain the positive electrode sheet.

[0114] [Positive electrode sheet]

[0115] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0116] As an example, the negative electrode current collector has two surfaces opposite in the thickness direction thereof, and the negative electrode film layer is disposed on either one or both of the two surfaces of the negative electrode current collector.

[0117] In some embodiments, the negative electrode current collector can employ a metal foil or a composite current collector. As a metal foil, for example, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer (e.g., a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0118] In some embodiments, the negative electrode active material can employ a negative electrode active material known in the art for use in a battery. As an example, the negative electrode active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, lithium titanate, and the like. The silicon-based material can be selected from at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can be selected from at least one of elemental tin, a tin oxide compound, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative electrode active material for a battery can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0119] In some embodiments, the negative electrode film layer can also optionally include a binder. As an example, the binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0120] In some embodiments, the negative electrode film layer can also optionally include a conductive agent. As an example, the conductive agent can be selected from at least one of super-P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0121] In some embodiments, the negative electrode film layer can also optionally include other additives, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)), etc.

[0122] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and after processes such as drying, cold pressing, etc., the negative electrode sheet can be obtained.

[0123] [Electrolyte]

[0124] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The type of electrolyte is not specifically limited in the present application and can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0125] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0126] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro oxalate borate, lithium di oxalate borate, lithium difluoro di oxalate phosphate, and lithium tetrafluoro oxalate phosphate.

[0127] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0128] In some embodiments, the electrolyte can also optionally include an additive. As an example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0129] [Separator]

[0130] In some embodiments, the secondary battery further comprises a separator. The type of the separator is not particularly limited in the present application, and any known porous separator having good chemical stability and mechanical stability can be used.

[0131] 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, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0132] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be used to form an electrode assembly by a winding process or a stacking process.

[0133] In some embodiments, the secondary battery can comprise an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0134] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. can be listed.

[0135] The shape of the secondary battery is not particularly limited in the present application, and it can be cylindrical, square, or any other shape. For example, Figure 1 is a square structure secondary battery 5 as an example.

[0136] In some embodiments, referring to Figure 2 , the outer package can comprise a shell 51 and a cover plate 53. The shell 51 can comprise 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 communicating with the receiving cavity, and the cover plate 53 can be arranged on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can be used to form an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and the person skilled in the art can select according to the specific actual needs.

[0137] In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by the person skilled in the art according to the application and capacity of the battery module.

[0138] Figure 3 is a battery module 4 as an example. Referring to Figure 3In the battery module 4, the plurality of secondary batteries 5 can be arranged in series along the length direction of the battery module 4. Of course, the plurality of secondary batteries 5 can be arranged in any other manner. The plurality of secondary batteries 5 can be further fixed by fasteners.

[0139] Optionally, the battery module 4 can further include a housing having an accommodation space, and the plurality of secondary batteries 5 can be accommodated in the accommodation space.

[0140] In some embodiments, the above-described battery module can be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0141] Figure 4 And Figure 5 is a battery pack 1 as an example. Referring to Figure 4 And Figure 5 In the battery pack 1, a battery box and a plurality of battery modules 4 arranged in the battery box can be included. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 and form a closed space for accommodating the battery module 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0142] In addition, the present application also provides a power utilization device, which includes at least one of the secondary battery, the battery module, or the battery pack provided by the present application. The secondary battery, the battery module, or the battery pack can be used as a power supply of the power utilization device, or can be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0143] As the power utilization device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirements thereof.

[0144] Figure 6 is a power utilization device as an example. The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the secondary battery for the power utilization device, the battery pack or the battery module can be used.

[0145] [Embodiment]

[0146] Hereinafter, the examples of the present application will be described. The examples described below are exemplary and are for the purpose of explanation of the present application and cannot be understood as a limitation of the present application. In the examples, the specific techniques or conditions not mentioned are performed in accordance with the techniques or conditions described in the literature in the art or in accordance with the product manual. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be obtained commercially.

[0147] Example 1

[0148] (I) Preparation of the first electrode core

[0149] (1) Preparation of the first positive electrode active material:

[0150] Iron phosphate, lithium carbonate, titanium oxide were used as raw materials, and the molar ratio of FePO4:Li2CO3:TiO2 was 0.996:0.498:0.004. Iron phosphate, lithium carbonate, titanium oxide were mixed, and glucose and polyethylene glycol were added as carbon source and reducing agent (the mass ratio of glucose and polyethylene glycol was 1:1, and the carbon source accounted for 6% of the total mass of the raw materials). Then, water was added as a solvent for wet grinding, and a mixed slurry was obtained. The obtained slurry was spray dried, and then the dried product was placed in a roller furnace and sintered at 500°C in an air-tight manner for 20h. After natural cooling to a material temperature <80°C, the material was discharged, and a calcined material was obtained. The calcined material was crushed, sieved, and demagnetized to obtain a lithium iron phosphate base material LiFe 0.998 Ti 0.002 PO4doped with about 0.3% carbon. The above base material was sintered in a roller furnace in a nitrogen atmosphere, and acetone solution was sprayed at the same time. The sintering temperature was kept at 600°C for 10h. After natural cooling of the material to a temperature <80°C, the material was discharged. After crushing and sieving, the material was placed in a roller furnace again, and acetone solution was sprayed again. The sintering temperature was kept at 780°C for 10h. After natural cooling of the material to a temperature <80°C, the material was discharged. The product of the second sintering was subjected to airflow crushing to obtain carbon-coated LiFe 0.998 Ti 0.002 PO4.

[0151] (2) Preparation of the positive electrode sheet:

[0152] The first positive electrode active material, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black were dissolved in the solvent N-methyl pyrrolidone (NMP) at a mass ratio of 96:2:2. After being thoroughly stirred and mixed uniformly, a positive electrode slurry was prepared. The positive electrode slurry was uniformly coated on the positive electrode current collector aluminum foil, and then subjected to drying, cold pressing, and slitting to obtain a positive electrode sheet.

[0153] (3) Preparation of the negative electrode sheet:

[0154] The negative active material artificial graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickening agent sodium carboxymethyl cellulose (CMC-Na) are dissolved in deionized water according to a mass ratio of 96:2:1:1, and a negative electrode slurry is prepared after being fully stirred and mixed uniformly; the negative electrode slurry is coated on a negative electrode current collector copper foil, and then is subjected to drying, cold pressing, and slitting to obtain a negative electrode sheet.

[0155] (4) Separating film: a polypropylene film is used.

[0156] (5) Preparation of the first battery cell:

[0157] The positive electrode sheet, the separating film, and the negative electrode sheet are stacked and wound in sequence to obtain the first battery cell, and the capacity C of the first battery cell in the widest voltage range in the whole life cycle is 100 Ah. A The design is 100 Ah.

[0158] (II) Preparation of the second battery cell

[0159] (1) Preparation of the second positive active material:

[0160] NiSO4, CoSO4, and MnSO4 are added to water to prepare a mixed solution according to a molar ratio of 0.55:0.141:0.249, wherein the concentration of NiSO4 in the mixed solution is 2 mol / L; a 5 mol / L NaOH solution is prepared;

[0161] 50 L of the mixed solution is introduced into a reaction kettle, and then 50 L of the NaOH solution and an appropriate amount of a 0.5 mol / L ammonia water solution are introduced into the reaction kettle, so that the pH value in the reaction kettle is 9.0-12.0, the reaction temperature is 40℃-80℃, and the reaction is performed under stirring for 60 h at a stirring speed of 300-1000 r / min; after completion, the precipitate is filtered and washed, and the washed precipitate is vacuum dried at 120℃ for 24 h to obtain a precursor;

[0162] Li2CO3, the precursor, Al2O3, and MgO are mixed, wherein the molar ratio of Li2CO3 (calculated based on the molar amount of Li element), the precursor (calculated based on the total molar amount of Ni, Co, and Mn elements in the mixed solution), Al2O3 (calculated based on the molar amount of Al element), and MgO is 1.05:0.94:0.04:0.02; after mixing, the mixture is placed in a ball mill jar and ball milled at a speed of 300 r / s for 2 h, and then is placed in a box-type furnace and pre-fired at 950℃ for 12 h under an air atmosphere at 0.2 MPa, at a heating rate of 1℃ / min, and then is sintered at 600℃ for 8 h at a rate of 1℃ / min, and then is cooled to 300℃ at a rate of 1℃ / min and naturally cooled to room temperature; after that, the mixture is subjected to airflow pulverization at a speed of 3000 r / min and a pressure of 0.5 MPa to obtain a second positive active material powder; 3The second positive active material LiNi0.5Co0.2Mn0.3O2 is pulverized for 0.5 h with a wind volume of 10 m3 / h, and then sieved through a 500-mesh screen to obtain the second positive active material LiNi0.5Co0.2Mn0.3O2. 0.55 Co 0.141 Mn 0.249 Al 0.04 Mg 0.02 O2.

[0163] (2) Preparation of the positive electrode tab:

[0164] The second positive active material, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are dissolved in the solvent N-methyl pyrrolidone (NMP) at a mass ratio of 96:2:2, and after being fully stirred and uniformly mixed, a positive electrode slurry is prepared; the positive electrode slurry is uniformly coated on the positive electrode current collector aluminum foil, and then after drying, cold pressing, and slitting, a positive electrode tab is obtained.

[0165] (3) Preparation of the negative electrode tab:

[0166] The negative active material artificial graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickening agent sodium carboxymethyl cellulose (CMC-Na) are dissolved in deionized water at a mass ratio of 96:2:1:1, and after being fully stirred and uniformly mixed, a negative electrode slurry is prepared; the negative electrode slurry is coated on the negative electrode current collector copper foil, and then after drying, cold pressing, and slitting, a negative electrode tab is obtained.

[0167] (4) Separating membrane: a polypropylene film is used.

[0168] (5) Preparation of the second electric core:

[0169] The above-mentioned positive electrode tab, the separating membrane, and the negative electrode tab are stacked and wound in sequence to obtain a second electric core, and the full life cycle application widest voltage interval capacity C of the second electric core is 100 Ah. B The design is 100 Ah.

[0170] (Three) Preparation of the electrolyte:

[0171] Ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed at a volume ratio of 1:1:1, and then LiPF6 is uniformly dissolved in the above solution to obtain an electrolyte. In the electrolyte, the concentration of LiPF6 is 1 mol / L.

[0172] (Four) Preparation of the secondary battery:

[0173] Three first electric cores and two second electric cores are assembled into an electrode assembly; the electrode assembly is placed in a shell, and the above-prepared electrolyte is added, and after processes such as packaging, standing, formation, and aging, a secondary battery is obtained.

[0174] Example 2-24 and Comparative Example 1-3 were prepared in a similar manner to the secondary battery of Example 1, except for the product parameters as shown in Table 1.

[0175] NPand NPare adjusted by adjusting the ratio of the coating mass of the positive electrode slurry on the positive electrode current collector and the coating mass of the negative electrode slurry on the negative electrode current collector in the first cell. A1 and NP A2 .

[0176] NPand NPare adjusted by adjusting the ratio of the coating mass of the positive electrode slurry on the positive electrode current collector and the coating mass of the negative electrode slurry on the negative electrode current collector in the second cell. B1 and NP B2 .

[0177] The design requirement of the full life cycle application widest voltage interval capacity C A or C B of the first cell or the second cell is achieved by using different sizes of the shell.

[0178] Comparative Example 3 uses 5 first cells. The first positive electrode active material of Example 2-24 and Comparative Example 1-3 is all carbon-coated core material.

[0179] Method for preparing the first positive electrode active material of Example 24

[0180] Step S1: Preparation of co-doped manganese oxalate

[0181] Put 689.6g of manganese carbonate, 455.3g of ferrous carbonate, 4.7g of cobalt sulfate, and 4.7g of vanadium dichloride into a mixer and mix well for 6h. Then transfer the obtained mixture into a reaction kettle, add 5L of deionized water and 1260.6g of dihydrate oxalic acid, heat to 80℃, and stir at a speed of 500rpm for 6h. Mix well until the reaction is complete and no bubbles are generated. Obtain a suspension of Fe, Co, and V co-doped manganese oxalate. Then filter the suspension, dry at 120℃, and then sand mill to obtain manganese oxalate particles with a particle size of 100nm.

[0182] Step S2: Preparation of core

[0183] Take 1793.1g of the prepared manganese oxalate, 369.8g of lithium carbonate, 1148.9g of ammonium dihydrogen phosphate, and 0.8g of silicic acid, and add them to 20L of deionized water. Stir well and mix uniformly at 80℃ for 10h to obtain a slurry. Transfer the slurry into a spray drying device for spray drying and granulation. Dry at a temperature of 250℃ to obtain a powder. Sinter the powder in a roller kiln at 700℃ for 4h in a protective atmosphere (90% nitrogen and 10% hydrogen) to obtain Li 1.001 Mn 0.60 Fe0.393 V 0.004 Co 0.003 P 0.999 Si 0.001 O4.

[0184] Method for preparing the third positive electrode active material of Examples 8-12, 21

[0185] Step S1: Preparation of Fe, Co, V and S co-doped manganese oxalate

[0186] Put 689.6 g of manganese carbonate, 455.3 g of ferrous carbonate, 4.7 g of cobalt sulfate, and 4.9 g of vanadium dichloride into a mixer and mix thoroughly for 6 h. Then transfer the obtained mixture into a reaction kettle, add 5 L of deionized water and 1260.6 g of oxalic acid dihydrate, heat to 80°C, and stir thoroughly at a speed of 500 rpm for 6 h until the reaction is complete and no bubbles are generated, to obtain a Fe, Co, and V co-doped manganese oxalate suspension. Then filter the suspension, dry at 120°C, and then perform sand milling to obtain manganese oxalate particles with a particle size of 100 nm.

[0187] Step S2: Preparation of the inner core

[0188] Take 1793.1 g of the manganese oxalate prepared in (1) and 369.8 g of lithium carbonate, 1148.9 g of ammonium dihydrogen phosphate, and 0.8 g of silicic acid, and add them to 20 L of deionized water, stir thoroughly, and mix uniformly at 80°C for 10 h to obtain a slurry. Transfer the slurry into a spray drying device for spray drying and granulation, dry at a temperature of 250°C to obtain a powder. Sinter the powder in a roller kiln at 700°C for 4 h in a protective atmosphere (90% nitrogen and 10% hydrogen) to obtain an inner core material. Detect the element content of the inner core material by inductively coupled plasma emission spectrometry (ICP) to obtain the inner core.

[0189] Step S3: Preparation of the first coating layer suspension

[0190] Preparation of a Li2FeP2O7 solution: dissolve 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 in 500 mL of deionized water, control the pH to be 5, then stir and react at room temperature for 2 h to obtain a solution, and then warm the solution to 80°C and maintain this temperature for 4 h to obtain the first coating layer suspension.

[0191] Step S4: Coating of the first coating layer

[0192] The doped 1571.9 g of lithium manganese phosphate core material obtained in step S2 was added to the first coating layer suspension (coating material content 15.7 g) obtained in step S3, and mixed by stirring for 6 h. After mixing, it was dried in a 120 °C oven for 6 h, and then sintered at 650 °C for 6 h to obtain a pyrophosphate coated material.

[0193] Step S5: Preparation of a second coating layer suspension

[0194] 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 h to obtain a solution. The solution was then heated to 120 °C and maintained at this temperature for 6 h to obtain a second coating layer suspension.

[0195] Step S6: Coating of a second coating layer

[0196] The 1586.8 g of pyrophosphate coated material obtained in step S4 was added to the second coating layer suspension (coating material content 47.1 g) obtained in step S5, and mixed by stirring for 6 h. After mixing, it was dried in a 120 °C oven for 6 h, and then sintered at 700 °C for 8 h to obtain a two-layer coated material.

[0197] Step S7: Preparation of a third coating layer aqueous solution

[0198] 37.3 g of sucrose was dissolved in 500 g of deionized water, and then stirred and dissolved to obtain a sucrose aqueous solution.

[0199] Step S8: Coating of a third coating layer

[0200] The two-layer coated material 1633.9 g obtained in step S6 was added to the sucrose solution obtained in step S7, and mixed by stirring for 6 h. After mixing, it was dried in a 150 °C oven for 6 h, and then sintered at 700 °C for 10 h to obtain a three-layer coated third positive electrode active material.

[0201]

[0202]

[0203]

[0204] Battery test

[0205] (1) When the state of charge (SOC) of the 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 when the state of charge (SOC) of the single cell battery changes by 1%:

[0206] The first or second cell is assembled into a single cell battery according to the above item (fourth).

[0207] Single cell battery test of the first cell: in a constant temperature environment of 25℃, after the battery is rested for 10 min, it is discharged at 0.1C constant current to a cut-off voltage of 2.8V, rested for 10 min, charged at 0.04C constant current to a target voltage of 3.65V, rested for 10 min, discharged at 0.04C constant current to a cut-off voltage of 2.8V, rested for 10 min, charged at 0.04C constant current to a target voltage of 3.65V, the charging capacity at this time is recorded as 100% SOC, rested for 10 min, discharged at 0.04C constant current to a cut-off voltage of 2.8V; the charging capacity of the last charging process is taken as the y-axis, and the voltage is taken as the x-axis to plot a graph, from which the voltage Vm corresponding to 95% SOC and the voltage Vn corresponding to 100% SOC are obtained, then 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 per 1% change in the state of charge of the battery. The target voltage adopted by the first cell of Example 24 is 4.25V.

[0208] Single cell battery test of the second cell: in a constant temperature environment of 25℃, after the battery is rested for 10 min, it is discharged at 0.1C constant current to a cut-off voltage of 2.8V, rested for 10 min, charged at 0.04C constant current to a target voltage of 4.25V, rested for 10 min, discharged at 0.04C constant current to a cut-off voltage of 2.8V, rested for 10 min, charged at 0.04C constant current to a target voltage of 4.25V, the charging capacity at this time is recorded as 100% SOC, rested for 10 min, discharged at 0.04C constant current to a cut-off voltage of 2.8V; the charging capacity of the last charging process is taken as the y-axis, and the voltage is taken as the x-axis to plot a graph, from which the voltage Vm corresponding to 95% SOC and the voltage Vn corresponding to 100% SOC are obtained, then 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 per 1% change in the state of charge of the battery.

[0209] (2) Test of the de-lithiation capacity of the positive electrode tab and the lithium intercalation capacity of the negative electrode tab:

[0210] The positive electrode tab and the negative electrode tab are respectively made into a button cell with a counter electrode lithium sheet.

[0211] Test of the button cell of the positive electrode tab: in a constant temperature environment of 25℃, charge at 0.1C constant current to 4.35V, then discharge at 0.1C to 2.8V, record the discharge capacity of the first circle, divide the discharge capacity of the first circle by the mass of the positive electrode active material in the positive electrode tab to obtain the first delithiation gram capacity of the positive electrode tab; continue to charge and discharge the button cell according to the above manner for 2 times, a total of 3 times, record the second charge and discharge capacity as the non-first circle discharge capacity, divide the non-first circle discharge capacity by the mass of the positive electrode active material in the positive electrode tab to obtain the non-first delithiation gram capacity of the positive electrode tab.

[0212] Test of the button cell of the negative electrode tab: in a constant temperature environment of 25℃, charge at 0.1C constant current to 2.0V, then discharge at 0.1C to 0V, record the discharge capacity of the first circle, divide the discharge capacity of the first circle by the mass of the negative electrode active material in the negative electrode tab to obtain the first lithium intercalation gram capacity of the negative electrode tab; continue to charge and discharge the button cell according to the above manner for 2 times, a total of 3 times, record the second charge and discharge capacity as the non-first circle discharge capacity, divide the non-first circle discharge capacity by the mass of the negative electrode active material in the negative electrode tab to obtain the non-first lithium intercalation gram capacity of the negative electrode tab.

[0213] (3) Determine whether the upper limit voltage of the second cell increases:

[0214] In a constant temperature environment of 25℃, the battery is discharged at 0.33C to the lower limit of the cut-off voltage 2.8V, rested for 10 minutes, charged at 0.33C constant current to the upper limit of the cut-off voltage 5V, constant voltage charging to ≤0.05C, the charging capacity is recorded as the nominal capacity, the voltage data of the second cell is monitored during the charging process to obtain the upper limit voltage of the second cell corresponding to the nominal capacity; according to the above manner, the discharge and charge is cycled for 100 times, the voltage data of the second cell is monitored during the charging process of the last cycle to obtain the upper limit voltage of the second cell of the last cycle. If the upper limit voltage of the second cell of the last cycle minus the upper limit voltage of the second cell corresponding to the nominal capacity is greater than 0.05V, it is determined that the upper limit voltage of the second cell increases, otherwise the upper limit voltage of the second cell does not increase.

[0215] (4) Overcharge protection test:

[0216] In a constant temperature environment of 25℃, the battery is charged at 0.1C to the upper limit of the cut-off voltage, then discharged at 0.33C to the lower limit of the cut-off voltage, the values of the upper limit of the cut-off voltage and the lower limit of the cut-off voltage are shown in Table 2; according to the above manner, the charge and discharge is cycled for 200 times; disassemble the battery, if the area of lithium precipitation on the negative electrode tab (excluding the corner position) accounts for >1 / 5 of the total area of the negative electrode tab, it is considered to fail the overcharge protection test, recorded as NG, otherwise it is considered to pass the overcharge protection test, recorded as OK.

[0217] (5) Test of cycle life:

[0218] After the battery is placed in a constant temperature environment at 25℃ for 10 minutes, it is discharged at 0.33C to 2.8V; after 10 minutes of standing, it is charged at 0.1C to 4.3V, and charged at constant voltage to a current ≤0.05C, and after 10 minutes of standing, it is discharged at 0.33C to 2.8V, and the discharge capacity of the first cycle of the battery is recorded as D1, and the above charging and discharging operations are repeated, and the discharge capacity of each cycle is recorded as D n (n = 2, 3, …); the degree of attenuation of the battery cell (State of health SOH) is calculated according to the following formula, and the cycle number n at which the degree of attenuation reaches 90% SOH is recorded.

[0219] Degree of attenuation of the battery cell = 100% x (D1-Dn) / D1 n / D3.

[0220] Table 2: Performance test results of Examples 1-24 and Comparative Examples 1-3

[0221]

[0222]

[0223] According to the above results, it can be seen that:

[0224] Compared with Comparative Examples 1-3, the batteries of Examples 1-24 of the present application have higher safety and longer cycle life.

[0225] Compared with Examples 5-7, 17, 19-22, the batteries of Examples 1-4, 8-16, 23-24 of the present application have longer cycle life.

[0226] It should be noted that the present application is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, and other ways constructed by combining part of the components of the embodiments are also included in the scope of the present application.

Claims

1. A battery cell assembly, 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 both the first battery cell and the second battery cell comprise a positive electrode and a negative electrode. Furthermore, the cell assembly 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 NP is the ratio of the initial lithium insertion capacity of the negative electrode to the initial lithium extraction capacity of the positive electrode in the first cell. B1 NP is the ratio of the initial lithium insertion capacity of the negative electrode to the initial lithium extraction 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 extraction capacity of the positive electrode in the first cell. B2 It 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 second cell; When the state of charge of a 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 5mV.

2. The cell assembly according to claim 1, wherein, When the state of charge of a 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 change of the first cell is less than or equal to 5mV.

3. The cell assembly according to claim 1, wherein it satisfies: 0.08 ≤ (1.1 - NP A1 ) / (NP B1 -1)≤20.

4. The cell assembly according to claim 1, wherein it satisfies: 0.1≤(1.1-NP A1 ) / (NP B1 -1)≤15.

5. The cell assembly according to claim 1, wherein it satisfies: 0.95≤C B / C A ≤1.4; in, C A C represents the widest voltage range capacity across the entire lifecycle of the first battery cell. B This refers to the widest voltage range capacity for the second battery cell throughout its entire lifecycle.

6. The cell assembly according to claim 1, wherein it satisfies: 1.0≤C B / C A ≤1.3; in, C A C represents the widest voltage range capacity across the entire lifecycle of the first battery cell. B This refers to the widest voltage range capacity for the second battery cell throughout its entire lifecycle.

7. The cell assembly according to any one of claims 1 to 6, wherein, The positive electrode in the first battery cell includes a first positive active material, which contains the 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 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.

8. The cell assembly according to claim 7, wherein, The first positive electrode active material includes a core and a coating layer covering the core; wherein the core contains 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.

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

10. The cell assembly according to claim 9, wherein, The M includes Mg and / or Al elements.

11. The cell assembly according to claim 9, wherein, The value of d is 0.047-0.

320.

12. The cell assembly according to claim 9, wherein, The positive electrode in the second 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 contains 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 contains crystalline phosphate X t PO4, the third coating layer contains carbon; Wherein, 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; R includes one or more elements selected from B, Si, N, and S; and the crystalline pyrophosphate Li j GP2O7 and G k (P2O7) r In each of the following, G independently includes one or more elements selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al; X includes one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al; g is -0.100 to 0.100; h is 0.001 to 0.600; i is 0.001 to 0.100; j is greater than 0 and less than or equal to 2; k is 1 to 4; r is 1 to 3; and t is greater than 0 and less than or equal to 2.

13. The cell assembly according to claim 12, wherein, The E includes one or more elements selected from Fe, V, Ni, and Co.

14. The cell assembly according to claim 12, wherein, The R includes one or more elements selected from Si, N, and S.

15. The cell assembly according to claim 12, wherein, The crystalline pyrophosphate Li j GP2O7 and G k (P2O7) r The G in each element independently includes one or more of Fe, Co, Ti, and Al.

16. The cell assembly according to claim 12, wherein, X includes one or more elements selected from Li, Fe, Ag, and Al.

17. The cell assembly according to any one of claims 12 to 16, wherein, In the positive electrode of the second 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.

18. The cell assembly according to any one of claims 12 to 16, wherein, In the positive electrode of the second cell, the mass of the second positive electrode active material accounts for 5%-95% of the total mass of the second and third positive electrode active materials.

19. A battery comprising the cell assembly of any one of claims 1 to 18.

20. The battery according to claim 19, wherein, The upper limit voltage of the second cell during the 90th-110th charge-discharge cycle of the battery is greater than the upper limit voltage of the second cell during the first charge-discharge cycle of the battery.

21. An electrical device comprising the battery of claim 19 or 20.

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