Battery module and lithium ion battery pack

Abstract

The invention provides a battery module and a lithium ion battery pack, and belongs to the technical field of lithium ion batteries. The battery module comprises a first battery cell and a second battery cell, the energy density of the first battery cell is higher than that of the second battery cell, the safety performance of the second battery cell is higher than that of the first battery cell, and the first battery cell and the second battery cell are combined in a parallel connection mode or a series connection mode. The battery module can have relatively high energy density and good safety performance at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery packs, and in particular relates to a battery module and a lithium-ion battery pack. Background Art

[0002] The existing power lithium-ion battery packs have the problem of not being able to balance energy density and safety. For example, when using a high energy density system such as a ternary cathode material, safety performance cannot be guaranteed, and when using a high safety performance system such as lithium iron phosphate, energy density cannot be met. Therefore, it is necessary to optimize the battery module design based on the existing pure high energy density system and pure high safety system to achieve the goal of balancing energy density and safety performance. Summary of the invention

[0003] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, an embodiment of the present invention provides a battery module and a lithium-ion battery pack.

[0004] An embodiment of the present invention provides a battery module, comprising: a first battery cell and a second battery cell, wherein the first battery cell comprises a first positive electrode active material, and the second battery cell comprises a second positive electrode active material;

[0005] The first positive electrode active material and the second positive electrode active material both include lithium nickelate and / or lithium nickel manganeseate, the mass fraction of nickel in the first positive electrode active material is higher than the mass fraction of nickel in the second positive electrode active material, and the first battery cell and the second battery cell are combined in parallel or in series;

[0006] Alternatively, the first positive electrode active material and the second positive electrode active material both include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and lithium nickel cobalt manganese aluminum oxide, the sum of the mass fractions of nickel and cobalt in the first positive electrode active material is higher than the sum of the mass fractions of nickel and cobalt in the second positive electrode active material, and the first battery cell and the second battery cell are combined in parallel or in series;

[0007] Alternatively, the first positive electrode active material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium nickel oxide and lithium nickel manganese oxide, and the second positive electrode active material includes at least one of lithium iron phosphate, lithium ferrous phosphate and lithium manganese iron phosphate, and the first battery cell and the second battery cell are combined in series.

[0008] The advantages and technical effects brought by the battery module of the embodiment of the present invention are:

[0009] (1) When the first battery cell is a high-nickel lithium battery cell and the second battery cell is a low-nickel lithium battery cell, the energy density of the first battery cell is higher than that of the second battery cell, and the safety performance of the second battery cell is higher than that of the first battery cell. After the first battery cell and the second battery cell are connected in parallel or in series, the obtained battery module can simultaneously take into account high energy density and good safety performance;

[0010] (2) When the first battery cell is a high-nickel-cobalt lithium battery cell and the second battery cell is a low-nickel-cobalt lithium battery cell, the energy density of the first battery cell is higher than that of the second battery cell, and the safety performance of the second battery cell is higher than that of the first battery cell. After the first battery cell and the second battery cell are connected in parallel or in series, the obtained battery module can simultaneously take into account high energy density and good safety performance;

[0011] (3) When the first battery cell is a nickel-containing lithium battery cell and the second battery cell is a lithium iron phosphate system battery cell, the energy density of the first battery cell is higher than the energy density of the second battery cell, and the safety performance of the second battery cell is higher than the safety performance of the first battery cell. After the first battery cell and the second battery cell are connected in series, the resulting battery module can simultaneously take into account a higher energy density and good safety performance.

[0012] In some embodiments, when the first positive electrode active material and the second positive electrode active material both include lithium nickel oxide and / or lithium nickel manganese oxide, the mass fraction of nickel in the first positive electrode active material is at least 6 percentage points higher than the mass fraction of nickel in the second positive electrode active material.

[0013] In some embodiments, when the first positive electrode active material and the second positive electrode active material both include lithium nickel oxide and / or lithium nickel manganese oxide, the mass fraction of nickel in the first positive electrode active material is at least 8 percentage points higher than the mass fraction of nickel in the second positive electrode active material.

[0014] In some embodiments, when the first positive electrode active material and the second positive electrode active material both include lithium nickel oxide and / or lithium nickel manganese oxide, the mass fraction of nickel in the first positive electrode active material is greater than 70%, and the mass fraction of nickel in the second positive electrode active material is less than 60%.

[0015] In some embodiments, when the first positive electrode active material and the second positive electrode active material both include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and lithium nickel cobalt manganese aluminum oxide, the sum of the mass fractions of nickel and cobalt in the first positive electrode active material is at least 6 percentage points higher than the sum of the mass fractions of nickel and cobalt in the second positive electrode active material.

[0016] In some embodiments, when the first positive electrode active material and the second positive electrode active material both include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and lithium nickel cobalt manganese aluminum oxide, the sum of the mass fractions of nickel and cobalt in the first positive electrode active material is at least 8 percentage points higher than the sum of the mass fractions of nickel and cobalt in the second positive electrode active material.

[0017] In some embodiments, when the first positive electrode active material and the second positive electrode active material both include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and lithium nickel cobalt manganese aluminum oxide, the total mass fraction of nickel and cobalt in the first positive electrode active material is greater than 70%, and the total mass fraction of nickel and cobalt in the second positive electrode active material is less than 60%.

[0018] In some embodiments, the capacity of the first battery cell and the second battery cell are the same; and / or the number of the first battery cell and the second battery cell are the same.

[0019] In some embodiments, the total number of the first battery cells and the second battery cells is 3-100; and / or, the first battery cells and the second battery cells are stacked with intervals.

[0020] An embodiment of the present invention further provides a lithium-ion battery pack, comprising the battery module of the embodiment of the present invention.

[0021] The advantages and technical effects brought by the lithium-ion battery pack of the embodiment of the present invention are: the lithium-ion battery pack of the embodiment of the present invention can have both high energy density and good safety performance, and can achieve high voltage output, which is beneficial to reducing the number of battery cells in the low-power battery pack. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram of the structure of a battery module formed in parallel in an embodiment of the present invention;

[0023] Figure 2 A schematic diagram of the structure of a battery module formed in series connection according to an embodiment of the present invention;

[0024] Figure 3 A schematic diagram of the structure of a battery module formed by another series connection method according to an embodiment of the present invention;

[0025] Description of the accompanying drawings: 1-first battery cell; 2-second battery cell. DETAILED DESCRIPTION

[0026] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0027] An embodiment of the present invention provides a battery module, comprising: a first battery cell and a second battery cell, wherein the first battery cell comprises a first positive electrode active material, and the second battery cell comprises a second positive electrode active material;

[0028] The first positive electrode active material and the second positive electrode active material both include lithium nickelate and / or lithium nickel manganeseate, the mass fraction of nickel in the first positive electrode active material is higher than the mass fraction of nickel in the second positive electrode active material, and the first battery cell and the second battery cell are connected in parallel (see Figure 1 ) or in series (see Figure 2 and Figure 3 )combination;

[0029] Alternatively, the first positive electrode active material and the second positive electrode active material both include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and lithium nickel cobalt manganese aluminum oxide, the sum of the mass fractions of nickel and cobalt in the first positive electrode active material is higher than the sum of the mass fractions of nickel and cobalt in the second positive electrode active material, and the first battery cell and the second battery cell are combined in parallel or in series;

[0030] Alternatively, the first positive electrode active material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium nickel oxide and lithium nickel manganese oxide, the second positive electrode active material includes at least one of lithium iron phosphate, lithium ferrous phosphate and lithium manganese iron phosphate, and the first battery cell and the second battery cell are connected in series (see Figure 2 and Figure 3 )combination.

[0031] When the first battery cell is a high-nickel lithium battery cell and the second battery cell is a low-nickel lithium battery cell, the energy density of the battery cell with a higher nickel content is higher, and the safety performance of the battery cell with a lower nickel content is higher. Therefore, the energy density of the first battery cell is higher than the energy density of the second battery cell, and the safety performance of the second battery cell is higher than the safety performance of the first battery cell.

[0032] Alternatively, when the first battery cell is a high-nickel-cobalt lithium battery cell and the second battery cell is a low-nickel-cobalt lithium battery cell, the higher the total nickel-cobalt content, the higher the energy density of the battery cell, and the lower the total nickel-cobalt content, the higher the safety performance of the battery cell. Therefore, the energy density of the first battery cell is higher than the energy density of the second battery cell, and the safety performance of the second battery cell is higher than the safety performance of the first battery cell.

[0033] Alternatively, when the first battery cell is a nickel-containing lithium battery cell and the second battery cell is a lithium iron phosphate system battery cell, the energy density of the first battery cell is higher than the energy density of the second battery cell, and the safety performance of the second battery cell is higher than the safety performance of the first battery cell.

[0034] After combining the first battery cell (high energy density system) and the second battery cell (high safety performance system) in the above three parallel schemes, the battery module of the embodiment of the present invention can have both high energy density and good safety performance. Compared with the high energy density battery module (hereinafter referred to as pure high energy density system) that uses all the first battery cells, although the battery module of the embodiment of the present invention will lose a very small part of the energy density, the safety performance can be significantly improved; and compared with the high safety performance battery module (hereinafter referred to as pure high safety performance system) that uses all the second battery cells, although the safety performance of the battery module of the embodiment of the present invention is slightly reduced, its energy density has been significantly improved, that is, the energy density of the battery module of the embodiment of the present invention is close to that of the pure high energy density system, and the safety performance is close to that of the pure high safety performance system. Therefore, it can be considered that the comprehensive performance of the battery module of the embodiment of the present invention is superior to that of the pure high energy density system and the pure high safety performance system, and has a higher practical value.

[0035] It should be noted that when the first battery cell is a high-nickel lithium battery cell and the second battery cell is a low-nickel lithium battery cell, or when the first battery cell is a high-nickel cobalt lithium battery cell and the second battery cell is a low-nickel cobalt lithium battery cell, the operating voltages of the two battery cells are equivalent, so both a parallel design and a series design can be used, and the effect is basically the same.

[0036] However, when the first battery cell is a nickel-containing lithium battery cell and the second battery cell is a lithium iron phosphate system battery cell, the first battery cell and the second battery cell in the battery module of the embodiment of the present invention cannot be designed in parallel and can only be designed in series. This is because the voltage usage ranges of the nickel-containing lithium battery cell and the lithium iron phosphate system battery cell are different. If they are connected in parallel, the loss of energy density will be very large, and the design effect of balancing energy density and safety performance cannot be achieved.

[0037] When the first battery cell is a high-nickel lithium battery cell and the second battery cell is a low-nickel lithium battery cell, the greater the difference between the mass fraction of nickel in the first positive electrode active material and the second positive electrode active material, the more conducive to improving the comprehensive performance of the battery module. For example, when the first battery cell is the same, the lower the nickel content in the second positive electrode active material, the better the safety performance of the second battery cell, and the better the comprehensive performance of the battery module obtained by combining the first battery cell and the second battery cell. Conversely, when the second battery cell is the same, the higher the nickel content in the first positive electrode active material, the higher the energy density of the first battery cell, and the better the comprehensive performance of the battery module obtained by combining the first battery cell and the second battery cell. Therefore, preferably, in some embodiments, the mass fraction of nickel in the first positive electrode active material is at least 6 percentage points higher than the mass fraction of nickel in the second positive electrode active material. More preferably, in some embodiments, the mass fraction of nickel in the first positive electrode active material is at least 8 percentage points higher than the mass fraction of nickel in the second positive electrode active material.

[0038] When the first battery cell is a high-nickel lithium battery cell and the second battery cell is a low-nickel lithium battery cell, the higher the mass fraction of nickel in the first positive electrode active material, the higher the energy density of the first battery cell, and the lower the mass fraction of nickel in the second positive electrode active material, the higher the safety performance of the second battery cell, and the better the comprehensive performance of the battery module obtained by combining the two. Preferably, in some embodiments, the mass fraction of nickel in the first positive electrode active material is greater than 70%, and the mass fraction of nickel in the second positive electrode active material is less than 60%.

[0039] When the first battery cell is a high-nickel-cobalt lithium battery cell and the second battery cell is a low-nickel-cobalt lithium battery cell, the greater the difference between the sum of the contents of nickel and cobalt in the first positive electrode active material and the second positive electrode active material, the more conducive to improving the comprehensive performance of the battery module. For example, when the first battery cell is the same, the lower the sum of the contents of nickel and cobalt in the second positive electrode active material, the better the safety performance of the second battery cell, and the better the comprehensive performance of the battery module obtained by combining the first battery cell and the second battery cell. Conversely, when the second battery cell is the same, the higher the sum of the contents of nickel and cobalt in the first positive electrode active material, the higher the energy density of the first battery cell, and the better the comprehensive performance of the battery module obtained by combining the first battery cell and the second battery cell. Therefore, preferably, in some embodiments, the sum of the mass fractions of nickel and cobalt in the first positive electrode active material is at least 6 percentage points higher than the sum of the mass fractions of nickel and cobalt in the second positive electrode active material. More preferably, in some embodiments, the sum of the mass fractions of nickel and cobalt in the first positive electrode active material is at least 8 percentage points higher than the sum of the mass fractions of nickel and cobalt in the second positive electrode active material.

[0040] When the first battery cell is a high-nickel-cobalt lithium battery cell and the second battery cell is a low-nickel-cobalt lithium battery cell, the higher the sum of the mass fractions of nickel and cobalt in the first positive electrode active material, the higher the energy density of the first battery cell, and the lower the sum of the mass fractions of nickel and cobalt in the second positive electrode active material, the higher the safety performance of the second battery cell, and the better the comprehensive performance of the battery module obtained by combining the two. Preferably, in some embodiments, the sum of the mass fractions of nickel and cobalt in the first positive electrode active material is more than 70%, and the mass fractions of nickel and cobalt in the second positive electrode active material are less than 60%.

[0041] When the first battery cell is a nickel-containing lithium battery cell such as lithium nickelate and / or lithium nickel manganeseate, and the second battery cell is a lithium iron phosphate system battery cell, the mass fraction of nickel in the first positive electrode active material is 60% or more. When the mass fraction of nickel in the first positive electrode active material is less than 60%, it is not conducive to improving the energy density of the first battery cell, and thus is not conducive to improving the energy density of the battery module. When the first battery cell is a nickel-containing lithium battery cell such as at least one of lithium nickel cobalt manganeseate, lithium nickel cobalt aluminum oxide and lithium nickel cobalt manganese aluminum oxide, and the second battery cell is a lithium iron phosphate system battery cell, the sum of the mass fractions of nickel and cobalt in the first positive electrode active material is more than 60%. When the sum of the mass fractions of nickel and cobalt in the first positive electrode active material is less than 60%, it is not conducive to improving the energy density of the first battery cell, and thus is not conducive to improving the energy density of the battery module.

[0042] When the first battery cell is a high-nickel lithium battery cell and the second battery cell is a low-nickel lithium battery cell, or, when the first battery cell is a high-nickel cobalt battery cell and the second battery cell is a low-nickel cobalt battery cell, the voltage usage range of the first battery cell and the second battery cell are the same, so the capacity designs of the first battery cell and the second battery cell may be the same or different.

[0043] When the first battery cell is a nickel-containing lithium battery cell and the second battery cell is a lithium iron phosphate system battery cell, the voltage usage range of the first battery cell and the second battery cell are inconsistent. Although the capacity design of the first battery cell and the second battery cell can be consistent or different, it is preferred that the capacity design of the first battery cell and the second battery cell is consistent. Because if the capacity of the first battery cell and the second battery cell is different, the overall capacity of the battery module is determined by the battery cell with the lower capacity of the first battery cell and the second battery cell, and the extra capacity of the other battery cell with a relatively higher capacity will not actually play a role. Therefore, in order to avoid waste and increase costs, it is preferred that the capacity of the first battery cell and the second battery cell is the same.

[0044] In the battery module of the embodiment of the present invention, the number of the first battery cell and the second battery cell can be the same or different, or the total number of the first battery cell and the second battery cell can be an odd number or an even number. Preferably, in some embodiments, the number of the first battery cell and the second battery cell is the same, that is, the total number of the battery cells is an even number, which is conducive to improving the energy density and safety performance of the battery module.

[0045] The greater the total number of battery cells, the more conducive it is to improving the capacity of the battery module. Therefore, in some embodiments, the total number of battery cells is at least 3, preferably 3-100.

[0046] When there are multiple battery cells, the first battery cell and the second battery cell are stacked with an interval (see Figure 1-Figure 3). The interleaved stacking method is more conducive to improving the safety of the battery module. Interleaved stacking means that at least one second battery cell is arranged between two first battery cells, or at least one first battery cell is arranged between two second battery cells. Preferably, in some embodiments, the first battery cells and the second battery cells are arranged alternately (see Figure 1 and Figure 2 ), that is, they are arranged in the order of first battery cell / second battery cell / first battery cell / second battery cell. When the first battery cell and the second battery cell are stacked and connected in series, the positive electrode of the first battery cell can be connected to the negative electrode of the second battery cell, or the negative electrode of the first battery cell can be connected to the positive electrode of the second battery cell.

[0047] The battery cell includes an electrode group and an electrolyte, and the electrode group includes a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet. In addition to the positive electrode active material, the positive electrode sheet may also include a conductive agent, a binder, and a solvent, and optionally, a thickener. The negative electrode sheet includes a negative electrode active material, a conductive agent, a binder, and a solvent, and optionally, a thickener.

[0048] In the battery module of the embodiment of the present invention, the first battery cell further includes a first negative electrode active material, and the second battery cell further includes a second negative electrode active material. The first negative electrode active material and the second negative electrode active material may be the same or different, but the energy density of the first battery cell is higher than the energy density of the second battery cell, and the safety performance of the second battery cell is higher than the safety performance of the first battery cell. For example, the first negative electrode active material and the second negative electrode active material may both be graphite; or, the first negative electrode active material and the second negative electrode active material may both be lithium titanate (LTO); or, the first negative electrode active material is graphite, and the second negative electrode active material is lithium titanate (LTO).

[0049] The battery module of the embodiment of the present invention has no particular limitation on the separator, as long as it is a material with high porosity that allows lithium ions to pass through, for example, it may include at least one of PP, PE and non-woven fabric.

[0050] The electrolyte of the battery cell of the embodiment of the present invention is not particularly limited, as long as it can conduct ions between the positive and negative electrodes of the lithium-ion battery pack. The electrolyte includes a lithium salt and a solvent that can dissolve the lithium salt. Among them, the lithium salt can include lithium fluoride (LiF), lithium hexafluorophosphate (LiPF 6 ), lithium perchlorate (LiClO 4 ), lithium bis(trifluoromethanesulfonyl)imide (LIFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium metaborate (LiBO 2 ), lithium tetrafluoroborate (LiBF 4 ) lithium hexafluoroarsenate (LiAsF 6 ), lithium trifluoromethanesulfonate (LiCF3 SO 3 ), lithium bis(trifluoromethylsulfonyl)imide (Li(SO 2 CF 3 ) 2 The solvent may include at least one of cyclic esters such as ethylene carbonate and propylene carbonate, and linear esters such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

[0051] The present invention also provides a method for preparing a battery module, comprising the following steps: connecting a first battery cell and a second battery cell in parallel (see Figure 1 ) or in series (see Figure 2 and Figure 3 ) are combined to form a battery module. For example, Figure 1 As shown, the first battery cell 1 and the second battery cell 2 are connected in parallel; Figure 2 As shown, the cells are arranged alternately in the order of first cell 1 / second cell 2 / first cell 1 / second cell 2, and the first cell 1 and the second cell 2 are connected in series; Figure 3 As shown, two first battery cells 1 are first connected in parallel to form a battery module unit, and two second battery cells 2 are first connected in parallel to form another battery module unit, and then the two battery module units of different chemical systems are connected in series to form a battery module.

[0052] The method for preparing a battery module according to the embodiment of the present invention can make the obtained battery module have both high energy density and good safety performance by combining the first battery cell and the second battery cell for use.

[0053] In some embodiments, the preparation method of the electrode group includes the following steps: obtaining the electrode group by winding or laminating in the order of negative electrode sheet / separator / positive electrode sheet / separator / negative electrode sheet.

[0054] In some embodiments, the preparation method of the positive electrode sheet includes the following steps: mixing the first positive electrode active material / the second positive electrode active material, the conductive agent, the binder and the solvent in a certain proportion, uniformly coating them on the surface of the aluminum foil substrate, and then baking, rolling and cutting to obtain the first positive electrode sheet / the second positive electrode sheet.

[0055] In some embodiments, the preparation method of the negative electrode sheet includes the following steps: mixing the negative electrode active material, conductive agent, binder and solvent and optionally thickener in a certain proportion, uniformly coating the mixture on the surface of the copper foil substrate, and then baking, rolling and cutting to obtain the negative electrode sheet.

[0056] The embodiment of the present invention further provides a lithium-ion battery pack, comprising the battery module of the embodiment of the present invention. The lithium-ion battery pack of the embodiment of the present invention can have both high energy density and high safety performance, and has excellent comprehensive performance.

[0057] The present invention is described in detail below with reference to the embodiments and the accompanying drawings.

[0058] Example 1

[0059] (1) Preparation of the first positive electrode sheet: The first positive electrode active material, lithium nickel cobalt manganese oxide C-1, the binder polyvinylidene fluoride (PVDF), and the conductive agent carbon black (SP) are homogenized and mixed in a weight ratio of 90:5:5, and a solvent N-methylpyrrolidone (NMP) is added to control the slurry viscosity to 6000-12000 mPa·s and the solid content to 60-75wt%, and then the slurry is evenly coated on the surface of an aluminum foil with a thickness of 12 μm, and the first positive electrode sheet is obtained by drying;

[0060] (2) Preparation of the first negative electrode sheet: artificial graphite, a first negative electrode active material, styrene-butadiene rubber (SBR), a thickener, carboxymethyl cellulose (CMC), and a conductive agent, carbon black (SP), are homogenized and mixed in a weight ratio of 95:2.5:1.5:1, and deionized water is added to control the slurry viscosity to 1000-5000 mPa·s and the solid content to 40-55 wt%. The slurry is then evenly coated on a copper foil surface with a thickness of 6 μm, and dried to obtain the first negative electrode sheet;

[0061] (3) Preparation of the second positive electrode sheet: The second positive electrode active material, lithium nickel cobalt manganese oxide C-2, the binder polyvinylidene fluoride (PVDF), and the conductive agent carbon black (SP) are homogenized and mixed in a weight ratio of 90:5:5, and a solvent N-methylpyrrolidone (NMP) is added to control the slurry viscosity to 6000-12000 mPa·s and the solid content to 60-75wt%. The slurry is then evenly coated on the surface of an aluminum foil with a thickness of 12 μm, and dried to obtain the second positive electrode sheet;

[0062] (4) Preparation of the second negative electrode sheet: the preparation method is the same as that of the first negative electrode sheet;

[0063] (5) Preparation of the first electrode group and the second electrode group: The first electrode group is prepared by stacking in the order of negative electrode sheet / pp separator / first positive electrode sheet / pp separator / negative electrode sheet; the second electrode group is prepared by stacking in the order of negative electrode sheet / pp separator / second positive electrode sheet / pp separator / negative electrode sheet; the capacities of the first electrode group and the second electrode group are controlled to be consistent by controlling the number of positive and negative electrode sheets.

[0064] (6) Preparation of the first battery cell and the second battery cell: welding the two first electrode groups in parallel, encapsulating them in a shell, baking, injecting liquid, forming, aging and dividing the capacity to obtain a first battery cell; welding the two second electrode groups in parallel, encapsulating them in a shell, baking, injecting liquid, forming, aging and dividing the capacity to obtain a second battery cell.

[0065] (7) Preparation of battery module: Figure 1 As shown, a single first battery cell 1 and a single second battery cell 2 are connected in parallel to obtain a battery module.

[0066] (8) Preparation of battery pack: Two battery modules are combined and welded in series to form a battery pack.

[0067] Example 2

[0068] The structure and preparation method of this embodiment are the same as those of Embodiment 1, except that the first positive electrode active material is lithium nickel cobalt manganese oxide C-1, and the second positive electrode active material is lithium nickel cobalt manganese oxide C-3.

[0069] Example 3

[0070] The structure and preparation method of this embodiment are the same as those of Embodiment 1, except that the first positive electrode active material is lithium nickel cobalt manganese oxide C-1, and the second positive electrode active material is lithium nickel cobalt manganese oxide C-4.

[0071] Example 4

[0072] The structure and preparation method of this embodiment are the same as those of Embodiment 1, except that the first positive electrode active material is lithium nickel cobalt manganese oxide C-1, and the second positive electrode active material is lithium nickel cobalt manganese oxide C-5.

[0073] Example 5

[0074] The structure and preparation method of this embodiment are the same as those of Embodiment 1, except that the first positive electrode active material is lithium nickel cobalt manganese oxide C-2, and the second positive electrode active material is lithium nickel cobalt manganese oxide C-3.

[0075] Example 6

[0076] The structure and preparation method of this embodiment are the same as those of Embodiment 1, except that the first positive electrode active material is lithium nickel cobalt manganese oxide C-2, and the second positive electrode active material is lithium nickel cobalt manganese oxide C-4.

[0077] Example 7

[0078] The structure and preparation method of this embodiment are the same as those of Embodiment 1, except that the first positive electrode active material is lithium nickel cobalt manganese oxide C-2, and the second positive electrode active material is lithium nickel cobalt manganese oxide C-5.

[0079] Example 8

[0080] The structure and preparation method of this embodiment are the same as those of Embodiment 1, except that the first positive electrode active material is lithium nickel cobalt manganese oxide C-3, and the second positive electrode active material is lithium nickel cobalt manganese oxide C-4.

[0081] Example 9

[0082] The structure and preparation method of this embodiment are the same as those of Embodiment 1, except that the first positive electrode active material is lithium nickel cobalt manganese oxide C-3, and the second positive electrode active material is lithium nickel cobalt manganese oxide C-5.

[0083] Example 10

[0084] The structure and preparation method of this embodiment are the same as those of Embodiment 1, except that the first positive electrode active material is lithium nickel cobalt manganese oxide C-4, and the second positive electrode active material is lithium nickel cobalt manganese oxide C-5.

[0085] Comparative Example 1

[0086] The structure and preparation method of this comparative example are the same as those of Example 1, except that the first positive electrode active material and the second positive electrode active material are both lithium nickel cobalt manganese oxide C-1.

[0087] Comparative Example 2

[0088] The structure and preparation method of this comparative example are the same as those of Example 1, except that both the first positive electrode active material and the second positive electrode active material are lithium nickel cobalt manganese oxide C-2.

[0089] Comparative Example 3

[0090] The structure and preparation method of this comparative example are the same as those of Example 1, except that the first positive electrode active material and the second positive electrode active material are both lithium nickel cobalt manganese oxide C-3.

[0091] Comparative Example 4

[0092] The structure and preparation method of this comparative example are the same as those of Example 1, except that the first positive electrode active material and the second positive electrode active material are both lithium nickel cobalt manganese oxide C-4.

[0093] Comparative Example 5

[0094] The structure and preparation method of this comparative example are the same as those of Example 1, except that the first positive electrode active material and the second positive electrode active material are both lithium nickel cobalt manganese oxide C-5.

[0095] The mass fractions of nickel and cobalt in the positive electrode active materials of different battery cells are shown in Table 1. The conditions of the first battery cell and the second battery cell in the battery packs of Examples 1-10 and Comparative Examples 1-5 are shown in Table 2.

[0096] Performance Testing

[0097] (1) Capacity, voltage, energy and energy density test

[0098] Three battery packs of the same embodiment or comparative example were taken, and their capacity, voltage, energy and energy density were measured. The test conditions were: room temperature, 0.33C CCCV to the upper limit voltage, stand for 30 minutes, 0.33C DC to the lower limit voltage, and the upper limit voltage and the lower limit voltage are shown in Table 3. The capacity and energy density test results of the battery packs of Examples 1-10 and Comparative Examples 1-5 are shown in Table 4.

[0099] (2) Thermal runaway and heat spread test

[0100] Two battery packs of the same embodiment or comparative example were taken for thermal runaway (hot box, needle puncture, overcharge) and heat spread tests. The specific test process is as follows:

[0101] ① Hot box: At room temperature, heat the 100% SOC fully charged battery cell at a heating rate of 5℃ / min to 200℃, and observe the state of thermal runaway of the battery cell;

[0102] ②Acupuncture: At room temperature, use a 3mm steel needle to pierce a 100% SOC fully charged battery cell at a speed of 1mm / s to observe the state of thermal runaway of the battery cell;

[0103] ③ Overcharge: At room temperature, charge a 100% SOC fully charged cell to 200% SOC at a charging current of 1C, and observe the state of thermal runaway of the cell;

[0104] ④ Heat spread: At room temperature, two 100% SOC full-level parallel sample cells are bound together, and a 3mm steel needle is used to pierce one of the cells at a speed of 1mm / s, and the state of thermal runaway of the other cell is observed, and the time interval from the occurrence of thermal runaway of the first cell to the occurrence of thermal runaway of the second cell is recorded, that is, the heat spread time. The thermal runaway and heat spread test results of the battery packs of Examples 1-10 and Comparative Examples 1-5 are shown in Table 5.

[0105] Table 1. Mass fraction of nickel and cobalt in positive electrode active materials of different cells

[0106]

[0107] Table 2. Types of the first battery cell and the second battery cell in the battery packs of Examples 1-10 and Comparative Examples 1-5

[0108]

[0109] Table 3. Test conditions for capacity and energy density of battery packs of Examples 1-10 and Comparative Examples 1-5

[0110] Group Upper limit voltage Lower voltage limit Example 1 400V 200V Example 2 400V 200V Example 3 400V 200V Example 4 400V 200V Example 5 400V 200V Example 6 400V 200V Example 7 400V 200V Example 8 400V 200V Example 9 400V 200V Example 10 400V 200V Comparative Example 1 400V 200V Comparative Example 2 400V 200V Comparative Example 3 400V 200V Comparative Example 4 400V 200V Comparative Example 5 400V 200V

[0111] Table 4. Test results of capacity and energy density of battery packs of Examples 1-10 and Comparative Examples 1-5

[0112]

[0113] Table 5. Thermal runaway and heat spread test results of battery packs of Examples 1-10 and Comparative Examples 1-5

[0114]

[0115] It can be seen from the test results in Tables 4 and 5 that by combining high-nickel ternary system cells and low-nickel ternary system cells into battery modules, the prepared battery pack can greatly improve safety performance while maintaining a high energy density.

[0116] Embodiment 11

[0117] The structure and preparation method of this embodiment are the same as those of embodiment 1, except that: the first positive electrode active material is lithium nickel cobalt manganese oxide NCM811, and the second positive electrode active material is lithium iron phosphate LFP; Figure 2 As shown, the cells are alternately arranged in the order of first cell 1 / second cell 2 / first cell 1 / second cell 2, connected in series and then assembled and welded to form a battery module; and two battery modules are then connected in series to form a battery pack.

[0118] Example 12

[0119] The structure and preparation method of this embodiment are the same as those of Embodiment 11, except that the first positive electrode active material is lithium nickel cobalt manganese oxide NCM622, and the second positive electrode active material is lithium iron phosphate LFP.

[0120] Embodiment 13

[0121] The structure and preparation method of this embodiment are the same as those of embodiment 11, except that: Figure 3 As shown, two first battery cells 1 are connected in parallel to form a battery module unit, two second battery cells 2 are connected in parallel to form a battery module unit, and then these two battery module units are combined and welded in series to obtain a battery module.

[0122] Comparative Example 6

[0123] The structure and preparation method of this comparative example are the same as those of Example 11, except that the first positive electrode active material and the second positive electrode active material are both nickel cobalt manganese oxide NCM811.

[0124] Comparative Example 7

[0125] The structure and preparation method of this comparative example are the same as those of Example 11, except that the first positive electrode active material and the second positive electrode active material are both nickel cobalt manganese oxide NCM622.

[0126] Comparative Example 8

[0127] The structure and preparation method of this comparative example are the same as those of Example 11, except that the first positive electrode active material and the second positive electrode active material are both lithium iron phosphate LFP.

[0128] The conditions of the first battery cell and the second battery cell in the battery packs of Examples 11-12 and Comparative Examples 6-8 are shown in Table 6. Three battery packs of each Example and Comparative Example were made. The capacity and energy density test conditions of the battery packs of Examples 11-12 and Comparative Examples 6-8 are shown in Table 7, and the test results are shown in Table 8. The thermal runaway and heat spread test process of the battery packs of Examples 11-12 and Comparative Examples 6-8 is the same as that of Examples 1-10 and Comparative Examples 1-5, and the test results are shown in Table 9.

[0129] Table 6. Types of the first and second cells in the battery packs of Examples 11-12 and Comparative Examples 6-8

[0130]

[0131] Table 7. Capacity and energy density test conditions of the battery packs of Examples 11-12 and Comparative Examples 6-8

[0132] Group Upper limit voltage Lower voltage limit Embodiment 11 400V 200V Example 12 400V 200V Comparative Example 6 400V 200V Comparative Example 7 400V 200V Comparative Example 8 400V 200V

[0133] Table 8. Capacity and energy density test results of the battery packs of Examples 11-12 and Comparative Examples 6-8

[0134]

[0135] Table 9. Thermal runaway and heat spread test results of battery packs of Examples 11-12 and Comparative Examples 6-8

[0136]

[0137] As can be seen from Table 8, Example 11 uses high nickel ternary system cells and lithium iron phosphate system cells to be combined in series to form a battery module. The capacity of the prepared battery pack is lower than that of Comparative Example 6. In terms of energy density, it is lower than the battery pack of the pure high nickel ternary system cell combination module of Comparative Example 6, but much higher than the battery pack of the pure lithium iron phosphate cell combination module of Comparative Example 8. Comparison between Example 12 and Comparative Examples 7-8 also shows the same pattern.

[0138] It can be seen from the test results in Table 9 that the safety performance of the prepared battery pack can be greatly improved by combining the high-nickel ternary system battery cells and the lithium iron phosphate system battery cells into a module.

[0139] In summary, the battery pack prepared by the present invention can take into account both high energy density and high safety performance, and greatly improve the safety performance without affecting the energy density.

[0140] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0141] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A battery module, characterized in that: include: A first battery cell and a second battery cell, wherein the first battery cell includes a first positive electrode active material, and the second battery cell includes a second positive electrode active material; The first positive electrode active material and the second positive electrode active material both include lithium nickelate and / or lithium nickel manganeseate, the mass fraction of nickel in the first positive electrode active material is higher than the mass fraction of nickel in the second positive electrode active material, and the first battery cell and the second battery cell are combined in parallel or in series; Alternatively, the first positive electrode active material and the second positive electrode active material both include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and lithium nickel cobalt manganese aluminum oxide, the sum of the mass fractions of nickel and cobalt in the first positive electrode active material is higher than the sum of the mass fractions of nickel and cobalt in the second positive electrode active material, and the first battery cell and the second battery cell are combined in parallel or in series; Alternatively, the first positive electrode active material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium nickel oxide and lithium nickel manganese oxide, and the second positive electrode active material includes at least one of lithium iron phosphate, lithium ferrous phosphate and lithium manganese iron phosphate, and the first battery cell and the second battery cell are combined in series.

2. The battery module according to claim 1, characterized in that: When both the first positive electrode active material and the second positive electrode active material include lithium nickel oxide and / or lithium nickel manganese oxide, the mass fraction of nickel in the first positive electrode active material is at least 6 percentage points higher than the mass fraction of nickel in the second positive electrode active material.

3. The battery module according to claim 2, characterized in that: When both the first positive electrode active material and the second positive electrode active material include lithium nickel oxide and / or lithium nickel manganese oxide, the mass fraction of nickel in the first positive electrode active material is at least 8 percentage points higher than the mass fraction of nickel in the second positive electrode active material.

4. The battery module according to claim 3, characterized in that: When both the first positive electrode active material and the second positive electrode active material include lithium nickel oxide and / or lithium nickel manganese oxide, the mass fraction of nickel in the first positive electrode active material is greater than 70%, and the mass fraction of nickel in the second positive electrode active material is less than 60%.

5. The battery module according to claim 1, characterized in that: When the first positive electrode active material and the second positive electrode active material both include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and lithium nickel cobalt manganese aluminum oxide, the sum of the mass fractions of nickel and cobalt in the first positive electrode active material is at least 6 percentage points higher than the sum of the mass fractions of nickel and cobalt in the second positive electrode active material.

6. The battery module according to claim 5, characterized in that: When the first positive electrode active material and the second positive electrode active material both include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and lithium nickel cobalt manganese aluminum oxide, the sum of the mass fractions of nickel and cobalt in the first positive electrode active material is at least 8 percentage points higher than the sum of the mass fractions of nickel and cobalt in the second positive electrode active material.

7. The battery module according to claim 6, characterized in that: In the case where the first positive electrode active material and the second positive electrode active material both include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and lithium nickel cobalt manganese aluminum oxide, the total mass fraction of nickel and cobalt in the first positive electrode active material is greater than 70%, and the total mass fraction of nickel and cobalt in the second positive electrode active material is less than 60%.

8. The battery module according to any one of claims 1 to 7, characterized in that: The first battery cell and the second battery cell have the same capacity; and / or the first battery cell and the second battery cell have the same number.

9. The battery module according to any one of claims 1 to 7, characterized in that: The total number of the first battery cells and the second battery cells is 3-100; and / or the first battery cells and the second battery cells are stacked with intervals.

10. A lithium-ion battery pack, characterized in that: A battery module comprising any one of claims 1 to 9.

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