Battery pack and electric device

Abstract

The application relates to a battery pack and a power utilization device. The battery pack comprises a battery box and a first battery monomer and a second battery monomer arranged in the battery box; wherein the heat dissipation capacity of the position of the first battery monomer is greater than the heat dissipation capacity of the position of the second battery monomer, the addition amount W1 of the lithium supplementing agent in the first battery monomer is greater than the addition amount W2 of the lithium supplementing agent in the second battery monomer, W1>0, and W2>=0.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to a battery pack and an electrical device. Background Technology

[0002] Rechargeable batteries, such as lithium-ion batteries, experience a certain degree of capacity loss during use, which leads to a reduction in lifespan. In particular, lithium-ion batteries are significantly affected by temperature during use, especially at low temperatures, where the usable capacity of individual battery cells decreases drastically and low-temperature power performance deteriorates rapidly.

[0003] Inside the battery pack, as the number of secondary batteries increases, the volume and capacity of the battery pack also increase. This further amplifies the temperature difference between the inside of the battery pack and the outer area near the edge, resulting in significant capacity differences between individual battery cells. This makes it impossible to ensure the balance of battery capacity, leading to poor overall performance of the battery pack. Summary of the Invention

[0004] In view of the above problems, this application provides a battery pack and power device that can improve the capacity balance between individual battery cells, thereby improving the overall performance.

[0005] In a first aspect, this application provides a battery pack, including a battery box and a first battery cell and a second battery cell disposed within the battery box;

[0006] Wherein, the heat dissipation capacity of the location of the first battery cell is greater than that of the location of the second battery cell, the amount of lithium replenishing agent added in the first battery cell W1 is greater than the amount of lithium replenishing agent added in the second battery cell W2, W1>0, W2≥0.

[0007] In a first aspect, this application also provides a battery pack, including a battery box and a first battery cell and a second battery cell disposed within the battery box;

[0008] In the battery box, due to the difference in heat dissipation, the temperature of the first battery cell is lower than that of the second battery cell, and the amount of lithium replenishing agent added in the first battery cell, W1, is greater than the amount of lithium replenishing agent added in the second battery cell, W1>0, W2≥0.

[0009] Compared with the prior art, this application includes at least the following beneficial effects:

[0010] This application arranges first and second battery cells with different lithium replenishment agent contents in different areas within the battery pack. Lithium loss is compensated for by the lithium replenishment agent, and different replenishment effects are achieved through varying agent contents. Furthermore, to address the differences in capacity loss between battery cells caused by temperature variations due to their arrangement, the lithium replenishment agent content is individually set for each battery cell. Specifically, battery cells in areas with greater heat dissipation capacity have a higher lithium replenishment agent content, while those in areas with less heat dissipation capacity have a relatively lower content. This differentiated approach compensates for lithium loss in each battery cell, thereby improving the capacity balance among the battery cells.

[0011] The aforementioned battery pack can achieve capacity self-balancing through the activation of lithium replenishment and the cell design of individual cells, without the need for BMS system equalization intervention and additional components such as self-heating devices. This allows the discharge capacity of each individual cell in the battery pack to maintain good consistency at room temperature or low temperature, thereby improving the overall performance of the battery pack.

[0012] In any embodiment of this application, the first battery cell and the second battery cell are formed by adding different amounts of lithium supplementing agent to battery cells with the same chemical system and the same capacity.

[0013] In any embodiment of this application, the lithium replenishing agent is added to the positive electrode active material layer of the battery cell, and the amount added is the mass content of the lithium replenishing agent in the corresponding positive electrode active material layer. By adjusting the amount of lithium replenishing agent added to the positive electrode active material layer of the battery cell, the capacity of the battery cell can be adjusted very easily and flexibly.

[0014] In any embodiment of this application, the amount of lithium replenishing agent added to the first battery cell and the second battery cell is no more than 25%.

[0015] In any embodiment of this application, the difference in discharge capacity between the second battery cell and the first battery cell due to the difference in heat dissipation caused by their different locations is ΔC; the difference in recovery capacity of the positive electrode active material between the first battery cell and the second battery cell due to the difference in the amount of lithium replenishing agent added is ΔD; and the difference in normal discharge capacity between the first battery cell and the second battery cell due to the difference in the amount of lithium replenishing agent added is ΔE. ΔC, ΔD, and ΔE satisfy the following conditions:

[0016] ΔC = ΔD + ΔE. The sum of the differences in recovery capacity and normal discharge capacity of the positive electrode active material caused by the difference in the amount of lithium replenishing agent added in this way exactly compensates for the differences in discharge capacity caused by different locations in the battery pack. In this way, capacity balance is achieved among the individual battery cells.

[0017] In any embodiment of this application, the temperature difference between the second battery cell and the first battery cell due to the difference in heat dissipation is ΔT, and the difference in the amount of lithium replenishing agent added to the first battery cell and the second battery cell is ΔW, where ΔW = W1 - W2. ΔT and ΔW satisfy the following conditions:

[0018] When 0 < ΔT ≤ 5℃, 0 < ΔW ≤ 6%;

[0019] When 5 < ΔT ≤ 10℃, 6% < ΔW ≤ 15%.

[0020] In any embodiment of this application,

[0021] When 0 < ΔT ≤ 5℃, 2% ≤ ΔW ≤ 4%;

[0022] When 5 < ΔT ≤ 10℃, 6% ≤ ΔW ≤ 12%.

[0023] In any embodiment of this application, the lithium supplement has the chemical formula Li. 1+x M y A z ;

[0024] Wherein, M is selected from at least one of Ni, Co, Mn, Mo, Ru, Fe and Ti;

[0025] A is selected from at least one of O, F, S, P and Cl.

[0026] In any embodiment of this application, 0 < x ≤ 5, 0.10 < y < 2, and 2 ≤ z ≤ 4.

[0027] In any embodiment of this application, the initial coulombic efficiency of the lithium replenishing agent is set to e, where e satisfies the following condition: 0.2 ≤ e ≤ 0.95.

[0028] In any embodiment of this application, within the battery box:

[0029] The first battery cell is located outside the second battery cell;

[0030] Alternatively, the heat exchange area between the first battery cell and the battery box is greater than the heat exchange area between the second battery cell and the battery box.

[0031] Thirdly, this application provides an electrical device that includes the battery pack described in the above embodiments, the battery pack being used to provide electrical energy.

[0032] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0033] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0034] Figure 1 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0035] Figure 2 This is a schematic diagram of the layout of individual battery cells in a battery pack according to a traditional implementation method.

[0036] Figure 3 yes Figure 1 The diagram shows a layout schematic of one embodiment of each battery cell in the battery pack.

[0037] Figure 4 yes Figure 1 The diagram shows a layout schematic of another embodiment of the individual battery cells in the battery pack.

[0038] Figure 5 yes Figure 1 The diagram shows a layout schematic of another embodiment of the individual battery cells in the battery pack.

[0039] Figure 6 This is a schematic diagram of a power supply device using a battery pack as a power source according to one embodiment of this application.

[0040] Explanation of reference numerals in the attached figures:

[0041] 10. Battery pack; 11. First battery cell; 12. Second battery cell; 13. Third battery cell; 14. Fourth battery cell. Detailed Implementation

[0042] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0044] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0045] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0046] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0047] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0048] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0049] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0050] Figure 1 This is battery pack 1 as an example. (See reference...) Figure 1 and Figure 2 The battery pack 10 may include a battery box (not shown) and multiple battery cells disposed within the battery box. The battery box includes an upper box and a lower box, with the upper box covering the lower box to form a closed space for accommodating the multiple battery cells. The multiple battery cells can be arranged in any manner within the battery box.

[0051] Generally, such as Figure 2 As shown, it does not consider differences in location or individual battery cells; instead, it places one battery cell at each location 1 of the battery pack. Furthermore, the battery cells at each location 1 are generally identical. Understandably, "identical battery cells" here refers to cells with the same chemical system and the same capacity. The same chemical system primarily refers to the same material for the battery cells; furthermore, the external dimensions of the battery cells can also be the same, for example, they can be battery cells from the same manufacturer and of the same model.

[0052] The researchers who developed this application discovered that the capacity loss of lithium-ion batteries during use mainly originates from the loss of active lithium and polarization, leading to a decline in lifespan. Secondary batteries, such as lithium-ion batteries, are significantly affected by temperature during use, especially at low temperatures, where the usable capacity of individual battery cells decreases dramatically, and low-temperature power performance deteriorates rapidly. Therefore, on the one hand, the significant capacity loss of individual battery cells can be reduced by increasing their operating temperature; on the other hand, the temperature difference between individual battery cells due to their placement can be minimized to avoid capacity imbalances among individual cells, which can lead to poor overall battery pack performance.

[0053] Therefore, the main methods for maintaining the capacity balance of individual battery cells generally include the following approaches:

[0054] The first method is to use a BMS system (also known as a battery nanny or battery manager) for balancing. Active balancing has high requirements for the design and configuration of the BMS, while passive balancing wastes some of the cell capacity.

[0055] The second method involves placing self-heating devices inside the battery pack to increase the overall temperature of the battery pack and improve battery performance. However, this increases costs, occupies internal space, and cannot achieve self-balancing.

[0056] The third method involves arranging cells with different chemical systems, placing batteries with better low-temperature resistance in areas with faster heat dissipation, thus ensuring capacity balance among individual battery cells.

[0057] Please see Figure 3 One embodiment of this application provides a battery pack 10, which includes a battery box and a first battery cell 11 and a second battery cell 12 disposed within the battery box.

[0058] Among them, the heat dissipation capacity of the first battery cell 11 at position 1 is greater than the heat dissipation capacity of the second battery cell 12 at position 2, the amount of lithium replenishing agent added in the first battery cell 11 W1 is greater than the amount of lithium replenishing agent added in the second battery cell 12 W2, W1>0, W2≥0.

[0059] Compared to the second battery cell 12, the first battery cell 11 experiences a greater temperature drop, resulting in a lower capacity utilization. To improve the battery's discharge capacity and ensure overall performance consistency, a greater capacity increase is needed for the first battery cell 11. Therefore, activating more lithium replenishing agent in the first battery cell 11 serves two purposes. First, by activating more lithium replenishing agent in the first battery cell 11, the thermodynamic capacity loss caused by lithium loss can be compensated for by mitigating the capacity loss due to temperature polarization. Second, since the impedance of the lithium replenishing agent is greater than that of the main cathode material, adding more lithium replenishing agent during charging and discharging will generate more heat to raise the temperature, mitigating the capacity loss caused by low-temperature polarization.

[0060] This application arranges first and second battery cells with different lithium replenishment agent contents in different areas within the battery pack. Lithium loss is compensated for by the lithium replenishment agent, and different replenishment effects are achieved through varying agent contents. Furthermore, to address the differences in capacity loss between battery cells caused by temperature variations due to their arrangement, the lithium replenishment agent content is individually set for each battery cell. Specifically, battery cells in areas with greater heat dissipation capacity have a higher lithium replenishment agent content, while those in areas with less heat dissipation capacity have a relatively lower content. This differentiated approach compensates for lithium loss in each battery cell, thereby improving the capacity balance among the battery cells.

[0061] The aforementioned battery pack can achieve capacity self-balancing through the activation of lithium replenishment and the cell design of individual cells, without the need for BMS system equalization intervention and additional components such as self-heating devices. This allows the discharge capacity of each individual cell in the battery pack to maintain good consistency at room temperature or low temperature, thereby improving the overall performance of the battery pack.

[0062] This application improves capacity by replenishing lithium at the positive electrode of secondary batteries such as lithium-ion batteries in the battery pack to compensate for lithium loss. This method is simple to operate and has low cost.

[0063] In some of these implementations, such as Figure 3 As shown, in the battery box, position 1 is closer to the edge, and position 2 is closer to the inside of position 1. Because position 1 is closer to the edge of the battery box, the maximum heat exchange between position 1 and the external environment of the battery box is obviously greater than that between position 2 and the external environment of the battery box. Therefore, position 1 has a greater heat dissipation capacity than position 2, and position 2 has a smaller heat dissipation capacity than position 1.

[0064] Furthermore, in the battery pack 10, the maximum heat exchange Q1 between the location 1 of the first battery cell 11 and the external environment of the battery box is greater than the maximum heat exchange Q2 between the location 2 of the second battery cell 12 and the external environment of the battery box. The amount of lithium replenishing agent added in the first battery cell 11 is greater than the amount of lithium replenishing agent added in the second battery cell 12, where W1 > 0 and W2 ≥ 0.

[0065] In some embodiments, the first battery cell 11 and the second battery cell 12 are both single-cell batteries with the same chemical system. Furthermore, all battery cells in the battery case are single-cell batteries with the same chemical system.

[0066] Specifically, the individual battery cells can be lithium-ion batteries such as lithium nickel cobalt manganese oxide ternary batteries, lithium nickel cobalt aluminum oxide ternary batteries, lithium iron phosphate batteries, lithium manganese iron phosphate batteries, lithium manganese oxide batteries, lithium nickel manganese oxide batteries, lithium titanate batteries, and lithium cobalt oxide batteries; they can also be sodium-ion batteries such as Prussian blue batteries, Prussian white batteries, metal oxide batteries, and phosphate batteries; or other rechargeable battery cells. Preferably, all battery cells in the battery pack are individual cells of the same chemical system, for example, all of them are lithium-ion batteries such as lithium nickel cobalt manganese oxide ternary batteries.

[0067] In some embodiments, each battery cell, such as the first battery cell 11 and the second battery cell 12, can be formed by adding different amounts of lithium supplementing agent to battery cells with the same chemical system and capacity.

[0068] In some implementations, the lithium replenisher is added to the positive electrode active material layer of the battery cell, and the amount added is the mass content of the lithium replenisher in the corresponding positive electrode active material layer. By adjusting the amount of lithium replenisher added to the positive electrode active material layer of the battery cell, the capacity of the battery cell can be easily and flexibly controlled.

[0069] In some embodiments, the amount of lithium supplementer added to each battery cell, such as the first battery cell and the second battery cell, is no more than 25%, for example, 2%, 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 23%, or 25%. Further, the amount of lithium supplementer added to each battery cell, such as the first battery cell and the second battery cell, is 2% to 15%, or 5% to 10%.

[0070] In some embodiments, the difference in discharge capacity between the second and first battery cells due to differences in heat dissipation at their locations is ΔC; the difference in recovery capacity of the positive electrode active material between the first and second battery cells due to differences in the amount of lithium replenishing agent is ΔD; and the difference in normal discharge capacity between the first and second battery cells due to differences in the amount of lithium replenishing agent is ΔE. ΔC, ΔD, and ΔE satisfy the following conditions:

[0071] ΔC = ΔD + ΔE.

[0072] In the above equation, the left side represents the difference in discharge capacity caused by different locations within the battery pack; the right side represents the sum of the differences in recovery capacity and normal discharge capacity of the positive electrode active material caused by the addition of lithium replenishing agent. The equation holds true, meaning that the sum of the differences in recovery capacity and normal discharge capacity of the positive electrode active material caused by the difference in the amount of lithium replenishing agent added precisely compensates for the differences in discharge capacity caused by different locations within the battery pack. This achieves a balance in capacity among the individual battery cells.

[0073] Specifically, let C1 and C2 be the discharge capacities of the first and second battery cells affected by heat dissipation due to their location, respectively; then ΔC = C2 - C1. Let D1 and D2 be the recovery capacities of the positive electrode active materials of the first and second battery cells due to the amount of lithium replenisher added, respectively; then ΔD = D1 - D2. Let E1 and E2 be the normal discharge capacities of the first and second battery cells due to the amount of lithium replenisher added, respectively; then ΔE = E1 - E2. Therefore:

[0074] C2-C1=D1-D2+E1-E2.

[0075] Furthermore, if the recovery capacity of the positive electrode active material of the first battery cell and the second battery cell due to lithium replenishment by a unit mass of lithium replenishing agent is denoted as d1 and d2 respectively; and the first battery cell and the second battery cell are respectively added with W1 and W2, then D1 = W1d1 and D2 = W2d2.

[0076] Furthermore, if the normal discharge capacity of the first battery cell and the second battery cell due to lithium replenishment by a unit mass of lithium replenishing agent is denoted as e1 and e2 respectively; and the first battery cell and the second battery cell are respectively added with W1 and W2, then E1 = W1e1 and E2 = W2e2.

[0077] Furthermore, C2-C1=W1d1-W2d2-+W1e1-W2e2.

[0078] By analogy, this can be extended to type N cells.

[0079] C i -C i-1 =W i D i -W i-1 D i-1 +W i E i -W i-1 E i-1 .

[0080] It is understandable that the difference in discharge capacity between the second and first battery cells due to the difference in heat dissipation caused by their different locations is ΔC. This ΔC is actually the temperature difference between the second and first battery cells themselves caused by the difference in heat dissipation, i.e., the temperature difference between the second and first battery cells due to the difference in heat dissipation is ΔT. This temperature difference, in turn, leads to the difference in discharge capacity. In other words, ΔC on the left side of the above equation is a parameter related to ΔT. However, in battery cells with the same chemical system, d1, d2, e1, and e2 can also be considered constant; therefore, the right side of the above equation represents parameters related to W1 and W2.

[0081] Therefore, based on specific examples and the experience of those skilled in the art, in some embodiments, the temperature difference between the second battery cell and the first battery cell due to the difference in heat dissipation is ΔT, and the difference in the amount of lithium replenishing agent added to the first battery cell and the second battery cell is ΔW, where ΔW = W1 - W2, and ΔT and ΔW satisfy the following conditions:

[0082] When 0 < ΔT ≤ 5℃, 0 < ΔW ≤ 6%; preferably, 2% ≤ ΔW ≤ 4%.

[0083] When 5 < ΔT ≤ 10℃, 6% < ΔW ≤ 15%; preferably, 6% ≤ ΔW ≤ 12%.

[0084] In some embodiments, the lithium supplement has the chemical formula Li. 1+x M y A z ;

[0085] Wherein, M is selected from at least one of the transition metal elements Ni, Co, Mn, Mo, Fe, Ru and Ti;

[0086] A is selected from at least one of the nonmetallic elements O, F, S, and Cl.

[0087] It is understood that the values ​​of x, y, and z can be chosen such that the oxidation state of the above compound is 0. In some embodiments, 0 < x ≤ 5, 0.10 < y < 2, and 2 ≤ z ≤ 4. Preferably, 0 < x ≤ 4, and 0.1 ≤ x ≤ 0.5, more preferably 0.1 ≤ x ≤ 0.3. Preferably, 0.55 ≤ y ≤ 0.90, more preferably 0.65 ≤ y ≤ 0.85. Preferably, 3.5 ≤ z ≤ 4 or z = 2.

[0088] Furthermore, the lithium supplement may include, but is not limited to, at least one of the following: Li 1.47 Mn 1.6 O 3.7 F 0.3 Li2Mn2O4, Li 1.16 Ni 0.22 Mn 0.6 O2, Li 1.13 Ni 0.07 Co 0.14 Mn 0.58 O2, Li2Ni 0.1 Cu 0.9 O2, Li2Ni 0.4 Cu 0.55 Mg 0.05 O2, Li6CoO4, Li6NiO4, Li6MnO4, Li6FeO4, Li5FeO4.

[0089] In some implementations, the initial coulombic efficiency of the lithium replenisher is set to e, where e satisfies the condition: 0.2 ≤ e ≤ 0.95.

[0090] Regarding the activation time of the lithium replenishing agent: Based on the introduction of lithium-rich lithium replenishing agents, activation can be carried out in the first week, or in stages and voltage gradients during battery cycling. This achieves precise lithium replenishment while improving battery performance and reducing energy density loss. The charging voltage in the first week can be selected from different potentials, ranging from 3.75 to 5V, depending on the type of lithium replenishing agent.

[0091] In some implementations, when the State of Health (SOH) value of a battery cell is less than or equal to a preset threshold, a lithium replenishing agent is activated to replenish lithium in the battery cell. The SOH value of the battery cell is obtained by acquiring the SOH value of the battery cell when the battery cell is at a preset charging node.

[0092] The preset charging node can be any one of at least two charging nodes set based on experimental data such as the cycle life or capacity decay of individual battery cells. Specifically, the preset charging node can be a time node or cycle number node where the loss of active lithium is predicted to be large based on the aforementioned experimental data.

[0093] SOH represents the remaining battery life of a single cell at the current moment, and it has a meaning known in the art. Specifically, SOH can be defined based on cycle life or capacity decay.

[0094] The aforementioned preset threshold is a pre-set SOH value used to measure the degree of active lithium loss in a single battery cell. When the SOH is less than or equal to the preset threshold, the battery cell is considered to be in a state requiring replenishment of active lithium. At this time, a lithium replenishment material can be activated to replenish the lithium in the battery cell. There are various methods to activate the lithium replenishment material, such as increasing the charging voltage or charging rate, increasing the temperature, or activating the lithium replenishment material by charging and discharging at a certain voltage or rate. Furthermore, the charging voltage can be 3.75–5V.

[0095] When the battery pack has the same initial temperature and is placed in the same external environment, as heat exchange occurs between the battery pack and the external environment, temperature differences gradually appear inside the battery pack due to variations in heat dissipation capacity at different locations (or differences in the maximum heat exchange capacity between the battery pack and the external environment). For example, in... Figure 3 In the example shown, the temperature at position 2 may be higher than that at position 1. Since the capacity of individual battery cells decreases significantly under low-temperature conditions, if the battery pack is under low-temperature conditions, the temperature at position 1 will be significantly lower than that at position 2. Furthermore, if the battery cells at positions 1 and 2 are the same, the capacity of the battery cell at position 1 will be significantly lower than that at position 2 due to the temperature drop.

[0096] This application takes this factor into account and adds lithium replenishing agent accordingly to compensate for the difference. Therefore, a first battery cell 11 is provided at position 1 and a second battery cell 12 is provided at position 2, and the amount of lithium replenishing agent added to the first battery cell 11, W1, is greater than the amount of lithium replenishing agent added to the second battery cell 12, so that the capacity of each battery cell can withstand a certain range of temperature difference changes, thereby achieving capacity self-balancing.

[0097] In this application, considering only the effect of location on heat dissipation capacity, the outer portion of the battery box near the edge has better heat dissipation capacity than the inner portion farther from the edge. For example, as... Figure 4As shown, position 1 is closer to the outer edge than position 2, and position 1 has better heat dissipation capabilities than position 2; position 2 is closer to the outer edge than position 3, and position 3 has better heat dissipation capabilities than position 2.

[0098] Furthermore, in the example shown in 4, position 1 is set with the first battery cell 11, position 2 is set with the second battery cell 12, and position 3 is set with the third battery cell 13; at this time, the amount of lithium replenishing agent added in the first battery cell 11, the second battery cell 12, and the third battery cell 13 are W1, W2, and W3, respectively, then W1 > W2 > W3, W1 > 0, W2 > 0, and W3 ≥ 0.

[0099] This application only considers the impact of positional differences on heat dissipation capacity. For the outermost position where the outermost battery cells are arranged, the heat exchange between the battery cells and the battery pack is more direct compared to the inner battery cells. Furthermore, the heat exchange area between the outermost position and the battery pack varies. Positions with a larger heat exchange area with the battery pack have better heat dissipation capacity than positions with a smaller heat exchange area.

[0100] For example, such as Figure 5 As shown above, positions 1-3 are closer to the edge and are on the outer side than position 4, thus their heat dissipation capacity is superior to that of position 2. Within positions 1-3, position 1 is located at a corner of the battery box, while positions 2-3 are located on the side wall of the battery box, not at a corner. Therefore, the heat exchange area between position 1 and the battery box is larger than that between positions 2-3 and the battery box. Consequently, position 1 has a greater heat dissipation capacity than positions 2-3.

[0101] Furthermore, in the example shown in 5, position 1 is set with the first battery cell 11, position 2 is set with the second battery cell 12, position 3 is set with the third battery cell 13, and position 4 is set with the fourth battery cell 14; at this time, the amount of lithium replenishing agent added in the first battery cell 11, the second battery cell 12, the third battery cell 13, and the fourth battery cell 14 are W1, W2, W3, and W4, respectively. Then W1 > W2 > W4, W1 > W3 > W4, W1 > 0, W2 > 0, and W4 ≥ 0.

[0102] As for W1 and W2, they can be set to be the same or different depending on the actual situation.

[0103] In summary, if the heat dissipation capacity of the first battery cell is greater than that of the second battery cell, it may be arranged in several ways, but is not limited to these.

[0104] Arrangement method 1: Inside the battery box, the first battery cell is located outside the second battery cell.

[0105] Arrangement Method 2: Inside the battery box, the heat exchange area between the first battery cell and the battery box is greater than the heat exchange area between the second battery cell and the battery box.

[0106] In any of the above arrangements, the heat dissipation capacity of the first battery cell is greater than that of the second battery cell.

[0107] Furthermore, in some examples, such as Figure 5 As shown, the battery cells 1 and 2 located at the outermost positions inside the battery box are configured to directly contact the interior of the battery box. In this case, the heat exchange area between the battery cell and the battery box mainly considers the contact area between the battery cell and the battery box. That is, inside the battery box, the contact area between the first battery cell and the battery box is greater than the contact area between the second battery cell and the battery box, therefore the heat dissipation capacity of the location of the first battery cell is greater than the heat dissipation capacity of the second battery cell.

[0108] In addition, this application also provides an electrical device, which includes at least one of the battery packs provided in this application. The battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0109] As the electrical device, the battery pack can be selected according to its usage requirements.

[0110] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0111] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0112] The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0113] Test Information Description

[0114] 1) Battery cell capacity C test: The initial discharge capacity of a battery cell is defined as the capacity of discharging from the upper limit of the cutoff voltage of each battery cell to the lower limit of the cutoff voltage of each battery cell at 0.33C under standard test temperature (-20℃ / 0℃).

[0115] 2) Test of discharge capacity d recovered after lithium replenishment by unit mass of lithium replenishing agent: Without considering the capacity release of the lithium replenishing agent itself, only the use of the lithium replenishing agent to recover the capacity loss caused by the absence of lithium ions in the positive electrode active material is considered. In this case, d = (Cap - Cap0 / W), where Cap0 refers to the discharge capacity of the battery before lithium replenishment, Cap refers to the discharge capacity of the battery after lithium replenishment, and W is the mass content of the lithium replenishing agent in the positive electrode active material layer. Cap and Cap0 can be obtained using the single-cell capacity C test described above.

[0116] 3) Battery cell capacity retention rate: The battery cell is fully charged and placed in a constant temperature chamber for 2 hours. It is then discharged at a rate of 0.33C to the lower limit cutoff voltage of the battery cell, and the capacity is recorded. The battery cell capacity retention rate is then obtained.

[0117] Comparative Example 1

[0118] In Comparative Example 1, all locations within the battery pack contain identical battery cells (same chemical system, same capacity, same material, and same size); such as Figure 3 As shown, the battery cell at position 1 (the outermost region closest to the battery box) is designated as the first battery cell 11, and the battery cell at position 2 (located in the middle of the outermost region of the battery box) is designated as the second battery cell 12. The ambient temperature of the battery box is -20℃. In other words, all battery cells are identical, with the same capacity, and no lithium supplement is added to their positive electrode active material layer. However, due to the difference in position of the first and second battery cells within the battery box, a temperature difference exists between them due to heat dissipation. This temperature difference further leads to a difference in battery cell capacity, where 0℃ < ΔT ≤ 5℃. See Table 1 for details.

[0119] Specifically, the testing timing for the cell temperature before lithium replenishment and the cell capacity before lithium replenishment are the same or similar. The cell temperature before lithium replenishment is obtained by attaching a temperature sensing wire to the middle of the cell casing. The temperature is measured after the battery box with the cells arranged is placed in the corresponding ambient temperature for 120 minutes, at which point thermal equilibrium is considered to have been reached.

[0120] Specifically, in Comparative Example 1, the positive electrode active material layer in both the first and second battery cells is based on the NCM523 system.

[0121] Comparative Example 2

[0122] The battery pack of Comparative Example 2 is basically the same as that of Comparative Example 1, except that the material and size of the battery box are slightly different, which leads to a temperature difference between the first and second battery cells before lithium replenishment, 5℃<ΔT≤10℃.

[0123] Example 1

[0124] The battery pack of Example 1 is basically the same as that of Comparative Example 1, except that lithium supplementation agents W1 and W2 are added to the positive electrode active material layers of the first and second battery cells, respectively, based on Comparative Example 1.

[0125] Specifically, the chemical formula of the lithium supplement is Li. 1.47 Mn 1.6 O 3.7 F 0.3 The initial coulombic efficiency e is 60% (defined as the ratio of the initial discharge capacity to the initial charge capacity per unit mass of lithium replenisher). That is, in Example 1, a first battery cell and a second battery cell with added lithium replenishers W1 and W2 are used to replace the first and second battery cells in Comparative Example 1, respectively.

[0126] The coulombic efficiency test procedure for lithium replenishing agents is: H2 / H1*100%. Wherein, the discharge specific capacity of the lithium replenishing agent H1 is the capacity per unit mass of additive, within the lithium replenishing voltage range and at standard test temperatures (-20℃ / 0℃), to be charged from the lower cutoff voltage of the lithium replenishing agent at 0.33C to the upper cutoff voltage of each individual cell. The discharge specific capacity of the lithium replenishing agent H2 is the capacity per unit mass of additive, within the lithium replenishing voltage range and at standard test temperatures (-20℃ / 0℃), to be discharged from the upper cutoff voltage of the lithium replenishing agent at 0.33C to the lower cutoff voltage of each individual cell. The following procedures are similar.

[0127] Example 2

[0128] The battery pack of Example 2 is basically the same as that of Comparative Example 2, except that lithium supplementation agents W1 and W2 are added to the positive electrode active material layers of the first and second battery cells, respectively, based on Comparative Example 2.

[0129] The test results for the overall usable capacity of the battery pack at 25°C, the temperature of individual cells before lithium replenishment, the capacity of individual cells before lithium replenishment, the overall usable capacity of the battery pack before lithium replenishment, the lithium replenishment dosage W (mass content of lithium replenishment agent in the positive electrode active material layer) in each cell, the capacity of individual cells after lithium replenishment, the overall usable capacity of the battery pack after lithium replenishment, and the improvement rate of battery pack capacity retention are shown in Table 1.

[0130] The overall usable capacity of the battery pack is the smaller of the actual capacities of the first and second individual battery cells within the pack; in other words, it is the minimum capacity among all individual battery cells. For example, before lithium replenishment, the overall usable capacity of the battery pack is the smaller of the actual capacities of the first and second individual battery cells before lithium replenishment. After lithium replenishment, the overall usable capacity of the battery pack is the smaller of the actual capacities of the first and second individual battery cells after lithium replenishment.

[0131] The overall usable capacity (Ah) of the battery pack at 25°C refers to the overall usable capacity of the battery pack at 25°C before lithium replenishment. Therefore, the comparative examples and embodiments in Table 1 are equivalent.

[0132] The overall usable capacity retention rate of the battery pack before lithium replenishment refers to the ratio of the overall usable capacity of the battery pack at a lower ambient temperature to the overall usable capacity of the battery pack at 25°C.

[0133] The overall usable capacity retention rate of the battery pack after lithium replenishment is the ratio of the overall usable capacity of the battery pack at a lower ambient temperature to the overall usable capacity of the battery pack at 25°C after lithium replenishment.

[0134] The table shows that after the lithium replenishment agent is added, it is activated by charging at a voltage of 4.4V in the first week.

[0135] The State of Emergency (SOH) threshold for lithium replenishment is used to define the activation time of the lithium replenishment agent. The SOH threshold is based on the definition of capacity decay, and the specific values ​​in the table represent the preset values ​​for the overall usable capacity retention rate of the battery pack. Taking a SOH threshold of 70% in Table 1 as an example, it means that when the overall usable capacity retention rate of the battery pack reaches 70% before lithium replenishment, each individual battery cell in the battery pack is activated. The overall usable capacity retention rate of the battery pack at the current moment refers to the ratio of the overall usable capacity of the battery pack at the current moment to the overall usable capacity of the battery pack at 25°C.

[0136] The improvement in battery pack capacity retention rate is the overall usable capacity retention rate of the battery pack after lithium replenishment minus the overall usable capacity retention rate of the battery pack before lithium replenishment.

[0137] The parameters mentioned above have the same or similar meanings in Table 2.

[0138] Table 1

[0139]

[0140] Comparative Examples 3-4

[0141] The battery pack of Comparative Example 3 is basically the same as that of Comparative Example 1. The same battery cells (same chemical system, same capacity, same material and size) are placed in all positions in each battery box. The difference is that the battery cells of Comparative Example 3 are different from those of Comparative Example 1, and the ambient temperature of the battery box is different, specifically 0℃.

[0142] Comparative Example 4

[0143] The battery pack of Comparative Example 4 is basically the same as that of Comparative Example 3, except that the material and size of the battery box are slightly different, which leads to a temperature difference between the first and second battery cells before lithium replenishment, 5℃<ΔT≤10℃.

[0144] Example 3

[0145] The battery pack of Example 3 is basically the same as that of Comparative Example 3, except that lithium supplementers W1 and W2 are added to the positive electrode active material layers of the first and second battery cells, respectively, based on Comparative Example 3. Specifically, the chemical formula of the lithium supplementer is L. i1.47 Mn 1.6 O 3.7 F 0.3 The initial coulombic efficiency is 60% (defined as the ratio of the initial discharge capacity to the initial charge capacity per unit mass of lithium replenishment).

[0146] Example 4

[0147] The battery pack of Example 4 is basically the same as that of Comparative Example 4, except that, based on Comparative Example 3, lithium supplementing agents W1 and W2 were added to the positive electrode active material layers of the first and second battery cells, respectively.

[0148] The test results for the overall usable capacity of the battery pack at 25°C for Comparative Examples 3-4 and Examples 3-4, the temperature of individual battery cells before lithium replenishment, the capacity of individual battery cells before lithium replenishment, the overall usable capacity of the battery pack before lithium replenishment, the lithium replenishment dosage W (mass content of lithium replenishment agent in the positive electrode active material layer) in each battery cell, the capacity of individual battery cells after lithium replenishment, the overall usable capacity of the battery pack after lithium replenishment, and the improvement rate of battery pack capacity retention are shown in Table 2.

[0149] Table 2

[0150]

[0151]

[0152] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A battery pack, characterized in that, It includes a battery box and a first battery cell and a second battery cell disposed within the battery box; Wherein, the heat dissipation capacity of the first battery cell is greater than that of the second battery cell, the amount of lithium replenishing agent added in the first battery cell W1 is greater than the amount of lithium replenishing agent added in the second battery cell W2, W1>0, W2≥0, the lithium replenishing agent is added to the positive electrode active material layer of the battery cell, the amount added is the mass content of the lithium replenishing agent in the corresponding positive electrode active material layer, and the impedance of the lithium replenishing agent is greater than the impedance of the main positive electrode material in the positive electrode active material layer; The chemical formula of the lithium supplement is Li 1+x M y A z The values ​​of x, y, and z make the valence of the lithium replenishing agent's chemical formula zero; Wherein, M is selected from at least one of Ni, Co, Mn, Fe, Mg, Mo, Ru and Ti; A is selected from at least one of O, F, S and Cl.

2. A battery pack, characterized in that, It includes a battery box and a first battery cell and a second battery cell disposed within the battery box; In this battery box, the temperature of the first battery cell is lower than that of the second battery cell due to heat dissipation. The amount of lithium replenishing agent added to the first battery cell, W1, is greater than the amount of lithium replenishing agent added to the second battery cell, W1 > 0, W2 ≥ 0. The lithium replenishing agent is added to the positive electrode active material layer of the battery cell. The amount added is the mass content of the lithium replenishing agent in the corresponding positive electrode active material layer. The impedance of the lithium replenishing agent is greater than the impedance of the main positive electrode material in the positive electrode active material layer. The chemical formula of the lithium supplement is Li 1+x M y A z The values ​​of x, y, and z make the valence of the lithium replenishing agent's chemical formula zero; Wherein, M is selected from at least one of Ni, Co, Mn, Fe, Mg, Mo, Ru and Ti; A is selected from at least one of O, F, S and Cl.

3. The battery pack according to any one of claims 1 to 2, characterized in that, The first battery cell and the second battery cell are both formed by adding different amounts of lithium supplementing agent to battery cells with the same chemical system and capacity.

4. The battery pack according to any one of claims 1 to 2, characterized in that, The amount of lithium supplementer added in both the first and second battery cells is no more than 25%.

5. The battery pack according to any one of claims 1 to 2, characterized in that, The difference in discharge capacity between the second battery cell and the first battery cell due to differences in heat dissipation or temperature caused by their different locations is ΔC. The difference in the recovery capacity of the positive electrode active material between the first battery cell and the second battery cell due to differences in the amount of lithium replenishing agent added is ΔD. The difference in normal discharge capacity between the first battery cell and the second battery cell due to differences in the amount of lithium replenishing agent added is ΔE. ΔC, ΔD, and ΔE satisfy the following conditions: ΔC = ΔD + ΔE.

6. The battery pack according to any one of claims 1 to 2, characterized in that, The temperature difference between the second battery cell and the first battery cell due to heat dissipation is ΔT, and the difference in the amount of lithium replenishing agent added to the first battery cell and the second battery cell is ΔW, where ΔW = W1 - W2. ΔT and ΔW satisfy the following conditions: When 0 < ΔT ≤ 5℃, 0 < ΔW ≤ 6%; When 5 < ΔT ≤ 10℃, 0.06 < ΔW ≤ 15%.

7. The battery pack as described in claim 6, characterized in that, When 0 < ΔT ≤ 5℃, 2% ≤ ΔW ≤ 4%; When 5 < ΔT ≤ 10℃, 6% ≤ ΔW ≤ 12%.

8. The battery pack according to any one of claims 1 to 2, characterized in that, 0<x≤5, 0.10<y<2, 2≤z≤4.

9. The battery pack according to any one of claims 1 to 2, characterized in that, The lithium supplementer includes at least one of the following: Li 1.47 Mn 1.6 O 3.7 F 0.3 Li2Mn2O4, Li 1.16 Ni 0.22 Mn 0.6 O2, Li 1.13 Ni 0.07 Co 0.14 Mn 0.58 O2, Li2Ni 0.1 Cu 0.9 O2, Li2Ni 0.4 Cu 0.55 Mg 0.05 O2, Li6CoO4, Li6NiO4, Li6MnO4, Li6FeO4, Li5FeO4.

10. The battery pack according to any one of claims 1 to 2, characterized in that, The initial coulombic efficiency of the lithium replenishing agent is set to e, which satisfies the following condition: 0.2≤e≤0.

9.

11. The battery pack according to any one of claims 1 to 2, characterized in that, In the battery box: The first battery cell is located outside the second battery cell; Alternatively, the heat exchange area between the first battery cell and the battery box is greater than the heat exchange area between the second battery cell and the battery box.

12. An electrical appliance, characterized in that, The electrical device includes a battery pack as described in any one of claims 1 to 11, the battery pack being used to provide electrical energy.

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