Battery packs and power consuming devices

Abstract

The battery pack includes a housing and battery cells, the housing includes a first region, a second region, and a third region, and a first battery cell, a second battery cell, and a third battery cell are disposed in each region. Each battery cell has a first discharge voltage plateau and a second discharge voltage plateau, and an average discharge voltage of the first discharge voltage plateau is higher than an average discharge voltage of the second discharge voltage plateau. The positive electrode active material of each battery cell is a mixture of a first positive electrode active material having the first discharge voltage plateau and a positive electrode functional auxiliary having the second discharge voltage plateau. When the sum of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau is 100%, the discharge capacity ratio corresponding to the second discharge voltage plateau of the third battery cell>the discharge capacity ratio corresponding to the discharge voltage plateau of the second battery cell>the discharge capacity ratio corresponding to the second discharge voltage plateau of the first battery cell.

Description

[Technical field]

[0001] This application relates to the field of lithium-ion batteries, and in particular to a battery pack having high energy retention at low temperatures and a power consuming device including the battery pack. [Background technology]

[0002] In recent years, with the continuous development of lithium-ion battery technology, lithium-ion batteries have been widely applied in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, as well as in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. Summary of the Invention [Problem to be solved by the invention]

[0003] In the above fields, the capacity of the lithium-ion secondary battery cell may not be sufficient to meet the needs of the application, in which case it is necessary to configure a battery pack by connecting multiple lithium-ion secondary battery cells in series or in parallel to improve the overall discharge capacity of the battery pack.

[0004] However, when a battery pack made of lithium-ion secondary battery cells is used in a low-temperature environment such as winter, the energy retention rate drops significantly. In other words, the driving range deteriorates at low temperatures. Therefore, how to improve the driving range of the entire battery pack at low temperatures has become an important issue that needs to be solved as soon as possible.

[0005] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a battery pack consisting of a lithium-ion secondary battery that has excellent energy retention at low temperatures and improved driving range at low temperatures, and a power consumption device equipped with this battery pack. [Means for solving the problem]

[0006] In order to achieve the above object, a first aspect of the present application provides a battery pack. The battery pack includes a battery pack housing and battery cells housed in the battery pack housing. The internal space of the battery pack housing includes a first region, a second region, and a third region. A first battery cell is arranged in the first region, a second battery cell is arranged in the second region, and a third battery cell is arranged in the third region. The second battery cell is arranged surrounding the periphery of the first battery cell, and the third battery cell is arranged surrounding the periphery of the second battery cell. The first battery cell, the second battery cell, and the third battery cell each have a first discharge voltage plateau and a second discharge voltage plateau. An average discharge voltage of the first discharge voltage plateau is higher than an average discharge voltage of the second discharge voltage plateau. The positive electrode active material of each of the first battery cell, the second battery cell, and the third battery cell is a mixture of a first positive electrode active material having the first discharge voltage plateau and a positive electrode function assistant having the second discharge voltage plateau. The positive electrode function assistant is titanium oxide, niobium oxide, or titanium niobium oxide. When the sum of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau is 100% in each of the first battery cell, the second battery cell, and the third battery cell, the discharge capacity percentage corresponding to the second discharge voltage plateau of the third battery cell>the discharge capacity percentage corresponding to the second discharge voltage plateau of the second battery cell>the discharge capacity percentage corresponding to the second discharge voltage plateau of the first battery cell.

[0007] Thus, the present application improves the energy retention rate of the entire battery pack at low temperatures by arranging battery cells with different discharge capacities at low temperatures according to the temperature distribution in the battery pack. Specifically, battery cells with different low-temperature energy retention rates having double discharge voltage plateaus (a first discharge voltage plateau with a high discharge voltage and a second discharge voltage plateau with a low discharge voltage) are arranged in regions with different temperatures in the internal space of the battery pack housing, and battery cells with higher low-temperature energy retention rates are arranged in regions with lower temperatures. By arranging battery cells with relatively low low-temperature performance (relatively low low-temperature energy retention rate) in regions with relatively high temperatures in the internal space of the battery pack housing and arranging battery cells with relatively high low-temperature performance (relatively high low-temperature energy retention rate) in regions with relatively low temperatures in the internal space of the battery pack housing, the cycle consistency of the battery cells in each region with different temperatures in the battery pack can be improved, the low-temperature energy retention rate of the entire battery pack can be improved, and the low-temperature driving capability of the entire battery pack can be improved.

[0008] In the present application, the positive electrode active material of the battery cell having a double discharge voltage plateau is a mixture of a normal positive electrode active material (first positive electrode active material) and a positive electrode functional assistant. The normal positive electrode active material has a first discharge voltage plateau with a high discharge voltage. The positive electrode functional assistant is titanium oxide, niobium oxide, or titanium niobium oxide. These positive electrode functional assistants have a second discharge voltage plateau with a low discharge voltage. The discharge capacity of the second discharge voltage plateau with a low discharge voltage in the battery cell can be adjusted by changing the content of the positive electrode functional assistant in the positive electrode active material. By using a battery cell having a double discharge voltage plateau, the battery cell can be discharged using the first discharge voltage plateau with a high discharge voltage, and then continue to be discharged using the second discharge voltage plateau with a low discharge voltage, thereby significantly improving the discharge power of the battery cell, especially the discharge power under low temperature conditions, and allowing the battery cell to have a higher low-temperature energy retention rate.

[0009] The shape of the battery pack described in this application is arbitrary and may be any shape designed according to customer requirements.

[0010] In the battery pack described in the present application, the internal space of the battery pack housing is not limited to being divided into the above three regions, and may include the above first region, second region, and third region. Specifically, the internal space of the battery pack housing may consist of the above first region, second region, and third region, or the internal space of the battery pack housing may have one or more regions outside the third region in addition to the above first region, second region, and third region, and the battery cells arranged in the outer region may be arranged to surround the battery cells arranged in the inner region.

[0011] The battery pack according to the present application only needs to satisfy the following condition when the internal space of the battery pack housing includes three or more regions as described above: the discharge capacity ratio corresponding to the second discharge voltage plateau of the battery cell is higher in the outer region (i.e., the mass ratio of the positive electrode functional auxiliary in the positive electrode active material of the battery cell is higher).

[0012] In some embodiments, when the internal space of the battery pack housing is rectangular, the four corners of the rectangular shape are defined as the outermost regions, in which the proportion of the discharge capacity corresponding to the second discharge voltage plateau of the battery cell is the highest (i.e., the mass proportion of the positive electrode functional assistant in the positive electrode active material of the battery cell is the highest).

[0013] In some embodiments, the interior space of the battery pack housing comprises the first region, the second region, and the third region.

[0014] This makes it possible to obtain the above-mentioned excellent effects in a battery pack in which the internal space of the housing of the battery pack is partitioned into three regions, the first region, the second region and the third region.

[0015] In some embodiments, the positive electrode functional additive is TiNb 2x O 4+5xwhere x is an integer of 1 or more. Preferably, the titanium niobium oxide is Ti2Nb2O9, TiNb2O7, Ti2Nb 10 O 29 and TiNb 24 O 62 One or more types are selected from the following:

[0016] Thus, by selecting titanium niobium oxide, which has excellent performance as a positive electrode functional assistant, a battery cell having a suitable second discharge voltage plateau can be obtained, and the present battery pack having excellent low-temperature performance can be realized.

[0017] In some embodiments, the discharge voltage range of the second discharge voltage plateau is 1.0-2.0 V, and preferably the discharge capacity of the second discharge voltage plateau at 1.2-1.6 V is 50% or more, preferably 70% or more, of the total discharge capacity of the second discharge voltage plateau.

[0018] Thus, by setting the discharge voltage of the second discharge voltage plateau within the above range, a significant difference can be made between the discharge voltage of the second discharge voltage plateau and the discharge voltage of the first discharge voltage plateau, and the above effect of having a double discharge voltage plateau can be significantly obtained. By setting the ratio of the discharge capacity at 1.2-1.6V of the second discharge voltage plateau to the total discharge capacity of the second discharge voltage plateau within the above range, it is ensured that the battery cells can release sufficient energy at low temperatures, and the low-temperature energy retention rate of the entire battery pack can be ensured.

[0019] In some embodiments, in the first battery cell, the second battery cell, and the third battery cell, a difference between the minimum discharge voltage of the first discharge voltage plateau and the maximum discharge voltage of the second discharge voltage plateau is 0.5 V or more, preferably 1.0 V or more.

[0020] This allows the battery pack to be discharged at a first discharge voltage plateau with a high discharge voltage, and then subsequently at a second discharge voltage plateau with a low discharge voltage, significantly increasing the amount of energy each battery cell can release at low temperatures and improving the energy retention rate of the entire battery pack at low temperatures.

[0021] In some embodiments, in the first battery cell, when the sum of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau is 100%, the discharge capacity corresponding to the first discharge voltage plateau accounts for 90%-100%, and the discharge capacity corresponding to the second discharge voltage plateau accounts for 0%-10%.

[0022] As a result, by setting the respective ratios of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the first battery cell within the above ranges, the energy that the first battery cell can release at low temperatures can be increased, thereby improving the low-temperature energy retention rate of the entire battery pack.

[0023] In some embodiments, in the second battery cell, when the sum of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau is 100%, the discharge capacity corresponding to the first discharge voltage plateau accounts for 73%-95%, and the discharge capacity corresponding to the second discharge voltage plateau accounts for 5%-27%.

[0024] As a result, by setting the respective ratios of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the second battery cell within the above range, the energy that the second battery cell can release at low temperatures can be increased, and the low-temperature energy retention rate of the entire battery pack can be further improved.

[0025] In some embodiments, in the third battery cell, when the sum of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau is 100%, the discharge capacity corresponding to the first discharge voltage plateau accounts for 54%-87%, and the discharge capacity corresponding to the second discharge voltage plateau accounts for 13%-46%.

[0026] As a result, by setting the respective ratios of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the third battery cell within the above ranges, the energy that the third battery cell can release at low temperatures can be increased, and the low-temperature energy retention rate of the entire battery pack can be further improved.

[0027] In some embodiments, the gram capacity of the positive electrode active material of the first battery cell is 148-285 mAh / g, the gram capacity of the positive electrode active material of the second battery cell is 155-295 mAh / g, and the gram capacity of the positive electrode active material of the third battery cell is 169-311 mAh / g.

[0028] As a result, by setting the gram capacity of each of the first battery cell, the second battery cell, and the third battery cell within the above range, the discharge capacities of the first battery cell, the second battery cell, and the third battery cell at low temperatures can be roughly uniform, thereby improving the energy retention rate of the entire battery pack at low temperatures.

[0029] In some embodiments, the theoretical gram capacity of the positive electrode functional additive is 350-410 mAh / g.

[0030] By using a positive electrode functional assistant having a theoretical gram capacity within the above range, it is possible to ensure sufficient energy density in each battery cell and improve the low-temperature discharge power of each battery cell and the entire battery pack.

[0031] In some embodiments, the first positive electrode active material is one selected from lithium manganate, lithium nickelate, lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, and lithium iron phosphate.

[0032] As a result, as long as the discharge voltage and discharge capacity ratio of the first discharge voltage plateau due to the first positive electrode active material and the second discharge voltage plateau due to the positive electrode functional auxiliary satisfy the above-mentioned relationship, the first positive electrode active material can be selected from various existing positive electrode active materials, and the battery pack of the present application can be easily realized by utilizing an existing positive electrode active material.

[0033] In some embodiments, when the first battery cell, the second battery cell, and the third battery cell contain the same type of the first positive electrode active material and the same type of the positive electrode functional auxiliary, the mass proportion of the first positive electrode active material in the positive electrode active material gradually decreases in the order of the first battery cell, the second battery cell, and the third battery cell, and the mass proportion of the positive electrode functional auxiliary in the positive electrode active material gradually increases in the order of the first battery cell, the second battery cell, and the third battery cell.

[0034] The higher the mass ratio of the positive electrode functional assistant for generating the second discharge voltage plateau with a lower discharge voltage, and the higher the discharge capacity ratio corresponding to the second discharge voltage plateau, the higher the low-temperature energy retention rate of the battery cell. By setting the mass ratio of the positive electrode functional assistant of the third battery cell arranged in the third region > the mass ratio of the positive electrode functional assistant of the second battery cell arranged in the second region > the mass ratio of the positive electrode functional assistant of the first battery cell arranged in the first region, the low-temperature energy retention rate of the third battery cell > the low-temperature energy retention rate of the second battery cell > the low-temperature energy retention rate of the first battery cell. As a result, the energy released at low temperatures by the first battery cell, the second battery cell, and the third battery cell can be almost equalized, and the low-temperature energy retention rate of the entire battery pack can be further improved.

[0035] In some embodiments, in the first battery cell, when the total mass of the first positive electrode active material and the positive electrode functional auxiliary is 100%, the mass of the first positive electrode active material accounts for 96.0%-100%, and the mass of the positive electrode functional auxiliary accounts for 0%-4.0%.

[0036] In this way, by setting the mass ratio of the first positive electrode active material and the positive electrode functional auxiliary in the first battery cell within the above range, the ratio of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the first battery cell can be set within the above range, thereby increasing the energy that the first battery cell can release at low temperatures and improving the low-temperature energy retention rate of the entire battery pack.

[0037] In some embodiments, in the second battery cell, when the total mass of the first positive electrode active material and the positive electrode functional assistant is 100%, the mass of the first positive electrode active material accounts for 88.5%-96.0%, and the mass of the positive electrode functional assistant accounts for 4.0%-11.5%.

[0038] In this way, by setting the mass ratio of the first positive electrode active material and the positive electrode functional auxiliary in the second battery cell within the above range, the ratio of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the second battery cell can be set within the above range, thereby increasing the energy that the second battery cell can release at low temperatures, and further improving the low-temperature energy retention rate of the entire battery pack.

[0039] In some embodiments, in the third battery cell, when the total mass of the first positive electrode active material and the positive electrode functional auxiliary is 100%, the mass of the first positive electrode active material accounts for 76.5%-88.5%, and the mass of the positive electrode functional auxiliary accounts for 11.5%-23.5%.

[0040] In this way, by setting the mass ratio of the first positive electrode active material and the positive electrode functional auxiliary in the third battery cell within the above range, the ratio of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the third battery cell can be set within the above range, thereby increasing the energy that the third battery cell can release at low temperatures, and further improving the low-temperature energy retention rate of the entire battery pack.

[0041] In some embodiments, the positive electrode functional assistant is a lithium-containing titanium niobium oxide coated with carbon.

[0042] As a result, by carbon-coating and prelithiating the titanium niobium oxide as a positive electrode functional assistant, the electrical conductivity of the titanium niobium oxide and the number of effective lithium ions in the battery unit can be increased, the structural stability of the titanium niobium oxide as a positive electrode functional assistant can be increased, and the energy density and cycle stability of the battery unit can be ensured.

[0043] In some embodiments, the negative electrodes of the first battery cell, the second battery cell, and the third battery cell are lithium-replenished.

[0044] In this way, the lithium ion deficiency caused by adding titanium niobium oxide to the positive electrode active material can be compensated for by performing lithium supplementation treatment on the negative electrodes of the first, second and third battery cells, and as a result, the total amount of effective lithium ions in the battery cells is not reduced, and the energy density of the battery cells is guaranteed.

[0045] In some embodiments, at a temperature below 0° C., the discharge cut-off voltage of the first battery cell is 1.4-1.6V, the discharge cut-off voltage of the second battery cell is 1.2-1.4V, and the discharge cut-off voltage of the third battery cell is 1.0-1.2V.

[0046] As a result, by setting discharge cutoff voltages for the first battery cell, the second battery cell, and the third battery cell as described above, the energy released by the first battery cell, the second battery cell, and the third battery cell at low temperatures can be roughly aligned, thereby improving the low-temperature energy retention rate of the entire battery pack.

[0047] In some embodiments, the number of first battery cells:the number of second battery cells:the number of third battery cells=(3-8):(8-13):(10-15). In other words, when the sum of the number of first battery cells, the number of second battery cells, and the number of third battery cells is 100%, the proportion of the number of first battery cells is about 10-30%, the proportion of the number of second battery cells is about 25-50%, and the proportion of the number of third battery cells is about 30-60%.

[0048] As a result, by setting the numbers of the first battery cells, the second battery cells, and the third battery cells in accordance with the temperature distribution range of a typical battery pack, the battery pack of the present application can be easily realized.

[0049] A second aspect of the present application provides a power consuming device including a battery pack according to the first aspect of the present application.

[0050] As a result, the power consuming device according to the second aspect of the present application has a strong driving range at low temperatures and can be used normally for a long period of time even at low temperatures. Effect of the Invention

[0051] According to the present invention, by arranging battery cells with different low-temperature energy retention rates having dual discharge voltage stages in areas of different temperatures inside the battery pack housing, it is possible to roughly align the energy released at low temperatures by the battery cells in the areas of different temperatures, thereby providing a battery pack and a power consuming device including the same with an improved low-temperature energy retention rate overall. [Brief description of the drawings]

[0052] [Figure 1]FIG. 1 is a schematic diagram of a battery pack according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a plan view of components of the battery pack according to one embodiment of the present application shown in FIG. 1, excluding the housing. [Diagram 3] 3 is a schematic diagram of a constant current discharge curve of a battery cell having a double discharge voltage plateau used in a battery pack according to one embodiment of the present invention, in which the positive electrode active material of the battery cell is composed of a first positive electrode active material LiNi0.6Co0.2Mn0.2O2 (NCM) and a positive electrode functional additive titanium niobium oxide (TNO, e.g. TiNb2O7). [Figure 4] FIG. 4 is a schematic diagram of a power consuming device that uses a battery pack as a power source according to one embodiment of the present application. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] Hereinafter, with reference to the drawings as appropriate, detailed descriptions will be given of embodiments specifically disclosing the battery pack and power consumption device of the present application. However, more detailed descriptions than necessary may be omitted. For example, detailed descriptions of already well-known matters and duplicate descriptions of substantially identical configurations may be omitted. This is to avoid the following description becoming unnecessarily redundant and to facilitate understanding by those skilled in the art. Note that the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

[0054] The "ranges" disclosed herein are defined in the form of lower and upper limits, and a given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner may or may not include the end values ​​and may be arbitrarily combined. That is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are recited for a particular parameter, then ranges of 60-110 and 80-120 are also contemplated. Also, if a minimum range value 1, a minimum range value 2, and a maximum range value 3, a maximum range value 4, and a maximum range value 5 are recited, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" refers to the abbreviation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0-5" indicates that the text enumerates all real numbers between "0-5" and "0-5" is merely an abbreviation for combinations of these numbers. Furthermore, expressing a parameter as an integer of 2 or greater is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0055] Unless otherwise stated, all embodiments and optional embodiments in the present application can be combined with each other to form a new technical solution.

[0056] Unless otherwise stated, all technical features and optional technical features in the present application can be combined with each other to form a new technical solution.

[0057] Unless otherwise stated, all steps in the present application may be performed in sequence or randomly, but are preferably performed in sequence. For example, when the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, when the method may further include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0058] Unless otherwise stated, the terms "comprise" and "contain" referred to in this application may be open ended or closed ended. For example, "comprise" and "contain" mean that the compound may further contain or include other components not listed, or may contain or include only the listed components.

[0059] In this application, unless otherwise stated, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, A being true (or existing) and B being false (or not existing), or A being false (or not existing) and B being true (or existing), or both A and B being true (or existing) all satisfy the condition "A or B."

[0060] The inventors have found that when a battery pack made of lithium-ion secondary battery cells is used in a low-temperature environment in winter, the heat dissipation capabilities and heat retention effects of the battery cells at different positions in the battery pack are different, so the charge and discharge performances of the battery cells at different positions are not consistent. Specifically, when used in a low-temperature environment, the temperature of the battery cells located inside the battery pack is relatively high, so the discharge performance at low temperatures is relatively good, while the temperature of the battery cells located outside the battery pack is relatively low, so the discharge performance at low temperatures is relatively poor. Due to the difference in the discharge capabilities at low temperatures of the battery cells at different positions in the battery pack, the energy retention rate of the entire battery pack at low temperatures is significantly reduced.

[0061] Therefore, the inventors conceived the idea that by arranging battery cells with superior low-temperature discharge performance in low-temperature areas of the battery pack, it is possible to roughly align the energy discharged by battery cells in different positions in the battery pack in a low-temperature environment, thereby improving the energy performance of the battery pack as a whole in a low-temperature environment and improving the driving range of a power consumption device using the battery pack as a power source in a low-temperature environment.

[0062] In order to achieve the above-mentioned object, the inventors conducted extensive research and discovered that battery cells arranged in a low temperature region have two discharge voltage plateaus, and by continuing to discharge at the lower discharge voltage plateau after discharging at the higher discharge voltage plateau has ended, the discharge amount of these battery cells can be increased, and the discharge performance of these battery cells at low temperatures is superior.

[0063] There are several known materials capable of providing a low discharge voltage plateau. Through extensive research, the inventors have found that titanium oxide, niobium oxide, or titanium niobium oxide, which are generally used as negative electrode active materials, have a low potential relative to lithium, and when these materials are added to a normal positive electrode active material as a positive electrode functional assistant, these materials can provide a low discharge voltage plateau, allowing the battery cell to release more energy at low temperatures, improving the discharge amount of the battery cell, and further improving the energy retention rate of the entire battery pack at low temperatures.

[0064] In addition, when the ratio of the mass of the positive electrode functional assistant in the battery cell to the total mass of the positive electrode active material (the sum of the masses of the normal positive electrode active material and the positive electrode functional assistant) does not exceed a certain ratio (for example, 50%), the higher the ratio of the discharge capacity corresponding to the low discharge voltage plateau to the total discharge capacity corresponding to the two high and low discharge voltage plateaus, the better the low-temperature performance of the battery cell. In this way, by using a battery cell in which the ratio of the discharge capacity corresponding to the low discharge voltage plateau is higher in the lower temperature region, the energy exerted at low temperatures by the battery cells arranged in each of the different temperature regions can be made almost uniform. This improves the energy retention rate at low temperatures of the entire battery pack, and improves the low-temperature driving capability of a power consumption device such as an electric vehicle using the battery pack as a power source.

[0065] <Battery pack> The battery pack 1 of the present invention will be specifically described below.

[0066] Fig. 1 is a schematic diagram of a battery pack 1 according to an embodiment of the present invention. Fig. 2 is a plan view of components of the battery pack 1 shown in Fig. 1, excluding the housing.

[0067] 1 and 2, a battery pack 1 of the present application includes a battery box and a plurality of battery cells (61, 62, 63) provided in the battery box. The battery box includes an upper housing 2 and a lower housing 3, and the upper housing 2 is covered by the lower housing 3 to form an enclosed space (battery pack cavity) for accommodating the plurality of battery cells.

[0068] 2, the first region R1 is a substantially rectangular region surrounded by a first boundary line BL1 and is located at the center of the rectangular shape of the internal space of the battery pack housing (for example, the length and width of the rectangular shape of the first region R1 may be approximately half the length and width of the rectangular shape of the internal space of the battery pack housing, respectively), the second region R2 is a substantially annular region between the first boundary line BL1 and the third boundary line BL3, and the third region R3 is a substantially annular region between the second boundary line BL2 and the third boundary line BL3. Here, the first boundary line BL1, the second boundary line BL2, and the third boundary line BL3 are imaginary lines drawn to clearly show the first region, the second region, and the third region.

[0069] Furthermore, a first battery cell 61 is arranged in the first region R1, a second battery cell 62 is arranged in the second region R2, and a third battery cell 63 is arranged in the third region R3. The second battery cell 62 is arranged surrounding the periphery of the first battery cell 61, and the third battery cell 63 is arranged surrounding the periphery of the second battery cell 62. The first battery cell 61, the second battery cell 62, and the third battery cell 63 each have a first discharge voltage plateau and a second discharge voltage plateau. The average discharge voltage of the first discharge voltage plateau is higher than the average discharge voltage of the second discharge voltage plateau. The positive electrode active material of each of the first battery cell 61, the second battery cell 62, and the third battery cell 63 is a mixture of a first positive electrode active material having the first discharge voltage plateau and a positive electrode functional assistant having the second discharge voltage plateau, and the positive electrode functional assistant is titanium oxide, niobium oxide, or titanium niobium oxide. In each of the first battery cell 61, the second battery cell 62, and the third battery cell 63, when the sum of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau is 100%, the discharge capacity ratio corresponding to the second discharge voltage plateau of the third battery cell 63>the discharge capacity ratio corresponding to the second discharge voltage plateau of the second battery cell 62>the discharge capacity ratio corresponding to the second discharge voltage plateau of the first battery cell 61. When placed in an external environment of the same temperature, within the battery pack 1, the temperature of the third region R3 is lower than the temperature of the second region R2, and the temperature of the second region R2 is lower than the temperature of the first region R1.

[0070] Although, throughout this specification, the first battery cell will be described as having a first discharge voltage plateau and a second discharge voltage plateau, or the positive electrode active material of the first battery cell will be described as comprising a mixture of a first positive electrode active material having a first discharge voltage plateau and a positive electrode functional auxiliary having a second discharge voltage plateau, a first battery cell that includes only the first discharge voltage plateau and not the second voltage discharge plateau, i.e., a first battery cell consisting only of the first positive electrode active material, is also within the scope of the present invention.

[0071] The "discharge voltage plateau" is a portion of the discharge curve where the discharge voltage is relatively gentle, and when discharging at the discharge voltage plateau, the amount of discharge per unit time is large. FIG. 3 is a schematic diagram of a constant current discharge curve of a battery cell having a double discharge voltage plateau used in a battery pack according to one embodiment of the present invention. Here, the positive electrode active material of the battery cell is a first positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 The battery is composed of a positive electrode functional additive titanium niobium oxide (TNO, for example, TiNb2O7) and a positive electrode functional additive titanium niobium oxide (NCM). As shown in FIG. 3, the lower limit of the discharge voltage plateau of NCM is 2.5 V (point A in FIG. 3), and the upper limit of the discharge voltage plateau of TNO is 1.8 V (point B in FIG. 3). Also, as shown in FIG. 3, when the discharge curve of the battery cell has two discharge voltage plateaus, the discharge voltage drops sharply after passing point A, and then becomes gentle again after dropping to point B, and the discharge continues due to the discharge voltage plateau.

[0072] 3, before point B where the first voltage drop ends, there is a first discharge voltage plateau (i.e., a high-voltage discharge plateau, i.e., the first discharge voltage plateau of the present application), which is equal in data value to the ratio of all energy released from the high-voltage positive electrode active material to the current (which is a balanced value and can also be roughly regarded as the average voltage before point B). After point B where the first voltage drop ends, there is a second discharge voltage plateau (i.e., a low-voltage discharge plateau, i.e., the second discharge voltage plateau of the present application), which appears as the ratio of all energy released from the low-voltage positive electrode active material (e.g., the positive electrode functional auxiliary of the present application) to the current (which is a balanced value and can also be roughly regarded as the average voltage after point B).

[0073] In the present application, battery cells 61, 62, 63 having dual discharge voltage plateaus (a first discharge voltage plateau with a high discharge voltage and a second discharge voltage plateau with a low discharge voltage) and different low-temperature energy retention rates are arranged in regions with different temperatures in the internal space of the battery pack housing, and the lower the temperature region, the higher the low-temperature energy retention rate is arranged. Specifically, according to the temperature distribution inside a normal battery pack, the temperature of the first region R1>the temperature of the second region R2>the temperature of the third region R3, and in the present application, the discharge capacity ratio corresponding to the second discharge voltage plateau of the third battery cell 63>the discharge capacity ratio corresponding to the second discharge voltage plateau of the second battery cell 62>the discharge capacity ratio corresponding to the second discharge voltage plateau of the first battery cell 61.

[0074] For specific definitions and test methods of the discharge capacity ratios corresponding to the second discharge voltage plateaus of the first / second / third battery cells of the present application, please refer to the "Related Tests" section of this specification.

[0075] Battery cells at different positions in a battery pack have different heat dissipation capabilities. Usually, the outer battery cells have stronger heat dissipation capabilities. That is, the heat dissipation speed is faster. Therefore, the heat dissipation speed of the battery cells gradually decreases from the outside of the battery pack to the inside of the battery pack, and conversely, the heat retention ability of the battery cells gradually decreases from the inside of the battery pack to the outside of the battery pack. Therefore, the temperature of the battery cells in different regions of the battery pack is different, and the charge and discharge performances thereof are not uniform. For example, in a low temperature external environment, the heat dissipation speed of the inner battery cells is relatively slow, the temperature is relatively high, and the performance in the low temperature external environment is relatively good (but the high temperature performance is poor). However, the heat dissipation speed of the outer battery cells is relatively fast, the temperature is relatively low, and the performance in the low temperature external environment is relatively poor (but the high temperature performance is good). As a result, the phenomenon that the difference in electrical performance between the battery cells in different regions of the battery pack is too large in the low temperature environment reduces the energy retention rate of the entire battery pack in the low temperature environment.

[0076] In order to solve the above problem, the inventors have installed a first battery cell 61, a second battery cell 62, and a third battery cell 63 having dual discharge voltage plateaus (i.e., a first discharge voltage plateau with a relatively high discharge voltage and a second discharge voltage plateau with a relatively low discharge voltage) in a first region R1, a second region R2, and a third region R3 with different temperatures. As a result, after the discharge of the first discharge voltage plateau is completed, the discharge can be continued using the second discharge voltage plateau (i.e., the staged discharge of the same battery cell is realized), thereby improving the energy released by each battery cell in a low temperature environment and improving the low temperature energy retention rate of the entire battery pack.

[0077] In the present application, the positive electrode active materials of the first battery cell 61, the second battery cell 62, and the third battery cell 63, each having a double discharge voltage plateau, are manufactured by mixing a normal positive electrode active material (first positive electrode active material) with a positive electrode functional assistant. The normal positive electrode active material has a first discharge voltage plateau with a high discharge voltage, and the positive electrode functional assistant is a titanium oxide, a niobium oxide, or a titanium niobium oxide having a layered structure with a ReO3 configuration. These positive electrode functional assistants have a second discharge voltage plateau with a low discharge voltage. The discharge capacity of the second discharge voltage plateau with a low discharge voltage in the battery cells can be adjusted by changing the content of the positive electrode functional assistant in the positive electrode active material.

[0078] The inventors of the present application further adjusted the discharge capacity ratios corresponding to the second discharge voltage plateaus of the first battery cell 61, the second battery cell 62, and the third battery cell 63 to obtain a battery pack 1 with a higher low-temperature energy retention rate as a whole. It was found that such a configuration significantly improves the low-temperature energy retention rate of the battery pack under low-temperature conditions in winter. Specifically, by setting the discharge capacity ratio corresponding to the second discharge voltage plateau of the third battery cell 63 > the discharge capacity ratio corresponding to the second discharge voltage plateau of the second battery cell 62 > the discharge capacity ratio corresponding to the second discharge voltage plateau of the first battery cell 61, the second battery cell 62 and the third battery cell 63 can be continuously discharged in a low-temperature environment where the first battery cell 61 cannot be continuously discharged, and the third battery cell 63 can be continuously discharged in a low-temperature environment where the first battery cell 61 and the second battery cell 62 cannot be continuously discharged, thereby ensuring that the discharge capacity of the entire battery pack is at a high level.

[0079] The inventors further conducted extensive research into the relationship between the discharge capacity percentage corresponding to the second discharge voltage plateau in each battery cell 61, 61, 63 having a double discharge voltage plateau located in each of the temperature regions R1, R2, R3 and the -20°C total energy retention rate of the battery pack. As a result, it has been found that, in each of the first battery cell 61, the second battery cell 62, and the third battery cell 63, when the sum of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau is 100%, by making the discharge capacity ratio corresponding to the second discharge voltage plateau of the third battery cell 63 > the discharge capacity ratio corresponding to the second discharge voltage plateau of the second battery cell 62 > the discharge capacity ratio corresponding to the second discharge voltage plateau of the first battery cell 61, it is possible to make the low temperature energy retention rate of the third battery cell 63 > the low temperature energy retention rate of the second battery cell 62 > the low temperature energy retention rate of the first battery cell 61. It is therefore possible to make the energy that can be released at low temperatures (discharge capacity at low temperatures) of each of the battery cells 61, 62, 63 arranged in each of the regions R1, R2, R3 having different temperatures of the battery pack approximately uniform, thereby improving the low temperature energy retention rate of the entire battery pack 1 (total energy retention rate of the battery pack at -20°C), and improving the driving range of the entire battery pack at low temperatures.

[0080] As shown in Fig. 2, among the multiple battery cells, battery cells located relatively outside may contact the inner surface of the battery pack housing (upper housing 2, lower housing 3) or may contact structural members provided on the inner surface of the battery pack housing. In the plan view shown in Fig. 2, gaps g1, g2 are formed between the outermost battery cell and the inner surface of the battery pack housing, and various structures of the battery pack can be provided in these gaps g1, g2. Capacitors, etc. can be provided in the gaps between different battery cells to improve the energy density of the entire battery pack.

[0081] In some embodiments, the positive electrode functional additive in the first battery cell 61, the second battery cell 62, and the third battery cell 63 is TiNb 2x O 4+5xHere, x is an integer of 1 or more, and preferably, the titanium niobium oxide is Ti2Nb2O9, TiNb2O7, Ti2Nb 10 O 29 and TiNb 24 O 62 One or more types are selected from the following:

[0082] Titanium niobium oxide is generally prepared by combining titanium oxide and niobium oxide in different ratios. Because the atomic radii of titanium and niobium are close, titanium niobium oxide both have a layered structure with the ReO3 configuration, and titanium ions and niobium ions have similar electrochemical properties, so Nb 5+ / Nb 4+ , Nb 4+ / Nb 3+ and Ti 4+ / Ti 3+ The redox potential difference is small, both within the range of 1-2 V.

[0083] Thus, by selecting titanium niobium oxide, which has excellent performance, as the positive electrode functional auxiliary, it is possible to obtain the first battery cell 61, the second battery cell 62, and the third battery cell 63, each having an appropriate second discharge voltage plateau, thereby realizing the battery pack of the present application, which has excellent low-temperature performance.

[0084] The titanium niobium oxides mentioned above are commercially available or can be obtained from Ti2Nb 2x O 4+5x According to the compounding ratio of each element, adjust the mass ratio of TiO2 and Nb2O5 powder and add a solvent. The solvent can be ethanol, water or acetone. The mixture can be ball milled, dried, heated and cooled to obtain the corresponding titanium niobium oxide.

[0085] In some embodiments, the discharge voltage range of the second discharge voltage plateau is 1.0-2.0 V. Preferably, the discharge capacity of the second discharge voltage plateau at 1.2-1.6 V is 50% or more, preferably 70% or more, of the total discharge capacity of the second discharge voltage plateau.

[0086] Thus, by setting the discharge voltage of the second discharge voltage plateau in the above range, a significant difference can be made between the discharge voltage of the second discharge voltage plateau and the discharge voltage of the first discharge voltage plateau, and the above effect of having a double discharge voltage plateau can be significantly obtained. By setting the ratio of the discharge capacity at 1.2-1.6V of the second discharge voltage plateau to the total discharge capacity of the second discharge voltage plateau within the above range, it is possible to ensure that the battery cells can release sufficient energy at low temperatures, and to ensure the low-temperature energy retention rate of the entire battery pack.

[0087] In some embodiments, in the first battery cell 61, the second battery cell 62, and the third battery cell 63, the difference between the minimum discharge voltage of the first discharge voltage plateau and the maximum discharge voltage of the second discharge voltage plateau is 0.5 V or more, preferably 1.0 V or more.

[0088] Referring to FIG. 3, the “minimum discharge voltage of the first discharge voltage plateau” described in the present application refers to the discharge voltage corresponding to point A, and the “maximum discharge voltage of the second discharge voltage plateau” refers to the discharge voltage corresponding to point B.

[0089] For a battery cell having two discharge voltage plateaus, the greater the difference in discharge voltage between the first and second discharge voltage plateaus, the more significant the above-mentioned effect of the second discharge voltage plateau is. When the difference between the minimum discharge voltage of the first discharge voltage plateau and the maximum discharge voltage of the second discharge voltage plateau is less than 0.5 V, the difference in discharge voltage between the first and second discharge voltage plateaus is small, and the above-mentioned effect of the second discharge voltage plateau cannot be obtained significantly.

[0090] By setting the difference between the minimum discharge voltage of the first discharge voltage plateau and the maximum discharge voltage of the second discharge voltage plateau within the above range, it is possible to discharge at the first discharge voltage plateau, which has a higher discharge voltage, and then subsequently at the second discharge voltage plateau, which has a lower discharge voltage. This significantly increases the energy that each battery cell can release at low temperatures, and improves the energy retention rate of the entire battery pack at low temperatures.

[0091] In some embodiments, when the sum of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau is 100%, the discharge capacity corresponding to the first discharge voltage plateau is 90%-100%, and the discharge capacity corresponding to the second discharge voltage plateau is 0%-10% in the first battery cell 61. The discharge capacity corresponding to the first discharge voltage plateau being 100% and the discharge capacity corresponding to the second discharge voltage plateau being 0% refers to the case where the first battery cell 61 has only one discharge voltage plateau, which is also within the scope of the present invention.

[0092] As a result, by setting the respective ratios of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the first battery cell 61 within the above range, the energy that the first battery cell 61 can release at low temperatures can be increased, thereby improving the low-temperature energy retention rate of the entire battery pack 1.

[0093] In some embodiments, in the second battery cell 62, when the sum of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau is 100%, the discharge capacity corresponding to the first discharge voltage plateau accounts for 73%-95%, and the discharge capacity corresponding to the second discharge voltage plateau accounts for 5%-27%.

[0094] As a result, by setting the respective ratios of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the second battery cell 62 within the above range, the energy that the second battery cell 62 can release at low temperatures can be increased, and the low-temperature energy retention rate of the entire battery pack 1 can be further improved.

[0095] In some embodiments, in the third battery cell 63, when the sum of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau is 100%, the discharge capacity corresponding to the first discharge voltage plateau accounts for 54%-87%, and the discharge capacity corresponding to the second discharge voltage plateau accounts for 13%-46%.

[0096] As a result, by setting the respective ratios of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the third battery cell 63 within the above ranges, the energy that the third battery cell 63 can release at low temperatures can be increased, and the low-temperature energy retention rate of the entire battery pack 1 can be further improved.

[0097] In some embodiments, the gram capacity of the positive electrode active material of the first battery cell 61 is 148-285 mAh / g, the gram capacity of the positive electrode active material of the second battery cell is 155-295 mAh / g, and the gram capacity of the positive electrode active material of the third battery cell is 169-311 mAh / g.

[0098] As a result, by setting the gram capacity of each of the first battery cell 61, the second battery cell 62, and the third battery cell 63 within the above range, the discharge capacities of the first battery cell 61, the second battery cell 62, and the third battery cell 63 at low temperatures can be roughly uniformed, thereby improving the energy retention rate of the entire battery pack 1 at low temperatures.

[0099] Here, the gram capacity of the positive electrode active material of each battery cell refers to the average gram capacity of the positive electrode active material, and can be calculated, for example, from the gram capacity and mass ratio of the first positive electrode active material and the positive electrode functional auxiliary contained in the positive electrode active material.

[0100] In some embodiments, the theoretical gram capacity of the positive electrode functional additive is 350-410 mAh / g.

[0101] By using a positive electrode functional assistant having a theoretical gram capacity within the above range, it is possible to ensure sufficient energy density in each battery cell and improve the low-temperature discharge power of each battery cell and the entire battery pack.

[0102] In some embodiments, the first positive electrode active material is one selected from lithium manganate, lithium nickelate, lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, and lithium iron phosphate.

[0103] As a result, as long as the ratio of the discharge voltage and discharge capacity between the first discharge voltage plateau due to the first positive electrode active material and the second discharge voltage plateau due to the positive electrode functional auxiliary satisfies the above relationship, the first positive electrode active material can be selected from various existing positive electrode active materials, and the battery pack of the present application can be easily realized by utilizing an existing positive electrode active material.

[0104] In some embodiments, when the first battery cell 61, the second battery cell 62, and the third battery cell 63 contain the same type of first positive electrode active material and the same type of positive electrode functional auxiliary, the mass proportion of the first positive electrode active material in the positive electrode active material gradually decreases in the order of the first battery cell 61, the second battery cell 62, and the third battery cell 63, and the mass proportion of the positive electrode functional auxiliary in the positive electrode active material gradually increases in the order of the first battery cell 61, the second battery cell 62, and the third battery cell 63.

[0105] The higher the mass ratio of the positive electrode functional assistant for generating the second discharge voltage plateau with a lower discharge voltage, and the higher the discharge capacity ratio corresponding to the second discharge voltage plateau, the higher the low-temperature energy retention rate of the battery cell. By setting the mass ratio of the positive electrode functional assistant of the third battery cell 63 arranged in the third region R3>the mass ratio of the positive electrode functional assistant of the second battery cell 62 arranged in the second region R2>the mass ratio of the positive electrode functional assistant of the first battery cell 61 arranged in the first region R1, the low-temperature energy retention rate of the third battery cell 63>the low-temperature energy retention rate of the second battery cell 62>the low-temperature energy retention rate of the first battery cell 61. This allows the energy released at low temperatures by the first battery cell 61, the second battery cell 62, and the third battery cell 63 to be approximately uniform, and the energy retention rate at low temperatures of the entire battery pack 1 can be improved.

[0106] In some embodiments, when the total mass of the first positive electrode active material and the positive electrode functional assistant is 100%, the mass of the first positive electrode active material is 96.0%-100%, and the mass of the positive electrode functional assistant is 0%-4.0% in the first battery cell 61. Here, the mass of the first positive electrode active material is 100% and the mass of the positive electrode functional assistant is 0% means that the first battery cell 61 is composed only of the first positive electrode active material, which is within the scope of the present invention.

[0107] In this manner, by setting the mass ratio of the first positive electrode active material to the positive electrode functional auxiliary in the first battery cell 61 within the above range, the ratio of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau in the first battery cell 61 can be set within the above range. This increases the energy that the first battery cell 61 can release at low temperatures, and improves the low-temperature energy retention rate of the entire battery pack 1.

[0108] In some embodiments, in the second battery cell 62, when the total mass of the first positive electrode active material and the positive electrode functional auxiliary is 100%, the mass of the first positive electrode active material accounts for 88.5%-96.0%, and the mass of the positive electrode functional auxiliary accounts for 4.0%-11.5%.

[0109] In this manner, by setting the mass ratio of the first positive electrode active material to the positive electrode functional auxiliary in the second battery cell 62 within the above range, the ratio of the discharge capacity corresponding to the first discharge voltage plateau to the discharge capacity corresponding to the second discharge voltage plateau in the second battery cell 62 can be set within the above range. This increases the energy that the second battery cell 62 can release at low temperatures, and further improves the low-temperature energy retention rate of the entire battery pack 1.

[0110] In some embodiments, in the third battery cell 63, when the total mass of the first positive electrode active material and the positive electrode functional assistant is 100%, the mass of the first positive electrode active material accounts for 76.5%-88.5%, and the mass of the positive electrode functional assistant accounts for 11.5%-23.5%.

[0111] In this manner, by setting the mass ratio of the first positive electrode active material to the positive electrode functional auxiliary in the third battery cell 63 within the above range, the ratio of the discharge capacity corresponding to the first discharge voltage plateau to the discharge capacity corresponding to the second discharge voltage plateau in the third battery cell 63 can be set within the above range. This increases the energy that the third battery cell 63 can release at low temperatures, and further improves the low-temperature energy retention rate of the entire battery pack 1.

[0112] In some embodiments, the positive electrode functional assistant is a lithium-containing titanium niobium oxide coated with carbon.

[0113] Thus, by performing a prelithiation process on a lithium-deficient material such as titanium niobium oxide as a positive electrode functional assistant, it is possible to compensate for the decrease in the number of lithium ions due to the decrease in the normal positive electrode active material, so that the battery cell has a lithium ion number that meets the requirements, and the energy density of the battery cell is guaranteed. In addition, by coating the prelithiation-treated titanium niobium oxide with carbon, the conductivity of the titanium niobium oxide can be increased. This improves the structural stability of the titanium niobium oxide as a positive electrode functional assistant, and ensures the energy density and cycle stability of the battery unit.

[0114] As a method for prelithiating titanium niobium oxide, a method for prelithiating a known lithium-deficient material can be adopted. For example, a method can be adopted in which the prepared titanium niobium oxide is mixed with lithium carbonate, then compressed and placed in an alumina ceramic crucible, placed in a blast furnace, heated to the melting temperature of lithium carbonate, cooled to room temperature, taken out, and dispersed in a ball mill to obtain a prelithiated product. By prelithiating titanium niobium oxide, the initial efficiency of the battery can be improved.

[0115] A known carbon coating method can be used to coat the prelithiated titanium niobium oxide with carbon. For example, titanium niobium oxide (Ti2Nb 2x O 4+5x A method can be used in which the mass ratio of prelithiated titanium niobium oxide and glucose is adjusted according to the compounding ratio of each element of (1) and the desired carbon coating amount, a solvent such as ethanol, water or acetone is added, and the mixture is subjected to ball milling, drying, granulation, and calcination to obtain a lithium-containing titanium niobium oxide material coated with carbon. By coating the prelithiated titanium niobium oxide with carbon, the electrical conductivity of the titanium niobium oxide can be improved.

[0116] In some embodiments, the negative electrodes of the first battery cell 61, the second battery cell 62, and the third battery cell 63 are lithium-replenished.

[0117] As a result, by performing lithium replenishing processing on the negative electrodes of each of the first battery cell 61, the second battery cell 62, and the third battery cell 63, the deficiency of lithium ions caused by adding titanium niobium oxide to the positive electrode active material can be compensated for, and the total amount of available lithium ions in the battery cells is not reduced, ensuring the energy density of the battery cells.

[0118] Various known methods can be used to replenish lithium in the negative electrode. For example, the following method can be used: (1) A binder, lithium powder, and an organic solvent are mixed to obtain a lithium powder solution, (2) the lithium powder solution is physically applied to a negative electrode sheet, and (3) the negative electrode sheet is dried and cold pressed to obtain a prelithiated negative electrode sheet. By replenishing lithium in the negative electrode, the initial efficiency of the battery can be improved.

[0119] At least one of the prelithiation treatment of the positive electrode functional assistant and the lithium supplementation treatment of the negative electrode may be carried out.

[0120] In some embodiments, at a temperature below 0° C., the discharge cut-off voltage of the first battery cell is 1.4-1.6V, the discharge cut-off voltage of the second battery cell is 1.2-1.4V, and the discharge cut-off voltage of the third battery cell is 1.0-1.2V.

[0121] Thus, by providing the discharge cutoff voltages for the first battery cell 61, the second battery cell 62, and the third battery cell 63 as described above, it is possible to substantially equalize the energy discharged at low temperatures from the first battery cell 61, the second battery cell 62, and the third battery cell 63. As a result, it is possible to improve the energy retention rate of the entire battery pack at low temperatures.

[0122] If the charge cut-off voltage is too high or the discharge cut-off voltage is too low, the cycle performance of the battery cell will be impaired. If the charge cut-off voltage is too high, the battery cell will be overcharged. When the battery cell is fully charged, if charging is continued, the structure of the positive electrode material will change, causing capacity loss, and the oxygen released by the decomposition of the positive electrode material will undergo a violent chemical reaction with the electrolyte, which may result in an explosion as a worst case scenario. If the discharge cut-off voltage is too low, the battery cell will be over-discharged, and the internal pressure of the battery cell will increase due to over-discharge, damaging the reversibility of the positive and negative electrode active materials, which can only be partially recovered even when charged, and the capacity will also be significantly attenuated. If the battery cell is deeply charged and discharged, the damage to the battery cell will increase, and the most ideal operating state of the battery cell is to be shallowly charged and discharged, thus prolonging the life of the battery cell.

[0123] In some embodiments, the number of first battery cells 61:the number of second battery cells 62:the number of third battery cells 63=(3-8):(8-13):(10-15). In other words, if the sum of the number of first battery cells 61, the number of second battery cells 62, and the number of third battery cells 63 is 100%, the proportion of the number of first battery cells 61 is about 10-30%, the proportion of the number of second battery cells 62 is about 25-50%, and the proportion of the number of third battery cells 63 is about 30-60%.

[0124] In some embodiments, the number of first battery cells 61 may be one.

[0125] As a result, by setting the numbers of the first battery cells 61, the second battery cells 62, and the third battery cells 63 in accordance with the temperature distribution range of a typical battery pack, the battery pack of the present application can be easily realized.

[0126] <Power consumption equipment> The present application further provides a power consuming device including the battery pack of the present application. The battery pack may be used as a power source for the power consuming device or as an energy storage unit for the power consuming device. The power consuming device may include, but is not limited to, mobile 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.), trains, ships and satellites, energy storage systems, etc.

[0127] The power consuming device can be a battery cell or a battery pack according to its usage needs.

[0128] 4 is an example of a power consuming device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. The battery pack of the present invention can be employed to meet the low temperature driving range needs of the power consuming device. EXAMPLES

[0129] The following examples of the present application are described. The examples described below are illustrative and are merely for the purpose of explaining the present application, and cannot be understood as limiting the present application. In the examples, specific techniques or conditions are not specified, and are carried out according to techniques or conditions described in the literature in this field, or according to the product specifications. Reagents or equipment used that do not specify the manufacturer are all ordinary products available from the market.

[0130] (1) Battery cell manufacturing

[0131] I. First Battery Cell Fabrication

[0132] [Example I-1] 1) Preparation of the positive electrode sheet The first positive electrode active material LiNi 0.6 Co0.2 Mn 0.2 O2 (NCM), positive electrode functional additive TiNb2O7, highly conductive carbon black SP as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder were dispersed in N-methylpyrrolidone (NMP) as a solvent and mixed uniformly to obtain a positive electrode slurry. The positive electrode slurry was uniformly applied to a positive electrode current collector aluminum foil, and then dried, cold pressed, stripped, and cut to obtain a positive electrode sheet.

[0133] Here, the positive electrode functional assistant is prelithiated and carbon-coated, the mass ratio of the positive electrode active material, conductive carbon black, and binder PVDF is 96:2:2:2, and the mass ratio of the positive electrode functional assistant TiNb2O7 and the first positive electrode active material NCM is 2:98.

[0134] 2) Preparation of negative electrode sheet The negative electrode active material graphite, the conductive agent high conductive carbon black SP, the binder SBR, and the thickener CMC-Na were dispersed in deionized water as a solvent in a mass ratio of 96:1:1:2 and mixed uniformly to obtain a negative electrode slurry. The negative electrode slurry was uniformly applied to a negative electrode current collector copper foil, and then dried, cold pressed, stripped, and cut to obtain a negative electrode sheet.

[0135] 3) Separator A polyethylene film was used as the separator.

[0136] 4) Preparation of electrolyte Ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) were mixed uniformly in a volume ratio of 1:1:1 to obtain an organic solvent, and then thoroughly dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte solution with a concentration of 1 mol / L.

[0137] 5) Battery cell fabrication The positive electrode sheet, separator, and negative electrode sheet were stacked in this order so that the separator was located between the positive electrode sheet and the negative electrode sheet to perform an insulating function. The stack was then rolled up to obtain a bare cell. The bare cell was placed in an exterior case, dried, and then injected with an electrolyte. The bare cell was vacuum sealed, left to stand, chemically formed, shaped, and other processes to obtain the first battery cell I-1.

[0138] [Example I-2] The first positive electrode active material is LiNi 0.6 Co 0.2 Mn 0.2 A first battery cell I-2 was obtained in the same manner as in Preparation Example I-1, except that O2(NCM) and the positive electrode functional additive TiO2 were used.

[0139] [Example I-3] The first positive electrode active material is LiNi 0.6 Co 0.2 Mn 0.2 A first battery cell I-3 was obtained in the same manner as in Preparation Example I-1, except that O2(NCM) and the positive electrode functional additive Nb2O5 were used.

[0140] [Example I-4] A first battery cell I-4 was obtained in the same manner as in Preparation Example I-1, except that lithium iron phosphate (LFP) as the first positive electrode active material and TiNb2O7 as the positive electrode functional assistant were used as the positive electrode active material.

[0141] [Example I-5] A first battery cell I-5 was obtained in the same manner as in Preparation Example I-1, except that lithium manganese oxide (LMO) as the first positive electrode active material and a positive electrode functional assistant TiNb2O7 were used as the positive electrode active material.

[0142] [Example I-6] The first positive electrode active material is LiNi 0.6 Co 0.2 Mn 0.2 A first battery cell I-6 was obtained in the same manner as in Preparation Example I-1, except that O2(NCM) and the positive electrode functional additive Ti2Nb2O9 were used.

[0143] [Example I-7] The first positive electrode active material is LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM) and positive electrode functional additive Ti2Nb 10 O 29 A first battery cell I-7 was obtained in the same manner as in Preparation Example I-1, except that the above was used.

[0144] [Example I-8] The first positive electrode active material is LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM) and positive electrode functional additive TiNb 24 O 62 A first battery cell I-8 was obtained in the same manner as in Preparation Example I-1, except that the above was used.

[0145] [Example I-9] A first battery cell I-9 was obtained in the same manner as in Preparation Example I-1, except that lithium iron phosphate (LFP) as the first positive electrode active material and a positive electrode functional assistant Ti2Nb2O9 were used as the positive electrode active material.

[0146] [Example I-10] The positive electrode active material is lithium manganese oxide (LMO), which is the first positive electrode active material, and the positive electrode functional additive Ti2Nb. 10 O 29 A first battery cell I-10 was obtained in the same manner as in Preparation Example I-1, except that the above was used.

[0147] [Example I-11] A first battery cell I-11 was obtained in the same manner as in Preparation Example I-1, except that only NCM was used as the positive electrode active material.

[0148] [Example I-12] A first battery cell I-12 was obtained in the same manner as in Preparation Example I-1, except that the mass ratio of the positive electrode functional additive TiNb2O7 to the first positive electrode active material NCM was set to 11.5:88.5.

[0149] [Example I-13] A first battery cell I-13 was obtained in the same manner as in Preparation Example I-1, except that only LFP was used as the positive electrode active material.

[0150] [Example I-14] A first battery cell I-14 was obtained in the same manner as in Preparation Example I-4, except that the mass ratio of the positive electrode functional assistant TiNb2O7 to the first positive electrode active material LFP was 4:96.

[0151] II. Fabrication of the Second Battery Cell [Example II-1] A second battery cell II-1 was obtained in the same manner as in Preparation Example I-1, except that the mass ratio of the positive electrode functional assistant TiNb2O7 to the first positive electrode active material NCM was 6.5:93.5.

[0152] [Preparation Example II-2] A second battery cell II-2 was obtained in the same manner as in Preparation Example I-2, except that the mass ratio of the positive electrode functional assistant TiO2 to the first positive electrode active material NCM was 6.5:93.5.

[0153] [Preparation Example II-3] A second battery cell II-3 was obtained in the same manner as in Preparation Example I-3, except that the mass ratio of the positive electrode functional assistant Nb2O5 to the first positive electrode active material NCM was 6.5:93.5.

[0154] [Preparation Example II-4] A second battery cell II-4 was obtained in the same manner as in Preparation Example I-4, except that the mass ratio of the positive electrode functional assistant TiNb2O7 to the first positive electrode active material LFP was set to 6.5:93.5.

[0155] [Preparation Example II-5] A second battery cell II-5 was obtained in the same manner as in Preparation Example I-5, except that the mass ratio of the positive electrode functional assistant TiNb2O7 to the first positive electrode active material LMO was 6.5:93.5.

[0156] [Example II-6] A second battery cell II-6 was obtained in the same manner as in Preparation Example I-6, except that the mass ratio of the positive electrode functional assistant Ti2Nb2O9 to the first positive electrode active material NCM was 6.5:93.5.

[0157] [Example II-7] Positive electrode functional additive Ti2Nb 10 O 29 A second battery cell II-7 was obtained in the same manner as in Preparation Example I-7, except that the mass ratio of the first positive electrode active material NCM to the first positive electrode active material NCM was set to 6.5:93.5.

[0158] [Example II-8] Positive electrode functional additive TiNb 24 O 62 A second battery cell II-8 was obtained in the same manner as in Preparation Example I-8, except that the mass ratio of the first positive electrode active material NCM to the first positive electrode active material NCM was set to 6.5:93.5.

[0159] [Example II-9] A second battery cell II-9 was obtained in the same manner as in Preparation Example I-9, except that the mass ratio of the positive electrode functional assistant Ti2Nb2O9 to the first positive electrode active material LFP was 6.5:93.5.

[0160] [Example II-10] Positive electrode functional additive Ti2Nb 10 O 29 A second battery cell II-10 was obtained in the same manner as in Preparation Example I-10, except that the mass ratio of the first positive electrode active material LMO to the first positive electrode active material LMO was 6.5:93.5.

[0161] [Preparation Example II-11] A second battery cell II-11 was obtained in the same manner as in Preparation Example II-11.

[0162] [Example II-12] A second battery cell II-12 was obtained in the same manner as in Preparation Example I-1, except that only LFP was used as the positive electrode active material.

[0163] [Example II-13] A second battery cell II-13 was obtained in the same manner as in Preparation Example I-1.

[0164] [Example II-14] A second battery cell II-14 was obtained in the same manner as in Preparation Example I-1, except that the mass ratio of the positive electrode functional assistant TiNb2O7 to the first positive electrode active material NCM was 4:96.

[0165] [Example II-15] A second battery cell II-15 was obtained in the same manner as in Preparation Example I-4, except that the mass ratio of the positive electrode functional assistant TiNb2O7 to the first positive electrode active material LFP was set to 11.5:88.5.

[0166] [Example II-16] A second battery cell II-16 was obtained in the same manner as in Preparation Example I-1, except that the first positive electrode active material, lithium manganese oxide (LMO), and the positive electrode functional additive Ti2Nb2O9 were used as the positive electrode active material, and the mass ratio of the positive electrode functional additive Ti2Nb2O9 to the first positive electrode active material LMO was 11.5:88.5.

[0167] [Example II-17] A second battery cell II-17 was obtained in the same manner as in Preparation Example I-1, except that the mass ratio of the positive electrode functional assistant TiNb2O7 to the first positive electrode active material NCM was set to 20:80.

[0168] III. Fabrication of the third battery cell [Preparation Example III-1] A third battery cell III-1 was obtained in the same manner as in Preparation Example I-1, except that the mass ratio of the positive electrode functional assistant TiNb2O7 to the first positive electrode active material NCM was set to 11.5:88.5.

[0169] [Preparation Example III-2] A third battery cell III-2 was obtained in the same manner as in Preparation Example I-2, except that the mass ratio of the positive electrode functional assistant TiO2 to the first positive electrode active material NCM was set to 11.5:88.5.

[0170] [Preparation Example III-3] A third battery cell III-3 was obtained in the same manner as in Preparation Example I-3, except that the mass ratio of the positive electrode functional assistant Nb2O5 to the first positive electrode active material NCM was 11.5:88.5.

[0171] [Preparation Example III-4] A third battery cell III-4 was obtained in the same manner as in Preparation Example I-4, except that the mass ratio of the positive electrode functional assistant TiNb2O7 to the first positive electrode active material LFP was set to 11.5:88.5.

[0172] [Preparation Example III-5] A third battery cell III-5 was obtained in the same manner as in Preparation Example I-5, except that the mass ratio of the positive electrode functional assistant TiNb2O7 to the first positive electrode active material LMO was set to 11.5:88.5.

[0173] [Preparation Example III-6] A third battery cell III-6 was obtained in the same manner as in Preparation Example I-6, except that the mass ratio of the positive electrode functional assistant Ti2Nb2O9 to the first positive electrode active material NCM was 11.5:88.5.

[0174] [Preparation Example III-7] Positive electrode functional additive Ti2Nb 10 O 29 A third battery cell III-7 was obtained in the same manner as in Preparation Example I-7, except that the mass ratio of the first positive electrode active material NCM to the first positive electrode active material NCM was set to 11.5:88.5.

[0175] [Preparation Example III-8] Positive electrode functional additive TiNb 24 O 62 A third battery cell III-8 was obtained in the same manner as in Preparation Example I-8, except that the mass ratio of the first positive electrode active material NCM to the first positive electrode active material NCM was set to 11.5:88.5.

[0176] [Preparation Example III-9] A third battery cell III-9 was obtained in the same manner as in Preparation Example I-9, except that the mass ratio of the positive electrode functional assistant Ti2Nb2O9 to the first positive electrode active material LFP was set to 11.5:88.5.

[0177] [Preparation Example III-10] Positive electrode functional additive Ti2Nb 10 O 29A third battery cell III-10 was obtained in the same manner as in Preparation Example I-10, except that the mass ratio of the first positive electrode active material LMO to the first positive electrode active material LMO was set to 11.5:88.5.

[0178] [Preparation Example III-11] A third battery cell III-11 was obtained in the same manner as in Preparation Example I-11.

[0179] [Preparation Example III-12] A third battery cell III-12 was obtained in the same manner as in Preparation Example I-1, except that only LMO was used as the positive electrode active material.

[0180] [Preparation Example III-13] A third battery cell III-13 was obtained in the same manner as in Preparation Example I-1.

[0181] [Preparation Example III-14] A third battery cell III-14 was obtained in the same manner as in Preparation Example I-1, except that the mass ratio of the positive electrode functional assistant TiNb2O7 to the first positive electrode active material NCM was set to 23.5:76.5.

[0182] [Preparation Example III-15] A third battery cell III-15 was obtained in the same manner as in Preparation Example I-4, except that the mass ratio of the positive electrode functional assistant TiNb2O7 to the first positive electrode active material LFP was set to 23.5:76.5.

[0183] [Preparation Example III-16] A third battery cell III-16 was obtained in the same manner as in Preparation Example II-16, except that the mass ratio of the positive electrode functional assistant Ti2Nb2O9 to the first positive electrode active material LMO was set to 23.5:76.5.

[0184] (2) Battery pack assembly [Example 1] 2, the internal space of the battery pack housing is divided into a first region R1, a second region R2, and a third region R3. A first battery cell I-1 is arranged as a first battery cell 61 in the first region R1, a second battery cell II-1 is arranged as a second battery cell 62 in the second region R2, and a third battery cell III-1 is arranged as a third battery cell 63 in the third region R3, to assemble the battery pack. The ratio of the number of first battery cells 61: the number of second battery cells 62: the number of third battery cells 63 is 12:32:40.

[0185] [Example 2] A battery pack was assembled in the same manner as in Example 1, except that the first battery cell I-2 was used instead of the first battery cell I-1, the second battery cell II-2 was used instead of the second battery cell II-1, and the third battery cell III-2 was used instead of the third battery cell III-1.

[0186] [Example 3] A battery pack was assembled in the same manner as in Example 1, except that a first battery cell I-3 was used instead of the first battery cell I-1, a second battery cell II-3 was used instead of the second battery cell II-1, and a third battery cell III-3 was used instead of the third battery cell III-1.

[0187] [Example 4] A battery pack was assembled in the same manner as in Example 1, except that a first battery cell I-4 was used instead of the first battery cell I-1, a second battery cell II-4 was used instead of the second battery cell II-1, and a third battery cell III-4 was used instead of the third battery cell III-1.

[0188] [Example 5] A battery pack was assembled in the same manner as in Example 1, except that the first battery cell I-5 was used instead of the first battery cell I-1, the second battery cell II-5 was used instead of the second battery cell II-1, and the third battery cell III-5 was used instead of the third battery cell III-1.

[0189] [Example 6] A battery pack was assembled in the same manner as in Example 1, except that a first battery cell I-6 was used instead of the first battery cell I-1, a second battery cell II-6 was used instead of the second battery cell II-1, and a third battery cell III-6 was used instead of the third battery cell III-1.

[0190] [Example 7] A battery pack was assembled in the same manner as in Example 1, except that a first battery cell I-7 was used instead of the first battery cell I-1, a second battery cell II-7 was used instead of the second battery cell II-1, and a third battery cell III-7 was used instead of the third battery cell III-1.

[0191] [Example 8] A battery pack was assembled in the same manner as in Example 1, except that the first battery cell I-8 was used instead of the first battery cell I-1, the second battery cell II-8 was used instead of the second battery cell II-1, and the third battery cell III-8 was used instead of the third battery cell III-1.

[0192] [Example 9] A battery pack was assembled in the same manner as in Example 1, except that a first battery cell I-9 was used instead of the first battery cell I-1, a second battery cell II-9 was used instead of the second battery cell II-1, and a third battery cell III-9 was used instead of the third battery cell III-1.

[0193] [Example 10] A battery pack was assembled in the same manner as in Example 1, except that a first battery cell I-10 was used instead of the first battery cell I-1, a second battery cell II-10 was used instead of the second battery cell II-1, and a third battery cell III-10 was used instead of the third battery cell III-1.

[0194] [Example 11] A battery pack was assembled in the same manner as in Example 1, except that the first battery cell I-1 was replaced with the first battery cell I-11, and the second battery cell II-1 was replaced with the second battery cell II-14.

[0195] [Example 12] A battery pack was assembled in the same manner as in Example 1, except that a first battery cell I-11 was used instead of the first battery cell I-1, a second battery cell II-14 was used instead of the second battery cell II-1, and a third battery cell III-14 was used instead of the third battery cell III-1.

[0196] [Example 13] A battery pack was assembled in the same manner as in Example 1, except that the first battery cell I-13 was used instead of the first battery cell I-1, the second battery cell II-1 was used instead of the second battery cell II-1, and the third battery cell III-15 was used instead of the third battery cell III-1.

[0197] [Example 14] A battery pack was assembled in the same manner as in Example 1, except that the first battery cell I-14 was used instead of the first battery cell I-1, the second battery cell II-1 was used instead of the second battery cell II-1, and the third battery cell III-16 was used instead of the third battery cell III-1.

[0198] [Example 15] A battery pack was assembled in the same manner as in Example 1, except that the first battery cell I-12 was used instead of the first battery cell I-1, the second battery cell II-17 was used instead of the second battery cell II-1, and the third battery cell III-14 was used instead of the third battery cell III-1.

[0199] [Example 16] A battery pack was assembled in the same manner as in Example 1.

[0200] [Example 17] A battery pack was assembled in the same manner as in Example 1.

[0201] [Example 18] A battery pack was assembled in the same manner as in Example 1.

[0202] [Example 19] A battery pack was assembled in the same manner as in Example 1.

[0203] [Comparative Example 1] A battery pack was assembled in the same manner as in Example 1, except that a first battery cell I-11 was used instead of the first battery cell I-1, a second battery cell II-11 was used instead of the second battery cell II-1, and a third battery cell III-11 was used instead of the third battery cell III-1.

[0204] [Comparative Example 2] A battery pack was assembled in the same manner as in Example 1, except that a first battery cell I-11 was used instead of the first battery cell I-1, a second battery cell II-12 was used instead of the second battery cell II-1, and a third battery cell III-12 was used instead of the third battery cell III-1.

[0205] [Comparative Example 3] A battery pack was assembled in the same manner as in Example 1, except that the second battery cell II-1 was replaced with the second battery cell II-13, and the third battery cell III-1 was replaced with the third battery cell III-13.

[0206] [Comparative Example 4] A battery pack was assembled in the same manner as in Example 1, except that the first battery cell I-12 was used instead of the first battery cell I-1, and the third battery cell III-13 was used instead of the third battery cell III-1.

[0207] In the embodiment of the present application, the internal space of the battery pack housing is divided into a first region, a second region, and a third region; however, the battery pack of the present application is not limited to dividing the internal space of the battery pack housing into three regions, and in addition to the first region, the second region, and the third region, the battery pack may have one or more regions outside the third region, and the battery cells arranged in the outer region may be arranged to surround the battery cells arranged in the inner region.

[0208] When the internal space of the battery pack housing includes three or more regions as described above, it is only necessary that the outermost region has a higher discharge capacity ratio corresponding to the second discharge voltage plateau of the battery cell (i.e., a higher mass ratio of the positive electrode functional auxiliary in the positive electrode active material of the battery cell).

[0209] In addition, when the internal space of the battery pack housing is rectangular, the four corners of the rectangle may be set as the outermost regions, in which the discharge capacity ratio corresponding to the second discharge voltage plateau of the battery cell is the highest (i.e., the mass ratio of the positive electrode functional auxiliary in the positive electrode active material of the battery cell is the highest).

[0210] (3) Correlation Test 1. Measuring the discharge capacity corresponding to a first discharge voltage plateau and the discharge capacity corresponding to a second discharge voltage plateau of a battery cell

[0211] For the first battery cell, the second battery cell, and the third battery cell in each battery pack of Examples 1-19 and Comparative Examples 1-4, the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau of each of the first battery cell, the second battery cell, and the third battery cell at 25° C. were measured using a NEWARE power battery tester (model number BTS-5V300A-4CH). Furthermore, the percentage of the discharge capacity corresponding to the second discharge voltage plateau of each of the first battery cell, the second battery cell, and the third battery cell was calculated.

[0212] The method for measuring the discharge capacity of the battery cell is as follows. (1) Leave the battery cell at 25°C for 2 hours to ensure that the battery cell temperature remains at 25°C. (2) The battery cell was charged at 25°C at 0.33C up to the charge cut-off voltage shown in Table 1 below, and then constant voltage charging was continued at this charge cut-off voltage until the current became 0.05C, after which the charge was cut off (where C indicates the rated capacity of the cell). (3) The battery cell was left to stand at 25°C for 1 hour. (4) The battery cell was discharged at 25°C at 0.33C to the discharge cut-off voltage shown in Table 1 below, and the total discharge capacity C0 of the battery cell was recorded. (5) The discharge curve in step (4) is obtained, for example, as shown in Figure 3 of the present application. In the discharge curve in Figure 3, the total discharge capacity before point B is the discharge capacity C1 corresponding to the first discharge voltage plateau, and the discharge capacity from point B to the discharge cutoff voltage is the discharge capacity C2 corresponding to the second discharge voltage plateau.

[0213] Therefore, the percentage of discharge capacity corresponding to the first discharge voltage plateau of the battery cell=C1 / C0, and the percentage of discharge capacity corresponding to the second discharge voltage plateau of the battery cell=C2 / C0.

[0214] [Table 1]

[0215] 2. Measurement of total energy retention rate of battery pack at -20℃ For each of the battery packs of Examples 1-19 and Comparative Examples 1-4, a NEWARE power battery tester (model number BTS-5V300A-4CH) was used to measure the total fully discharged energy of the battery pack at 25°C and the total fully discharged energy of the battery pack at -20°C. The total fully discharged energy of the battery pack at -20°C was divided by the total fully discharged energy of the battery pack at 25°C to calculate the total energy retention rate (%) of the battery pack at -20°C.

[0216] The total fully discharged energy of the battery pack at 25°C was measured in accordance with "7.1.2 Capacity and Energy Test at Room Temperature" in "GBT 31467.2-2015 Battery Pack and System High Energy Application Test Protocol."

[0217] The total fully discharged energy of the battery packs at -20°C was measured according to "7.1.4 Capacity and Energy Test at Low Temperature" in "GBT 31467.2-2015 Battery Pack and System High Energy Application Test Protocol". The compositions and test results of each battery pack of Examples 1-19 and Comparative Examples 1-4 are shown in Tables 2-4 below.

[0218] [Table 2]

[0219] As can be seen from the results in Table 2 above, in Examples 1-10, the first battery cell, the second battery cell and the third battery cell all have a first discharge voltage plateau and a second discharge voltage plateau, and the discharge capacity percentage corresponding to the second discharge voltage plateau of the third battery cell > the discharge capacity percentage corresponding to the second discharge voltage plateau of the second battery cell > the discharge capacity percentage corresponding to the second discharge voltage plateau of the first battery cell, and the total energy retention rate of the battery pack at -20°C reaches 65.0%-76.7%.

[0220] In Comparative Example 1 and Comparative Example 2, the first battery cell, the second battery cell and the third battery cell all had only one discharge voltage plateau, and the total energy retention rates of the battery packs at -20°C were only 60.5% and 56.7%.

[0221] In Comparative Example 3, the first battery cell, the second battery cell, and the third battery cell all have a first discharge voltage plateau and a second discharge voltage plateau, but the percentage of discharge capacity corresponding to the second discharge voltage plateau in the first battery cell, the second battery cell, and the third battery cell is the same, and the total energy retention rate of the battery pack at -20°C is only 62.9%.

[0222] In Comparative Example 4, the first battery cell, the second battery cell, and the third battery cell all have a first discharge voltage plateau and a second discharge voltage plateau, but the discharge capacity percentage corresponding to the second discharge voltage plateau of the third battery cell < the discharge capacity percentage corresponding to the second discharge voltage plateau of the second battery cell < the discharge capacity percentage of the second discharge voltage plateau of the first battery cell, and the total energy retention rate of the battery pack at -20°C is only 60.7%.

[0223] [Table 3]

[0224] As can be seen from the results in Table 3 above, in Examples 1, 11-14, the second battery cell and the third battery cell both have a first discharge voltage plateau and a second discharge voltage plateau, the discharge capacity percentage corresponding to the second discharge voltage plateau of the third battery cell>the discharge capacity percentage corresponding to the second discharge voltage plateau of the second battery cell>the discharge capacity percentage corresponding to the second discharge voltage plateau of the first battery cell, and the mass percentage of the positive electrode functional assistant and the discharge capacity percentage corresponding to the second discharge voltage plateau in each of the first battery cell, the second battery cell and the third battery cell are within the preferred ranges described in the present application, and the total energy retention rate of the battery pack at -20°C reaches 64.1%-70.0%.

[0225] In Example 15, the mass percentage of the positive electrode functional auxiliary in each of the first battery cell and the second battery cell and / or the discharge capacity percentage corresponding to the second discharge voltage plateau are outside the preferred ranges described in the present application, and the total energy retention rate of the battery pack at -20°C is 59.3%.

[0226] [Table 4]

[0227] As can be seen from the results in Table 4 above, in Example 1, the first battery cell, the second battery cell and the third battery cell all have a first discharge voltage plateau and a second discharge voltage plateau, the discharge capacity percentage corresponding to the second discharge voltage plateau of the third battery cell>the discharge capacity percentage corresponding to the second discharge voltage plateau of the second battery cell>the discharge capacity percentage corresponding to the second discharge voltage plateau of the first battery cell, and the discharge cut-off voltages of the first battery cell, the second battery cell and the third battery cell at -20°C are all within the preferred ranges described in the present application, and the total energy retention rate of the battery pack at -20°C reaches 70%.

[0228] In Example 16, the discharge cut-off voltage of the second and third battery cells at -20°C was too high, and the total energy retention rate of the battery pack at -20°C was 55%, indicating that the cut-off voltage has a significant effect on the total energy retention rate at -20°C.

[0229] In Example 17, the discharge cut-off voltage of the first battery cell and the second battery cell is too low, and the total energy retention rate of the battery pack at −20° C. is 71%. If the cut-off voltage is too low, the total energy retention rate at −20° C. can be improved, but it corresponds to over-discharge, which causes performance degradation of the battery cells and generates gas, affecting the life of the battery cells.

[0230] In Example 18, the discharge cut-off voltage of the second battery cell at -20°C is too high and is greater than the discharge cut-off voltage of the first battery cell, and the total energy retention rate of the battery pack at -20°C is 62%.

[0231] In Example 19, the discharge cut-off voltage of the first battery cell at -20°C is too low, the discharge cut-off voltage of the third battery cell is too high, and the discharge cut-off voltage of the third battery cell > the discharge cut-off voltage of the second battery cell > the discharge cut-off voltage of the first battery cell, and the total energy retention rate of the battery pack at -20°C is 58%.

[0232] The present invention is not limited to the above-mentioned embodiment. The above-mentioned embodiment is an example, and any configuration that has substantially the same technical idea as the technical scope of the present invention and exhibits similar effects is included in the technical scope of the present invention. In addition, various modifications that a person skilled in the art may make to the embodiment, and other forms constructed by combining some of the components in the embodiment, are also included in the scope of the present invention, as long as they do not deviate from the gist of the present invention. [Explanation of symbols]

[0233] 1: Battery pack 2: Upper case 3: Lower case g1, g2: gap BL1: First boundary BL2: The second boundary BL3: The third boundary R1: First region R2: Second Region R3: The third region 61: First battery cell 62: Second battery cell 63: 3rd battery cell

Claims

1. A battery pack housing; A battery pack including a battery cell accommodated in a housing of the battery pack, an internal space of a housing of the battery pack includes a first region, a second region, and a third region; a first battery cell is arranged in the first region, a second battery cell is arranged in the second region, a third battery cell is arranged in the third region, the second battery cell is arranged surrounding a periphery of the first battery cell, and the third battery cell is arranged surrounding a periphery of the second battery cell, wherein: the first battery cell, the second battery cell, and the third battery cell each have a first discharge voltage plateau and a second discharge voltage plateau, and an average discharge voltage of the first discharge voltage plateau is higher than an average discharge voltage of the second discharge voltage plateau; a positive electrode active material of each of the first battery cell, the second battery cell, and the third battery cell is formed by mixing a first positive electrode active material having the first discharge voltage plateau and a positive electrode functional auxiliary having the second discharge voltage plateau; The positive electrode functional assistant is titanium oxide, niobium oxide, or titanium niobium oxide, In each of the first battery cell, the second battery cell, and the third battery cell, when a sum of a discharge capacity corresponding to the first discharge voltage plateau and a discharge capacity corresponding to the second discharge voltage plateau is 100%, a discharge capacity ratio corresponding to the second discharge voltage plateau of the third battery cell>a discharge capacity ratio corresponding to the second discharge voltage plateau of the second battery cell>a discharge capacity ratio corresponding to the second discharge voltage plateau of the first battery cell. A battery pack characterized by:

2. The internal space of the battery pack housing is composed of the first region, the second region, and the third region.

2. The battery pack according to claim 1 .

3. The positive electrode functional assistant is Ti 2 Nb 2x O 4+5x where x is an integer of 1 or more.

2. The battery pack according to claim 1 .

4. The titanium niobium oxide is Ti 2 Nb 2 O 9 , TiNb 2 O 7 , Ti 2 Nb 10 O 29 and TiNb 24 O 62 One or more selected from 2. The battery pack according to claim 1 .

5. The discharge voltage range of the second discharge voltage plateau is 1.0-2.0 V.

2. The battery pack according to claim 1 .

6. The discharge capacity at 1.2-1.6 V of the second discharge voltage plateau is 50% or more of the total discharge capacity of the second discharge voltage plateau.

6. The battery pack according to claim 5.

7. The discharge capacity at 1.2-1.6 V of the second discharge voltage plateau is 70% or more of the total discharge capacity of the second discharge voltage plateau.

7. The battery pack according to claim 6.

8. In the first battery cell, the second battery cell, and the third battery cell, a difference between a minimum discharge voltage of the first discharge voltage plateau and a maximum discharge voltage of the second discharge voltage plateau is 0.5 V or more.

2. The battery pack according to claim 1 .

9. In the first battery cell, the second battery cell, and the third battery cell, a difference between a minimum discharge voltage of the first discharge voltage plateau and a maximum discharge voltage of the second discharge voltage plateau is 1.0 V or more.

9. The battery pack according to claim 8.

10. In the first battery cell, when the sum of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau is 100%, the discharge capacity corresponding to the first discharge voltage plateau occupies 90%-100%, and the discharge capacity corresponding to the second discharge voltage plateau occupies 0%-10%.

2. The battery pack according to claim 1 .

11. In the second battery cell, when the sum of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau is 100%, the discharge capacity corresponding to the first discharge voltage plateau accounts for 73%-95%, and the discharge capacity corresponding to the second discharge voltage plateau accounts for 5%-27%.

2. The battery pack according to claim 1 .

12. In the third battery cell, when the sum of the discharge capacity corresponding to the first discharge voltage plateau and the discharge capacity corresponding to the second discharge voltage plateau is 100%, the discharge capacity corresponding to the first discharge voltage plateau accounts for 54%-87%, and the discharge capacity corresponding to the second discharge voltage plateau accounts for 13%-46%.

2. The battery pack according to claim 1 .

13. The gram capacity of the positive electrode active material of the first battery cell is 148-285 mAh / g, the gram capacity of the positive electrode active material of the second battery cell is 155-295 mAh / g, and the gram capacity of the positive electrode active material of the third battery cell is 169-311 mAh / g.

2. The battery pack according to claim 1 .

14. The theoretical gram capacity of the positive electrode functional assistant is 350-410 mAh / g.

2. The battery pack according to claim 1 .

15. The first positive electrode active material is one selected from the group consisting of lithium manganate, lithium nickel oxide, lithium cobalt oxide, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, and lithium iron phosphate.

2. The battery pack according to claim 1 .

16. When the first battery cell, the second battery cell, and the third battery cell use the same type of the first positive electrode active material and the same type of the positive electrode functional auxiliary, the mass ratio of the first positive electrode active material to the positive electrode active material gradually decreases in the order of the first battery cell, the second battery cell, and the third battery cell, and the mass ratio of the positive electrode functional auxiliary to the positive electrode active material gradually increases in the order of the first battery cell, the second battery cell, and the third battery cell.

2. The battery pack according to claim 1 .

17. In the first battery cell, when the total mass of the first positive electrode active material and the positive electrode functional assistant is 100%, the mass of the first positive electrode active material is 96.0%-100%, and the mass of the positive electrode functional assistant is 0%-4.0%.

2. The battery pack according to claim 1 .

18. In the second battery cell, when the total mass of the first positive electrode active material and the positive electrode functional assistant is 100%, the mass of the first positive electrode active material is 88.5%-96.0%, and the mass of the positive electrode functional assistant is 4.0%-11.5%.

2. The battery pack according to claim 1 .

19. In the third battery cell, when the total mass of the first positive electrode active material and the positive electrode functional assistant is 100%, the mass of the first positive electrode active material is 76.5%-88.5%, and the mass of the positive electrode functional assistant is 11.5%-23.5%.

2. The battery pack according to claim 1 .

20. The positive electrode functional assistant is a lithium-containing titanium niobium oxide coated with carbon.

2. The battery pack according to claim 1 .

21. The negative electrodes of the first battery cell, the second battery cell, and the third battery cell are subjected to a lithium replenishment treatment.

2. The battery pack according to claim 1 .

22. At a temperature below 0° C., the discharge cut-off voltage of the first battery cell is 1.4-1.6V, the discharge cut-off voltage of the second battery cell is 1.2-1.4V, and the discharge cut-off voltage of the third battery cell is 1.0-1.2V.

2. The battery pack according to claim 1 .

23. The number of the first battery cells:the number of the second battery cells:the number of the third battery cells=(3-8):(8-13):(10-15) 2. The battery pack according to claim 1 .

24. A power consuming device comprising the battery pack according to any one of claims 1 to 23.

Images