Battery pack and electrical device

Abstract

A battery pack and an electrical device, the battery pack comprising a plurality of first battery cells, the lower limit voltage of the first battery cells being 2.5-3.0 V; and a plurality of second battery cells, the second battery cells and the first battery cells being arranged in series, and the lower limit voltage of the second battery cells being ≤2.0 V. A negative electrode current collector of each second battery cell comprises metal, the metal comprises at least one of aluminum, nickel, molybdenum, titanium, niobium and iron, and the mass ratio of the metal is ≥40% on the basis of the total mass of the negative electrode current collector of the second battery cell.

Description

Battery packs and electrical equipment Technical Field

[0001] The present application relates to the field of batteries, and in particular, to battery packs and electrical equipment. Background Art

[0002] Batteries are not only used in energy storage systems such as hydropower, thermal, wind, and solar power plants, but are also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric vehicles, as well as in military equipment and aerospace. When battery packs in related technologies contain both lithium-ion and sodium-ion batteries, the sodium-ion battery's lower voltage limit is higher, resulting in the inability to fully utilize the capacity of the sodium-ion battery within certain voltage ranges, reducing the overall capacity of the battery pack.

[0003] Summary of the Invention

[0004] In view of the technical problems existing in the background technology, the present application provides a battery pack that can improve the battery capacity.

[0005] The first aspect of the present application proposes a battery pack comprising a plurality of first battery cells, wherein the lower limit voltage of the first battery cells is 2.5V-3.0V; and a plurality of second battery cells, wherein the second battery cells are arranged in series with the first battery cells, and the lower limit voltage of the second battery cells is ≤2.0V, wherein the negative electrode current collector of the second battery cells comprises a metal, wherein the metal comprises at least one of aluminum, nickel, molybdenum, titanium, niobium, and iron, and the mass proportion of the metal based on the total mass of the negative electrode current collector of the second battery cells is ≥40%. Thus, when the second battery cells continue to discharge at a lower voltage, the probability of oxidation of the negative electrode current collector of the second battery cells can be reduced, allowing the second battery cells to continue to discharge to a lower voltage, thereby improving the capacity of the second battery cells and, in turn, improving the capacity of the battery pack as a whole.

[0006] According to some embodiments of the present application, the metal accounts for 75% to 100% of the total mass of the negative electrode current collector of the second battery cell. Thus, by ensuring that the metal accounts for 75% to 100% of the total mass of the negative electrode current collector of the second battery cell within the above range, the probability of oxidation of the negative electrode current collector of the second battery cell when the second battery cell is discharged to a lower voltage is reduced.

[0007] According to some embodiments of the present application, the metal includes at least one of aluminum or titanium. Therefore, when the negative electrode potential of the second battery cell increases during discharge, the oxidation product of the aluminum or titanium has strong oxidation resistance, which can reduce the probability of corrosion caused by continued oxidation of the negative electrode current collector.

[0008] According to some embodiments of the present application, the lower limit voltage of the second battery cell is 1.0 V to 2.0 V. This allows the second battery cell to be used at a low voltage and reduces the probability of oxidation of the negative electrode current collector of the second battery cell.

[0009] According to some embodiments of the present application, the lower limit voltage of the first battery cell is V1, the number of the first battery cells is n1, the lower limit voltage of the second battery cell is V2, the number of the second battery cells is n2, and V1×n1+V2×n2≥200 V. Thus, when the first battery cell and the second battery cell are discharged to the lower limit voltage, a certain voltage can still be provided to start the motor.

[0010] According to some embodiments of the present application, n1:n2=0.125-8. Thus, by setting the ratio of n1 to n2 within the above range, when the first and second battery cells are discharged to the lower voltage limit, the plurality of first and second battery cells can still provide a certain voltage to start the motor.

[0011] According to some embodiments of the present application, the state of charge of the second battery cell when discharged to the lower voltage limit is smaller than the state of charge of the first battery cell when discharged to the lower voltage limit, thereby improving the capacity of the second battery cell.

[0012] According to some embodiments of the present application, the state of charge of the first battery cell when discharged to the lower voltage limit is 3%-20%; and / or the state of charge of the second battery cell when discharged to the lower voltage limit is 0%-10%. Thus, the capacity of the battery pack is improved.

[0013] According to some embodiments of the present application, the first battery cell includes at least one of a lithium-ion battery cell and a potassium-ion battery cell, and the second battery cell is different from the first battery cell and includes at least one of a sodium-ion battery cell, a zinc-ion battery cell, and a magnesium-ion battery cell. This increases the capacity of the battery pack.

[0014] The second aspect of the present application provides an electrical device, including the battery pack proposed in the first aspect of the present application.

[0015] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0017] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0018] FIG2 is an exploded view of the battery cell according to one embodiment of the present application shown in FIG1 .

[0019] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0020] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0021] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application.

[0022] FIG6 is a schematic diagram of an electrical device using a battery pack as a power source according to an embodiment of the present application.

[0023] Description of reference numerals:

[0024] 1 Battery pack; 2 Upper case; 3 Lower case; 4 Battery module; 5 First battery cell; 6 Second battery cell; 51 Casing; 52 First electrode assembly; 53 Cover plate. DETAILED DESCRIPTION

[0025] The following embodiments of the technical solution of the present application are described in detail. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only used as examples and are not intended to limit the scope of protection of the present application.

[0026] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0027] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0028] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0029] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating 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.

[0030] Currently, market developments indicate that batteries are increasingly being used. They are not only used in energy storage systems such as hydropower, thermal, wind, and solar power plants, but are also widely used in electric vehicles like electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. As battery applications continue to expand, market demand is also growing.

[0031] Sodium is abundant, widely distributed, and relatively low-cost, and shares a similar operating principle to lithium-ion batteries, making it a popular and widely studied element. However, during discharge, as the negative electrode potential of sodium-ion batteries increases, the negative electrode current collector is susceptible to continuous oxidation and corrosion, resulting in a high lower voltage limit for sodium-ion batteries. This makes the capacity in the low-voltage range unusable, reducing the battery's full capacity.

[0032] The present application proposes a battery pack comprising a plurality of first cells and a plurality of second cells. The metal on the negative electrode current collector of the second cell comprises at least one of aluminum, nickel, molybdenum, titanium, niobium, and iron, and the content of the aforementioned metal is limited. The oxidation products of the aforementioned metals have strong oxidation resistance, which can reduce the probability of corrosion caused by continuous oxidation of the negative electrode current collector, allowing the second cell to be discharged to a lower voltage for use, thereby improving the capacity of the second cell and, in turn, improving the overall capacity of the battery pack. The lower limit voltage of the first cell is greater than the lower limit voltage of the second cell. When the first cell and the second cell are discharged to the lower limit voltage, even if the lower limit voltage of the second cell is lower, the combination of the first cell and the second cell can provide sufficient voltage for starting the electrical device. In other words, the battery pack provided by the present application can, on the basis of improving the capacity of the second cell, output a corresponding voltage to start the electrical device according to the needs of the electrical device through the combination of the first cell and the second cell.

[0033] The battery pack proposed in this application can be used in various energy storage systems that use the battery pack as a power source or as an energy storage element. The electrical equipment may include, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, battery cars, electric cars, ships, spacecraft, etc. Among them, electric toys may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc.

[0034] In the first aspect of the present application, a battery pack is proposed, comprising a plurality of first battery cells, the lower limit voltage of the first battery cells being 2.5V-3.0V; and a plurality of second battery cells, the second battery cells being arranged in series with the first battery cells, the lower limit voltage of the second battery cells being ≤2.0V, wherein the negative electrode current collector of the second battery cells comprises a metal, the metal comprising at least one of aluminum, nickel, molybdenum, titanium, niobium, and iron, and the mass proportion of the metal based on the total mass of the negative electrode current collector of the second battery cells being ≥40%. Thus, when the second battery cells continue to discharge at a lower voltage, the probability of oxidation of the negative electrode current collector of the second battery cells can be reduced, allowing the second battery cells to continue to discharge to a lower voltage, thereby improving the capacity of the second battery cells and, in turn, improving the capacity of the battery pack as a whole.

[0035] In this application, the lower limit voltage refers to the lowest voltage at which the battery cell can be discharged.

[0036] The following is a detailed description of the principle by which this application can achieve the above beneficial effects:

[0037] The battery pack proposed in the present application includes a plurality of first battery cells and a plurality of second battery cells. After charging, the first battery cells and the second battery cells have different initial voltages (for example, the initial voltage of the first battery cell is 3.8V, and the initial voltage of the second battery cell is 3V). During discharge, the first battery cells and the second battery cells connected in series are discharged at the same rate. Due to the different initial voltages, the first battery cells and the second battery cells can be discharged to different lower limit voltages (for example, the lower limit voltage of the first battery cell is 2.8V, and the lower limit voltage of the second battery cell is 1V). After the first battery cells and the second battery cells are discharged to the lower limit voltage, the sum of the voltages of the plurality of first battery cells and the plurality of second battery cells is greater than or equal to the starting voltage of the motor to start the motor. In the present application, by making the metal on the negative electrode collector of the second battery cell include at least one of aluminum, nickel, molybdenum, titanium, niobium, and iron, and at the same time limiting the content of the above-mentioned types of metals, the products of the above-mentioned types of metals after oxidation have strong oxidation resistance, which can reduce the probability of the negative electrode collector being continuously oxidized and corroded, so that even when the second battery cell is discharged to a lower voltage, the probability of the metal on the negative electrode collector of the second battery cell being oxidized can be reduced, thereby further utilizing the capacity of the second battery cell at low voltage, improving the capacity of the second battery cell, and further improving the capacity of the battery pack.

[0038] The metal content of the negative electrode current collector in this application can be measured by inductively coupled plasma (ICP) spectroscopy. For example, reference can be made to standards YS / T 1006.2-2014, GB / T 23367.2-2009, or YS / T 1028.5-2015. Specifically, according to the embodiments of this application, an inductively coupled plasma optical emission spectrometer (equipment model: iCAP 7400) can be used for measurement according to the manufacturer's instructions. Specifically, for different types of current collector materials, the composition of each component is determined by ICP analysis.

[0039] In this application, the testing method for the lower limit voltage is: taking the second battery cell as an example, the second battery cell is discharged at 0.33C until the battery management system performs discharge protection, and the voltage values ​​of multiple second battery cells are recorded, and the average value is taken as the lower limit voltage of the second battery cell.

[0040] According to some embodiments of the present application, the negative electrode current collector of the second battery cell may be a metal foil, and the material forming the metal foil includes at least one of aluminum, nickel, molybdenum, titanium, niobium, and iron.

[0041] According to some embodiments of the present application, based on the total mass of the negative electrode current collector of the second battery cell, the mass proportion of the metal is ≥40%. For example, it can be 40%, 50%, 60%, 70%, 80%, 90% or 100%, or it can be a range composed of any of the above values. Thus, by making the content of the metal within the above range, the product after the oxidation of the above-mentioned type of metal has strong oxidation resistance, which can prevent the metal on the negative electrode current collector from being continuously oxidized and corroded, so that the second battery cell can be used at a lower lower voltage. By making the mass proportion of the above-mentioned metal ≥50%, when the negative electrode current collector includes other metals that are prone to corrosion, the mass proportion of the metal that is prone to corrosion can be reduced, further reducing the probability of corrosion on the negative electrode current collector. According to some embodiments of the present application, based on the total mass of the negative electrode current collector of the second battery cell, the mass proportion of the metal is 75%-100%.

[0042] According to some embodiments of the present application, the metal includes at least one of aluminum or titanium. As a result, when the negative electrode potential increases during discharge, aluminum is oxidized into Al2O3 and AlF3, and Ti is oxidized into TiO2. Al2O3, AlF3, and TiO2 have strong oxidation resistance, which can reduce the probability of further corrosion of the negative electrode current collector, thereby enabling the second battery cell to be used at a low voltage and thereby increasing the capacity of the second battery cell.

[0043] As an example, the negative electrode current collector of the second battery cell may be aluminum foil or titanium foil.

[0044] According to some embodiments of the present application, the negative electrode current collector of the second battery cell may also be a composite current collector, which may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate, and the material forming the metal layer includes at least one of aluminum, nickel, molybdenum, titanium, niobium, and iron.

[0045] As an example, the material forming the polymer material substrate includes at least one of polyamide, polyterephthalate, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, aramid, polyphenylene diamine, acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate, polyparaphenylene terephthalamide, polypropylene, polyformaldehyde, epoxy resin, phenolic resin, polytetrafluoroethylene, polyvinylidene fluoride, silicone rubber, polycarbonate, cellulose and its derivatives, starch and its derivatives, protein and its derivatives, polyvinyl alcohol and its crosslinked products, polyethylene glycol and its crosslinked products.

[0046] According to some embodiments of the present application, the thickness of the negative electrode current collector of the first battery cell (hereinafter referred to as the first negative electrode current collector) and the negative electrode current collector of the second battery cell (hereinafter referred to as the second negative electrode current collector) are independently 3μm-100μm, for example, 3μm, 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm or 100μm, etc., or can be a range consisting of any of the above values. According to some specific embodiments of the present application, the thickness of the first negative electrode current collector and the thickness of the second negative electrode current collector are independently 3μm-60μm.

[0047] The thickness of the negative electrode current collector in this application can be measured using a micrometer.

[0048] According to some embodiments of the present application, the lower limit voltage of the first battery cell may be 2.5V-3.0V. For example, it may be 2.5V, 2.6V, 2.7V, 2.8V, 2.9V or 3.0V, or a range consisting of any of the above values.

[0049] According to some embodiments of the present application, the lower limit voltage of the second battery cell is ≤2.0V. For example, it can be 2.0V, 1.8V, 1.6V, 1.4V, 1.2V, 1.0V, 0.8V, 0.6V, 0.4V, 0.2V or 0V, etc., or it can be a range composed of any of the above values. As a result, the capacity of the second battery cell at low voltage can be further utilized, thereby increasing the capacity of the second battery cell and further increasing the capacity of the entire battery pack. According to some specific embodiments of the present application, the lower limit voltage of the second battery cell can be 1.0V-2.0V.

[0050] According to some embodiments of the present application, the number of the first battery cells is n1, the number of the second battery cells is n2, and n1:n2 = 0.125-8. For example, it can be 0.125, 0.5, 1, 2, 3, 4, 5, 6, 7 or 8, or it can be a range consisting of any of the above values. Therefore, based on the lower limit voltage of the first battery cell and the second battery cell when discharging, the number of the first battery cell and the second battery cell in the battery pack can be designed so that the sum of the voltages of the multiple first battery cells and the sum of the voltages of the multiple second battery cells is greater than or equal to the starting voltage of the motor.

[0051] According to some embodiments of the present application, when the starting voltage of the motor is 200 V, the lower limit voltage of the first battery cell is V1, the number of the first battery cells is n1, the lower limit voltage of the second battery cell is V2, the number of the second battery cells is n2, and V1×n1+V2×n2≥200 V is satisfied. Thus, the motor can be started.

[0052] According to some embodiments of the present application, the state of charge of the second cell when discharged to the lower voltage limit is lower than the state of charge of the first cell when discharged to the lower voltage limit. For example, when the first cell is discharged to the lower voltage limit, the first cell has a state of charge of 20%, and when the second cell is discharged to the lower voltage limit, the second cell has a state of charge of 10%. This improves the overall capacity of the battery pack.

[0053] In this application, the state of charge refers to the ratio of the remaining capacity of a battery after it has been used for a period of time or has been left unused for a long time to its capacity in a fully charged state.

[0054] According to some embodiments of the present application, the state of charge of the first cell when discharged to the lower voltage limit can be 3%-20%; and / or the state of charge of the second cell when discharged to the lower voltage limit can be 0%-10%, thereby improving the overall capacity of the battery pack.

[0055] The state of charge (SOC) test method used in this application is as follows: Based on the battery's current voltage, discharge the battery to the lower voltage limit at the operating current specified in the battery specification. The resulting capacity is divided by the capacity when charged from the lower voltage limit to the upper voltage limit. For example, if the battery's operating voltage is 2.8V (lower voltage limit) - 3.65V (upper voltage limit), the battery is currently at 3.0V, and the operating rate is 0.33C. Discharge the battery from 3.0V to 2.8V at 0.33C, record Cn1, and then charge the battery from 2.8V to 3.65V to obtain the charge capacity Cn. Therefore, SOC = Cn1 / Cn * 100%.

[0056] According to some embodiments of the present application, the first battery cell includes at least one of a lithium ion battery cell and a potassium ion battery cell, and the second battery cell is different from the first battery cell, and the second battery cell includes at least one of a sodium ion battery cell, a zinc ion battery cell, and a magnesium ion battery cell.

[0057] As an example, the first battery cell is a lithium-ion battery cell, and the second battery cell is a sodium-ion battery cell. Thus, by making the metal on the negative electrode current collector of the sodium-ion battery cell include at least one of aluminum, nickel, molybdenum, titanium, niobium, and iron, and at the same time limiting the content of the above-mentioned types of metals, the products after the oxidation of the above-mentioned types of metals have strong oxidation resistance, which can reduce the probability of the negative electrode current collector being continuously oxidized and corroded, so that even when the sodium-ion battery cell is discharged to a lower voltage, the probability of the metal on the negative electrode current collector of the sodium-ion battery cell being oxidized can be reduced, thereby further utilizing the capacity of the sodium-ion battery cell at low voltage, improving the capacity of the sodium-ion battery cell, and then improving the capacity of the battery pack. At the same time, the battery pack proposed in this application includes multiple lithium-ion batteries and multiple sodium-ion batteries. After charging, the lithium-ion batteries and the sodium-ion batteries have different initial voltages. During discharge, the lithium-ion cells and sodium-ion cells connected in series are discharged at the same rate. Due to the different initial voltages, the lithium-ion cells and sodium-ion cells can be discharged to different lower limit voltages. After the lithium-ion cells and sodium-ion cells are discharged to the lower limit voltage, the sum of the voltages provided by multiple lithium-ion cells and the sum of the voltages provided by multiple sodium-ion cells can still start the motor.

[0058] The battery cells (including the first and second cells) include a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charge and discharge process of the battery cells, active ions are embedded and released back and forth between the positive and negative electrode sheets. The electrolyte conducts ions between the positive and negative electrode sheets. The separator is located between the positive and negative electrode sheets, primarily preventing a short circuit between the positive and negative electrodes while allowing ions to pass through.

[0059] [Positive electrode]

[0060] The positive electrode sheet (the positive electrode sheet of the first battery cell and the positive electrode sheet of the second battery cell) includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material.

[0061] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is provided on either or both of the two facing surfaces of the positive electrode current collector.

[0062] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0063] In some embodiments, when the first battery cell is a lithium-ion battery cell, the positive electrode active material may adopt the positive electrode active material for lithium-ion battery cells that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15 Al 0.05O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0064] In some embodiments, when the second battery cell is a sodium ion battery cell, as an example, the positive electrode active material may include, but is not limited to, at least one of a layered transition metal oxide, a polyanion compound, and a Prussian blue analog.

[0065] Examples of the layered transition metal oxides include:

[0066] Na 1-x Cu h Fe k Mn l M 1 m O 2-y , where M 1 One or more of Li, Be, B, Mg, Al, K, Ca, Ti, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, In, Sn and Ba, 0 <x≤0.33,0<h≤0.24,0≤k≤0.32,0<l≤0.68,0≤m<0.1,h+k+l+m=1,0≤y<0.2;

[0067] Na 0.67 Mn 0.7 Ni z M 2 0.3-z O2, where M 2 is one or more of Li, Mg, Al, Ca, Ti, Fe, Cu, Zn and Ba, 0 <z≤0.1;

[0068] Na a Li b Ni c Mn d Fe e O2, of which 0.67 <a≤1,0<b<0.2,0<c<0.3,0.67<d+e<0.8,b+c+d+e=1。

[0069] Examples of the polyanionic compound include:

[0070] A 1 f M 3 g (PO4)i O j X 1 3-j , where A 1 is one or more of H, Li, Na, K, and NH4, M 3 is one or more of Ti, Cr, Mn, Fe, Co, Ni, V, Cu, and Zn, X 1 is one or more of F, Cl, and Br, 0 < f ≤ 4, 0 < g ≤ 2, 1 ≤ i ≤ 3, 0 ≤ j ≤ 2;

[0071] Na n M 4 PO4X 2 , where M 4 is one or more of Mn, Fe, Co, Ni, Cu, and Zn, X 2 is one or more of F, Cl, and Br, 0 < n ≤ 2;

[0072] Na p M 5 q (SO4)3, where M 5 is one or more of Mn, Fe, Co, Ni, Cu, and Zn, 0 < p ≤ 2, 0 < q ≤ 2;

[0073] Na s Mn t Fe 3-t (PO4)2(P2O7), where 0 < s ≤ 4, 0 ≤ t ≤ 3, for example, t is 0, 1, 1.5, 2, or 3.

[0074] As examples of the above Prussian blue analogs, for example, the following can be listed:

[0075] A u M 6 v [M 7 [[ID=**57**]](CN)6] w ·xH2O, where A is H + , NH4 + , one or more of alkali metal cations and alkaline earth metal cations, M 6 and M 7 are each independently one or more of transition metal cations, 0 < u ≤ 2, 0 < v ≤ 1, 0 < w ≤ 1, 0 < x < 6. For example, A is H + , Li + , Na + , K + , NH4 + , Rb + , Cs + , Fr+ 、Be 2+ Mg 2+ , Ca 2+ 、Sr 2+ 、Ba 2+ and Ra 2+ One or more of M 6 and M 7 Each is independently a cation of one or more transition metal elements selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn and W.

[0076] The modified compounds of the above materials may be doping-modified and / or surface-coated modified materials.

[0077] In some embodiments, the positive electrode active material layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0078] In some embodiments, the positive electrode active material layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0079] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0080] [Negative electrode]

[0081] The negative electrode sheet (the negative electrode sheet of the first battery cell and the negative electrode sheet of the second battery cell) includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0082] As an example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is provided on either or both of the two facing surfaces of the negative electrode current collector.

[0083] In some embodiments, the negative electrode current collector of the first battery cell may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0084] In some embodiments, the specific configuration of the negative electrode current collector of the second battery cell refers to the configuration of the negative electrode current collector of the second battery cell described above, and will not be repeated here.

[0085] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and titanates. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. When the battery is a lithium-ion battery, lithium titanate is used as the titanate; when the battery is a sodium-ion battery, sodium titanate is used as the titanate. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0086] In some embodiments, the negative electrode active material layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0087] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0088] In some embodiments, the negative electrode active material layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0089] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0090] In some embodiments, the second battery cell may also include a second battery cell without a negative electrode. For example, taking the second battery cell as a sodium ion battery cell as an example, a sodium battery cell without a negative electrode means that during the manufacturing process of the second negative electrode plate, a negative electrode active material layer is not actively set on the second negative electrode current collector. For example, during the manufacturing process of the second negative electrode plate, a negative electrode active material layer is not set at the second negative electrode current collector through coating or deposition. During the first charge, the sodium ions obtain electrons on the negative electrode side and metallic sodium is deposited on the surface of the second negative electrode current collector to form a sodium metal phase. During discharge, the metallic sodium can be converted into sodium ions and return to the positive electrode plate to achieve cyclic charge and discharge. Compared with other sodium batteries, sodium batteries without a negative electrode can achieve higher energy density due to the lack of a negative electrode active material layer.

[0091] [Electrolytes]

[0092] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. This application has no specific restrictions on the type of electrolyte, and it can be selected according to needs.

[0093] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0094] In some embodiments, when the first battery cell is a lithium ion battery cell, the electrolyte salt in the lithium ion battery cell may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0095] In some embodiments of the present application, when the second battery cell is a sodium ion battery cell, the electrolyte sodium salt in the sodium ion battery cell may include at least one of sodium hexafluorophosphate, sodium difluorooxalatoborate, sodium tetrafluoroborate, sodium bisoxalatoborate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethylsulfonate or sodium bis(trifluoromethylsulfonyl)imide.

[0096] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0097] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve the overcharge performance of the battery cell, and additives that improve the high or low temperature performance of the battery cell.

[0098] [Isolation film]

[0099] In some embodiments, the battery cell further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0100] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0101] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0102] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the positive electrode sheet, the negative electrode sheet, and the electrolyte.

[0103] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a bag-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0104] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square, or any other shape. For example, FIG1 shows a first battery cell 5 (or second battery cell 6 ) of a square structure as an example.

[0105] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the first battery cell 5 (or the second battery cell 6) can be one or more, and those skilled in the art can select according to specific actual needs.

[0106] In some embodiments, the battery cells may be assembled into a battery module. The battery module may contain one or more battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0107] Figure 3 shows an example battery module 4. Referring to Figure 3 , in the battery module 4, a plurality of first cells 5 and second cells 6 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the plurality of first cells 5 and second cells 6 may be secured together using fasteners.

[0108] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of first battery cells 5 and second battery cells 6 are received in the receiving space.

[0109] In some embodiments, the number of battery modules included in the battery pack may be one or more, and those skilled in the art may select the specific number based on the application and capacity of the battery pack.

[0110] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0111] In addition, the present application also provides an electric device, which includes the battery pack provided in the present application. The battery pack can be used as a power source for the electric device, or as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0112] Figure 6 shows an example of an electric device. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the electric device, a battery pack can be used.

[0113] In order to make the technical problems, technical solutions and beneficial effects solved by the embodiments of the present application clearer, the following will be further described in detail with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0114] Example 1

[0115] 1. Prepare the first battery cell

[0116] 1.1 Preparation of the first positive electrode sheet

[0117] The lithium iron phosphate material, the conductive agent carbon black, and the binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in an N-methylpyrrolidone (NMP) solvent system in a weight ratio of 95:2.5:2.5 to obtain a positive electrode slurry. The positive electrode slurry is evenly coated on both surfaces of the first positive electrode current collector aluminum foil. After drying, cold pressing, and slitting, the first positive electrode sheet is obtained.

[0118] 1.2 Preparation of the first negative electrode sheet

[0119] The active material artificial graphite, the conductive agent carbon black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC-Na) are dissolved in the solvent deionized water in a weight ratio of 96.2:0.8:0.8:1.2, mixed evenly and prepared into a negative electrode slurry, and the negative electrode slurry is evenly coated on both surfaces of the first negative electrode current collector copper foil once or multiple times, and the first negative electrode sheet is obtained after drying, cold pressing and slitting.

[0120] 1.3 Preparation of electrolyte

[0121] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), the organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed uniformly in a volume ratio of 3:7, and LiPF6 was added thereto to obtain an electrolyte with a LiPF6 concentration of 1 mol / L.

[0122] 1.4 Isolation film

[0123] Polyethylene film.

[0124] 1.5 Preparation of the first battery cell

[0125] The first positive electrode sheet, separator, and first negative electrode sheet are stacked in sequence, with the separator positioned between the first positive and first negative electrodes to provide insulation. The cells are then wound to form a bare cell. The tabs are welded to the bare cell and placed in an aluminum shell. The cells are baked at 80°C to remove moisture, and then electrolyte is injected and sealed to produce an uncharged cell. The uncharged cell then undergoes a series of processes, including resting, hot and cold pressing, forming, shaping, and capacity testing, to produce the first cell.

[0126] 2. Prepare the second battery cell

[0127] 2.1 Preparation of the second positive electrode sheet

[0128] Sodium iron pyrophosphate, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are thoroughly stirred and mixed in an N-methylpyrrolidone (NMP) solvent system in a weight ratio of 95:2.5:2.5 to obtain a positive electrode slurry. The positive electrode slurry is evenly coated on both surfaces of the second positive electrode current collector aluminum foil, and after drying, cold pressing, and slitting, the second positive electrode sheet is obtained.

[0129] 2.2 Preparation of the second negative electrode sheet

[0130] The carbon nanotube dispersion is stirred into a negative electrode slurry with a viscosity range of 2000mPa·s-10000mPa·s, and the negative electrode slurry is evenly coated on both surfaces of the second negative electrode collector aluminum alloy. After drying, cold pressing and slitting, the second negative electrode sheet is obtained.

[0131] 2.3 Preparation of electrolyte

[0132] Equal volumes of ethylene glycol dimethyl ether (DME) and / or diethylene glycol dimethyl ether (DEGDME) are mixed to obtain an organic solvent, and then NaPF6 is dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0133] 2.4 Isolation Film

[0134] Polyethylene film.

[0135] 2.5 Preparation of the second battery cell

[0136] The second positive electrode sheet, separator, and second negative electrode sheet are stacked in sequence, with the separator positioned between the second positive and negative electrodes to provide insulation. The cells are then wound to form a bare cell. The tabs are welded to the bare cell and placed in an aluminum shell. The cells are baked at 80°C to remove moisture, and then electrolyte is injected and sealed to produce an uncharged cell. The uncharged cell then undergoes a series of processes, including resting, hot and cold pressing, forming, shaping, and capacity testing, to produce the second cell.

[0137] 3. Assemble the battery pack

[0138] The battery pack includes 6 battery modules, which are connected in series. Each battery module includes 6 first battery cells and 12 second battery cells.

[0139] The parameters of the battery packs in Examples 2 to 10, Comparative Examples 1 and 2 are the same as those in Example 1. The differences are detailed in Table 1.

[0140] Table 1

[0141] Performance Testing

[0142] (1) Test method for battery cell capacity

[0143] At 25°C, the prepared battery cell was charged at a constant current of 1C to the upper limit voltage, and then charged at a constant voltage of the upper limit voltage to a current of 0.05C. After standing for 5 minutes, the battery was discharged at a constant current of 1C to the lower limit voltage. This is a charge and discharge cycle process, and the capacity of the battery cell was recorded.

[0144] (2) Cyclic performance test

[0145] At 45°C, the prepared battery pack was charged at a constant current of 1C to the upper voltage limit. It was then charged at the upper voltage limit to a current of 0.05C. After standing for 5 minutes, the battery was discharged at a constant current of 1C to the lower voltage limit. This constitutes one charge-discharge cycle, and the discharge capacity is the discharge capacity after the first cycle. The battery was cycled 500 times in this manner. The capacity retention rate of the battery after 500 cycles = discharge capacity after 500 cycles / discharge capacity after the first cycle.

[0146] (3) Calculation method of battery pack capacity (full charge design)

[0147] Battery pack capacity (fully charged design) = capacity of the first battery cell × number of first battery cells in a single battery module + capacity of the second battery cell × number of second battery cells in a single battery module.

[0148] (4) Calculation method of battery pack capacity (usage performance)

[0149] Battery pack capacity (usage performance) = capacity of first cell × (1 - state of charge of first cell when discharged to the lower voltage limit) × number of first cells + capacity of second cell × (1 - state of charge of second cell when discharged to the lower voltage limit) × number of second cells.

[0150] (5) Calculation method of power utilization rate

[0151] Power utilization rate = (battery pack capacity (usage performance) / battery pack capacity (full charge design)) × 100%.

[0152] (6) Calculation method of battery pack voltage

[0153] Battery pack voltage = (number of first cells in a single battery module × lower limit voltage of the first cells + number of second cells in a single battery module × lower limit voltage of the second cells) × number of battery modules.

[0154] The test results of the battery packs in Examples 1 to 10, Comparative Example 1 and Comparative Example 2 are shown in Table 2.

[0155] Table 2

[0156] Conclusion: It can be seen from Table 2 that the present application can reduce the probability of oxidation of the negative electrode collector of the second battery cell by making the mass proportion of metal in the negative electrode collector of the second battery cell ≥40%, thereby improving the battery capacity and improving the battery cycle capacity retention rate.

[0157] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A battery pack, wherein: include: A plurality of first battery cells, wherein the lower limit voltage of the first battery cells is 2.5V-3.0V; A plurality of second battery cells, wherein the second battery cells and the first battery cells are arranged in series, and the lower limit voltage of the second battery cells is ≤2.0V, wherein: The negative electrode current collector of the second battery cell includes metal, and the metal includes at least one of aluminum, nickel, molybdenum, titanium, niobium, and iron. Based on the total mass of the negative electrode current collector of the second battery cell, the mass of the metal accounts for ≥40%.

2. The battery pack according to claim 1, wherein: Based on the total mass of the negative electrode current collector of the second battery cell, the mass of the metal accounts for 75%-100%.

3. The battery pack according to claim 1 or 2, wherein: The metal includes at least one of aluminum or titanium.

4. The battery pack according to claim 3, wherein: The lower limit voltage of the second battery cell is 1.0V-2.0V.

5. The battery pack according to claim 1, wherein: The lower limit voltage of the first battery cell is V1, the number of the first battery cells is n1, the lower limit voltage of the second battery cell is V2, the number of the second battery cells is n2, and V1×n1+V2×n2≥200V is satisfied.

6. The battery pack according to claim 5, wherein: n1:n2=0.125-8.

7. The battery pack according to claim 3, wherein: The state of charge of the second battery cell when discharged to the lower limit voltage is smaller than the state of charge of the first battery cell when discharged to the lower limit voltage.

8. The battery pack according to claim 7, wherein: The state of charge of the first battery cell when discharged to the lower limit voltage is 3%-20%; and / or the state of charge of the second battery cell when discharged to the lower limit voltage is 0%-10%.

9. The battery pack according to claim 1, wherein: The first battery cell includes at least one of a lithium ion battery cell and a potassium ion battery cell. The second battery cell is different from the first battery cell. The second battery cell includes at least one of a sodium ion battery cell, a zinc ion battery cell, and a magnesium ion battery cell.

10. An electrical device, wherein: A battery pack comprising the battery pack according to any one of claims 1 to 9.

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