Secondary batteries and electrical equipment

Abstract

The present invention provides a secondary battery and an electric device, the secondary battery including a positive electrode sheet and a negative electrode sheet, the CB value, the charge energy and the discharge energy of the secondary battery satisfy the relationship of 0.74≦(W2 / W1)*CB≦1.03, so that the secondary battery has a higher energy density, a longer cycle life and better storage performance.

Description

[Technical Field]

[0001] This application claims priority from a Chinese patent application filed with the China Patent Office on October 27, 2022, bearing application number 202211327756.8 and titled "Secondary Battery and Electrical Device," the entire contents of which are incorporated herein by reference.

[0002] The present application relates to the technical field of energy storage devices, and in particular to secondary batteries and electrical equipment. [Background technology]

[0003] New energy vehicles are setting the trend for the development of the global automotive industry. Secondary batteries are a new type of high-voltage, high-energy density rechargeable battery, with excellent characteristics such as light weight, high energy density, pollution-free, no memory effect, and long life, and are widely used in new energy vehicles and energy storage technology fields. Currently, lithium-ion secondary batteries are widely used in pure electric vehicles (PEVs) and plug-in hybrid vehicles (HEVs). Considering the service life of a vehicle, battery life poses serious challenges. Existing lithium-ion batteries are increasingly unable to meet the demand for longer vehicle ranges. Therefore, how to further improve the cycle performance of batteries has become an important technological challenge in the research and development of secondary batteries. Summary of the Invention [Means for solving the problem]

[0004] The present application provides a secondary battery and an electrical device that aim to solve the problems of poor cycle life and storage performance of existing secondary batteries.

[0005] In one embodiment, a secondary battery is provided, the secondary battery including a positive electrode sheet and a negative electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode film sheet disposed on at least one surface of the positive electrode current collector, the positive electrode film sheet including a positive electrode active material. The negative electrode sheet includes a negative electrode current collector and a negative electrode film sheet disposed on at least one surface of the negative electrode current collector, the negative electrode film sheet including a negative electrode active material. The secondary battery satisfies 0.74≦(W2 / W1)*CB≦1.03, where W1 is the charge energy of the secondary battery, W2 is the discharge energy of the secondary battery, and W1 and W2 are expressed in watt-hours. CB is the ratio of the capacity per unit area of ​​the negative electrode sheet to the capacity per unit area of ​​the positive electrode sheet.

[0006] Furthermore, the secondary battery satisfies 0.92≦W2 / W1. Furthermore, the range of CB is 0.8≦CB≦1.08. Furthermore, the positive electrode active material is Li x A y Fe (1-y) PO4, where 0.8≦x≦1.2, 0≦y<1, and the element A includes one or more of nickel, cobalt, manganese, magnesium, calcium, barium, titanium, and vanadium.

[0007] Furthermore, the positive electrode sheet includes a positive electrode membrane sheet, and the negative electrode sheet includes a negative electrode membrane sheet, where the area of ​​the positive electrode membrane sheet is S1m 2 and the area of ​​the negative electrode film sheet is S2m 2 and S1 and S2 satisfy S1 / S2≦0.995. Furthermore, the capacity per gram of the positive electrode active material is 130 to 159 mAh / g, and the areal density of the positive electrode membrane sheet is 150 to 600 g / m 2 is. Furthermore, S1 / S2 and W2 / W satisfy S1 / S2≧W2 / W1.

[0008] Furthermore, the secondary battery further includes an electrolyte solution, the electrolyte solution including an organic solvent, the organic solvent including an unsaturated carbonate and / or a sulfur-oxygen double bond compound, the unsaturated carbonate including vinylene carbonate and / or vinylethylene carbonate, and the sulfur-oxygen double bond compound including one or more of 1,3-propane sultone, ethylene sulfate, 1,4-butane sultone, ethylene sulfite, and methylenemethane disulfonate.

[0009] Furthermore, based on the weight of the electrolyte, when the content of the unsaturated carbonate is a % and the content of the sulfur-oxygen double bond compound is b %, the secondary battery satisfies one or more of the following characteristics: (I) 0.1≦a+b≦7. (II) 0.1≦a / b≦10. (III) 0.05≦a≦3. (IV) 0.05≦b≦4. (V) 0.06≦a / CB≦3.75. (VI) 0.06≦b / CB≦5.0.

[0010] Furthermore, the actual CB' value of the secondary battery is 1.10 to 1.30, where CB and CB' satisfy 0.88≦CB*CB'≦1.375. On the other hand, an embodiment of the present application further provides an electrical device that uses the secondary battery according to any one of the above embodiments as a power supply.

[0011] Compared with the prior art, the present application provides a secondary battery and an electrical device, the secondary battery including a positive electrode sheet and a negative electrode sheet, and the secondary battery satisfies 0.74≦(W2 / W1)*CB≦1.03, and the above relationship is satisfied between the CB value of the battery, the charge energy, and the discharge energy, so the secondary battery has a higher energy density, a longer cycle life, and better storage performance. DETAILED DESCRIPTION OF THE INVENTION

[0012] The following clearly and completely describes the technical solutions according to the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, and are not all of the embodiments. Based on the embodiments of the present application, all other embodiments that can be obtained by those skilled in the art without any creative efforts belong to the scope of the claims of the present application.

[0013] This embodiment provides a secondary battery including a positive electrode sheet and a negative electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode film sheet disposed on at least one surface of the positive electrode current collector, the positive electrode film sheet including a positive electrode active material. The negative electrode sheet includes a negative electrode current collector and a negative electrode film sheet disposed on at least one surface of the negative electrode current collector, the negative electrode film sheet including a negative electrode active material. The secondary battery satisfies 0.74≦(W2 / W1)*CB≦1.03, where W1 is the charge energy of the secondary battery, W2 is the discharge energy of the secondary battery, and W1 and W2 are expressed in watt-hours. CB is the ratio of the capacity per unit area of ​​the negative electrode sheet to the capacity per unit area of ​​the positive electrode sheet. In this embodiment, the relationship between the CB value and the charge and discharge energy of the battery has a significant impact on the performance of the battery. When the charge energy W1, discharge energy W2, and CB value of the secondary battery satisfy the relationship 0.74≦(W2 / W1)*CB≦1.03, the secondary battery has good cycle performance, fast charging capability, and higher energy density, thereby providing the secondary battery with both higher energy efficiency and longer cycle life.

[0014] According to some embodiments of the present application, the capacity per gram of the positive electrode active material is 130 to 159 mAh / g, and the areal density of the positive electrode membrane sheet is 150 to 600 g / m 2 Preferably, the capacity per gram of the positive electrode active material may be any of 133 mAh / g, 135 mAh / g, 143 mAh / g, 145 mAh / g, 153 mAh / g, 155 mAh / g, and 158 mAh / g, or may be in a range consisting of any two of these values. The areal density of the positive electrode membrane sheet is 155 g / m 2 , 200 g / m 2 , 255 g / m 2 , 300 g / m 2, 355 g / m 2 , 400 g / m 2 , 455 g / m 2 , 500 g / m 2 , 555 g / m 2 or may be any value between any two of the above values. If the capacity per gram of the positive electrode active material is too small, it will affect the energy density of the secondary battery. If the capacity per gram of the positive electrode active material is too large, it will affect the stability of the positive electrode active material, resulting in poor stability and affecting the cycle life of the secondary battery. If the areal density of the positive electrode membrane sheet is too small, it will affect the energy density of the secondary battery. If the areal density of the positive electrode membrane sheet is too large, it will poorly function as a secondary battery's system kinetics, resulting in poor cycle life. Therefore, by appropriately determining the capacity per gram of the positive electrode active material and the areal density of the positive electrode membrane sheet according to this embodiment, higher electron conductivity performance can be ensured and the positive electrode sheet can be provided with a higher capacity utilization rate, which is advantageous for the kinetic performance, cycle performance, storage performance, and energy density of the battery.

[0015] In some embodiments of the present application, the capacity per gram of the negative electrode active material is 260 to 380 mAh / g. For example, the capacity per gram of the negative electrode active material may be any value of 265 mAh / g, 270 mAh / g, 275 mAh / g, 280 mAh / g, 285 mAh / g, 290 mAh / g, 295 mAh / g, 300 mAh / g, 315 mAh / g, 325 mAh / g, 335 mAh / g, 345 mAh / g, 355 mAh / g, 365 mAh / g, or 375 mAh / g, or may be in a range consisting of any two of these values.

[0016] The surface density of the negative electrode film sheet is 80 to 290 g / m 2 and the surface density of the negative electrode film sheet is 90 g / m 2 , 100g / m 2 , 110g / m 2 , 120g / m 2 , 130g / m 2 , 140g / m 2, 150g / m 2 , 160g / m 2 , 170g / m 2 , 180g / m 2 , 190g / m 2 , 200g / m 2 , 210g / m 2 , 220g / m 2 , 230g / m 2 , 240g / m 2 , 250g / m 2 , 260g / m 2 , 270g / m 2 , 280g / m 2 , 285g / m 2 , 288g / m 2 or may be any value between any two values. In some embodiments of the present application, the secondary battery satisfies 0.92≦W2 / W1, and the range of CB is 0.8≦CB≦1.08. By further limiting the ranges of W2 / W1 and CB, the energy efficiency can be ensured and the cycle life and storage performance of the secondary battery can be further improved. In this embodiment, W2 / W1 is 1.15 or less.

[0017] In some embodiments of the present application, the actual CB' value of the secondary battery is 1.10 to 1.30. Here, CB and CB' satisfy the relationship 0.88≦CB*CB'≦1.375, which on the one hand ensures that lithium deposition does not occur during charging of the secondary battery, thereby extending the cycle life and storage performance of the secondary battery. On the other hand, it also prevents the presence of a large amount of excess lithium-implanted vacancies in the negative electrode during operation of the secondary battery. Note that CB here is the design CB value, and CB' is the practical CB value.

[0018] In some embodiments of the present application, the molecular formula of the positive electrode active material is Li x A y Fe (1-y) PO4, where 0.8≦x≦1.2 and 0≦y<1. The element A includes one or more of nickel, cobalt, manganese, magnesium, calcium, barium, titanium, and vanadium. For example, the positive electrode active material is LiFePO4, LiFe0.97 Co 0.03 PO4, LiFe 0.98 Ti 0.02 PO4, LiFe 0.995 Mg 0.005 PO4, LiFe 0.99 Mn 0.01 Contains one or more of PO4.

[0019] In some embodiments of the present application, the element A accounts for 0% to 36% of the total weight of the positive electrode active material. For example, the proportion of the element A in the total weight of the positive electrode active material may be any of 1%, 5%, 9%, 11%, 15%, 19%, 21%, 25%, 29%, 31%, and 35%, or may be in a range consisting of any two of these values. The inclusion of the element A in the positive electrode active material can improve the voltage platform and energy density of the secondary battery.

[0020] In some embodiments of the present application, the positive electrode membrane sheet further comprises an adhesive, a conductive agent, and a dispersant, where the positive electrode active material content is 80% to 99%, the adhesive content is 1% to 6%, the conductive agent content is 0% to 20%, and the dispersant content is 0% to 8% based on the weight of the positive electrode membrane sheet. This ensures the energy density of the secondary battery, improves the kinetics of the secondary battery system, balances the lithium desorption rate of the positive and negative electrode sheets, suppresses excessive expansion of the negative electrode sheet during the lithium intercalation process, reduces the loss of active lithium, and improves the cycle life.

[0021] In some embodiments, the adhesive agent is PVDF, the conductive agent is a carbon material such as carbon black, and the dispersant is PVP (polymethylpyrrolidone). Therefore, when the positive and negative electrode sheets contain active materials in the above capacity per gram range and the secondary battery satisfies 0.74≦(W2 / W1)*CB≦1.03, the positive and negative electrode sheets can be more effectively matched, resulting in a secondary battery with higher capacity and improved capacity retention during storage and cycling, as well as improved electronic conductivity of the positive electrode sheet and power performance of the battery, resulting in a secondary battery with higher energy density, cycle performance, storage performance, and kinetic performance.

[0022] In this embodiment, the area of ​​the positive electrode membrane sheet is S1m 2 and the area of ​​the negative electrode film sheet is S2m 2 where S1 and S2 satisfy the relationship S1 / S2≦0.995. For example, S1 / S2 may be any of the following values: 0.702, 0.902, 0.922, 0.945, 0.955, 0.965, 0.975, and 0.985, or may be within a range consisting of any two values. If S1 and S2 satisfy this relationship, sufficient lithium vacancies can be secured in the negative electrode sheet during secondary battery operation, preventing lithium deposition due to a lack of lithium-embedded vacancies in the negative electrode sheet during charging, and improving the cycle stability of the secondary battery. In this embodiment, the S1 / S2 value is 0.70 or greater. If the S1 / S2 value is less than 0.70, the capacity utilization rate of the battery will be affected.

[0023] In some embodiments, S1 / S2 and W2 / W satisfy S1 / S2≧W2 / W1. By limiting the area ratio between the positive electrode film sheet and the negative electrode film sheet and the ratio between the discharge energy and the charge energy of the battery within the above ranges, the energy density and energy efficiency of the secondary battery can be effectively balanced, ensuring the energy efficiency and improving the energy density of the secondary battery.

[0024] In another embodiment, the secondary battery further comprises an electrolyte, the electrolyte comprising an organic solvent, the organic solvent comprising an unsaturated carbonate and / or a sulfur-oxygen double bond compound, the unsaturated carbonate comprising vinylene carbonate and / or vinylethylene carbonate, and the sulfur-oxygen double bond compound comprising one or more of 1,3-propane sultone, ethylene sulfate, 1,4-butane sultone, ethylene sulfite, and methylenemethane disulfonate.

[0025] Furthermore, the content of the unsaturated carbonate is a%, the content of the sulfur-oxygen double bond compound is b%, and the secondary battery satisfies one or more of the following characteristics: (I) 0.1≦a+b≦7. (II) 0.1≦a / b≦10. (III) 0.05≦a≦3. (IV) 0.05≦b≦4. (V) 0.06≦a / CB≦3.75. (VI) 0.06≦b / CB≦5.0.

[0026] The value of a+b may be any of 0.15, 0.55, 1.5, 1.55, 2.5, 2.55, 3.5, 3.55, 4.5, 4.55, and 7, or may be within a range consisting of any two values. Here, if the value of a+b is within the range of 0.1 to 5, the energy efficiency of the secondary battery can be improved while ensuring the battery's lifespan.

[0027] The value of a / b may be any of 1.2, 2, 2.2, 3, 3.2, 4, 4.2, 5, 5.2, 6, 6.2, 7, 7.2, 8, 8.2, 9, and 9.2, or may be within a range consisting of any two values. Here, if the value of a / b is within the range of 0.1 to 10, the energy efficiency of the secondary battery can be improved while ensuring the lifespan.

[0028] The value of a may be any of 0.15, 0.55, 1, 1.15, 1.55, 2, 2.15, 2.55, 2.85, and 2.95, or may be within a range consisting of any two values. Here, if the value of a is within the range of 0.1 to 3, the energy efficiency of the secondary battery can be improved while ensuring the lifespan.

[0029] The value of b may be any of 0.15, 0.55, 1, 1.15, 1.55, 2, 2.15, 2.55, 3.15, 3.55, 3.85, and 3.95, or may be within a range consisting of any two values. Here, if the value of b is within the range of 0.1 to 4, the energy efficiency of the secondary battery can be improved while ensuring the lifespan.

[0030] In one embodiment, the value of a / CB may be any one of 0.06, 0.15, 0.55, 1.5, 1.55, 2.5, 2.55, 2.65, 2.75, 2.85, 2.95, 3, and 3.75, or may be in a range consisting of any two values. Here, when the value of a / CB is in the range of 0.06 to 3.75, the energy efficiency of the secondary battery can be improved while ensuring the lifespan.

[0031] The value of b / CB may be any of 0.15, 0.55, 1.5, 1.55, 2.5, 2.55, 3.5, 3.55, 4.1, 4.15, 4.2, 4.25, and 5.0, or may be within a range consisting of any two values. Here, if the value of b / CB is within the range of 0.06 to 5, the energy efficiency of the secondary battery can be improved while ensuring the lifespan.

[0032] In this embodiment, the positive and negative electrode sheets are immersed in an electrolyte, and lithium ions travel back and forth between the positive and negative electrode sheets using the electrolyte as a medium, thereby achieving battery charging and discharging. To prevent the positive and negative electrodes from shorting due to the electrolyte, a separator is required to separate the positive and negative electrode sheets. The secondary battery may be in the form of, for example, an aluminum case or a SoftBank battery. The separator may be selected from polyethylene film, polypropylene film, polyvinylidene fluoride film, and multilayer composite films thereof.

[0033] The present invention will be described in more detail below with reference to specific examples, but it should be understood that these examples do not limit the scope of the claims of the present invention.

[0034] Example 1 The provided method for manufacturing a secondary battery includes the following steps. 1) The positive electrode sheet, the separator, and the negative electrode sheet are stacked in this order so that the separator is disposed between the positive electrode sheet and the negative electrode sheet to serve as an insulator. 2) The positive electrode sheet, the separator, and the negative electrode sheet are wound together to obtain a core body. 3) The core body is placed in a packaging case, and the electrolyte is injected into the packaging case. After vacuum packaging, leaving it to stand, chemical conversion, molding, and other processes, a secondary battery is obtained.

[0035] Regarding the production of positive electrode sheets The positive electrode active material LiFePO4, conductive agent SP, adhesive agent PVDF, and dispersant PVP are uniformly mixed in NMP in a weight ratio of 97:0.7:2.2:0.1 to form a positive electrode slurry. The positive electrode slurry is coated on two surfaces of an aluminum foil positive electrode current collector, which is then dried, cold-pressed, divided, and cut to obtain a positive electrode sheet.

[0036] Regarding the production of negative electrode sheets The negative electrode active material graphite, conductive agent SP, dispersant CMC, and adhesive SBR are mixed uniformly with water in a weight ratio of 96.3:0.7:1.1:1.9 to form a uniform negative electrode slurry. The negative electrode slurry is then coated onto both surfaces of the negative electrode current collector copper foil. After division and cutting, negative electrode sheets are obtained.

[0037] Regarding the production of electrolyte The organic solvents ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a 1:1:1 mass ratio. In an argon-atmosphere glove box with a water content of <10 ppm, thoroughly dried LiPF6 lithium salt was dissolved in the organic solvent, and vinylene carbonate (VC) and 1,3-propane sultone (PS) were added and mixed uniformly to obtain the electrolyte. The VC content was 1.5% of the total electrolyte weight, and PS was 2% of the total electrolyte weight. The LiPF6 concentration in the electrolyte was 1 mol / L. Regarding the separator, a polyethylene (PE) separator or a polypropylene (PP) separator is used.

[0038] About the measurement 1. Measurement of battery energy efficiency value W2 / W1 (1) Charge the secondary battery to its nominal capacity at a constant current of 1C, and let the charging energy be W1. (2)Stand for 30min. (3) Discharge to the lower voltage limit (2.5V) at a constant current of 1C, and let the discharge energy be W2. Here, the secondary battery energy efficiency value is W2 / W1.

[0039] 2. Measurement of the excess capacity factor CB value of secondary batteries [Measurement of positive electrode reversible capacity] The single-sided coated positive electrode sheet was cut into a 14 mm diameter circular sheet, weighed, and subtracted from the mass of the positive electrode current collector to determine the mass Mc of the positive electrode film sheet, measured in mg. A button cell was assembled in a glove box using a small circular lithium metal sheet as the counter electrode and the electrolyte prepared above. After standing at 25°C for 6 hours, the cell was charged to 4.25 V at a constant current of 0.1 C, then charged to 4.25 V at a constant current of 0.05 C, then allowed to stand for 5 minutes, and discharged to 2.8 V at a constant current of 0.1 C. The discharge capacity was measured in mAh.

[0040] [Measurement of negative electrode reversible capacity] The one-sided coated negative electrode sheet was cut into a 14 mm diameter circular sheet, weighed, and subtracted from the mass of the negative electrode current collector to determine the mass Ma of the negative electrode film sheet, expressed in mg. A button battery was assembled in a glove box, using a small circular lithium metal sheet as the counter electrode and the above-prepared electrolyte. After leaving the battery at 25°C for 6 hours, it was discharged to 5 mV at a constant current of 0.1 C, then discharged to 5 mV at a constant current of 0.01 C, left for 5 minutes, and charged to 0.7 V at a constant current of 0.1 C. The charge capacity was expressed in Ca, expressed in mAh. After determining the discharge capacity Cc of the positive electrode and the charge capacity Ca of the negative electrode, the excess capacity coefficient CB of the battery is calculated by the formula CB=Ca / Cc.

[0041] 3. Measurement of cycle life of secondary batteries At 25°C, the lithium ion secondary batteries manufactured in the examples and comparative examples were charged at a constant capacity of 1C to their nominal capacity, and then discharged at 1C to 2.5V. Cycle measurements were performed until the capacity of the lithium ion secondary batteries was reduced to 80% of the initial capacity, and the number of cycles was recorded.

[0042] 4. Measurement of storage life of secondary batteries At 25°C, the lithium-ion secondary batteries manufactured in the examples and comparative examples were charged to their nominal capacity at 1C and discharged to 2.5V at 1C to determine the initial capacity of the battery. After fully charging the battery at 1C, the battery was stored in a thermostatic box at 60°C until the capacity of the lithium-ion secondary battery had decayed to 80% of the initial capacity, and the number of days of storage was recorded.

[0043] 5. Measurement of lithium deposition in batteries At 25°C, the lithium-ion secondary batteries manufactured in the examples and comparative examples were charged at a constant rate of 1C to their nominal capacity and then fully discharged at 1C to 2.5V. After repeating this 10 times, the lithium-ion secondary batteries were fully charged at 1C to their nominal capacity, and then the negative electrode sheet was removed and the flatness and surface lithium deposition of the negative electrode sheet were observed. Here, if the area of ​​the lithium deposition region on the negative electrode surface was 1% or more but less than 5%, it was considered to be mild lithium deposition; if the area of ​​the lithium deposition region on the negative electrode surface was 5% to 40%, it was considered to be moderate lithium deposition; and if the area of ​​the lithium deposition region on the negative electrode surface was more than 40%, it was considered to be severe lithium deposition.

[0044] Examples 2 to 21, Comparative Examples 1 to 3 The manufacturing and performance measurement processes of the secondary battery were the same as in Example 1, except that the parameters of the electrode sheet during the manufacturing process were adjusted to manufacture secondary batteries with different performance. Specifically, the different parameters of the electrode sheet are shown in Table 1.

[0045] Examples 22 to 35 The manufacturing and performance measurement processes for the secondary battery were the same as in Example 1, except that the additive parameters during the manufacturing process were adjusted to manufacture secondary batteries with different performance. Specifically, the different electrolyte parameters are shown in Table 2.

[0046] Here, different CB values ​​are controlled by adjusting the coating weight of the positive electrode slurry and the negative electrode slurry. Different CB' values ​​are controlled by adjusting the charging capacity of the secondary battery. Different positive electrode membrane sheet areas S1 and S2 are obtained by adjusting the coating areas of the positive electrode slurry and the negative electrode slurry on the current collector. Different unsaturated carbonate contents (a%) and different sulfur-oxygen double bond compound contents (b%) are obtained by adjusting the amounts of ethylene carbonate and 1,3-propane sultone added.

[0047] The parameters and measurement results for the secondary batteries of Examples 1 to 35 and Comparative Examples 1 to 3, which were manufactured based on the above methods, are listed in Tables 1 to 3, where the value of K in Table 1 represents K=(W2 / W1)*CB.

[0048] [Table 1] TIFF0007727823000002.tif14170

[0049] [Table 2]

[0050] [Table 3]

[0051] As shown in Tables 1-3 for Examples 1-35 and Comparative Examples 1-3, when K=(W2 / W1)*CB is within the range of 0.74-1.03 and the CB value is within the range of 0.8-1.08, the secondary battery positive electrode contains sufficient lithium to replenish the active lithium lost during operation, and the battery exhibits good cycle life, storage performance, and kinetic performance. When K is within the range of 0.84-0.95, the battery exhibits superior cycle life and storage performance. When K is less than 0.74 or greater than 1.03, the battery's cycle performance and storage performance are significantly reduced, and moderate lithium deposition occurs.

[0052] As shown in Examples 7 to 11 in Tables 1 to 3, as the practical CB value, CB', increases from 1.1 to 1.3, the cycle and storage life of the secondary battery tend to initially increase and then decrease. This is due to the fact that as CB' increases, the depth of lithium desorption from the negative electrode decreases during secondary battery operation, reducing the expansion of the negative electrode and the resulting new interfaces. This reduces the consumption of active lithium to form SEI at the new interfaces, thereby increasing the battery life. However, if CB' is too large, the negative electrode active material content is too high, increasing the number of interfaces, and the resulting SEI formation at the interfaces increases the consumption of active lithium, which in turn decreases the cycle and storage life.

[0053] As shown in Examples 17 to 21 in Tables 1 to 3, doping a small amount of Ti, Co, Mg, Ni, or Mn into the positive electrode material increases both the cycle and storage life of the secondary battery. This is because the doping of these elements improves the voltage platform of the secondary battery, slightly worsens the system kinetics of the secondary battery, and reduces the rate of side reactions during the charge and discharge process, thereby slightly improving the cycle and storage performance.

[0054] Since the values ​​of K (i.e., (W2 / W1)*CB) of the batteries of Comparative Examples 1 to 3 in Table 1 are not within the range (0.74 to 1.03), the cycle life, storage life, and kinetic performance of the battery cannot be simultaneously achieved. Therefore, the secondary battery of this example can achieve both high energy efficiency and long life. As shown in the data in Tables 2 and 3, the addition of unsaturated carbonates and sulfur-oxygen double bond compounds can further improve the overall performance of the secondary battery, and the performance is even better when both unsaturated carbonates and sulfur-oxygen double bond compounds are contained in the battery.

[0055] This embodiment further provides an electric device, which includes the secondary battery according to any one of the above embodiments, and the secondary battery is used as a power supply for the electric device, which may be, but is not limited to, a mobile device (e.g., a mobile phone, a laptop, etc.), an electric vehicle (e.g., an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), a train, a ship, a satellite, an energy storage system, etc. Although the secondary battery and electrical device according to the embodiments of the present application have been described in detail above and the principles and embodiments of the present application have been described in detail using specific examples in the specification, the description of the above embodiments is only used to facilitate understanding of the technical solutions and inventive ideas of the present application. Those skilled in the art may make amendments to the technical solutions described in the above embodiments or changes to some of the technical features therein, but it should be understood that such amendments and changes do not deviate from the essence of the technical solutions in the embodiments of the present application.

Claims

1. A secondary battery, It includes a positive electrode sheet and a negative electrode sheet, the positive electrode sheet includes a positive electrode current collector and a positive electrode film sheet disposed on at least one surface of the positive electrode current collector, the areal density of the positive electrode film sheet being 150 to 600 g / m 2 , the positive electrode film sheet including a positive electrode active material, the content of the positive electrode active material in the positive electrode film sheet being 80% to 99%, the positive electrode active material including LixAyFe(1-y)PO 4 , where 0.8≦X≦1.2 and 0≦y<1 are satisfied, the A element includes one or more of nickel, cobalt, manganese, magnesium, calcium, barium, titanium, and vanadium, and the capacity per gram of the positive electrode active material is 130 to 159 mAh / g; the negative electrode sheet includes a negative electrode current collector and a negative electrode film sheet disposed on at least one surface of the negative electrode current collector, the negative electrode film sheet including a negative electrode active material, the negative electrode active material including graphite, The secondary battery has a temperature of 0.74≦(W ２ / W １ ) *CB≦1.03 is satisfied, Here, W １ is the charging energy of the secondary battery, and W ２ is the discharge energy of the secondary battery, and W １ and W ２ is expressed in watt-hours, CB is the ratio of the charge capacity per unit area of ​​the negative electrode sheet to the discharge capacity per unit area of ​​the positive electrode sheet, The area of ​​the positive electrode film sheet is S 1 m 2 , the area of ​​the negative electrode film sheet is S 2 m 2 , S 1 and S 2 satisfy S 1 / S 2 ≦0.995; A secondary battery characterized by:

2. The secondary battery has a W ２ / W １ fulfill, 2. The secondary battery according to claim 1 .

3. The range of CB is 0.8≦CB≦1.

08.

2. The secondary battery according to claim 1 .

4. S １ / S ２ and W ２ / W １ is S １ / S ２ ≧W ２ / W １ fulfill, 2. The secondary battery according to claim 1 .

5. The secondary battery further includes an electrolyte solution, the electrolyte solution includes an organic solvent, and the organic solvent includes an unsaturated carbonate and a sulfur-oxygen double bond compound; the unsaturated carbonate includes at least one of vinylene carbonate and vinyl ethylene carbonate, The sulfur-oxygen double bond compound includes one or more of 1,3-propane sultone, ethylene sulfate, 1,4-butane sultone, ethylene sulfite, and methylenemethane disulfonate; 2. The secondary battery according to claim 1 .

6. Based on the weight of the electrolyte, the content of the unsaturated carbonate is a %, the content of the sulfur-oxygen double bond compound is b %, and the secondary battery is (I) 0.1≦a+b≦7, (II) 0.1≦a / b≦10, (III) 0.05≦a≦3, (IV) 0.05≦b≦4, (V) 0.06≦a / CB≦3.75, (VI) 0.06≦b / CB≦5.0, Satisfy one or more of the above characteristics 6. The secondary battery according to claim 5.

7. The actual CB' value of the secondary battery is 1.10 to 1.30, and CB and CB' satisfy 0.88≦CB*CB'≦1.

375.

2. The secondary battery according to claim 1 .

8. An electrical device, The secondary battery according to any one of claims 1 to 7 is included, and the secondary battery is used as a power supply for the electrical device. An electrical device characterized by:

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