Secondary battery and electric equipment

Abstract

The embodiment of the invention provides a secondary battery and electric equipment, the secondary battery provided by the embodiment of the invention comprises a roll core and an electrolyte, the roll core comprises a positive pole piece, a diaphragm and a negative pole piece which are stacked in sequence; the mass of the electrolyte which can be accommodated by 0.85-0.95 time of the sum of the pore volume of the diaphragm, the pore volume of the positive pole piece and the pore volume of the negative pole piece in the roll core is determined as the total electrolyte retention capacity of the secondary battery, so that the electrolyte supply requirements in the charge-discharge cycle process and the storage process of the secondary battery are met; the lithium precipitation risk at the two sides of the roll core is reduced, the capacity retention ratio of the secondary battery cycle is improved, and the cycle life and storage performance of the secondary battery are further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary battery manufacturing, in particular to a secondary battery and an electrical device. Background Art

[0002] Cylindrical batteries are one of the development trends of core components of new energy electric vehicles. Due to their advantages such as high energy density, high safety performance and high consistency, they have received widespread attention in the industry.

[0003] Electrolyte is an important component of cylindrical batteries, which not only affects the initial performance of cylindrical batteries, but also has an important impact on the long-term stability and life of cylindrical batteries. At present, in order to ensure that cylindrical batteries can maintain good performance during long-term use, high electrolyte retention design is generally adopted in the industry.

[0004] However, the shell of a cylindrical battery is relatively strong, and the expansion force of the core during the charge and discharge cycle is not enough to cause the shell to expand significantly. During the charge and discharge cycle, the cylindrical battery cannot expand outward due to the constraints of the shell, but expands inward, which reduces the porosity of the positive and negative electrode sheets and the porosity of the diaphragm, and reduces the electrolyte that can be stored in the positive and negative electrode sheets and the diaphragm. When the electrolyte retention volume is high, a large amount of electrolyte in the porosity of the positive and negative electrode sheets and the diaphragm is squeezed out and concentrated on both sides of the core during the charge and discharge cycle, making the electrolyte concentration on both sides of the core high, which is prone to lithium precipitation problems, and then leads to an accelerated decline in the battery cycle capacity retention rate, seriously affecting the battery cycle life. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a secondary battery and an electrical device to solve the problem that the cycle capacity retention rate and cycle life of the existing high-liquid-retention cylindrical battery decrease due to lithium deposition on both sides of the winding core.

[0006] In order to solve the above problems, the present invention is achieved through the following technical solutions:

[0007] The present invention provides a secondary battery, comprising a winding core and an electrolyte, wherein the winding core comprises a positive electrode sheet, a separator and a negative electrode sheet stacked in sequence; the secondary battery satisfies the following conditions when in a 0% SOC state:

[0008] 0.85×(V0 / 1000)×ρ≤m≤0.95×(V0 / 1000)×ρ,

[0009] Wherein, mg represents the liquid retention capacity of the secondary battery;

[0010] V0mm 3represents the total volume of the pores in the winding core; the total volume of the pores in the winding core is the sum of the pore volume of the separator, the pore volume of the positive electrode sheet and the pore volume of the negative electrode sheet;

[0011] ρg / cm 3 represents the density of the electrolyte.

[0012] Furthermore, in the secondary battery, the ratio between the pore volume of the negative electrode plate and the pore volume of the separator is 3.2 to 7.4.

[0013] Furthermore, in the secondary battery, the ratio of the pore volume of the negative electrode plate to the pore volume of the positive electrode plate is 1.2 to 4.3.

[0014] Furthermore, in the secondary battery, the porosity of the separator is 30% to 60%.

[0015] Furthermore, in the secondary battery, the porosity of the positive electrode sheet is 15% to 50%.

[0016] Furthermore, in the secondary battery, the positive electrode plate includes a positive electrode current collector, and a first positive electrode film layer and a second positive electrode film layer disposed on two opposite surfaces of the positive electrode current collector;

[0017] Wherein, the porosity of the first positive electrode film layer is 15% to 50%, and the porosity of the second positive electrode film layer is 15% to 50%.

[0018] Furthermore, in the secondary battery, the absolute value of the difference between the porosity of the first positive electrode film layer and the porosity of the second positive electrode film layer is 0-5%.

[0019] Furthermore, in the secondary battery, the porosity of the negative electrode plate is 30% to 60%.

[0020] Furthermore, in the secondary battery, the negative electrode plate includes a negative electrode current collector, and a first negative electrode film layer and a second negative electrode film layer disposed on two opposite surfaces of the negative electrode current collector;

[0021] Wherein, the porosity of the first negative electrode film layer is 30% to 60%, and the porosity of the second negative electrode film layer is 30% to 60%.

[0022] Furthermore, in the secondary battery, the absolute value of the difference between the porosity of the first negative electrode film layer and the porosity of the second negative electrode film layer is 0-5%.

[0023] Furthermore, in the secondary battery, the density of the electrolyte is 1.1 g / cm 3 ~1.5g / cm3 .

[0024] Furthermore, the secondary battery comprises a shell, and the shell is a columnar structure.

[0025] The present invention further provides an electric device, which includes the above-mentioned secondary battery, and the secondary battery serves as a power supply for the electric device.

[0026] Compared with the prior art, the embodiments of the present invention have the following advantages:

[0027] In the embodiment of the present invention, the liquid retention volume of the provided secondary battery under the 0% SOC state is less than the electrolyte that can be accommodated by the sum of the pore volume of the diaphragm in the core, the pore volume of the positive electrode sheet and the pore volume of the negative electrode sheet, and the mass of the electrolyte that can be accommodated by 0.85 times to 0.95 times the sum of the pore volume of the diaphragm in the core, the pore volume of the positive electrode sheet and the pore volume of the negative electrode sheet is determined as the total liquid retention volume of the secondary battery. While meeting the electrolyte replenishment needs during the charge and discharge cycle and storage process of the secondary battery, during the charge and discharge cycle of the secondary battery, due to the inward expansion due to the constraint of the shell, only a small amount of electrolyte or even no electrolyte is squeezed out to the positions on both sides of the core, so that the electrolyte concentration at the positions on both sides of the core is basically the same as the electrolyte concentration at other positions of the secondary battery, and the polarization is also basically the same, which reduces the risk of lithium plating at the positions on both sides of the core, improves the capacity retention rate of the secondary battery cycle, and thereby improves the cycle life and storage performance of the secondary battery.

[0028] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic diagram of a roll core structure of a secondary battery provided by an embodiment of the present invention;

[0030] Figure 2 is a schematic structural diagram of another secondary battery provided by an embodiment of the present invention;

[0031] Figure 3 is a schematic structural diagram of a diaphragm provided by an embodiment of the present invention;

[0032] Figure 4 It is a structural schematic diagram of a positive electrode sheet provided by an embodiment of the present invention;

[0033] Figure 5 It is a schematic diagram of the structure of a negative electrode plate provided in an embodiment of the present invention.

[0034] Description of reference numerals:

[0035] 10-winding core; 100-diaphragm; 101-negative electrode plate; 1011-negative electrode current collector; 1012-first negative electrode film layer; 1013-second negative electrode film layer; 102-positive electrode plate; 1021-positive electrode current collector; 1022-first positive electrode film layer; 1023-second positive electrode film layer; 201-negative electrode current collector plate; 202-cover plate; 203-shell; 204-positive electrode current collector plate; 205-insulating gasket; 206-positive electrode column. DETAILED DESCRIPTION

[0036] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] The applicant of the present invention has found that since the shell of a cylindrical secondary battery has high strength and the expansion force of the winding core during the charge and discharge cycle is insufficient to cause significant expansion of the shell, in addition, the gas production of the cylindrical secondary battery during formation or normal use is limited and will not cause significant expansion of the shell; therefore, during the charge and discharge cycle, the cylindrical secondary battery cannot expand outward due to the constraint of the shell, but expands inward, which reduces the porosity of the positive electrode sheet, the porosity of the negative electrode sheet and the porosity of the diaphragm, and reduces the amount of electrolyte that can be stored in the positive electrode sheet, the negative electrode sheet and the diaphragm. When the electrolyte retention volume in a cylindrical secondary battery is high, a large amount of electrolyte in the positive electrode sheet, negative electrode sheet and separator is squeezed out and concentrated on both sides of the core during the charge and discharge cycle, making the electrolyte concentration on both sides of the core higher than the electrolyte concentration at other positions of the cylindrical secondary battery, which increases the polarization at both sides of the core and is prone to lithium precipitation, which in turn leads to an accelerated decrease in the battery cycle capacity retention rate, especially under high-rate fast charging conditions, where lithium precipitation will quickly occur at both sides of the core, causing a sharp drop in the capacity retention rate of the cylindrical secondary battery, seriously affecting the cycle life of the cylindrical secondary battery. When the electrolyte retention volume of a cylindrical secondary battery is low, during the charge and discharge cycle and storage process, the cylindrical secondary battery cannot be effectively replenished with electrolyte in a timely manner, resulting in problems such as lithium precipitation, decreased capacity retention rate, and low storage capacity during the charge and discharge cycle, affecting the cycle life and storage performance of the cylindrical secondary battery.

[0038] In order to solve the above problems, the embodiment of the present invention provides a secondary battery. Figure 1 The secondary battery comprises a winding core 10 and an electrolyte, wherein the winding core 10 comprises a positive electrode sheet 102, a separator 100 and a negative electrode sheet 101 stacked in sequence; the secondary battery satisfies the following conditions when in a 0% SOC (State of Charge):

[0039] 0.85×(V0 / 1000)×ρ≤m≤0.95×(V0 / 1000)×ρ (1)

[0040] Wherein, mg represents the liquid content of the secondary battery; V0 mm 3 Represents the total volume of pores in the winding core 10; the total volume of pores in the winding core 10 is the sum of the pore volume of the separator 100, the pore volume of the positive electrode sheet 102, and the pore volume of the negative electrode sheet 101; ρg / cm 3 Indicates the density of the electrolyte.

[0041] In an embodiment of the present invention, the secondary battery is a cylindrical secondary battery.

[0042] The total volume of the pores in the winding core 10 refers to the sum of the pore volume of the separator 100, the pore volume of the positive electrode sheet 102, and the pore volume of the negative electrode sheet 101 in the winding core 10; specifically, when the pore volume of the separator 100 is V1, the pore volume of the positive electrode sheet 102 is V2, and the pore volume of the negative electrode sheet 101 is V3:

[0043] V0=V1+V2+V3 (2)

[0044] When the electrolyte is injected into the winding core 10 , the electrolyte will fill the pores of the diaphragm 100 , the pores of the positive electrode sheet 102 , and the pores of the negative electrode sheet 101 , so as to realize the timely replenishment of the electrolyte during the charge and discharge process of the secondary battery and ensure the performance and storage performance of the secondary battery.

[0045] It should be noted that the positive electrode sheet 102 includes a positive electrode current collector and a positive electrode film layer disposed on the positive electrode current collector, and the pore volume of the positive electrode sheet 102 refers to the volume of the pores in the positive electrode film layer disposed on the positive electrode current collector. The negative electrode sheet 101 includes a negative electrode current collector and a negative electrode film layer disposed on the negative electrode current collector, and the pore volume of the negative electrode sheet 101 refers to the volume of the pores in the negative electrode film layer disposed on the negative electrode current collector.

[0046] It can be understood that (V0 / 1000)×ρ in Formula 1 represents the mass of the electrolyte contained in the total volume of the pores in the core 10. In the embodiment of the present invention, the liquid retention of the secondary battery is set within this relationship range, and while meeting the electrolyte replenishment requirements during the charge and discharge cycle and storage process of the secondary battery, too much electrolyte will not be injected into the core 10. In the case of inward expansion during the charge and discharge cycle of the secondary battery, only a small amount of electrolyte or even no electrolyte is squeezed out to the two sides of the core 10, so that the electrolyte concentration at the two sides of the core 10 is basically the same as the electrolyte concentration at other positions of the secondary battery, and the polarization is also basically the same, which reduces the risk of lithium plating at the two sides of the core 10, improves the capacity retention rate of the secondary battery cycle, and thus improves the cycle life and storage performance of the secondary battery.

[0047] In some embodiments, the liquid retention capacity m of the secondary battery can be a range value of one or any two of 0.85×(V0 / 1000)×ρ, 0.87×(V0 / 1000)×ρ, 0.89×(V0 / 1000)×ρ, 0.91×(V0 / 1000)×ρ, 0.93×(V0 / 1000)×ρ and 0.95×(V0 / 1000)×ρ.

[0048] In the embodiment of the present invention, the electrolyte comprises an organic solvent, an electrolyte lithium salt and an additive, which is obtained by mixing the above substances in a certain proportion under certain conditions and stirring them fully. It is understandable that by adjusting the proportion and type of the organic solvent, the electrolyte lithium salt and the additive, electrolytes of different densities can be prepared.

[0049] After the electrolyte is injected into the secondary battery, it is left to stand for soaking before the first charge and discharge. The secondary battery is sealed and weighed to determine the amount of electrolyte retained in the secondary battery.

[0050] Reference Figure 2 The secondary battery provided by the embodiment of the present invention includes a winding core 10, a negative electrode current collecting disk 201, a negative electrode, a cover plate 202, a shell 203, a positive electrode current collecting disk 204, an insulating gasket 205 and a positive electrode column 206.

[0051] Among them, the winding core 10 includes a positive electrode sheet 102, a separator 100 and a negative electrode sheet 101 stacked in sequence; empty foil is left on both sides of the positive electrode sheet 102 and the negative electrode sheet 101 as electrode ears, and the positive electrode sheet 102, the separator 100 and the negative electrode sheet 101 are stacked and wound in sequence to form the winding core 10.

[0052] The housing 203 is a columnar housing.

[0053] The housing 203 is a cylindrical housing.

[0054] The tab of the negative electrode plate 101 is connected to the negative electrode current collecting disk 201 , the negative electrode current collecting disk 201 is connected to the cover plate 202 , and the cover plate 202 is connected to the shell 203 , so that the negative electrode plate 101 is electrically connected.

[0055] The pole ear of the positive electrode plate 102 is connected to the positive current collecting disk 204, and the positive current collecting disk 204 is connected to the positive electrode column 206, so as to realize the electrical connection and conduction of the positive electrode plate 102; wherein, the positive current collecting disk 204 and the shell 203 are insulated by the insulating gasket 205, and the positive electrode column 206 and the shell 203 are also insulated by the insulating gasket 205.

[0056] Optionally, in some embodiments, the ratio between the pore volume of the negative electrode plate 101 and the pore volume of the separator 100 is 3.2 to 7.4.

[0057] Specifically:

[0058]

[0059] In the embodiment of the present invention, the volume of the pores in the negative electrode film layer disposed on the negative electrode current collector in the negative electrode plate 101 and the volume of the pores in the diaphragm 100 can be adjusted so that the ratio between the pore volume of the negative electrode plate 101 and the pore volume of the diaphragm 100 satisfies 3.2 to 7.4.

[0060] The pore volume of the negative electrode sheet 101 can be adjusted by adjusting the ratio between the negative electrode active material and the conductive agent in the negative electrode film layer, the content of the binder in the negative electrode film layer, the coating speed, coating thickness, coating uniformity of the negative electrode film layer, the drying temperature and drying time of the negative electrode film layer, and the compaction pressure.

[0061] Accordingly, the pore volume of the diaphragm 100 can be adjusted by adjusting the constituent materials, stretching process, film forming process, heat treatment process, chemical treatment process, etc. of the diaphragm 100 .

[0062] In the embodiment of the present invention, the ratio between the pore volume of the negative electrode plate 101 and the pore volume of the diaphragm 100 is set to 3.2 to 7.4, which can ensure that the negative electrode plate 101 has a good electrolyte infiltration effect, and the lithium-ion battery shuttles between the diaphragm and the negative electrode plate more smoothly, thereby improving the performance of the secondary battery. In some embodiments, the ratio between the pore volume of the negative electrode plate 101 and the pore volume of the diaphragm 100 can be 3.2, 3.4, 3.6, 3.8, 4.0, 4.2, 4.4, 4.6, 4.8, 5.0, 5.2, 5.4, 5.6, 5.8, 6.0, 6.2, 6.4, 6.6, 6.8, 7.0, 7.2 and 7.4, or any two of the range values.

[0063] Optionally, in some embodiments, the ratio between the pore volume of the negative electrode plate 101 and the pore volume of the positive electrode plate 102 is 1.2 to 4.3.

[0064] Specifically:

[0065]

[0066] In the embodiment of the present invention, the volume of the pores in the negative electrode film layer disposed on the negative electrode current collector in the negative electrode plate 101 and the volume of the pores in the positive electrode film layer disposed on the positive electrode current collector in the positive electrode plate 102 can be adjusted so that the ratio between the pore volume of the negative electrode plate 101 and the pore volume of the positive electrode plate 102 satisfies 1.2 to 4.3.

[0067] The pore volume of the negative electrode sheet 101 can be adjusted by adjusting the ratio between the negative electrode active material and the conductive agent in the negative electrode film layer, the content of the binder in the negative electrode film layer, the coating speed, coating thickness, coating uniformity of the negative electrode film layer, the drying temperature and drying time of the negative electrode film layer, and the compaction pressure.

[0068] Accordingly, the pore volume of the positive electrode sheet 102 can be adjusted by adjusting the ratio of the positive electrode active material to the conductive agent and the adhesive in the positive electrode film layer, the coating speed, coating thickness, coating uniformity of the positive electrode film layer, the drying temperature and drying time of the positive electrode film layer, and the compaction pressure.

[0069] In the embodiment of the present invention, the ratio between the pore volume of the negative electrode plate 101 and the pore volume of the positive electrode plate 102 is set to 1.2 to 4.3, which can ensure that the negative electrode plate 101 has a good electrolyte infiltration effect, and at the same time ensure that the electric field distribution of the battery is uniform during the deintercalation process, thereby improving the performance of the secondary battery. In some embodiments, the ratio between the pore volume of the negative electrode plate 101 and the pore volume of the positive electrode plate 102 can be 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, 4.0 and 4.3, or any two of the range values.

[0070] Optionally, in some embodiments, the porosity of the diaphragm 100 is 30% to 60%; illustratively, the porosity of the diaphragm 100 can be a range of one or any two of 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58% and 60%.

[0071] The porosity of the diaphragm 100 refers to the ratio between the pore volume of the diaphragm 100 and the volume of the diaphragm 100 .

[0072] Specifically, refer to Figure 3 , when the length of the diaphragm 100 is L0, the width is W0, and the thickness is H0, the porosity S of the diaphragm 100 is:

[0073]

[0074] Here, S represents the porosity of the separator 100 .

[0075] It can be understood that the porosity of the diaphragm 100 directly affects the absorption capacity of the diaphragm 100 for the electrolyte. Appropriate porosity can ensure that the electrolyte fully infiltrates the diaphragm 100, improve the ion conduction efficiency, reduce the internal resistance of the secondary battery, and facilitate the rapid transmission of ions in the secondary battery. At the same time, the porosity of the diaphragm 100 is also closely related to the mechanical strength of the diaphragm 100. The embodiment of the present invention sets the porosity range of the diaphragm 100 to 30% to 60%. While ensuring the mechanical strength of the diaphragm 100, it also improves the absorption capacity of the diaphragm 100 for the electrolyte.

[0076] Optionally, in some embodiments, the porosity of the positive electrode plate 102 is 15% to 50%; illustratively, the porosity of the positive electrode plate 102 can be a range of one or any two of 15%, 17%, 19%, 21%, 23%, 25%, 27%, 29%, 31%, 33%, 35%, 37%, 39%, 41%, 43%, 45%, 47% and 50%.

[0077] In the embodiment of the present invention, the positive electrode plate 102 includes a positive electrode collector and a positive electrode film layer arranged on the positive electrode collector; the positive electrode collector is generally an aluminum foil or a composite current collector. It can be understood that in order to ensure the conductivity of the current collector, the density of the aluminum foil and the density of the conductive layer in the composite current collector are generally high. In the embodiment of the present invention, it is assumed that the positive electrode collector does not have the ability to absorb the electrolyte, and the porosity of the positive electrode film layer in the positive electrode plate 102 can be determined as the porosity of the positive electrode plate 102.

[0078] It can be understood that the porosity of the positive electrode plate 102 is related to the energy density and cycle life of the secondary battery; a higher porosity of the positive electrode plate 102 can provide more active sites, which is beneficial to the infiltration of the electrolyte and the transmission of ions, thereby improving the energy density and cycle life of the secondary battery; in the embodiment of the present invention, the porosity of the positive electrode plate 102 is determined to be 15% to 50%, which can not only ensure the stability and reliability of the secondary battery, but also improve the infiltration effect of the electrolyte, thereby improving the energy density and cycle life of the secondary battery.

[0079] Optionally, refer to Figure 4 The positive electrode sheet 102 includes a positive electrode current collector 1021, and a first positive electrode film layer 1022 and a second positive electrode film layer 1023 arranged on two opposite surfaces of the positive electrode current collector 1021; wherein the porosity of the first positive electrode film layer 1022 is 15% to 50%, and the porosity of the second positive electrode film layer 1023 is 15% to 50%.

[0080] The length of the first positive electrode film layer 1022 is L 11 , width W 11 , thickness is H 11In the case of a for:

[0081]

[0082] Among them, X a represents the porosity of the first positive electrode film layer 1022; V 21 represents the pore volume of the first positive electrode film layer 1022 .

[0083] Accordingly, when the length of the second positive electrode film layer 1023 is L 12 , width W 12 , thickness is H 12 In the case of b for:

[0084]

[0085] Among them, X b V represents the porosity of the second positive electrode film layer 1023; 22 represents the pore volume of the second positive electrode film layer 1023, then the pore volume of the positive electrode sheet V2=V 21 +V 22 =X a ×L 11 ×W 11 ×H 11 +X b ×L 12 ×W 12 ×H 12 .

[0086] Optionally, in some embodiments, the absolute value of the difference between the porosity of the first positive electrode film layer 1022 and the porosity of the second positive electrode film layer 1023 is 0-5%, so that both the first positive electrode film layer 1022 and the second positive electrode film layer 1023 achieve optimal electrolyte infiltration effect, thereby improving the performance of the secondary battery; exemplarily, the absolute value of the difference between the porosity of the first positive electrode film layer 1022 and the porosity of the second positive electrode film layer 1023 can be a range value of one or any two of 0, 1%, 2%, 3%, 4% and 5%.

[0087] Specifically, the absolute value of the difference between the porosity of the first positive electrode film layer 1022 and the porosity of the second positive electrode film layer 1023 can be expressed as:

[0088] |X a -X b |≤5% (8)

[0089] Among them, |X a -X b| represents the absolute value of the difference between the porosity of the first positive electrode film layer 1022 and the porosity of the second positive electrode film layer 1023. In the present embodiment, the difference between the porosity of the first positive electrode film layer 1022 and the porosity of the second positive electrode film layer 1023 is within the above range, indicating that the porosity of the first positive electrode film layer 1022 and the porosity of the second positive electrode film layer 1023 are highly consistent, so that the first positive electrode film layer 1022 and the second positive electrode film layer 1023 have similar resistivity and ion transfer rate, avoiding large differences in ion deintercalation rate and electrochemical reaction on both sides of the positive electrode plate during the cycle process, thereby improving the cycle performance of the battery.

[0090] In the embodiment of the present invention, the length L of the first positive electrode film layer 1022 is 11 The length L of the second positive electrode film layer 1023 12 They may be equal or unequal, and this is not limited in the embodiment of the present invention.

[0091] Optionally, in some embodiments, the width W of the first positive electrode film layer 1022 is 11 The width W of the second positive electrode film layer 1023 12 are equal, and the thickness H of the first positive electrode film layer 1022 is 11 The thickness H of the second positive electrode film layer 1023 is 12 equal.

[0092] Optionally, in some embodiments, the porosity of the negative electrode plate 101 is 30% to 60%; illustratively, the porosity of the negative electrode plate 101 can be a range of one or any two of 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58% and 60%.

[0093] In the embodiment of the present invention, the negative electrode plate 101 includes a negative electrode current collector and a negative electrode film layer arranged on the negative electrode current collector; the negative electrode current collector is generally a copper foil or a composite current collector. It can be understood that in order to ensure the conductivity of the current collector, the density of the copper foil and the density of the conductive layer in the composite current collector are generally high. In the embodiment of the present invention, it is assumed that the negative electrode current collector does not have the ability to absorb the electrolyte, and the porosity of the negative electrode film layer in the negative electrode plate 101 can be determined as the porosity of the negative electrode plate 101.

[0094] It can be understood that the porosity of the negative electrode plate 101 is related to the discharge capacity and cycle life of the secondary battery. In the embodiment of the present invention, the porosity of the negative electrode plate 101 is determined to be 30% to 60%, which can improve the discharge capacity of the secondary battery while ensuring the stability and cycle life of the secondary battery.

[0095] Optionally, refer to Figure 5The negative electrode sheet 101 includes a negative electrode current collector 1011, and a first negative electrode film layer 1012 and a second negative electrode film layer 1013 arranged on two opposite surfaces of the negative electrode current collector 1011; wherein the porosity of the first negative electrode film layer 1012 is 30% to 60%, and the porosity of the second negative electrode film layer 1013 is 30% to 60%.

[0096] The length of the first negative electrode film layer 1012 is L 21 , width W 21 , thickness is H 21 In the case of a for:

[0097]

[0098] Among them, Y a represents the porosity of the first negative electrode film layer 1012; V 31 represents the pore volume of the first negative electrode film layer 1012 .

[0099] Accordingly, when the length of the second negative electrode film layer 1013 is L 22 , width W 22 , thickness is H 22 In the case of b for:

[0100]

[0101] Among them, Y b represents the porosity of the second negative electrode film layer 1013; V 32 represents the pore volume of the second negative electrode film layer 1013, then the pore volume of the negative electrode sheet V3=V 31 +V 32 =Y a ×L 21 ×W 21 ×H 21 +Y b ×L 22 ×W 22 ×H 22 .

[0102] Optionally, in some embodiments, the absolute value of the difference between the porosity of the first negative electrode film layer 1012 and the porosity of the second negative electrode film layer 1013 is 0-5%, so that both the first negative electrode film layer 1012 and the second negative electrode film layer 1013 achieve optimal electrolyte infiltration effect, thereby improving the performance of the secondary battery; exemplarily, the absolute value of the difference between the porosity of the first negative electrode film layer 1012 and the porosity of the second negative electrode film layer 1013 can be a range value of one or any two of 0, 1%, 2%, 3%, 4% and 5%.

[0103] Specifically, the absolute value of the difference between the porosity of the first negative electrode film layer 1012 and the porosity of the second negative electrode film layer 1013 can be expressed as:

[0104] |Y a -Y b |≤5% (11)

[0105] Among them, |Y a -Y b | represents the absolute value of the difference between the porosity of the first negative electrode film layer 1012 and the porosity of the second negative electrode film layer 1013. In the present embodiment, the difference between the porosity of the first negative electrode film layer 1012 and the porosity of the second negative electrode film layer 1013 is within the above range, indicating that the porosity of the first negative electrode film layer 1012 and the porosity of the second negative electrode film layer 1013 are highly consistent, so that the first negative electrode film layer 1012 and the second negative electrode film layer 1013 have similar resistivity and ion transfer rate, avoiding large differences in ion insertion and extraction rates and electrochemical reactions on both sides of the negative electrode plate during the cycle process, which is beneficial to reducing local lithium deposition on the negative electrode plate. In the embodiment of the present invention, the length L of the first negative electrode film layer 1012 is 21 The length L of the second negative electrode film layer 1013 22 They may be equal or unequal, and this is not limited in the embodiment of the present invention.

[0106] Optionally, in some embodiments, the width W of the first negative electrode film layer 1012 is 21 The width W of the second negative electrode film layer 1013 22 are equal, and the thickness H of the first negative electrode film layer 1012 is 21 The thickness H of the second negative electrode film layer 1013 is 22 equal.

[0107] Optionally, in some embodiments, the density of the electrolyte is 1.1 g / cm 3 ~1.5g / cm 3 ; For example, the density of the electrolyte can be 1.1 g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 and 1.5g / cm 3 When the density of the electrolyte is within the above range, the penetration rate of the electrolyte and the electromotive force of the secondary battery can be increased, which is beneficial to increase the capacity of the secondary battery.

[0108] Optionally, in some embodiments, the diaphragm 100 includes a base film and a coating disposed on at least one surface of the base film, wherein the base film includes at least one of polyethylene (PE), polypropylene (PP), and cellulose; and the coating includes at least one of a ceramic coating and an adhesive layer.

[0109] Optionally, in some embodiments, the adhesive layer includes at least one of acrylic resin and polyurethane resin.

[0110] Optionally, in some embodiments, the thickness of the base film is 0.003 mm to 0.03 mm. The base film thickness within the above range can ensure that the diaphragm has both high mechanical strength and excellent ion transfer efficiency, which has a positive impact on the safety performance and cycle performance of the battery; in some implementations, the thickness of the coating is 1 μm to 10 μm. The coating thickness within the above range can ensure that the diaphragm has strong adhesion or thermal stability.

[0111] The positive electrode sheet 102 includes a positive electrode current collector 1021 and a positive electrode film layer disposed on the positive electrode current collector 1021. The positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes a lithium ion transition metal oxide. The lithium ion transition metal oxide includes at least one of lithium cobalt oxide, lithium manganese oxide, and nickel cobalt lithium manganese oxide.

[0112] Optionally, in one embodiment, the positive electrode plate 102 further includes a conductive agent and a binder, and the conductive agent may include at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene. The binder includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

[0113] In some embodiments, the positive electrode sheet comprises a positive electrode active material, and the positive electrode active material comprises a lithium transition metal oxide of Ni, Mn and Co.

[0114] In some embodiments, the molar ratio of Ni in the lithium transition metal oxide to the total amount of metal elements other than Li is 75% to 95%. The molar ratio of Ni within the above range can increase the energy density of the battery and improve the battery life.

[0115] In some embodiments, the molar ratio of Ni in the lithium transition metal oxide to the total amount of metal elements other than Li is 80% to 92%. In some embodiments, the molar ratio of Ni in the lithium transition metal oxide to the total amount of metal elements other than Li is 88% to 91%.

[0116] In some embodiments, the average particle size of the lithium transition metal oxide is 5 to 15 μm, for example, 5 μm, 8 μm, 10 μm, 12 μm, or 15 μm. The average particle size of the lithium transition metal oxide within the above range is conducive to improving the compaction density of the positive electrode sheet, and at the same time can ensure that the positive electrode sheet has a suitable porosity, thereby improving the electrochemical performance of the battery.

[0117] In some embodiments, the positive electrode sheet 102 is prepared as follows: the components for preparing the positive electrode sheet 102, such as the positive electrode active material, 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 both sides of a positive electrode collector 1021 such as aluminum foil; after baking, rolling, cutting, striping and other processes, the positive electrode sheet 102 can be obtained.

[0118] The secondary battery provided by the embodiment of the present invention further includes a negative electrode plate 101 , a separator 100 and an electrolyte.

[0119] Among them, the negative electrode plate 101 includes a negative electrode current collector 1011 and a negative electrode film layer arranged on the negative electrode current collector 1011. The above-mentioned negative electrode film layer can adopt negative electrode active materials used for batteries, for example, selected from metal negative electrode materials or non-metallic negative electrode materials; the metal negative electrode material is preferably metal foil or alloy compound such as metallic sodium, sodium alloy, tin, antimony, etc.; the non-metallic negative electrode material is preferably any one of hard carbon, soft carbon, graphite, and silicon oxide, or a combination of at least two of them.

[0120] In some embodiments, the negative electrode sheet 101 is prepared as follows: the components for preparing the negative electrode sheet 101, such as the negative electrode active material, binder and conductive agent, are dispersed in a solvent such as deionized water to form a negative electrode slurry; the negative electrode slurry is coated on both sides of a negative electrode collector 1011 such as copper foil; after baking, rolling, cutting, striping and other processes, the negative electrode sheet 101 can be obtained.

[0121] The electrolyte plays the role of conducting ions between the positive electrode plate 102 and the negative electrode plate 101, and the electrolyte can be liquid, gel or all-solid. In some embodiments, the above-mentioned electrolyte adopts a liquid electrolyte, and the electrolyte includes an electrolyte salt and a solvent. The electrolyte salt is a lithium salt, and the solvent includes a cyclic ester solvent and a chain ester solvent. In some embodiments, the cyclic ester solvent includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate and γ-butyrolactone; the chain ester solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate and diphenyl carbonate. In some embodiments, the organic solvent includes ethylene carbonate, propylene carbonate and ethyl methyl carbonate.

[0122] In practical applications, the negative electrode sheet 101, the separator 100 and the positive electrode sheet 102 are stacked in order and wound to obtain the core 10, the core 10 is packaged to obtain a bare cell, and the bare cell is baked and then injected, formed, sealed and sorted to obtain the above-mentioned secondary battery.

[0123] The present invention further provides an electric device, which includes the above-mentioned secondary battery, and the secondary battery serves as a power supply for the electric device.

[0124] For the above-mentioned electrical equipment embodiment, it includes the above-mentioned secondary battery and can achieve the same technical effect. In order to avoid repetition, it will not be described here. For relevant matters, please refer to the partial description of the secondary battery embodiment.

[0125] In order to make the invention purpose, technical scheme and beneficial effect of the present invention clearer, the present invention is further described below in conjunction with embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0126] The present invention is described in detail below by way of examples.

[0127] Example 1

[0128] (1) Preparation of positive electrode slurry

[0129] The positive electrode active material LiNi with an average particle size of 9.6 μm 0.9 Co 0.05 Mn 0.05 O2 (NCM90), conductive agent acetylene black, binder polyvinylidene fluoride and dispersant polyvinyl pyrrolidone (PVP) are mixed evenly in a mass ratio of 97.5:1.2:1.2:0.1, and evenly dispersed in 1-methyl-2-pyrrolidone to prepare a uniform first positive electrode slurry.

[0130] (2) Preparation of positive electrode sheet

[0131] The first positive electrode slurry obtained in step (1) is uniformly coated on the first surface of the positive electrode current collector aluminum foil by a coating machine to obtain a first positive electrode coating; the first positive electrode slurry obtained in step (1) is uniformly coated on the second surface of the positive electrode current collector aluminum foil opposite to the first surface by a coating machine to obtain a second positive electrode coating; then placed in an oven at a high temperature of 110° C. for drying, and a positive electrode sheet can be prepared through processes such as rolling, cutting, and slitting;

[0132] The positive electrode sheet includes a first positive electrode coating having a compaction density of 3.55 g / cm 3 The compaction density of the first positive electrode film layer and the second positive electrode coating layer is 3.55 g / cm 3 The first positive electrode film layer has a length of 6397 mm, a width of 83.8 mm, a thickness of 0.045 mm, a porosity of 35%, and a pore volume of 8443 mm 3 The second positive electrode film layer has a length of 6397 mm, a width of 83.8 mm, a thickness of 0.045 mm, a porosity of 35%, and a pore volume of 8443 mm 3 .

[0133] (3) Preparation of negative electrode slurry

[0134] The negative electrode active material graphite with an average particle size of 12.5 μm, the electrolyte acetylene black, the binder styrene butadiene rubber (SBR), and the thickener carboxymethyl cellulose (CMC) were mixed evenly in a mass ratio of 96.5:1.5:1.8:0.2, and evenly dispersed in deionized water to prepare a uniform first negative electrode slurry.

[0135] (4) Preparation of negative electrode sheet

[0136] The first negative electrode slurry obtained in step (3) is uniformly coated on the first surface of the negative electrode current collector copper foil by a coating machine to obtain a first negative electrode coating; the first negative electrode slurry obtained in step (3) is uniformly coated on the second surface of the negative electrode current collector copper foil opposite to the first surface by a coating machine to obtain a second negative electrode coating; then placed in an oven at a high temperature of 120° C. for drying, and a negative electrode sheet can be prepared through processes such as rolling, cutting, and slitting;

[0137] The negative electrode sheet includes a first negative electrode coating having a compaction density of 1.55 g / cm 3 The compaction density of the first negative electrode film layer and the second negative electrode coating layer is 1.55 g / cm 3 The first negative electrode film layer has a length of 6501 mm, a width of 86.3 mm, a thickness of 0.062 mm, a porosity of 45%, and a pore volume of 15653 mm 3The second negative electrode film layer has a length of 6501 mm, a width of 86.3 mm, a thickness of 0.062 mm, a porosity of 45%, and a pore volume of 15653 mm 3 .

[0138] (5) Preparation of diaphragm

[0139] A polyethylene polymer film with a porosity of 45% is selected as the base film of the diaphragm, and a ceramic coating is provided on one side of the base film; the length of the diaphragm is 13314mm, the width is 88.3mm, the thickness is 0.012mm, and the pore volume of the diaphragm is 6348mm 3 .

[0140] (6) Preparation of electrolyte

[0141] The organic solvent ethylene carbonate, the electrolyte lithium salt lithium hexafluorophosphate and the additive (ethylene carbonate and fluoroethylene carbonate in a mass ratio of 1:1) were mixed in a mass ratio of 80:15:5 and stirred sufficiently under an inert atmosphere to obtain a density of 1.3 g / cm 3 of electrolyte.

[0142] (7) Preparation of secondary batteries

[0143] The positive electrode sheet prepared in step (2), the negative electrode sheet prepared in step (4), and the separator prepared in step (5) are wound in a predetermined order to prepare a bare cell. The bare cell is placed in an outer packaging aluminum-plastic film, baked to remove moisture, and then 63.8 g of the electrolyte prepared in step (6) is injected and vacuum packaged to prepare a secondary battery.

[0144] Embodiment 2-3

[0145] The difference between Examples 2 to 3 and Example 1 is that:

[0146] In step (7), 60.3 g and 67.4 g of the electrolyte prepared in step (6) are injected into the bare cell respectively, and vacuum packaging is performed to prepare a secondary battery.

[0147] Embodiment 4-5

[0148] The difference between Examples 4 to 5 and Example 1 is that:

[0149] In step (5), polyethylene polymer films with porosity of 30% and 50% are respectively selected as the base film of the diaphragm; wherein the pore volume of the diaphragm with the polyethylene polymer film with porosity of 30% as the base film is 4232mm 3 The pore volume of the diaphragm with a porosity of 50% polyethylene polymer film as the base membrane is 8465mm 3.

[0150] Embodiment 6-7

[0151] The difference between Examples 6 to 7 and Example 1 is that:

[0152] In step (4), while ensuring that the size of the first negative electrode film layer remains unchanged, the average particle size of graphite is adjusted to adjust the compaction density of the first negative electrode film layer to 1.70 g / cm 3 and 1.40g / cm 3 The first negative electrode coating is formed into a first negative electrode film layer with a porosity of 30% and 60% respectively; wherein the compaction density is 1.70g / cm 3 The pore volume of the first negative electrode film layer is 10435.5 mm 3 , compacted density is 1.40g / cm 3 The pore volume of the first negative electrode film layer is 20870.5 mm 3 ;

[0153] In step (4), while ensuring that the size of the second negative electrode film layer remains unchanged, the average particle size of graphite is adjusted to adjust the compaction density of the second negative electrode film layer to 1.70 g / cm 3 and 1.40g / cm 3 , so that the second negative electrode coating forms a second negative electrode film layer with a porosity of 30% and 60% respectively; wherein the compaction density is 1.70g / cm 3 The pore volume of the second negative electrode film layer is 10435.5 mm 3 , compacted density is 1.40g / cm 3 The pore volume of the second negative electrode film layer is 20870.5mm 3 .

[0154] Embodiments 8 to 9

[0155] The difference between Examples 8 to 9 and Example 1 is that:

[0156] In step (3), graphite, an active negative electrode material, and acetylene black, an electrolyte, styrene butadiene rubber, and a thickener, respectively, with particle sizes of 15.0 μm and 10.5 μm, are mixed uniformly in a mass ratio of 96.5:1.5:1.8:0.2, and are uniformly dispersed in deionized water to prepare a uniform second negative electrode slurry and a third negative electrode slurry;

[0157] In step (4), the second negative electrode slurry and the third negative electrode slurry obtained in step (3) are uniformly coated on the second surface of the negative electrode current collector copper foil opposite to the first surface by a coating machine to obtain a second negative electrode coating, so that the second negative electrode coating forms a second negative electrode film layer with a porosity of 40% and 50%, respectively; wherein the pore volume of the second negative electrode film layer formed based on the second negative electrode slurry is 13914mm 3 The pore volume of the second negative electrode film layer formed based on the third negative electrode slurry is 17392 mm 3 .

[0158] Embodiments 10 to 11

[0159] The difference between Examples 10 and 11 and Example 1 is that:

[0160] In step (2), while ensuring that the size of the first positive electrode film layer remains unchanged, the average particle size of NCM90 is adjusted to adjust the compaction density of the first positive electrode film layer to 3.70 g / cm 3 and 3.40g / cm 3 The first positive electrode coating is formed into a first positive electrode film layer with porosity of 15% and 50% respectively; wherein the compaction density is 3.70g / cm 3 The pore volume of the first positive electrode film layer is 3618.5 mm 3 , compacted density is 3.40g / cm 3 The pore volume of the first positive electrode film layer is 12061.5mm 3 ;

[0161] In step (2), while ensuring that the size of the second positive electrode film layer remains unchanged, the average particle size of NCM90 is adjusted to adjust the compaction density of the second positive electrode film layer to 3.70 g / cm 3 and 3.40g / cm 3 , so that the second positive electrode coating forms a second positive electrode film layer with porosity of 15% and 50% respectively; wherein the compaction density is 3.70g / cm 3 The pore volume of the second positive electrode film layer is 3618.5 mm 3 , compacted density is 3.40g / cm 3 The pore volume of the second positive electrode film layer is 12061.5mm 3 .

[0162] Embodiments 12 to 13

[0163] The difference between Examples 12 to 13 and Example 1 is that:

[0164] In step (1), the positive electrode active materials LiNi and LiNi with average particle sizes of 11.5 μm and 7.5 μm respectively are 0.9Co 0.05 Mn 0.05 O2 (NCM90), conductive agent acetylene black, binder polyvinylidene fluoride and dispersant polyvinyl pyrrolidone are mixed uniformly in a mass ratio of 97.5:1.2:1.2:0.1, and uniformly dispersed in 1-methyl-2-pyrrolidone to prepare uniform second positive electrode slurry and third positive electrode slurry;

[0165] In step (2), the second positive electrode slurry and the third positive electrode slurry obtained in step (1) are uniformly coated on the second surface of the positive electrode current collector aluminum foil opposite to the first surface by a coating machine to obtain a second positive electrode coating, so that the second positive electrode coating forms a second positive electrode film layer with porosities of 30% and 40%, respectively; wherein the pore volume of the second positive electrode film layer formed based on the second positive electrode slurry is 7237mm 3 The pore volume of the second positive electrode film layer formed based on the second positive electrode slurry is 9649 mm 3 .

[0166] Embodiments 14 to 15

[0167] The difference between Examples 14 to 15 and Example 1 is that:

[0168] In step (6), the organic solvent ethylene carbonate, the electrolyte lithium salt lithium hexafluorophosphate and the additive (ethylene carbonate and fluoroethylene carbonate in a mass ratio of 1:1) are mixed in a mass ratio of 85:10:5 and 75:20:5 respectively, and are fully stirred under an inert atmosphere to obtain a density of 1.1 g / cm 3 and 1.5g / cm 3 of electrolyte.

[0169] Embodiments 16 to 17

[0170] The difference between Examples 16 to 17 and Example 1 is that:

[0171] In step (5), the thickness of the diaphragm is 0.01 mm and 0.02 mm respectively; wherein the pore volume of the diaphragm with a thickness of 0.01 mm is 5290 mm 3 , the pore volume of the 0.02 mm thick diaphragm is 7935 mm 3 .

[0172] Embodiment 18

[0173] The difference between Example 18 and Example 1 is that:

[0174] In step (2), the width of the first positive electrode film layer and the second positive electrode film layer are both 75.5 mm, and the pore volume of the first positive electrode film layer and the second positive electrode film layer are both 7607 mm 3 ;

[0175] In step (4), the width of the first negative electrode film layer and the second negative electrode film layer are both 78 mm, and the pore volume of the first negative electrode film layer and the second negative electrode film layer are both 14147.5 mm 3 ;

[0176] In step (5), the width of the diaphragm is 80 mm and the pore volume of the diaphragm is 5752 mm 3 .

[0177] Embodiment 19

[0178] The difference between Example 19 and Example 1 is that:

[0179] In step (2), the width of the first positive electrode film layer is 111 mm, and the width of the second positive electrode film layer is 110.5 mm; the pore volume of the first positive electrode film layer and the second positive electrode film layer is 11133 mm 3 ;

[0180] In step (4), the width of the first negative electrode film layer and the second negative electrode film layer is 113 mm; the pore volume of the first negative electrode film layer and the second negative electrode film layer is 20495.5 mm 3 ;

[0181] In step (5), the width of the diaphragm is 115 mm and the pore volume of the diaphragm is 8268 mm 3 .

[0182] Embodiment 20

[0183] The difference between Example 20 and Example 1 is that:

[0184] In step (2), the lengths of the first positive electrode film layer and the second positive electrode film layer are both 3045 mm; the pore volumes of the first positive electrode film layer and the second positive electrode film layer are both 4019 mm 3 ;

[0185] In step (4), the lengths of the first negative electrode film layer and the second negative electrode film layer are both 3208 mm; the pore volumes of the first negative electrode film layer and the second negative electrode film layer are both 7724 mm 3 ;

[0186] In step (5), the length of the diaphragm is 6676 mm and the pore volume of the diaphragm is 3183 mm 3 .

[0187] Embodiment 21

[0188] The difference between Example 21 and Example 1 is that:

[0189] In step (2), the lengths of the first positive electrode film layer and the second positive electrode film layer are both 11345 mm; the pore volumes of the first positive electrode film layer and the second positive electrode film layer are both 14973.5 mm 3 ;

[0190] In step (4), the lengths of the first negative electrode film layer and the second negative electrode film layer are both 11460 mm; the pore volumes of the first negative electrode film layer and the second negative electrode film layer are both 27593 mm 3 ;

[0191] In step (5), the length of the diaphragm is 23262 mm and the pore volume of the diaphragm is 11092 mm 3 .

[0192] Comparative Examples 1-2

[0193] The difference between Comparative Examples 1 to 2 and Example 1 is that:

[0194] In step (7), 56.7 g and 70.9 g of the electrolyte prepared in step (6) are injected into the bare cell respectively, and vacuum packaging is performed to prepare a secondary battery.

[0195] The components and parameters of the secondary batteries prepared in various embodiments and comparative examples are shown in Table 1.

[0196] Table 1

[0197]

[0198]

[0199]

[0200] It should be noted that L0, W0, H0, L 11 , W 11 , H 11 , L 12 , W 12 , H 12 , L 21 , W 21 , H 21 , L 22 , W 22 , H 22 The unit of V0, V1, V2 and V3 is mm 3 ; The unit of ρ is g / cm 3 ; The unit of m is g.

[0201] Test method:

[0202] (1) Secondary battery cycle test method: In an environment of 25±3℃, step 1. stand for 30 minutes; step 2. charge at a constant current rate of 2.0C to the upper limit cut-off voltage, and then switch to constant voltage to 0.02C; step 3. stand for 30 minutes; step 4. discharge at a constant current rate of 1.0C to the lower limit cut-off voltage; repeat steps 1 to 4. When the discharge capacity of the Nth cycle divided by the first discharge capacity is less than 80%, the number of cycles is recorded as N.

[0203] (2) Secondary battery storage test method: Step 1. First, place it in a 25±3℃ environment for 30 minutes, charge it to the upper cutoff voltage at a constant current rate of 1 / 3C; then switch to constant voltage to 0.02C; discharge it to the lower cutoff voltage at a constant current rate of 1 / 3C, and record the discharged capacity as the initial capacity; finally, charge it to the upper cutoff voltage at a constant current rate of 1 / 3C, and switch to constant voltage to 0.02C. Step 2. Transfer to a 60±3℃ environment and place it for 300 days. Step 3. Transfer to a 25±3℃ environment and place it for 30 minutes, discharge it to the lower cutoff voltage at a constant current rate of 1 / 3C, and record the discharged capacity as the residual capacity, and the residual capacity divided by the initial capacity is recorded as the residual capacity retention rate. Step 4. Charge it to the upper cutoff voltage at a constant current rate of 1 / 3C, and then switch to constant voltage to 0.02C; discharge it to the lower cutoff voltage at a constant current rate of 1 / 3C, and record the discharged capacity as the recovered capacity, and the recovered capacity divided by the initial capacity is recorded as the recovered capacity retention rate.

[0204] The lower cut-off voltage and the upper cut-off voltage are 2.8 V and 4.0 V, respectively. The secondary batteries prepared in the embodiments and comparative examples were subjected to the above tests, and the test data are shown in Table 2.

[0205] Table 2

[0206]

[0207]

[0208] According to the above test data, compared with Comparative Examples 1 and 2, Examples 1 to 21 provided in the embodiments of the present invention control the liquid retention amount of the secondary battery between 0.85×(V0 / 1000)×ρ and 0.95×(V0 / 1000)×ρ, thereby maintaining the number of charge and discharge cycles of the secondary battery above 1000, while also increasing the storage residual capacity retention rate to above 40% and the storage recovery capacity retention rate to above 75%. It can be seen that the embodiment of the present invention determines the mass of electrolyte that can be accommodated by 0.85 to 0.95 times the sum of the pore volume of the diaphragm in the core, the pore volume of the positive electrode sheet and the pore volume of the negative electrode sheet as the total liquid retention volume of the secondary battery. While meeting the electrolyte replenishment needs during the charge and discharge cycle and storage process of the secondary battery, when the secondary battery expands inward due to the constraint of the shell during the charge and discharge cycle, only a small amount of electrolyte or even no electrolyte is squeezed out to the two sides of the core, so that the electrolyte concentration at the two sides of the core is basically the same as the electrolyte concentration at other positions of the secondary battery, and the polarization is also basically the same, which reduces the risk of lithium plating at the two sides of the core and improves the cycle life, cycle capacity retention rate and storage performance of the secondary battery.

[0209] The secondary battery and electrical equipment provided by the present invention are introduced in detail above. The principle and implementation mode of the present invention are explained by using specific examples in this article. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation mode and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A secondary battery, characterized in that: The invention comprises a winding core and an electrolyte, wherein the winding core comprises a positive electrode sheet, a separator and a negative electrode sheet stacked in sequence; and the secondary battery satisfies the following conditions when in a 0% SOC state: 0.85×(V0 / 1000)×ρ≤m≤0.95×(V v / 1000)×ρ, Wherein, mg represents the liquid retention capacity of the secondary battery; V0mm 3 represents the total volume of the pores in the winding core; the total volume of the pores in the winding core is the sum of the pore volume of the separator, the pore volume of the positive electrode sheet and the pore volume of the negative electrode sheet; ρg / cm 3 represents the density of the electrolyte.

2. The secondary battery according to claim 1, characterized in that: The ratio between the pore volume of the negative electrode plate and the pore volume of the separator is 3.2 to 7.

4.

3. The secondary battery according to claim 1, characterized in that: The ratio of the pore volume of the negative electrode plate to the pore volume of the positive electrode plate is 1.2 to 4.

3.

4. The secondary battery according to claim 1, characterized in that: The porosity of the diaphragm is 30% to 60%.

5. The secondary battery according to claim 1, characterized in that: The porosity of the positive electrode sheet is 15% to 50%.

6. The secondary battery according to claim 1, characterized in that: The positive electrode sheet comprises a positive electrode current collector, and a first positive electrode film layer and a second positive electrode film layer arranged on two opposite surfaces of the positive electrode current collector; Wherein, the porosity of the first positive electrode film layer is 15% to 50%, and the porosity of the second positive electrode film layer is 15% to 50%.

7. The secondary battery according to claim 6, characterized in that: The absolute value of the difference between the porosity of the first positive electrode film layer and the porosity of the second positive electrode film layer is 0-5%.

8. The secondary battery according to claim 1, characterized in that: The porosity of the negative electrode plate is 30% to 60%.

9. The secondary battery according to claim 1, characterized in that: The negative electrode plate comprises a negative electrode current collector, and a first negative electrode film layer and a second negative electrode film layer arranged on two opposite surfaces of the negative electrode current collector; Wherein, the porosity of the first negative electrode film layer is 30% to 60%, and the porosity of the second negative electrode film layer is 30% to 60%.

10. The secondary battery according to claim 9, characterized in that: The absolute value of the difference between the porosity of the first negative electrode film layer and the porosity of the second negative electrode film layer is 0-5%.

11. The secondary battery according to claim 1, characterized in that: The density of the electrolyte is 1.1 g / cm 3 ~1.5g / cm 3 .

12. The secondary battery according to any one of claims 1 to 11, characterized in that: The secondary battery includes a shell, and the shell is a columnar structure.

13. An electrical equipment, characterized in that: The invention comprises a secondary battery as claimed in any one of claims 1 to 12, wherein the secondary battery is used as a power supply for the electrical device.

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