Secondary battery and method for manufacturing the same, and electric device

Abstract

The application relates to the technical field of batteries, and specifically discloses a secondary battery, a preparation method of the secondary battery and an electric device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, a diaphragm and an electrolyte; the electrolyte comprises free-state electrolyte and non-free-state electrolyte; the non-free-state electrolyte comprises electrolyte in pores of the positive electrode sheet, electrolyte in pores of the negative electrode sheet and electrolyte in pores of the diaphragm; the non-free-state electrolyte and the free-state electrolyte independently comprise at least one of sulfonic acid ester compounds and sulfuric acid ester compounds; wherein the mass ratio of the sulfonic acid ester compounds to the sulfuric acid ester compounds in the non-free-state electrolyte is T1, the mass ratio of the sulfonic acid ester compounds to the sulfuric acid ester compounds in the free-state electrolyte is T2, and the T1 and the T2 satisfy 0.1 <= T1 <= 10 and 0 <= T2 <= 5.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a secondary battery and a preparation method thereof, and an electric device. BACKGROUND

[0002] With the increase of renewable energy installed capacity, the power system needs high flexibility to ensure the reliability and continuity of energy supply. Lithium ion batteries with lithium iron phosphate (LiFePO4) positive electrode and graphite negative electrode system have the characteristics of low cost, high safety and long service life, and have been applied in the field of electrochemical energy storage power stations.

[0003] The ratio of discharge energy to charge energy of the battery during the cycle process is the round-trip energy efficiency (RTE). During the charging and discharging process, the battery and the connection resistance will consume part of the electric energy, at the same time, the growth of SEI (solid electrolyte interface film) and irreversible lithium precipitation loss will also cause energy loss. In the economic benefit calculation method of energy storage power station, the cost is settled according to the grid output energy, and the income is settled according to the battery output energy, therefore, the energy efficiency becomes one of the important reasons restricting the cost recovery of energy storage power station.

[0004] Generally, the improvement of RTE is mainly through the battery control management system to regulate the battery to work in the appropriate SOC (State of Charge) interval, and through the temperature regulation system to keep the battery working near room temperature. The above method can basically ensure that the energy efficiency of the battery is about 80-85% (25℃, 1P, 2.0-3.65V), but it is difficult to further improve the energy efficiency. SUMMARY

[0005] The present application aims to at least solve one of the technical problems in the related art. To this end, the purpose of the present application is to provide a secondary battery and a preparation method thereof, and an electric device, which has low impedance and high stability, and can realize the purpose of regulating the SEI structure according to the demand to improve the cycle energy efficiency.

[0006] In one aspect of the present application, the present application provides a secondary battery. According to the embodiments of the present application, the secondary battery comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte;

[0007] The electrolyte comprises a free-state electrolyte and a non-free-state electrolyte, and the non-free-state electrolyte comprises electrolyte in positive electrode sheet pores, electrolyte in negative electrode sheet pores and electrolyte in separator pores;

[0008] The non-free-state electrolyte and the free-state electrolyte independently comprise at least one of a sulfonate compound and a sulfate compound;

[0009] The mass ratio of the sulfonate compound to the sulfate compound in the non-free electrolyte is T1, the mass ratio of the sulfonate compound to the sulfate compound in the free electrolyte is T2, and T1, T2 satisfy 0.1≤T1≤10 and 0≤T2≤5.

[0010] The application can optimize the charge-discharge performance of the battery, improve the safety and stability, etc. by designing the localization distribution characteristics of the free electrolyte and the non-free electrolyte. When the mass ratio (T1) of the sulfonate compound to the sulfate compound in the non-free electrolyte satisfies 0.1≤T1≤10, the sulfonate compound and the sulfate compound in the non-free electrolyte can support the generation of the required structure SEI in a suitable ratio. In combination with the mass ratio (T2) of the sulfonate compound to the sulfate compound in the free electrolyte satisfying 0≤T2≤5, the mass ratio of the sulfonate compound to the sulfate compound in the non-free electrolyte can be maintained at a suitable level at all times, the structure of the SEI formed by chemical reaction, and the structure of the SEI after the rupture and repair in the cycle or storage, i.e. the inorganic components are always preferentially enriched in the inner layer to provide efficient ion conduction capacity, and the organic components are always dispersed in the outer layer to play a repair capacity, the whole presents the characteristics of low impedance and high stability, and the purpose of regulating the SEI structure according to the requirements to improve the cycle energy efficiency is achieved.

[0011] In some embodiments of the application, T1, T2 satisfy T2

[0012] In some embodiments of the application, the sulfonate compound includes at least one of a linear sulfonate compound and a cyclic sulfonate compound.

[0013] And / or, the sulfate compound includes at least one of a linear sulfate compound and a cyclic sulfate compound.

[0014] In some embodiments of the application, the sulfonate compound includes at least one of trimethylsilyl trifluoromethanesulfonate, diethylene glycol dimethyl sulfonate, 3,3-difluoropropyl methyl sulfonate, 4-(trifluoromethyl)phenyl trifluoromethanesulfonate, 2-cyanophenyl trifluoromethyl sulfonate, p-tolyl methyl sulfonate, 4-nitrobenzyl methyl sulfonate, propenyl-1,3-propane sulfonolactone, 1,4-propane sulfonolactone, 1,4-butane sulfonolactone, 2,4-butane sulfonolactone, tetrafluoro sulfonolactone, 1,2,2-trifluoro-2-hydroxy-1-trifluoromethyl ethane sulfonic acid, 3-fluoro-1,3-propane sulfonolactone, and methanedisulfonate methylene.

[0015] And / or, the sulfate ester compound includes at least one of trimethylene sulfate, 2-methyl-1,3-propanedisulfite, vinyl sulfate, 4-methyl vinyl sulfate, 4-ethyl vinyl sulfate, 4-propyl vinyl sulfate, 4-butyl vinyl sulfate, pentaerythritol bicyclic sulfate, and erythrose disulfate.

[0016] In some embodiments of the present application, the enrichment degree of sulfonate groups in the free electrolyte is F o , the F o Satisfy F o =0 or 1≤F o ≤2;

[0017] And / or, the enrichment degree of sulfate groups in the free electrolyte is F a , the F a Satisfy 1≤F a ≤1.8.

[0018] In some embodiments of the present application, the F o Satisfy 1.5≤F o ≤2;

[0019] and / or, the F a Satisfy 1≤F a ≤1.5.

[0020] In some embodiments of the present application, the positive electrode plate has a first region and a second region on a side close to the separator, the first region has a flat outer surface, and the second region is convex relative to the first region;

[0021] And / or, the negative electrode plate has a third region and a fourth region on a side close to the separator, the third region has a flat outer surface, and the fourth region is convex relative to the third region.

[0022] In some embodiments of the present application, the positive electrode sheet has the first region and the second region on one side close to the diaphragm, and the design coefficient t of the positive electrode sheet is c =1+S ci / S c , the t c Satisfy 1.0≤t c ≤1.5;

[0023] Among them, S c S is the sum of the projected areas of the first region and the second region on the negative electrode sheet in the direction perpendicular to the diaphragm in the positive electrode sheet, ci is the surface area of ​​the positive electrode sheet increased by the second region;

[0024] And / or, the negative electrode plate has a third region and a fourth region on one side close to the separator, and the design coefficient t of the negative electrode plate is a =1+S ai / S a , the t a Satisfy 1.0≤t a ≤1.5;

[0025] Among them, S a S is the sum of the projected areas of the third region and the fourth region on the positive electrode sheet in the direction perpendicular to the diaphragm in the negative electrode sheet, ai is the surface area of ​​the negative electrode sheet increased by the fourth region;

[0026] And / or, the design coefficient t of the positive electrode plate c and the design coefficient t of the negative electrode sheet a Satisfy 2.0<t c +t a ≤2.7.

[0027] In some embodiments of the present application, the enrichment degree F of the sulfonate groups in the free electrolyte is o , the enrichment degree F of sulfate groups in the free electrolyte a , the design coefficient t of the positive electrode sheet c and the design coefficient t of the negative electrode sheet a At least one of the following conditions is met:

[0028] F o / (t c +t a )=0;

[0029] 0.5≤F o / (t c +t a )≤1;

[0030] 0≤F a -0.7(t c +t a )+0.55≤0.8.

[0031] In a second aspect of the present application, the present application provides a method for preparing the secondary battery described in the first aspect, comprising the following steps of injecting an electrolyte:

[0032] After the first injection is completed, the second injection is performed;

[0033] The electrolyte used in the first injection is a first electrolyte, and the electrolyte used in the second injection is a second electrolyte.

[0034] The mass ratio of the sulfonate compound in the first electrolyte is Mpo, and the mass ratio of the sulfate compound is Mpa, and the Mpa and Mpo satisfy 0

[0035] The mass ratio of the sulfonate compound in the second electrolyte is Mdo, and the mass ratio of the sulfate compound is Mda, and the Mda and Mdo satisfy 0

[0036] The secondary injection flexibly controls the local distribution characteristics of the non-free state electrolyte and the free state electrolyte of the initial state of the battery by separating the electrolyte components required in the battery formation stage and the electrolyte components required in the cycle stage. In addition, limiting the addition amount of each compound in the first electrolyte and the second electrolyte can meet the film formation and not be excessive reaction, and limiting the size of Mpa and Mpo and the size of Mda and Mdo can realize the requirement of T2

[0037] In some embodiments of the present application, the mass ratio of the first electrolyte to the second electrolyte is (6:4) to (8:2);

[0038] And / or, the injection coefficient sum of the first electrolyte and the second electrolyte is 2.5 g / Ah to 5 g / Ah.

[0039] In a third aspect of the present application, a power utilization device is provided. According to embodiments of the present application, the power utilization device comprises the secondary battery of the first aspect.

[0040] Therefore, the power utilization device has all the advantages of the secondary battery, which will not be repeated here.

[0041] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter in the description of embodiments of the present application, which will be described with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0042] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the description of embodiments of the present application, which will be described with reference to the following drawings:

[0043] Figure 1 One of the structure diagrams of the positive electrode sheet in the secondary battery provided by the present application is shown;

[0044] Figure 2One of the structure diagrams of the negative electrode tab in the secondary battery provided by the present application is shown;

[0045] Figure 3 One of the structure diagrams of the negative electrode tab in the secondary battery provided by the present application is shown;

[0046] Figure 4 One of the structure diagrams of the negative electrode tab in the secondary battery provided by the present application is shown;

[0047] Figure 5 One of the structure diagrams of the negative electrode tab in the secondary battery provided by the present application is shown.

[0048] Reference signs:

[0049] Positive electrode tab 1, first area 10, second area 20, negative electrode tab 2, third area 30, fourth area 40, width d1 of the fourth area, depth h1 of the fourth area. DETAILED DESCRIPTION

[0050] The embodiments of the present application are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar notations represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0051] In one aspect of the present application, the present application provides a secondary battery. According to an embodiment of the present application, the secondary battery comprises a positive electrode tab, a negative electrode tab, a separator and an electrolyte;

[0052] The electrolyte comprises free-state electrolyte and non-free-state electrolyte, and the non-free-state electrolyte comprises electrolyte in positive electrode tab pores, electrolyte in negative electrode tab pores and electrolyte in separator pores;

[0053] The non-free-state electrolyte and the free-state electrolyte independently comprise at least one of sulfonate compounds and sulfate compounds;

[0054] Wherein, the mass ratio of sulfonate compounds to sulfate compounds in the non-free-state electrolyte is T1, the mass ratio of sulfonate compounds to sulfate compounds in the free-state electrolyte is T2, and the T1, T2 satisfy 0.1≤T1≤10, 0≤T2≤5.

[0055] The applicant finds that the inner layer inorganic component and the outer layer organic component is an ideal structure for enhancing the stability of SEI. As an additive that can effectively form SEI, the S-O bond of the sulfate compound is broken after electron is obtained, and the -OSO2- group at the chain end combines with lithium ions to generate SEI products rich in ROSO2Li organic components. The sulfonate compound is also broken after electron is obtained, and the difference is that the -SO2- and -O- at the chain end combine with lithium ions to generate SEI products rich in Li2CO3 and Li2SO3 inorganic components. The inorganic component in the layered SEI structure is more conducive to the ion conduction ability of SEI, and the organic component is more conducive to the self-repairing ability of SEI. The combination of the two components forms an inner and outer layered distribution, so that SEI exhibits low impedance and high stability, and improves the cycle energy efficiency.

[0056] In addition, the application is designed to have a localized distribution feature, i.e. the electrolyte includes free-state electrolyte and non-free-state electrolyte. There is no absolute physical barrier between the non-free-state electrolyte and the free-state electrolyte in the battery cell. When the non-free-state electrolyte is insufficient, the free-state electrolyte is automatically absorbed as a supplement through the capillary action of the electrode and the separator. The electrolyte compositions in the two regions have dynamic differences during the cycle consumption process, so the component content of the battery is also dynamically changed during use. The application limits the mass ratio T1 of the sulfonate compound to the sulfate compound in the non-free-state electrolyte to satisfy 0.1≤T1≤10, which can ensure that the sulfonate compound and the sulfate compound in the non-free-state electrolyte support the generation of the required structure SEI at a suitable ratio. Specifically, T1 can be 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, etc. If T1 is too low, the sulfate compound in the non-free-state electrolyte will compete for the first reaction due to the concentration advantage, which is easy to cause the SEI to have more organic components in the inner layer and more inorganic components in the outer layer, resulting in large cell impedance, SEI instability, and energy efficiency deterioration due to repeated SEI generation during the cycle process. If T1 is too high, the sulfonate compound in the non-free-state electrolyte will have a concentration advantage for continuous reaction, which is easy to cause the SEI to have a large amount of inorganic components in the inner and outer layers and lack of organic components, resulting in easy destruction of SEI and also deterioration of energy efficiency.

[0057] T2 satisfies 0≤T2≤5, the mass ratio of the sulfonate compound and the sulfate compound in the non-free electrolyte can be maintained at a suitable level at all times, the SEI formed by chemical reaction, and the structure of the SEI after the SEI is broken and repaired during cycling or storage, has inorganic components always preferentially enriched in the inner layer to provide efficient ion conduction capability, and has organic components always dispersed in the outer layer to provide repair capability, and the overall structure has the characteristics of low impedance and high stability, thereby achieving the purpose of regulating the SEI structure as needed to improve the cycling energy efficiency. Specifically, T2 can be 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or the like. When T2 is equal to 0, it indicates that the free electrolyte does not contain a sulfonate compound, but T1 is not 0, that is, the sulfonate compound in the non-free electrolyte does not affect the film formation.

[0058] Specifically, the electrolyte of the present application includes a free electrolyte and a non-free electrolyte, the non-free electrolyte includes electrolyte in the pores of the positive electrode sheet, electrolyte in the pores of the negative electrode sheet, and electrolyte in the pores of the separator, and the rest is the free electrolyte.

[0059] According to an embodiment of the present application, T1 and T2 satisfy T2

[0060] According to an embodiment of the present application, the non-free electrolyte and the free electrolyte independently include at least one of a sulfonate compound and a sulfate compound, that is, the non-free electrolyte can include at least one of a sulfonate compound and a sulfate compound, the free electrolyte can include at least one of a sulfonate compound and a sulfate compound, and the types of the sulfonate compound and the sulfate compound in the non-free electrolyte and the free electrolyte can be the same or different.

[0061] According to the embodiments of the present application, the type of sulfonate compound is not particularly limited, and those skilled in the art can select according to actual needs. As some specific examples, the sulfonate compound can be selected from linear sulfonate compounds, cyclic sulfonate compounds, and the like, including but not limited to trimethylsilyl trifluoromethanesulfonate, diethylene glycol dimethyl sulfonate, 3,3-difluoropropyl methyl sulfonate, 4-(trifluoromethyl)phenyl trifluoromethanesulfonate, 2-cyanophenyl trifluoromethyl sulfonate, p-tolyl methyl sulfonate, 4-nitrobenzyl methyl sulfonate, propenyl-1,3-propane sulfonolactone, 1,4-propane sulfonolactone, 1,4-butane sulfonolactone, 2,4-butane sulfonolactone, tetrafluoro sulfonolactone, 1,2,2-trifluoro-2-hydroxy-1-trifluoromethyl ethane sulfonic acid, 3-fluoro-1,3-propane sulfonolactone, and methane disulfonate.

[0062] According to the embodiments of the present application, the type of sulfonate compound is not particularly limited, and those skilled in the art can select according to actual needs. As some specific examples, the sulfonate compound can be selected from linear sulfonate compounds, cyclic sulfonate compounds, and the like, including but not limited to trimethylsilyl trifluoromethanesulfonate, diethylene glycol dimethyl sulfonate, 3,3-difluoropropyl methyl sulfonate, 4-(trifluoromethyl)phenyl trifluoromethanesulfonate, 2-cyanophenyl trifluoromethyl sulfonate, p-tolyl methyl sulfonate, 4-nitrobenzyl methyl sulfonate, propenyl-1,3-propane sulfonolactone, 1,4-propane sulfonolactone, 1,4-butane sulfonolactone, 2,4-butane sulfonolactone, tetrafluoro sulfonolactone, 1,2,2-trifluoro-2-hydroxy-1-trifluoromethyl ethane sulfonic acid, 3-fluoro-1,3-propane sulfonolactone, and methane disulfonate.

[0063] According to the embodiments of the present application, the enrichment degree of sulfonate groups in the free-state electrolyte is F o , and the F o satisfies F o =0 or 1≤F o ≤2.

[0064] And / or, the enrichment degree of sulfate groups in the free-state electrolyte is F a , and the F a satisfies 1≤F a ≤1.8. The sulfonate groups and the sulfate groups are effective film-forming functional groups introduced by adding sulfonate compounds and sulfate compounds in the electrolyte. The applicant found that the functional group enrichment degree has more accurate significance for predicting battery performance compared with the compound content. For the same content of compounds, the higher the functional group enrichment degree, the higher the content of groups participating in the reaction to form a film, and the more significant the effect. By introducing the enrichment degree F o of the sulfonate groups and the enrichment degree F a of the sulfate groups, the battery cycle performance can be improved, which is more scientific compared with the conventional empirical formula addition and test method. As some specific examples, F o may be 0, 1, 1.5, 2, etc., preferably 1.5≤F o ≤2; and F aIt can be 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, etc., preferably satisfying 1≤F a ≤1.5.

[0065] Specifically, the sulfonate group enrichment F o Refers to the sulfonate unit The ratio of the number of moles of sulfonate to the total number of moles of compounds containing sulfonate groups, i.e. where m on represents the mass content (g) of the nth compound containing a sulfonate group, M on represents the molar molecular weight (g / mol) of the nth compound containing a sulfonate group, x on represents the number of sulfonate units in the nth compound containing sulfonate groups, n is a natural number, when n = 0, F o =0.

[0066] Specifically, sulfate richness refers to the sulfate unit The ratio of the molar number of to the total molar number of compounds containing sulfate groups, i.e. where m an represents the mass content (g) of the nth compound containing sulfate group, M an represents the molar molecular weight (g / mol) of the nth compound containing sulfate groups, x an represents the number of sulfonate units in the nth compound containing sulfate groups, n is a natural number, when n = 0, F a =0.

[0067] According to the embodiments of this application, referring to Figures 1-2 The positive electrode plate 1 has a first region 10 and a second region 20, the first region 10 has a flat outer surface, and the second region 20 is convex relative to the first region 10;

[0068] And / or, the negative electrode plate 2 has a third region 30 and a fourth region 40 on the side close to the separator, wherein the third region 30 has a flat outer surface, and the fourth region 40 is arranged to protrude relative to the third region 30. This improves the winding accuracy of the wound structure battery cell and reserves a certain amount of space for the plate to expand.

[0069] Specifically, the number of the first area, the second area, the third area, and the fourth area is not particularly limited, and can be adjusted by those skilled in the art according to actual conditions.

[0070] Specifically, the second region is convexly arranged relative to the first region, wherein the second region can be arranged towards the separator or away from the separator, i.e. a convex or concave structure. The shape of the second region is not particularly limited, including but not limited to a sphere, a cylinder, a cube, a cone, etc. The width and depth of the second region are also not particularly limited, wherein the depth is preferably 0.1-0.3 times the thickness of the electrode design, so as to avoid breaking the tab. The distribution of the second region on the tab is also not particularly limited, and is preferably regularly distributed, for example, equidistantly distributed.

[0071] Specifically, the fourth region is convexly arranged relative to the third region, wherein the fourth region can be arranged towards the separator or away from the separator, i.e. a convex or concave structure. The shape of the fourth region is not particularly limited, including but not limited to a sphere, a cylinder, a cube, a cone, etc., see Figures 2-4 . The width d1 and the depth h1 of the fourth region are also not particularly limited, and the depth h1 is preferably 0.1-0.3 times the thickness of the electrode design, so as to avoid breaking the tab. The distribution of the fourth region on the tab is also not particularly limited, and is preferably regularly distributed, for example, equidistantly distributed.

[0072] According to an embodiment of the present application, the positive electrode tab has the first region and the second region on the side close to the separator, and the design coefficient t c of the positive electrode tab satisfies 1.0≤t ci ≤1.5. c c c

[0073] wherein S c is the sum of the projection areas of the first region and the second region on the negative electrode tab in the direction perpendicular to the separator in the positive electrode tab, and S ci is the surface area of the positive electrode tab increased due to the second region.

[0074] And / or, the negative electrode tab has the third region and the fourth region on the side close to the separator, and the design coefficient t a of the negative electrode tab satisfies 1.0≤t ai ≤1.5. a a a

[0075] wherein S a is the sum of the projection areas of the third region and the fourth region on the positive electrode tab in the direction perpendicular to the separator in the negative electrode tab, and S ai is the surface area of the negative electrode tab increased due to the fourth region.

[0076] ​​​​​​The applicant discovered that the addition of the second and / or fourth regions to the electrode increases the contact area between the electrode and the electrolyte, which, to a certain extent, exacerbates electrolyte consumption and increases cell impedance, impacting energy efficiency and cycle performance. The applicant also discovered that the increase in electrode surface area due to the second and fourth regions also affects the amount of additives required in the free electrolyte. Therefore, a design factor was introduced to limit the change in contact area caused by the second and / or fourth regions to improve the aforementioned issues.

[0077] Specifically, when the positive electrode sheet has the first region and the second region on the side close to the separator, the design coefficient t is introduced. c =1+S ci / S c , limiting it to satisfy 1.0≤t c ≤1.5, for example, t c is 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, etc. Among them, S c S is the sum of the projected areas of the first and second regions on the negative electrode sheet in the direction perpendicular to the diaphragm, that is, the portion of the positive electrode sheet that is directly opposite to the negative electrode sheet through the diaphragm is the area of ​​the positive electrode sheet that participates in the charge and discharge reaction. ci is the increase in the surface area of ​​the pole piece caused by the second region.

[0078] Specifically, when the negative electrode sheet has a third region and a fourth region on the side close to the separator, the design coefficient t is introduced. a =1+S ai / S a , limiting it to satisfy 1.0≤t a ≤1.5, for example, t a is 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, etc. Among them, S a The sum of the projected areas of the third and fourth regions on the positive electrode sheet in the direction perpendicular to the diaphragm, i.e., the portion of the negative electrode sheet that is directly opposite to the positive electrode sheet through the diaphragm, is the area of ​​the negative electrode sheet that participates in the charge and discharge reaction. S ai is the increase in the surface area of ​​the pole piece caused by the fourth region.

[0079] About S ci 、S c 、S ai 、S a The calculation method is to take the negative electrode as an example, see Figures 2-5 .in Figure 5 The negative electrode plate 2 has no fourth region, that is, no protrusion and depression structure, then the S of the negative electrode plate aS is the projection area of the third region 30 on the positive electrode tab in the direction perpendicular to the diaphragm ai S is 0. Figure 2 The negative electrode tab 2 has a third region 30 and a fourth region 40, and the fourth region 40 is a square, in which case S a S is the projection area of the third region 30 and the fourth region 40 on the positive electrode tab in the direction perpendicular to the diaphragm ai S is the projection area of the third region 30 and the fourth region 40 on the positive electrode tab in the direction perpendicular to the diaphragm

[0080] S ai = 5d1 2 - d1 2 = 4d1 2 .

[0081] This formula corresponds to the case where only one fourth region is provided on the negative electrode tab, and if multiple fourth regions are provided on the negative electrode tab, the tab surface area increments caused by each fourth region should be added. The following is the same.

[0082] Similarly, Figure 3 The fourth region 40 of the negative electrode tab 2 is a hemisphere, in which case d1 corresponds to the diameter of the hemisphere. S a S is the projection area of the third region 30 and the fourth region 40 on the positive electrode tab in the direction perpendicular to the diaphragm ai S is the projection area of the third region 30 and the fourth region 40 on the positive electrode tab in the direction perpendicular to the diaphragm

[0083] S ai = 2π(d1 / 2) 2 - π(d1 / 2) 2 = π(d1 / 2) 2 .

[0084] Figure 4 The fourth region 40 of the negative electrode tab 2 is set to be a circular cone, in which case d1 corresponds to the diameter of the circular base of the cone, and h1 corresponds to the height of the circular cone. S a S is the projection area of the third region 30 and the fourth region 40 on the positive electrode tab in the direction perpendicular to the diaphragm ai S is the projection area of the third region 30 and the fourth region 40 on the positive electrode tab in the direction perpendicular to the diaphragm

[0085]

[0086] Specifically, the second region and the fourth region can be prepared by conventional methods, such as embossing process, that is, processing the pole piece by a roller press. The shape, width, depth and other parameters of the second region and the fourth region can also be adjusted by adjusting the parameters of the roller press equipment.

[0087] According to an embodiment of the present application, the design coefficient t of the positive electrode plate is c and the design coefficient t of the negative electrode sheet a Further satisfying 2.0<t c +t a ≤2.7. This can significantly suppress electrolyte consumption and avoid sudden impedance increase or electrode bulging caused by the structural design of the electrode. As some specific examples, t c +t a It can be 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, etc.

[0088] According to an embodiment of the present application, the enrichment degree F of the sulfonate groups in the free electrolyte is o , the enrichment degree F of sulfate groups in the free electrolyte a , the design coefficient t of the positive electrode sheet c and the design coefficient t of the negative electrode sheet a At least one of the following conditions is met:

[0089] F o / (t c +t a )=0;

[0090] 0.5≤F o / (t c +t a )≤1;

[0091] 0≤F a -0.7(t c +t a )+0.55≤0.8.

[0092] The applicant found that if there are too many sulfonate groups in the free electrolyte, SEI cannot be repaired in time, and the protrusions or depressions are more likely to cause continuous loss of electrolyte due to weak interfaces. If there are too few sulfonate groups in the free electrolyte, lithium ions cannot be effectively transmitted, and the protrusions or depressions are more likely to aggravate lithium precipitation due to weak interfaces. Therefore, the F o With t c +t a The relationship between them can ensure the number of sulfonate groups in the free electrolyte, thereby improving the energy efficiency of the battery. o / (t c +t a ) can satisfy Fo F(t + t) = 0, or 0.5 < F(t + t) < 1, as some specific examples, F(t + t) can be 0, 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc. c F(t + t) = 0, or 0.5 < F(t + t) < 1, as some specific examples, F(t + t) can be 0, 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc. a F(t + t) = 0, or 0.5 < F(t + t) < 1, as some specific examples, F(t + t) can be 0, 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc. o F(t + t) = 0, or 0.5 < F(t + t) < 1, as some specific examples, F(t + t) can be 0, 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc. c F(t + t) = 0, or 0.5 < F(t + t) < 1, as some specific examples, F(t + t) can be 0, 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc. a F(t + t) = 0, or 0.5 < F(t + t) < 1, as some specific examples, F(t + t) can be 0, 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc. o F(t + t) = 0, or 0.5 < F(t + t) < 1, as some specific examples, F(t + t) can be 0, 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc. c F(t + t) = 0, or 0.5 < F(t + t) < 1, as some specific examples, F(t + t) can be 0, 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc. a F(t + t) = 0, or 0.5 < F(t + t) < 1, as some specific examples, F(t + t) can be 0, 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc.

[0093] In addition, the applicant also found that too many sulfate groups in the free electrolyte cannot effectively transport lithium ions, and the protrusions or depressions are more prone to lithium precipitation. If there are too few sulfate groups in the free electrolyte, the SEI cannot be repaired in time, and the protrusions or depressions are more prone to accumulate by-products and produce stains. The lithium precipitation and by-product stains caused by unreasonable addition of additives and protrusions or depressions will directly deteriorate the energy efficiency of the battery. Therefore, 0 < F(t + t) < 0.8 can also be defined, which can significantly inhibit the consumption of electrolyte and inhibit the accumulation of by-products, without causing the impedance of the battery to rise sharply or the electrode sheet to swell. a -0.7(t + t) + 0.55 < 0.8, which can significantly inhibit the consumption of electrolyte and inhibit the accumulation of by-products, without causing the impedance of the battery to rise sharply or the electrode sheet to swell. c -0.7(t + t) + 0.55 < 0.8, which can significantly inhibit the consumption of electrolyte and inhibit the accumulation of by-products, without causing the impedance of the battery to rise sharply or the electrode sheet to swell. a -0.7(t + t) + 0.55 < 0.8, which can significantly inhibit the consumption of electrolyte and inhibit the accumulation of by-products, without causing the impedance of the battery to rise sharply or the electrode sheet to swell.

[0094] According to some specific embodiments of the present application, during the charging and discharging process of the battery, active ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte conducts ions between the positive electrode sheet and the negative electrode sheet. The separation film is arranged between the positive electrode sheet and the negative electrode sheet to prevent short circuiting of the positive and negative electrodes, while allowing ions to pass through.

[0095] According to some specific embodiments of the present application, the secondary battery is a lithium ion secondary battery.

[0096] According to some specific embodiments of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer arranged on at least one side surface of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material and the above-mentioned lithium supplementing agent. The positive electrode active material is preferably a lithium iron phosphate material.

[0097] According to some specific embodiments of the present application, the positive electrode current collector can include a metal foil or a composite positive electrode current collector. For example, the metal foil can be an aluminum foil. The composite positive electrode current collector can include a polymer material base layer and a metal layer formed on at least one side surface of the polymer material base layer, for example, the composite negative electrode current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material base material (such as a polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc. base material).

[0098] According to some embodiments of the present application, the positive active material layer can further optionally include a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0099] According to some embodiments of the present application, the positive active material layer can further optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic resin.

[0100] According to some embodiments of the present application, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive active material, the lithium supplement agent, the conductive agent, and the binder, in a solvent (e.g., N-methylpyrrolidone, NMP) to form a positive electrode slurry, coating the positive electrode slurry on a positive electrode current collector, and then performing processes such as drying and cold pressing to obtain the positive electrode sheet.

[0101] According to some embodiments of the present application, the negative electrode sheet includes a negative electrode current collector and a negative active material layer disposed on at least one side surface of the negative electrode current collector, and the negative active material layer includes a negative active material.

[0102] According to some embodiments of the present application, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one side surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material base layer (e.g., a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0103] According to some embodiments of the present application, the negative active material can be a negative active material known in the art for use in a battery. As an example, the negative active material can include at least one of graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, and lithium titanate, etc. The silicon-based material can include at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can include at least one of elemental tin, a tin oxide compound, and a tin alloy.

[0104] According to some embodiments of the present application, the negative active material layer can further optionally include a binder. The binder can include at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0105] According to some embodiments of the present application, the negative active material layer can further optionally include a conductive agent. The conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0106] According to some embodiments of the present application, the negative active material layer can further optionally include other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like.

[0107] According to some embodiments of the present application, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative current collector, and after drying, cold pressing, and the like, the negative electrode sheet can be obtained.

[0108] According to some embodiments of the present application, the type of the separator film is not particularly limited, and any known porous structure separator film with good chemical stability and mechanical stability can be selected. In some embodiments of the present application, the material of the separator film can include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, or polyvinylidene fluoride.

[0109] According to some embodiments of the present application, the positive electrode sheet, the negative electrode sheet, and the separator film can be made into an electrode assembly through a winding process or a stacking process.

[0110] According to some embodiments of the present application, the above-mentioned secondary battery can include an outer package. The outer package can be used to package the above-mentioned electrode assembly and the electrolyte.

[0111] According to some embodiments of the present application, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, and the like. The outer package of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate, and the like can be listed.

[0112] In a second aspect of the present application, a preparation method of the secondary battery of the first aspect is provided. According to embodiments of the present application, the preparation method includes the following step of injecting an electrolyte:

[0113] a second liquid injection is performed after a first liquid injection;

[0114] The electrolyte used in the first liquid injection is a first electrolyte, and the electrolyte used in the second liquid injection is a second electrolyte. The first electrolyte and the second electrolyte independently comprise at least one of a sulfonate compound and a sulfate compound.

[0115] The mass percentage of the sulfonate compound in the first electrolyte is Mpo, and the mass percentage of the sulfate compound is Mpa. The Mpa and Mpo satisfy 0 < Mpa < Mpo ≤ 3.

[0116] The mass percentage of the sulfonate compound in the second electrolyte is Mdo, and the mass percentage of the sulfate compound is Mda. The Mda and Mdo satisfy 0 ≤ Mdo ≤ Mda ≤ 3.

[0117] The application adopts a two-step liquid injection method to prepare the aforementioned secondary battery. By separating the electrolyte components required in the battery formation stage and the electrolyte components required in the cycle stage, the local distribution characteristics of the non-free electrolyte and the free electrolyte in the initial state of the battery can be flexibly controlled. The applicant found that the local distribution characteristics of the initial state of the electrolyte determine the local distribution characteristics of the electrolyte in the subsequent working state: under the premise of sufficient total electrolyte and smooth transmission, the local distribution proportion of the additive in the initial state of the electrolyte can qualitatively determine the local distribution proportion of the additive in the subsequent working state. Therefore, by limiting the addition amount of the sulfonate compound and the sulfate compound in the two-step liquid injection, the local distribution of the electrolyte can be realized. Specifically, the product of the sulfate compound is rich in ROSO2Li organic components, which is more conducive to the self-repairing ability of SEI, and the product of the sulfonate compound is rich in Li2CO3 and Li2SO3 inorganic components, which is more conducive to the ion conduction ability of SEI. By limiting Mpo to be not less than Mpa in the first electrolyte and Mda to be not less than Mdo in the second electrolyte, T2 < T1 can be realized. At the same time, by limiting M pa , M po , M do , M da The upper limit value is 3, which can realize sufficient film formation and not excessive reaction.

[0118] According to the embodiments of the application, the first electrolyte and the second electrolyte independently comprise at least one of a sulfonate compound and a sulfate compound, i.e., the first electrolyte can comprise at least one of a sulfonate compound and a sulfate compound, the second electrolyte can comprise at least one of a sulfonate compound and a sulfate compound, and the types of the sulfonate compound and the sulfate compound in the first electrolyte and the second electrolyte can be the same or different.

[0119] According to embodiments of the present application, the mass ratio of the first electrolyte to the second electrolyte is (6:4) to (8:2), and as some specific examples, the mass ratio of the first electrolyte to the second electrolyte can be 6:4, 7:3, 8:2, etc. In this way, the battery cycle performance can be improved. When the mass ratio of the first electrolyte to the second electrolyte is less than 6:4, the amount of electrolyte in the first injection is not sufficient to fully soak, the SEI protective layer obtained by formation is not uniform, and after the second injection, the area without SEI is not formed and the electrolyte is electronically conductive, causing the electrolyte to decompose and accumulate by-products; if the mass ratio of the first electrolyte to the second electrolyte is too high, i.e., greater than 8:2, the second injection ratio is low, and the free-state electrolyte composition mainly comes from the electrolyte composition that is not consumed in the first injection, and the non-free-state electrolyte composition is basically the same. At such a ratio, there is basically no difference between the second injection and the traditional first injection, and it is difficult to achieve the design of localized electrolyte.

[0120] According to embodiments of the present application, the sum of the injection coefficients of the first electrolyte and the second electrolyte is 2.5 g / Ah to 5 g / Ah, and as some specific examples, the sum of the injection coefficients of the first electrolyte and the second electrolyte can be 2.5 g / Ah, 3 g / Ah, 3.5 g / Ah, 4 g / Ah, 4.5 g / Ah, 5 g / Ah, etc., and preferably 3.5 g / Ah to 4.5 g / Ah. Specifically, the injection coefficient (amount of electrolyte / cell capacity) represents the amount of electrolyte required, and for energy storage lithium ion batteries, a higher injection coefficient can maintain a long cycle life. The present application limits the sum of the injection coefficients of the two injections to a suitable range, which can achieve sufficient soaking of the separator and the pole piece, and avoid swelling due to excessive amount of electrolyte or accumulation at the bottom of the battery causing local lithium precipitation.

[0121] According to specific embodiments of the present application, the preparation method can be carried out by the following steps: first injection, standing formation, second injection, high-temperature aging, and capacity distribution, to obtain the secondary battery. The standing aging and formation process are not particularly limited, and can ensure sufficient soaking and uniform film formation. The battery can be disassembled after full charging before the second injection and before capacity distribution, and the positive and negative electrodes and the separator in the battery are distributed with visible electrolyte, and the negative electrode has no abnormal spots or dark marks, i.e., the requirements are met. The full charging process can be constant current charging at 0.2C to 3.65V.

[0122] In a third aspect of the present application, a power consuming device is provided. According to embodiments of the present application, the power consuming device comprises the secondary battery of the first aspect.

[0123] According to some specific embodiments of the present application, the secondary battery can be used as a power source of the electric device, and can also be used as an energy storage unit of the electric device. The electric device can be, but is not limited to, a mobile phone, a tablet, a notebook computer, an electric toy, an electric tool, an electric vehicle, an electric car, a ship, a spacecraft, and the like. The electric toy can include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, an electric plane toy, and the like. The spacecraft can include an airplane, a rocket, a space shuttle, a spacecraft, and the like.

[0124] The embodiments of the present application are described in detail below. It should be noted that the embodiments described below are exemplary and are used to explain the present application, and should not be construed as limiting the present application. In addition, if not specifically stated, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known methods, and the reaction conditions not listed are also readily available to those skilled in the art.

[0125] The batteries of each embodiment and comparative example were prepared according to the following method:

[0126] (1) Preparation of the positive electrode tab:

[0127] The positive electrode active material lithium iron phosphate (LiFeP04), conductive carbon black (SP), and the binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 97:2.5:0.5, dispersed in the solvent N-methyl pyrrolidone (NMP) to obtain a positive electrode slurry, and the positive electrode slurry was coated on the positive electrode current collector aluminum foil. The coating weight of the positive electrode slurry per unit area was 33 mg / cm 2 After embossing, drying, cold pressing, slitting, and cutting, the positive electrode tab was obtained.

[0128] (2) Preparation of the negative electrode tab:

[0129] The negative electrode active material artificial graphite, conductive carbon black (SP), thickening agent (CMC), and binder (SBR) were mixed in a mass ratio of 96.5:0.5:1:2, dispersed in deionized water to obtain a negative electrode slurry, and the negative electrode slurry was coated on the negative electrode current collector copper foil. The coating weight of the negative electrode slurry per unit area was 16 mg / cm 2 After drying, cold pressing, embossing, slitting, and cutting, the negative electrode tab was obtained.

[0130] (3) Preparation of the electrolyte:

[0131] In an argon atmosphere glove box with water and oxygen content ≤0.1 ppm, ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate were mixed in a mass ratio of 1:1:1, 1M lithium hexafluorophosphate, 3% vinylene carbonate and the additive shown in the table were added according to Tables 1-3, and stirred until completely dissolved;

[0132] (4) Preparation of the separator:

[0133] A 16 μm polyethylene film was used as the separator;

[0134] (5) Assembly of the battery:

[0135] The prepared positive electrode sheet, separator and negative electrode sheet were stacked in order, with the separator in the middle of the positive and negative electrode sheets, and wound into a bare cell. After welding the tabs, the cell was assembled into an outer package, heat-pressed, vacuum-dried, and then subjected to the liquid injection process.

[0136] Among them, the first injection group, such as Comparative Example 1-1 and Comparative Example 1-6, used the following preparation method: injecting electrolyte, packaging the cell, standing, formation, high-temperature standing, capacity testing, etc., to finally prepare a soft-pack lithium ion battery with a capacity of 3.2 Ah.

[0137] The second injection group used the following preparation method: injecting electrolyte for the first time, packaging the cell, standing, formation, injecting electrolyte for the second time, high-temperature standing, capacity testing, etc., to finally prepare a soft-pack lithium ion battery with a capacity of 3.2 Ah.

[0138] Among them, the formation of the first injection and the second injection both used the following steps:

[0139] (1) The cell was placed in a 45℃ formation cabinet for 10 min, and charged at 0.1C rate for 7 min to 1.17% SOC;

[0140] (2) Stand for 3 min, charge at 0.2C rate to 30% SOC.

[0141] Different t a , t c The positive and negative electrode sheets are not limited to being obtained by adjusting the parameters of the roller press equipment, and can also include designing embossing shapes, embossing single-point distribution, embossing local distribution, etc., or other processing methods performed on the bare cell thereafter, such as cold pressing parameter adjustment, etc.

[0142] In Table 1, the positive and negative electrode sheets were not embossed; the injection coefficient was 4.0 g / Ah; the first and second injection injection ratio was 7:3; the standing condition after the first injection was 45±5℃ for 24 hours, the formation temperature was 45℃, and the standing (high-temperature aging) condition after the second injection was 45±5℃ for 24 hours.

[0143] In Table 2, the parameters of the positive and negative electrode sheet embossing design are specifically listed; the injection coefficient, the one-injection and two-injection injection ratio, the temperature and time parameters in the secondary injection are consistent with Table 1. Among them, the one-injection and two-injection electrolyte in Example 2-1 is consistent with Example 1-1, the one-injection and two-injection electrolyte in Example 2-2 is consistent with Example 1-11, and the one-injection and two-injection electrolyte in Example 2-3 is consistent with Example 1-28. The one-injection and two-injection electrolyte of Example 2-12 to Example 2-15 is consistent, and the one-injection and two-injection electrolyte of Example 2-16 to Example 2-17 is consistent with Comparative Example 2-1. Specific examples are shown in Table 2.

[0144] In Table 3, the injection coefficient, the one-injection and two-injection injection ratio are specifically listed; the temperature and time conditions in the secondary injection are consistent with Table 1 and Table 2. Among them, the one-injection and two-injection electrolyte composition and the proportion of substances in Example 3-1 to Example 3-10 remain unchanged, and are consistent with Example 1-28 and Example 2-3.

[0145] (1) S ci , S c , S ai , S a Calculation:

[0146] S c is the sum of the projection areas of the first region and the second region on the negative electrode sheet in the direction perpendicular to the separator in the positive electrode sheet;

[0147] S a is the sum of the projection areas of the third region and the fourth region on the positive electrode sheet in the direction perpendicular to the separator in the negative electrode sheet;

[0148] S ci is the sum of the sheet surface area increments caused by each second region, wherein the calculation method of the sheet surface area increment caused by each second region is: the surface area of the second region minus the projection area of the second region on the negative electrode sheet (in the direction perpendicular to the separator);

[0149] S ai is the sum of the sheet surface area increments caused by each fourth region, wherein the calculation method of the sheet surface area increment caused by each fourth region is: the surface area of the fourth region minus the projection area of the fourth region on the positive electrode sheet (in the direction perpendicular to the separator).

[0150] (2) Test of free-state electrolyte composition:

[0151] The battery with the outer package was discharged to 0% SOC (2.5V) at a current of 0.05C, a gap of about 0.5 cm was cut on the right side of the battery facing the positive pole, and a gap of the same size was cut on the right side facing the negative pole, ensuring that the two gaps were on the diagonal line. The free electrolyte was poured into a fluorinated bottle from the small hole on the positive pole side until intermittent liquid drops flowed down for 30 s.

[0152] The relative mass content of the additives in the collected electrolyte was tested using a gas chromatograph-mass spectrometer (GC-MS).

[0153] (3) Non-free state (pore) electrolyte test:

[0154] The outer package was removed, and the individual bare cell was taken out, the pole piece was quickly peeled off, and it was placed in an aluminum plastic bag. A sufficient amount of acetonitrile solvent was added to completely immerse the pole piece. The aluminum plastic bag containing the acetonitrile solvent and the pole piece was sealed and left still at 35±10°C for 3 days.

[0155] The relative mass content of the additives in the collected electrolyte was tested using a gas chromatograph-mass spectrometer (GC-MS).

[0156] (4) Additive design parameter enrichment degree calculation:

[0157] Sulfonate group enrichment degree

[0158] wherein m on represents the mass content (g) of the n th compound containing a sulfonate group, M on represents the molar molecular weight (g / mol) of the n th compound containing a sulfonate group, x on represents the number of sulfonate group units in the n th compound containing a sulfonate group, and n is a natural number, F o = 0 when n = 0.

[0159] Sulfate group enrichment degree

[0160] wherein m an represents the mass content (g) of the n th compound containing a sulfonate group, M an represents the molar molecular weight (g / mol) of the n th compound containing a sulfonate group, x an represents the number of sulfonate group units in the n th compound containing a sulfonate group, and n is a natural number, F a = 0 when n = 0.

[0161] (5) Energy efficiency performance test:

[0162] Charge at 0.5P constant power to 3.65V and then discharge at 0.5P constant power to 2.5V at 25℃, the capacity of the Xth cycle of charge and discharge is recorded as CCX, DCX, the energy of the Xth cycle of charge and discharge is recorded as CEX, DEX, until X = 500.

[0163] The battery RTE is evaluated by the energy efficiency η after cycling, η = DE 500 / CE 500 .

[0164] Table 1

[0165]

[0166]

[0167] Table 1 continued

[0168]

[0169]

[0170]

[0171] Wherein " / " means the absence.

[0172] Table 1 tests the relationship between the design parameters and the cycle energy efficiency of the free state electrolyte and the non-free state electrolyte. Comparative Examples 1-7 use a traditional one-time injection process, and both sulfonic acid ester (1,3-propane sulfone lactone) and sulfuric acid ester (vinyl sulfate) additives are used at the same time; Comparative Example 1-8 uses a two-time injection process, and only the sulfonic acid ester and the sulfuric acid ester additives are used at the same time in the first injection; Comparative Example 1-9 uses a two-time injection process, and only the sulfonic acid ester and the sulfuric acid ester additives are used at the same time in the second injection; Comparative Example 1-10 uses a two-time injection process, and only the sulfuric acid ester additive is used in the first injection, and only the sulfonic acid ester additive is used in the second injection; Comparative Example 1-11 uses a two-time injection process, and only the sulfonic acid ester additive is used in the first injection, and only the sulfuric acid ester additive is used in the second injection. Because the two-time injection process adopts an injection ratio of 7:3, the content of the sulfonic acid ester (1,3-propane sulfone lactone) and the sulfuric acid ester (vinyl sulfate) additives in Comparative Examples 1-7 to 1-11 is adjusted to keep the actual amount of additives used consistent.

[0173] The test results show that the design parameters T1 and T2 of Comparative Examples 1-7 to 1-11 all exceed the limited range of the present application, and the characteristic of localized distribution of the sulfuric acid ester and the sulfonic acid ester additive in the battery cannot be realized, and the cycle energy efficiency is poor, basically less than 87%.

[0174] Comparative Examples 1-12 use the conventional one-time injection process, and only the compound type of the sulfonate and sulfate additives is changed. From the test results, it can be seen that only the compound type of the additive is optimized, and the design parameters T1 and T2 are still beyond the limited range, and the cycle energy efficiency is improved, but still cannot exceed 90%.

[0175] Examples 1-1 to 1-33 and Comparative Example 1-6 use the two-time injection process, and there is no restriction on whether the sulfonate and sulfate additives in the first injection and the second injection are the same. From the test values of the design parameters T1, T2, and cycle energy efficiency, the localized distribution of the sulfonate compounds and the sulfate compounds in the electrolyte can be analyzed, and the direct impact on the battery performance.

[0176] For Examples 1-1 to 1-9 and Comparative Examples 1-1 to 1-4, the addition amounts Mdo and Mda of the sulfonate (1,3-propane sultone) and sulfate (vinyl sulfate) additives in the second injection electrolyte are fixed, and the addition amounts Mpo and Mpa of the sulfonate (1,3-propane sultone) and sulfate (vinyl sulfate) additives in the first injection electrolyte are adjusted to obtain different T1 and T2 design parameters. It can be seen that compared with the comparative examples, when T2 < T1, the battery cycle energy efficiency can be effectively improved, because the mass ratio of the sulfonate compound / sulfate compound in the non-free electrolyte is at an appropriate level, and whether the SEI formed during formation or the structure after the SEI is broken and repaired during the cycle or storage, the inorganic components always preferentially enrich in the inner layer to provide efficient ion conduction, and the organic components always disperse in the outer layer to provide repair capability, thus the overall characteristics of low impedance and high stability are exhibited, thereby improving the cycle energy efficiency. However, the distribution range of T1 and T2 needs to be controlled, if T1 is too low, such as lower than 0.1 in Comparative Examples 1-1 and 1-2, the sulfate compound in the non-free electrolyte has a concentration advantage to compete for the first reaction, which easily causes the SEI to have more organic components in the inner layer and more inorganic components in the outer layer, which exhibits a large cell impedance, and the SEI is unstable and the repeated formation of the SEI during the cycle makes the energy efficiency low; if T1 is too high, such as higher than 10 in Comparative Example 1-4, the sulfonate compound in the non-free electrolyte has a concentration advantage to continuously react, which easily causes the SEI to have a large amount of inorganic components in the inner and outer layers and lack of organic components, which exhibits that the SEI is easily damaged, and also makes the energy efficiency poor. Similarly, in Comparative Example 1-13, because mpa is 0 and mda is 0, the range of T1 and T2 tends to infinity, the sulfonate compound has a concentration advantage to continuously react, which also leads to poor energy efficiency. In addition, the cycle energy efficiency of Example 1-1 performs best and can reach more than 94%.

[0177] For Examples 1-10 to 1-18 and Comparative Examples 1-5 to 1-6, the addition amounts Mpo and Mpa of the sulfonate (1,3-propane sultone) and sulfate (vinyl sulfate) additives in the first electrolyte were fixed, and the addition amounts Mdo and Mda of the sulfonate (1,3-propane sultone) and sulfate (vinyl sulfate) additives in the second electrolyte were adjusted to obtain different T1 and T2 design parameters. It can be seen that when T2 < T1, the battery cycle energy efficiency can be effectively improved, but the distribution range of T1 and T2 needs to be controlled. If T2 is too high, such as Comparative Examples 1-5 to 1-6 which are higher than 5, the sulfonate-based compound in the free state electrolyte has a concentration advantage. After being supplemented to the non-free state part, the continuous reaction easily causes the SEI inner and outer layers to contain a large amount of inorganic components and lack of organic components, which shows that the SEI is easily damaged, and the energy efficiency is also poor.

[0178] For Examples 1-19 to 1-33, the addition amounts Mpo, Mpa, Mdo, and Mda of the sulfonate and sulfate additives in the first and second injections were fixed, the compound types of the sulfonate and sulfate additives were adjusted, and mixed multiple compound additives were designed and verified. It can be seen from the results that compared with Example 1-1, replacing the compound types or combined use of the sulfonate and sulfate additives has a slight effect on the design parameters T1, T2, and cycle energy efficiency, among which Examples 1-26, 1-28, 1-31, and 1-32 can further optimize the cycle energy efficiency. Replacing the compound types or combined use of the sulfonate and sulfate additives does not affect the relationship of T2 < T1, which shows that the effect of the scheme of the present application on this type of substance is universal.

[0179] Table 2

[0180]

[0181]

[0182] Table 2 (continued)

[0183]

[0184]

[0185] wherein " / " represents the absence.

[0186] Table 2 tests the relationship between the additive design parameters in the free state electrolyte and the embossing design coefficient in terms of the influence on the cycle energy efficiency. Examples 1-1, 1-11, 1-28 and Comparative Example 2-1 in Table 2 are not embossed, so the design parameters tc=ta=1.00, tc+ta=2.00. By comparing Example 1-1 with Example 2-1, Example 1-11 with Example 2-2, Example 1-28 with Example 2-3, and Comparative Example 2-1 with Example 2-17, it can be found that the introduction of the electrode embossing on the original electrolyte design system does not necessarily improve the cycle energy efficiency. For example, the energy efficiency of Example 2-1 and Example 2-17 decreases slightly after using the embossed electrode, and the energy efficiency of Example 2-3 changes insignificantly after using the embossed electrode. Through the analysis of the relationship between Fo, Fa and tc+ta, it can be found that exceeding the required range of the design parameters will cause a certain degree of performance degradation. This is because the increase in the area of the electrode caused by embossing is different, and the demand for sulfonate and sulfate groups in the free state electrolyte is also different. If the sulfonate group in the free state electrolyte is too much, the SEI cannot be repaired in time, and the interface of the embossed part is weak, which is more prone to cause continuous loss of electrolyte. If the sulfonate group in the free state electrolyte is too little, it cannot effectively transport lithium ions, and the interface of the embossed part is weak, which is more prone to exacerbate lithium precipitation. Conversely, if the sulfate group in the free state electrolyte is too much, it cannot effectively transport lithium ions, and the embossed part is more prone to lithium precipitation. If the sulfate group in the free state electrolyte is too little, it cannot repair the SEI in time, and the embossed part is more prone to accumulate by-products and produce stains. Lithium precipitation and by-product stains caused by unreasonable additive and embossing design will directly worsen the battery energy efficiency.

[0187] Examples 2-3 to 2-17 adjust the types and contents of sulfonate and sulfate additives in the free state electrolyte to obtain different Fo and Fa, and further adjust the embossing design coefficients tc and ta to obtain the change values of the design parameters Fo / (tc+ta) and Fa-0.7(tc+ta)+0.55. From the test results, it can be found that when 1.5≤Fo≤2, 1≤Fa≤1.5, and 2.0<tc+ta≤2.7, a higher cycle energy efficiency can be achieved, especially in Examples 2-8 and 2-15, the energy efficiency can exceed 95%. The value range of Fo and Fa indicates that the free state electrolyte tends to use rich sulfonate compounds and oligosulfate compounds, which also means that when mixed with additives, the free state electrolyte needs to contain polysulfonate compounds and monosulfate compounds. The value range of tc+ta indicates that the embossing degree should not be excessive. Even if the electrode has good pressure resistance and does not break, but the increased area of the reaction with the electrolyte will also cause serious deterioration of the battery performance.

[0188] Table 3

[0189]

[0190]

[0191] Table 3 tests the influence of the injection coefficient of the secondary injection electrolyte, the injection mass ratio on the additive enrichment degree in the free state electrolyte, the design parameters, and the cycle energy efficiency.

[0192] In Example 3-1, the injection mass ratio is too low, the separator and the pole piece cannot be fully infiltrated, causing the local lack of film formation protection of the pole piece not entering the electrolyte in the formation stage. At this time, F o / (t c +t a ) is also less than 0.5, which exceeds the design range requirement, and the energy efficiency is deteriorated. In Example 3-6, the electrolyte is swollen due to excessive electrolyte, and the redundant electrolyte will accumulate at the bottom of the battery to cause lithium precipitation. At this time, F o / (t c +t a ) is also less than 0.5, which exceeds the limit range, so the injection coefficient of the total of the first injection electrolyte and the second injection electrolyte is limited to 2.5 g / Ah~5 g / Ah. From the energy efficiency influence, 3.5 g / Ah~4.5 g / Ah is preferred.

[0193] In Example 3-7, the ratio of the first injection and the second injection is too low, i.e., less than 6:4, so the injection amount of the first injection is not enough to fully infiltrate, and the SEI protective layer obtained in the formation is not uniform. After the second injection, the area without SEI and the electrolyte are electronically conductive, causing the electrolyte to decompose and accumulate by-products. In Example 3-10, the ratio of the first injection and the second injection is too high, i.e., greater than 8:2, so the second injection has a low proportion, and the composition of the free state electrolyte mainly comes from the electrolyte composition not consumed in the first injection, which is basically the same as the non-free state electrolyte composition. Under such a proportion, the second injection and the traditional first injection are basically the same, and it is difficult to achieve the design of localized electrolyte, so the injection mass ratio range of the first injection and the second injection is limited to 6:4~8:2. In Example 3-11, the injection coefficient and the second injection mass ratio are fine-tuned based on Example 2-15, and the cycle capacity retention rate and the energy efficiency are also improved, reaching as high as 96.5%.

[0194] By comparing Example 2-3 and Example 3-3, Example 3-4, and comparing Example 2-15 and Example 3-11, it can be seen that within the appropriate injection coefficient and injection mass ratio range, the additive distribution in the free state electrolyte has a very small influence, and under the premise of meeting the design parameters, the scheme can still be implemented.

[0195] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are contained in at least one embodiment or example of the present application. In the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0196] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and the person skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

Claims

1. A secondary battery, characterized in that: The secondary battery comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; The electrolyte includes a free electrolyte and a non-free electrolyte, and the non-free electrolyte includes the electrolyte in the pores of the positive electrode plate, the electrolyte in the pores of the negative electrode plate, and the electrolyte in the pores of the diaphragm; The non-free electrolyte includes a sulfonate compound and a sulfate compound; the free electrolyte includes at least one of a sulfonate compound and a sulfate compound; The mass ratio of the sulfonate compound to the sulfate compound in the non-free electrolyte is T1, and the mass ratio of the sulfonate compound to the sulfate compound in the free electrolyte is T2, wherein T1 and T2 satisfy 0.1≤T1≤10, 0≤T2≤5; The T1 and T2 satisfy T2<T1.

2. The secondary battery according to claim 1, wherein The sulfonate compound includes at least one of a linear sulfonate compound and a cyclic sulfonate compound; And / or, the sulfate ester compound includes at least one of a linear sulfate ester compound and a cyclic sulfate ester compound.

3. The secondary battery according to claim 1, wherein The sulfonate compound includes at least one of trimethylsilyl trifluoromethanesulfonate, diethylene glycol dimethanesulfonate, 3,3-difluoropropyl methanesulfonate, 4-(trifluoromethyl)phenyl trifluoromethanesulfonate, 2-cyanophenyl trifluoromethanesulfonate, p-tolyl methanesulfonate, 4-nitrobenzyl methanesulfonate, propenyl-1,3-propane sultone, 1,4-propane sultone, 1,4-butane sultone, 2,4-butane sultone, tetrafluorosultone, 1,2,2-trifluoro-2-hydroxy-1-trifluoromethylethanesulfonic acid, 3-fluoro-1,3-propane sultone, and methylene methanedisulfonate; And / or, the sulfate ester compound includes at least one of trimethylene sulfate, 2-methyl-1,3-propanedisulfite, vinyl sulfate, 4-methyl vinyl sulfate, 4-ethyl vinyl sulfate, 4-propyl vinyl sulfate, 4-butyl vinyl sulfate, pentaerythritol bicyclic sulfate, and erythrose disulfate.

4. The secondary battery according to claim 1, wherein The enrichment degree of sulfonate groups in the free electrolyte is F o , the F o Satisfy F o =0 or 1≤F o ≤2; And / or, the enrichment degree of sulfate groups in the free electrolyte is F a , the F a Satisfy 1≤F a ≤1.

8.

5. The secondary battery according to claim 4, wherein The F o Satisfy 1.5≤F o ≤2; and / or, the F a Satisfy 1≤F a ≤1.

5.

6. The secondary battery according to claim 4 or 5, characterized in that: The positive electrode sheet has a first area and a second area on a side close to the separator, the first area has a flat outer surface, and the second area is convex relative to the first area; And / or, the negative electrode plate has a third region and a fourth region on a side close to the separator, the third region has a flat outer surface, and the fourth region is convex relative to the third region.

7. The secondary battery according to claim 6, characterized in that The positive electrode sheet has the first region and the second region on the side close to the separator, and the design coefficient t of the positive electrode sheet is c =1+S ci / S c , the t c Satisfy 1.0≤t c ≤1.5; Among them, S c S is the sum of the projected areas of the first region and the second region on the negative electrode sheet in the direction perpendicular to the diaphragm, ci is the surface area of ​​the positive electrode sheet increased by the second region; And / or, the negative electrode plate has a third region and a fourth region on one side close to the separator, and the design coefficient t of the negative electrode plate is a =1+S ai / S a , the t a Satisfy 1.0≤t a ≤1.5; Among them, S a S is the sum of the projected areas of the third region and the fourth region on the positive electrode sheet in the direction perpendicular to the diaphragm in the negative electrode sheet, ai is the surface area of ​​the negative electrode sheet increased by the fourth region; And / or, the design coefficient t of the positive electrode plate c and the design coefficient t of the negative electrode sheet a Satisfy 2.0<t c +t a ≤2.

7.

8. The secondary battery according to claim 7, wherein The enrichment degree F of sulfonate groups in the free electrolyte o , the enrichment degree F of sulfate groups in the free electrolyte a , the design coefficient t of the positive electrode sheet c and the design coefficient t of the negative electrode sheet a Meet at least one of the following conditions: F o / (t c +t a )=0; 0.5≤F o / (t c +t a )≤1; 0≤F a -0.7(t c +t a )+0.55≤0.8。 9. A method for preparing a secondary battery according to any one of claims 1 to 8, characterized in that: The steps of injecting electrolyte include: After the first injection is completed, the second injection is performed; The electrolyte used in the first injection is a first electrolyte, and the electrolyte used in the second injection is a second electrolyte. The first electrolyte includes a sulfonate compound and a sulfate compound, and the second electrolyte includes at least one of a sulfonate compound and a sulfate compound. The mass proportion of the sulfonate compound in the first electrolyte is Mpo, and the mass proportion of the sulfate compound is Mpa, and the Mpa and Mpo satisfy 0<Mpa<Mpo≤3; The mass proportion of the sulfonate compound in the second electrolyte is Mdo, and the mass proportion of the sulfate compound is Mda, and the Mda and Mdo satisfy 0≤Mdo≤Mda≤3.

10. The preparation method according to claim 9, characterized in that The mass ratio of the first electrolyte to the second electrolyte is (6:4) to (8:2); And / or, the sum of the injection coefficients of the first electrolyte and the second electrolyte is 2.5 g / Ah to 5 g / Ah.

11. An electrical device, characterized in that: The electrical device comprises the secondary battery according to any one of claims 1 to 8.

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