Battery

Abstract

The utility model provides a battery which comprises a shell and a battery cell positioned in the shell, and the battery cell comprises a first pole piece, a second pole piece and a diaphragm positioned between the first pole piece and the second pole piece; the battery meets the condition that (T1-T2) / T0 < = 0.3%, T0 is the thickness of the battery when the battery is charged to a full charge state after circulation, T1 is the thickness of the battery after the battery is subjected to open-circuit shelving for 30 days at the temperature of 45 + / -2 DEG C when the battery is charged to the full charge state after circulation, and T2 is the thickness of the battery after the battery is subjected to open-circuit shelving for 30 days at the temperature of 45 + / -2 DEG C and then shelved for 2 hours at the temperature of 25 + / -2 DEG C. The battery has relatively low pole piece rebound rate and thickness swelling rate, the energy density of the battery can be effectively improved, and the cycle life of the battery can be effectively prolonged.

Description

Technical Field

[0001] The utility model belongs to the technical field of secondary batteries and relates to a battery. Background Art

[0002] Lithium-ion batteries are widely used in communication equipment, power tools, aerospace and other fields due to their advantages such as high working voltage, high specific energy, wide working temperature range, no memory effect, and no toxic and harmful substances. With the continuous progress of technology, higher requirements are put forward for lithium-ion batteries. As an important part of lithium-ion batteries, the electrode sheet occupies a large proportion in lithium-ion batteries and will greatly affect the performance of the battery.

[0003] The electrode sheet is generally made by slurry preparation, coating active substances on the current collector, rolling the electrode sheet, and slitting the electrode sheet. After the electrode sheet is rolled, the thickness of the electrode sheet will change from thick to thin. However, in actual production, it is found that the thickness of the electrode sheet increases compared with the thickness after rolling after a period of time or after other processes. The main manifestations include the thickness change of the electrode sheet during static state after rolling, the rebound change of the electrode sheet after baking, the volume change after injecting electrolyte, and the volume change caused by the insertion and extraction of lithium ions during the charge and discharge cycle. Especially under high-temperature storage conditions, this change will be aggravated, resulting in the expansion of the battery cell and causing safety problems.

[0004] Therefore, it is urgent to study a battery with a lower electrode sheet rebound rate and thickness expansion rate. Content of the Utility Model

[0005] In view of the above defects, the utility model provides a battery with a lower electrode sheet rebound rate and thickness expansion rate.

[0006] The utility model provides a battery, which includes a housing and a battery cell located inside the housing. The battery cell includes a first electrode sheet, a second electrode sheet, and a separator located between the first electrode sheet and the second electrode sheet;

[0007] The thickness of the battery satisfies Equation 1,

[0008] (T1 - T2) / T0 ≤ 0.3% Equation 1

[0009] In Equation 1, T0 is the thickness of the battery after cycling and charged to full charge state, with the unit of mm; T1 is the thickness of the battery after cycling and charged to full charge state after being open-circuited and stored at 45 ± 2°C for 30 days, with the unit of mm; T2 is the thickness of the battery after being open-circuited and stored at 45 ± 2°C for 30 days and then stored at 25 ± 2°C for 2 h, with the unit of mm.

[0010] Furthermore, the battery satisfies Equation 2 and / or Equation 3,

[0011] (H1 - H2) / H0 ≤ 0.4% Equation 2

[0012] (h1 - h2) / h0 ≤ 0.2% Equation 3

[0013] Among them, H0 is the thickness of the first electrode sheet when the battery is cycled and charged to the full charge state, with the unit of mm; h0 is the thickness of the second electrode sheet when the battery is cycled and charged to the full charge state, with the unit of mm; H1 is the thickness of the first electrode sheet when the battery is cycled and charged to the full charge state and left open - circuit at 45 ± 2°C for 30 days, with the unit of mm; h1 is the thickness of the second electrode sheet when the battery is cycled and charged to the full charge state and left open - circuit at 45 ± 2°C for 30 days, with the unit of mm; H2 is the thickness of the first electrode sheet after the battery is left open - circuit at 45 ± 2°C for 30 days and then left at 25 ± 2°C for 2 h, with the unit of mm; h2 is the thickness of the second electrode sheet after the battery is left open - circuit at 45 ± 2°C for 30 days and then left at 25 ± 2°C for 2 h, with the unit of mm.

[0014] Furthermore, the battery satisfies Equation 4,

[0015] (T3 - T4) / T0 ≤ 0.4% Equation 4

[0016] Among them, T3 is the thickness of the battery after the battery body temperature drops to 25 ± 2°C and is left open - circuit at 70 ± 2°C for 24 h, with the unit of mm; T4 is the thickness of the battery after being left open - circuit at 70 ± 2°C for 24 h and then left at 25 ± 2°C for 2 h, with the unit of mm.

[0017] Furthermore, the battery satisfies Equation 5 and / or Equation 6,

[0018] (H3 - H4) / H0 ≤ 0.6% Equation 5

[0019] (h3 - h4) / h0 ≤ 0.25% Equation 6

[0020] Among them, H3 is the thickness of the first electrode sheet after the battery body temperature drops to 25 ± 2°C and is left open - circuit at 70 ± 2°C for 24 h, with the unit of mm; h3 is the thickness of the second electrode sheet after the battery body temperature drops to 25 ± 2°C and is left open - circuit at 70 ± 2°C for 24 h, with the unit of mm; H4 is the thickness of the first electrode sheet after being left open - circuit at 70 ± 2°C for 24 h and then left at 25 ± 2°C for 2 h, with the unit of mm; h4 is the thickness of the second electrode sheet after being left open - circuit at 70 ± 2°C for 24 h and then left at 25 ± 2°C for 2 h, with the unit of mm.

[0021] Furthermore, the battery satisfies Equation 7 and / or Equation 8,

[0022] 1 ≤ ((H2 - H0) / H0) / ((h2 - h0) / h0) ≤ 10 Equation 7

[0023] 1 ≤ ((H4 - H0) / H0) / ((h4 - h0) / h0) ≤ 10, Equation 8.

[0024] Furthermore, T0 is 2.0 - 10.0 mm, and / or, T1 is 2.0 - 11.0 mm, and / or, T2 is 2.0 - 10.5 mm;

[0025] and / or, H0 is 0.035 - 0.18 mm, and / or, H1 is 0.035 - 0.185 mm, and / or, H2 is 0.035 - 0.183 mm;

[0026] and / or, h0 is 0.035 - 0.120 mm, and / or, h1 is 0.035 - 0.125 mm, and / or, h2 is 0.035 - 0.123 mm;

[0027] and / or, T3 is 2.0 - 12.0 mm, and / or, T4 is 2.0 - 11.5 mm;

[0028] and / or, H3 is 0.035 - 0.190 mm, and / or, H4 is 0.035 - 0.188 mm;

[0029] and / or, h3 is 0.035 - 0.130 mm, and / or, h4 is 0.035 - 0.128 mm.

[0030] Furthermore, the first electrode includes a negative electrode active layer and a negative electrode current collector, and the negative electrode active layer is disposed on at least one functional surface of the negative electrode current collector;

[0031] In the thickness direction of the first electrode, from the side close to the negative electrode current collector to the side far from the negative electrode current collector, the negative electrode active layer includes a first region, a second region, and a third region distributed in sequence;

[0032] The cross-sectional porosity of the first region is less than the cross-sectional porosity of the second region, and / or, the cross-sectional porosity of the third region is less than the cross-sectional porosity of the second region.

[0033] Furthermore, the cross-sectional porosity of the first region is 5% - 35%, and / or, the cross-sectional porosity of the second region is 7% - 40%, and / or, the cross-sectional porosity of the third region is 5% - 35%.

[0034] Furthermore, the first electrode satisfies the following relationship:

[0035] (The cross-sectional porosity of the first region + the cross-sectional porosity of the third region) / 2 ≤ the cross-sectional porosity of the second region.

[0036] Further, the thickness ratio of the first zone, the second zone and the third zone is (1-4):(2-8):(1-4).

[0037] Further, the thickness of the first zone is 0.007-0.021 mm, and / or the thickness of the second zone is 0.015-0.055 mm, and / or the thickness of the third zone is 0.007-0.021 mm.

[0038] Further, the first electrode includes a negative current collector and a negative active layer disposed on at least one functional surface of the negative current collector;

[0039] The mass percentage content of silicon in the negative active layer is not less than 30 wt%, and the bounce rate of the first electrode is not higher than 50%.

[0040] By making the battery satisfy Formula 1, the present invention can effectively reduce the electrode bounce and the cell thickness expansion during the charge and discharge process of the battery under high-temperature storage conditions, can significantly improve the stability of the battery in a high-temperature environment, and helps to improve the energy density and service life of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a schematic cross-sectional view of the first electrode in one embodiment of the present invention;

[0042] Figure 2 is a schematic cross-sectional view of the first electrode in another embodiment of the present invention;

[0043] Figure 3 is a cross-sectional SEM image of the first electrode of Example 1 of the present invention at 800X;

[0044] Figure 4 is a cross-sectional SEM image of the first electrode of Example 1 of the present invention at 2.00KX. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045] In order to make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0046] The present invention provides a battery, including a housing and a cell located inside the housing. The cell includes a first electrode, a second electrode and a separator located between the first electrode and the second electrode;

[0047] The battery satisfies Equation 1,

[0048] (T1 - T2) / T0 ≤ 0.3% Equation 1

[0049] In Equation 1, T0 is the thickness of the battery after cycling and being charged to the full charge state, with the unit of mm; T1 is the thickness of the battery after cycling and being charged to the full charge state and being open - circuit shelved at 45 ± 2°C for 30 days, with the unit of mm; T2 is the thickness of the battery after being open - circuit shelved at 45 ± 2°C for 30 days and then being open - circuit shelved at 25 ± 2°C for 2 h, with the unit of mm.

[0050] T0, T1, and T2 in the present utility model are measured by including the following methods:

[0051] First, discharge the battery after grading (electrochemical window is 4.2V - 4.55V) at a rate of 0.3C to 3.0V at 25°C. After shelving for 5 min, charge it at a rate of 0.5C to 4.2V - 4.55V, and then charge it at a constant voltage of 4.2V - 4.55V until the cut - off current of 0.05C, and let it stand for 10 min; then discharge it at a rate of 0.7C to 3.0V and let it stand for 10 min; after cycling 2 laps according to the aforementioned charge - discharge mechanism, charge the battery at a rate of 0.5C to 4.2V - 4.55V, and then charge it at a constant voltage of 4.2V - 4.55V until the cut - off current of 0.05C. When the test battery is in the full - charge state, measure the thickness of the full - charged battery within 1 - 3 min to obtain T0. Then, take out the battery that has been cycled 2 laps and charged to the full - charge state and place it at 45 ± 2°C for open - circuit shelving for 30 days within 30 min, and measure the thickness of the battery within 5 min to obtain T1. Finally, place the battery that has been open - circuit shelved at 45 ± 2°C for 30 days at 25.0 ± 2°C for open - circuit shelving for 2 h. At this time, the body temperature of the battery is 25 ± 2°C, and measure the thickness of the battery within 10 min to obtain T2.

[0052] The battery thickness in the present utility model is measured by a flat - plate pressure PPG thickness gauge. The measurement pressure is 0.6 kgf, and the test method is as follows: First, use the thickness gauge to check the upper - left, lower - left, middle, lower - right, and upper - right positions of a 4 - mm standard block. The deviations between the thicknesses measured at the five positions and the thickness of the standard block are respectively less than or equal to 5 μm. If it is greater than 5 μm, the marble plate of the thickness gauge needs to be leveled. After the check passes, test the battery after cycling and being charged to the full - charge state.

[0053] The present utility model does not make special limitations on the preparation method of the above - mentioned battery, as long as the battery satisfies Equation 1.

[0054] The present utility model controls the battery thickness T0 when the battery is cycled and charged to the full charge state, the battery thickness T1 when the battery is cycled and charged to the full charge state and then open-circuit stored at 45 ± 2 °C for 30 days, and the battery thickness T2 when the battery is open-circuit stored at 45 ± 2 °C for 30 days and then stored at 25 ± 2 °C for 2 h, so that T0, T1, and T2 satisfy Equation 1, which can effectively reduce the pole piece rebound rate and battery thickness expansion rate during charge and discharge of the battery under high-temperature storage conditions, thereby improving the stability of the battery in a high-temperature environment and enhancing the energy density and cycle life of the battery.

[0055] In a specific embodiment, the battery satisfies Equation 2 and / or Equation 3.

[0056] (H1 - H2) / H0 ≤ 0.4% Equation 2

[0057] (h1 - h2) / h0 ≤ 0.2% Equation 3

[0058] Among them, H0 is the thickness of the first pole piece when the battery is cycled and charged to the full charge state, with the unit of mm; h0 is the thickness of the second pole piece when the battery is cycled and charged to the full charge state, with the unit of mm; H1 is the thickness of the first pole piece when the battery is cycled and charged to the full charge state and then open-circuit stored at 45 ± 2 °C for 30 days, with the unit of mm; h1 is the thickness of the second pole piece when the battery is cycled and charged to the full charge state and then open-circuit stored at 45 ± 2 °C for 30 days, with the unit of mm; H2 is the thickness of the first pole piece when the battery is open-circuit stored at 45 ± 2 °C for 30 days and then stored at 25 ± 2 °C for 2 h, with the unit of mm; h2 is the thickness of the second pole piece when the battery is open-circuit stored at 45 ± 2 °C for 30 days and then stored at 25 ± 2 °C for 2 h, with the unit of mm.

[0059] H0, h0, H1, h1, H2, and h2 in the present utility model are measured by including the following methods:

[0060] The battery that has been cycled and charged to the full charge state is disassembled within 1 - 3 min to obtain the first pole piece (negative pole piece) and the second pole piece (positive pole piece), and the thicknesses of the first pole piece and the second pole piece are measured to obtain H0 and h0; then the battery that has been cycled and charged to the full charge state and then open-circuit stored at 45 ± 2 °C for 30 days is disassembled within 5 min to obtain the first pole piece and the second pole piece, and the thicknesses of the first pole piece and the second pole piece are measured to obtain H1 and h1; the battery that has been open-circuit stored at 45 ± 2 °C for 30 days and then open-circuit stored at 25.0 ± 2 °C for 2 h is disassembled within 5 min to obtain the first pole piece and the second pole piece, and the thicknesses of the first pole piece and the second pole piece are measured to obtain H2 and h2.

[0061] The thickness of the first electrode and the second electrode in the present utility model is measured by a Mitutoyo micrometer. Before the test, the Mitutoyo micrometer needs to be used to check the upper left, lower left, middle, lower right, and upper right positions of a standard gauge block with a thickness of 0.100 - 0.150 mm. The difference between the measured thickness and the standard gauge block should not exceed 0.001 mm. If it is greater than 0.001 mm, the Mitutoyo micrometer needs to be calibrated.

[0062] In a specific embodiment, the battery satisfies Equation 4,

[0063] (T3 - T4) / T0 ≤ 0.4% Equation 4

[0064] Wherein, T3 is the thickness of the battery after the battery body temperature drops to 25 ± 2 °C and then is open-circuited and placed for 24 h at 70 ± 2 °C; T4 is the thickness of the battery after the battery is open-circuited and placed for 24 h at 70 ± 2 °C and then placed for 2 h at 25 ± 2 °C.

[0065] T3 and T4 in the present utility model are measured by including the following methods:

[0066] The battery after being open-circuited and placed for 2 h at 25.0 ± 2 °C is placed at 70 ± 2 °C and open-circuited for 24 h within 10 min. After taking it out, the thickness of the battery is measured within 5 min to obtain T3; the battery after being open-circuited and placed for 24 h at 70 ± 2 °C is placed at 25.0 ± 2 °C and open-circuited for 2 h. At this time, the body temperature of the battery is 25 ± 2 °C, and the thickness of the battery is measured within 10 min to obtain T4.

[0067] The measurement method of the battery thickness in the present utility model is the same as above and will not be elaborated here.

[0068] When the battery satisfies Equation 4, the battery has better high-temperature storage performance, enabling the battery to have a lower electrode rebound rate and thickness expansion rate at a higher storage temperature, thereby further improving the energy density and cycle life of the battery.

[0069] In a specific embodiment, the battery satisfies Equation 5 and / or Equation 6,

[0070] (H3 - H4) / H0 ≤ 0.6% Equation 5

[0071] (h3 - h4) / h0 ≤ 0.25% Equation 6

[0072] Among them, H3 is the thickness of the first electrode after the battery body temperature drops to 25±2°C and is open-circuited and left standing at 70±2°C for 24 hours, with the unit of mm; h3 is the thickness of the second electrode after the battery body temperature drops to 25±2°C and is open-circuited and left standing at 70±2°C for 24 hours, with the unit of mm; H4 is the thickness of the first electrode after the battery is open-circuited and left standing at 70±2°C for 24 hours and then left standing at 25±2°C for 2 hours, with the unit of mm; h4 is the thickness of the second electrode after the battery is open-circuited and left standing at 70±2°C for 24 hours and then left standing at 25±2°C for 2 hours, with the unit of mm.

[0073] H3, h3, H4, and h4 in the present utility model are measured by including the following methods:

[0074] After the temperature of the above battery body drops to 25±2°C and is open-circuited and left standing at 70±2°C for 24 hours, the battery is disassembled within 5 minutes to obtain the first electrode (negative electrode) and the second electrode (positive electrode), and the thicknesses of the first electrode and the second electrode are measured to obtain H3 and h3; after the above battery is open-circuited and left standing at 70±2°C for 24 hours and then left standing at 25±2°C for 2 hours, the battery is disassembled within 10 minutes to obtain the first electrode (negative electrode) and the second electrode (positive electrode), and the thicknesses of the first electrode and the second electrode are measured to obtain H4 and h4.

[0075] The measurement methods of the thickness of the first electrode and the second electrode in the present utility model are the same as above, and will not be elaborated here.

[0076] When the battery satisfies Equation 5 and / or Equation 6, the battery can have better high-temperature storage performance, and further reduce the electrode rebound rate and thickness expansion rate under high-temperature storage.

[0077] In a specific embodiment, the battery satisfies Equation 7,

[0078] 1((H2 - H0) / H0) / ((h2 - h0) / h0) ≤ 10 Equation 7. In this range, it helps to further improve the high-temperature storage performance of the battery, enables the battery to reach a lower battery thickness expansion rate at 45±2°C, and improves the cycle performance of the battery.

[0079] In a specific embodiment, the battery satisfies Equation 8,

[0080] 1((H4 - H0) / H0) / ((h4 - h0) / h0) ≤ 30 Equation 8. In this range, it helps to improve the stability of the battery at a higher storage temperature, enables the battery to have a lower battery thickness expansion rate at 70±2°C, and further improves the cycle performance of the battery.

[0081] In a specific embodiment, T0 is 2.0 to 10.0 mm, and / or, T1 is 2.0 to 11.0 mm, and / or, T2 is 2.0 to 10.5 mm;

[0082] and / or, H0 is 0.035 to 0.18 mm, and / or, H1 is 0.035 to 0.185 mm, and / or, H2 is 0.035 to 0.183 mm;

[0083] and / or, h0 is 0.035 to 0.120 mm, and / or, h1 is 0.035 to 0.125 mm, and / or, h2 is 0.035 to 0.123 mm;

[0084] and / or, T3 is 2.0 to 12.0 mm, and / or, T4 is 2.0 to 11.5 mm;

[0085] and / or, H3 is 0.035 to 0.190 mm, and / or, H4 is 0.035 to 0.188 mm;

[0086] and / or, h3 is 0.035 to 0.130 mm, and / or, h4 is 0.035 to 0.128 mm.

[0087] For example, T0 is 2.0 mm, 3.0 mm, 4.0 mm, 5.0 mm, 6.0 mm, 7.0 mm, 8.0 mm, 9.0 mm or 10.0 mm.

[0088] For example, T1 is 2.0 mm, 3.0 mm, 4.0 mm, 5.0 mm, 6.0 mm, 7.0 mm, 8.0 mm, 9.0 mm, 10.0 mm or 11 mm.

[0089] For example, T2 is 2.0 mm, 3.0 mm, 4.0 mm, 5.0 mm, 6.0 mm, 7.0 mm, 8.0 mm, 9.0 mm, 10.0 mm, 11 mm or 12 mm.

[0090] For example, H0 is 0.035 mm, 0.045 mm, 0.055 mm, 0.065 mm, 0.075 mm, 0.085 mm, 0.095 mm, 0.105 mm, 0.115 mm, 0.125 mm, 0.135 mm, 0.145 mm, 0.155 mm, 0.165 mm, 0.175 mm or 0.180 mm.

[0091] For example, H1 is 0.035 mm, 0.045 mm, 0.055 mm, 0.065 mm, 0.075 mm, 0.085 mm, 0.095 mm, 0.105 mm, 0.115 mm, 0.125 mm, 0.135 mm, 0.145 mm, 0.155 mm, 0.165 mm, 0.175 mm or 0.185 mm.

[0092] For example, H2 is 0.035 mm, 0.040 mm, 0.050 mm, 0.060 mm, 0.070 mm, 0.080 mm, 0.090 mm, 0.100 mm, 0.110 mm, 0.120 mm, 0.130 mm, 0.140 mm, 0.150 mm, 0.160 mm, 0.170 mm, 0.180 mm or 0.183 mm.

[0093] For example, h0 is 0.035 mm, 0.045 mm, 0.055 mm, 0.065 mm, 0.075 mm, 0.085 mm, 0.095 mm, 0.105 mm, 0.115 mm or 0.120 mm.

[0094] For example, h1 is 0.035 mm, 0.045 mm, 0.055 mm, 0.065 mm, 0.075 mm, 0.085 mm, 0.095 mm, 0.105 mm, 0.115 mm or 0.125 mm.

[0095] For example, h2 is 0.035 mm, 0.040 mm, 0.050 mm, 0.060 mm, 0.070 mm, 0.080 mm, 0.090 mm, 0.100 mm, 0.110 mm, 0.120 mm or 0.123 mm.

[0096] For example, T3 is 2.0 mm, 3.0 mm, 4.0 mm, 5.0 mm, 6.0 mm, 7.0 mm, 8.0 mm, 9.0 mm, 10.0 mm, 11 mm or 12 mm.

[0097] For example, T4 is 2.0 mm, 2.5 mm, 3.5 mm, 4.5 mm, 5.5 mm, 6.5 mm, 7.5 mm, 8.5 mm, 9.5 mm, 10.5 mm or 11.5 mm.

[0098] For example, H3 is 0.035 mm, 0.040 mm, 0.050 mm, 0.060 mm, 0.070 mm, 0.080 mm, 0.090 mm, 0.100 mm, 0.110 mm, 0.120 mm, 0.130 mm, 0.140 mm, 0.150 mm, 0.160 mm, 0.170 mm, 0.180 mm or 0.190 mm.

[0099] For example, H4 is 0.035 mm, 0.040 mm, 0.050 mm, 0.060 mm, 0.070 mm, 0.080 mm, 0.090 mm, 0.100 mm, 0.110 mm, 0.120 mm, 0.130 mm, 0.140 mm, 0.150 mm, 0.160 mm, 0.170 mm, 0.180 mm or 0.188 mm.

[0100] For example, h3 is 0.035 mm, 0.045 mm, 0.055 mm, 0.065 mm, 0.075 mm, 0.085 mm, 0.095 mm, 0.105 mm, 0.115 mm, 0.125 mm or 0.130 mm.

[0101] For example, h4 is 0.035 mm, 0.040 mm, 0.050 mm, 0.060 mm, 0.070 mm, 0.080 mm, 0.090 mm, 0.100 mm, 0.110 mm, 0.120 mm or 0.128 mm.

[0102] When at least one of T0, T1, T2, T3, T4, H0, H1, H2, H3, H4, h0, h1, h2, h3, h4 is within the aforementioned range, the cycle life and energy density of the battery can be further improved.

[0103] In a specific embodiment, the areal density of the first electrode sheet before rolling is 0.02 g / mm 2 ~0.130 mg / mm 2 , and the tap density of the first electrode sheet after rolling is 1.40 g / cm 3 ~1.82 g / cm 3 . Within this range, the pore size distribution of the obtained first electrode sheet (negative electrode sheet) is relatively uniform, and the active material particles are not easily broken; at the same time, the conductivity of the electrode sheet can be improved and the lithium ion transmission path can be shortened, effectively reducing the battery impedance.

[0104] In a specific embodiment, the areal density of the second electrode sheet before rolling is 0.05 mg / mm 2 ~0.24 mg / mm 2 , and the tap density of the second electrode sheet after rolling is 4.0 g / cm3 ~4.45 g / cm 3 Within this range, the second electrode sheet (positive electrode sheet) has high toughness and a relatively uniform pore size distribution, which can effectively improve the conductivity of the electrode sheet and shorten the lithium ion transmission path, thereby reducing the battery impedance.

[0105] In a specific embodiment, the first electrode sheet includes a negative electrode active layer and a negative electrode current collector, and the negative electrode active layer is disposed on at least one functional surface of the negative electrode current collector;

[0106] In the thickness direction of the first electrode sheet, from the side close to the negative electrode current collector to the side far from the negative electrode current collector, the negative electrode active layer includes a first region, a second region, and a third region that are sequentially distributed;

[0107] The cross-sectional porosity of the first region is less than the cross-sectional porosity of the second region, and / or the cross-sectional porosity of the third region is less than the cross-sectional porosity of the second region.

[0108] In one embodiment, as Figure 1 shown, it is a cross-sectional schematic diagram of the first electrode sheet (negative electrode sheet), the h direction is the thickness direction of the first electrode sheet, the negative electrode active layer 2 is disposed on one functional surface of the negative electrode current collector 1, and the negative electrode active layer includes a first region 21, a second region 22, and a third region 23.

[0109] In another embodiment, as Figure 2 shown, it is a cross-sectional schematic diagram of the first electrode sheet (negative electrode sheet), the h direction is the thickness direction of the first electrode sheet, the negative electrode active layer 2 is disposed on two functional surfaces of the negative electrode current collector 1, and the negative electrode active layer includes a first region 21, a second region 22, and a third region 23.

[0110] The cross-sectional porosity of the present utility model is measured by including the following steps: disassembling the battery after formation to obtain the first electrode sheet (negative electrode sheet), taking more than three positions in the length direction of the first electrode sheet, respectively preparing cross-sections CP (argon ion polishing method) for these positions, and then using a scanning electron microscope (SEM) to test the cross-section to obtain cross-sectional SEM images at different positions. Using Image J software to adjust the threshold of the obtained cross-sectional SEM images to be the same, performing zoning calculations to obtain the cross-sectional porosity at different positions, and taking the average value to obtain the cross-sectional porosity of the first region 21, the second region 22, and the third region 23 respectively.

[0111] When the cross-sectional porosity of the first region 21 is less than the cross-sectional porosity of the second region 22, the negative electrode active material in the second region 22 binds the negative electrode active material in the first region 21, effectively improving the bond strength between particles and increasing, thereby inhibiting the physical and electrochemical rebound of the negative electrode active material in the first region 21, which helps to improve the volumetric energy density and cycle stability of the battery, and is also beneficial to improving the conductivity.

[0112] When the cross-sectional porosity of the third region 23 is less than that of the second region 22, it helps to reduce the contact area between the negative active material and the electrolyte, thereby reducing the occurrence of side reactions during cycling, improving the stability of the electrode, and further improving the cycling performance of the battery.

[0113] In a specific embodiment, the cross-sectional porosity of the first region 21 is 5% to 35%, and / or the cross-sectional porosity of the second region 22 is 7% to 40%, and / or the cross-sectional porosity of the third region 23 is 5% to 35%. For example, the cross-sectional porosity of the first region is 5%, 10%, 15%, 20%, 25%, 30%, or 35%; the cross-sectional porosity of the second region 22 is 7%, 10%, 15%, 20%, 25%, 30%, 35%, or 40%; the cross-sectional porosity of the third region 23 is 5%, 10%, 15%, 20%, 25%, 30%, or 35%. Within this range, not only can a high energy density and charge-discharge performance be ensured, but also the stability and conductivity of the electrode can be improved.

[0114] In a specific embodiment, the first electrode sheet satisfies the following relationship:

[0115] (The cross-sectional porosity of the first region 21 + the cross-sectional porosity of the third region 23) / 2 ≤ the cross-sectional porosity of the second region 22. Within this range, the volumetric energy density and conductivity can be improved, and the lithium-ion transmission rate and electrolyte infiltration rate of the product can be ensured.

[0116] In a specific embodiment, the thickness ratio of the first region 21, the second region 22, and the third region 23 is (1 to 4):(2 to 8):(1 to 4). Within this range, the volumetric energy density and conductivity of the battery can be further improved, and the wettability of the electrolyte can also be improved, thereby effectively improving the rate performance and cycling performance of the battery.

[0117] The thicknesses of the first region 21, the second region 22, and the third region 23 in the present utility model are measured by including the following steps: disassembling the battery after grading to obtain the first electrode sheet (negative electrode sheet), taking more than three positions in the length direction of the first electrode sheet, respectively preparing cross-sections CP (argon ion polishing method) at these positions, then using a scanning electron microscope (SEM) to test the cross-section to obtain cross-sectional SEM images at different positions, using Image J software to adjust the thresholds of the obtained cross-sectional SEM images to be the same, partitioning according to different porosities to obtain the first region 21, the second region 22, and the third region 23 at each position, measuring the thickness values, and taking the average value to obtain the thicknesses of the first region 21, the second region 22, and the third region 23.

[0118] In a specific embodiment, the thickness of the first region 21 is 0.007 - 0.021 mm. For example, the thickness of the first region 1 is 0.007 mm, 0.008 mm, 0.010 mm, 0.012 mm, 0.014 mm, 0.016 mm, 0.018 mm, or 0.021 mm. Within this range, the battery can have a higher volumetric energy density and conductivity.

[0119] In a specific embodiment, the thickness of the second region 22 is 0.015 - 0.055 mm. For example, the thickness of the second region 2 is 0.015 mm, 0.020 mm, 0.025 mm, 0.030 mm, 0.035 mm, 0.040 mm, 0.045 mm, 0.050 mm, or 0.055 mm. Within this range, it can ensure that lithium ions can be quickly inserted and extracted into and from the first region 1, and the electrolyte can quickly infiltrate into the first region 1. At the same time, it can also ensure a relatively high conductivity and avoid an increase in resistance.

[0120] In a specific embodiment, the thickness of the third region 23 is 0.007 - 0.021 mm. For example, the thickness of the third region 3 is 0.007 mm, 0.008 mm, 0.010 mm, 0.012 mm, 0.014 mm, 0.016 mm, 0.018 mm, or 0.021 mm. Within this range, it can improve the volumetric energy density and conductivity of the battery.

[0121] In a specific embodiment, the first electrode plate includes a negative current collector and a negative active layer provided on at least one functional surface of the negative current collector;

[0122] The mass percentage content of silicon in the negative active layer is not less than 30 wt%, and the rebound rate of the first electrode plate is not higher than 50%.

[0123] At this time, the first electrode plate (negative electrode plate) not only has a relatively high silicon content, but also has a relatively low electrode plate rebound rate, which helps to further improve the energy density and cycle life of the battery.

[0124] Hereinafter, the battery of the present invention will be introduced in detail through specific examples.

[0125] Example 1

[0126] 1) Mix the cathode active material lithium cobaltate, conductive agent Super P, carbon nanotubes, and binder PVDF in a weight ratio of 97:1.2:0.6:1.2 and stir evenly in N,N-dimethylformamide (NMP) to obtain a cathode slurry that meets the usage requirements. Coat the cathode slurry evenly on both sides of a 10-μm-thick metal aluminum foil, and the coating areal density is 0.15 mg / mm 2, dried, roll-pressed at a roll-pressing temperature of 80 °C, with 1 roll-pressing pass, and then slit to obtain a positive electrode sheet with a tap density of 4.25 g / cm 3 ;

[0127] 2) Dispersed the negative electrode active material graphite and silicon-carbon material (mass ratio 96:4), conductive agent Super P, and binder PVDF in deionized water according to a weight ratio of 97:1.5:1.5, mixed and stirred evenly to obtain a negative electrode paste meeting the usage requirements. Coated the negative electrode paste on a negative electrode current collector with a total thickness of 6 μm, with a coating areal density of 0.08 mg / mm 2 ; Conducted hot roll-pressing at a roll-pressing temperature of 80 °C, with 2 roll-pressing passes, to obtain a negative electrode sheet with a thickness of 0.11 mm and a tap density of 1.7 g / cm 3 ;

[0128] 3) Selected a PE porous polymer film as the separator, stacked the above-prepared positive electrode sheet, negative electrode sheet, and separator in sequence, placed the separator between the positive electrode sheet and the negative electrode sheet, wound them to obtain an electric core, placed the electric core in an outer package, and injected a conventional lithium battery electrolyte into the electric core in a glove box. After encapsulation, formation, aging, and grading, the preparation of the battery was completed.

[0129] As Figure 3 and Figure 4 shown, they are respectively the cross-sectional SEM images of the first electrode sheet (negative electrode sheet) in this embodiment at 800X and 2.00KX. In the figures, negative electrode active layers 2 are provided on two functional surfaces of the negative electrode current collector 1. In the thickness direction h of the negative electrode sheet, from the side close to the negative electrode current collector 1 to the side far from the negative electrode current collector 1, the negative electrode active layer includes a first region 21, a second region 22, and a third region 23 distributed in sequence; among them, the single-sided thickness of the negative electrode active layer is L, the thickness of the first region is L1, the thickness of the second region is L2, the thickness of the third region is L3, and there are pores 20 between the active materials in the first region 21, the second region 22, and the third region 23.

[0130] Example 2

[0131] The preparation method of the battery in this example is basically the same as that in Example 1. In step 1), the coating areal density of the positive electrode sheet was adjusted to 0.05 mg / mm 2 , to obtain a positive electrode sheet with a tap density of 4.00 g / cm 3 ;

[0132] In step 2), the coating areal density of the negative electrode sheet was adjusted to 0.02 mg / mm 2 , to obtain a tap density of 1.4 g / cm 3 .

[0133] Example 3

[0134] The preparation method of the battery in this embodiment is basically the same as that in Embodiment 1. In step 1), the coating areal density of the positive electrode sheet is adjusted to 0.23 mg / mm 2 , and the compaction density is 4.45 g / cm 3 for the positive electrode sheet;

[0135] In step 2), the coating areal density of the negative electrode sheet is adjusted to 0.130 mg / mm 2 , and the compaction density is 1.82 g / cm 3 .

[0136] Embodiment 4

[0137] The preparation method of the battery in this embodiment is basically the same as that in Embodiment 1. In step 1), the coating areal density of the positive electrode sheet is adjusted to 0.102 mg / mm 2 , and the compaction density is 4.25 g / cm 3 for the positive electrode sheet;

[0138] In step 2), the coating areal density of the negative electrode sheet is adjusted to 0.050 mg / mm 2 , and the compaction density is 1.81 g / cm 3 .

[0139] Embodiment 5

[0140] The preparation method of the battery in this embodiment is basically the same as that in Embodiment 1. In step 1), the coating areal density of the positive electrode sheet is adjusted to 0.180 mg / mm 2 , and the compaction density is 4.45 g / cm 3 for the positive electrode sheet;

[0141] In step 2), the coating areal density of the negative electrode sheet is adjusted to 0.100 mg / mm 2 , and the compaction density is 1.45 g / cm 3 .

[0142] Embodiment 6

[0143] The preparation method of the battery in this embodiment is basically the same as that in Embodiment 1. In step 1), the negative active material is graphite and does not include silicon-carbon materials;

[0144] In step 2), the coating areal density of the positive electrode sheet is adjusted to 0.160 mg / mm 2 .

[0145] Embodiment 7

[0146] The preparation method of the battery in this embodiment is basically the same as that in Embodiment 1. In step 1), the mass percentage content of the silicon-carbon material in the negative electrode active material is 5 wt%;

[0147] In step 2), the coating surface density of the positive electrode sheet is adjusted to 0.152 mg / mm 2 .

[0148] Embodiment 8

[0149] The preparation method of the battery in this embodiment is basically the same as that in Embodiment 1. In step 1), the mass percentage content of the silicon-carbon material in the negative electrode active material is 7 wt%;

[0150] In step 2), the coating surface density of the positive electrode sheet is adjusted to 0.156 mg / mm 2 .

[0151] Embodiment 9

[0152] The preparation method of the battery in this embodiment is basically the same as that in Embodiment 1. In step 1), the mass percentage content of the silicon-carbon material in the negative electrode active material is 10 wt%;

[0153] In step 2), the coating surface density of the positive electrode sheet is adjusted to 0.162 mg / mm 2 .

[0154] Embodiment 10

[0155] The preparation method of the battery in this embodiment is basically the same as that in Embodiment 1. In step 1), the mass percentage content of the silicon-carbon material in the negative electrode active material is 15 wt%;

[0156] In step 2), the coating surface density of the positive electrode sheet is adjusted to 0.172 mg / mm 2 .

[0157] Embodiment 11

[0158] The preparation method of the battery in this embodiment is basically the same as that in Embodiment 1. In step 1), the mass percentage content of the silicon-carbon material in the negative electrode active material is 20 wt%;

[0159] In step 2), the coating surface density of the positive electrode sheet is adjusted to 0.182 mg / mm 2 .

[0160] Embodiment 12

[0161] The preparation method of the battery in this embodiment is basically the same as that in Embodiment 1. In step 1), the mass percentage content of the silicon-carbon material in the negative electrode active material is 25 wt%;

[0162] In step 2), the coating surface density of the positive electrode sheet is adjusted to 0.192 mg / mm 2 .

[0163] Example 13

[0164] The preparation method of the battery in this example is basically the same as that in Example 1. In step 1), the mass percentage content of the silicon-carbon material in the negative active material is 30 wt%;

[0165] In step 2), the coating surface density of the positive electrode sheet is adjusted to 0.202 mg / mm 2 .

[0166] Example 14

[0167] The preparation method of the battery in this example is basically the same as that in Example 1. In step 1), the coating surface density of the positive electrode sheet is adjusted to 0.1175 mg / mm 2 , and the compaction density is 4.15 g / cm 3 of the positive electrode sheet;

[0168] In step 2), the mass ratio of graphite to silicon-carbon material is adjusted to 70:30, and the coating surface density of the negative electrode sheet is adjusted to 0.030 mg / mm 2 , and the compaction density is 1.80 g / cm 3 .

[0169] Comparative Example 1

[0170] The preparation method of the battery in this example is basically the same as that in Example 1. In step 1), normal temperature rolling is carried out at a rolling temperature of 25 °C to obtain a positive electrode sheet;

[0171] In step 2), normal temperature rolling is carried out at a rolling temperature of 25 °C to obtain a negative electrode sheet.

[0172] The basic parameters are shown in Table 1 and Table 2.

[0173] Table 1

[0174]

[0175]

[0176] Table 2

[0177]

[0178] Test Example

[0179] 1. The batteries prepared in the above examples and comparative examples are tested, including the following steps:

[0180] First, discharge the batteries prepared in the above embodiments and comparative examples at a rate of 0.5C to 3.0V at 25°C. After leaving them standing for 5 minutes, charge them at a rate of 0.7C to 4.4V, and then charge them at a constant voltage of 4.4V until the cut-off current is 0.05C, and let them stand still for 10 minutes; then discharge them at a rate of 0.7C to 3.0V and let them stand still for 10 minutes; after cycling 2 times according to the aforementioned charge and discharge mechanism, charge the battery at a rate of 0.5C to 4.4V, and then charge it at a constant voltage of 4.4V until the cut-off current is 0.05C, and test that the battery is in a fully charged state; within 3 minutes, use a flat plate pressure PPG thickness gauge to measure the thickness of the battery after cycling and charging to the fully charged state to obtain H0, and disassemble the battery to obtain the positive electrode sheet and the negative electrode sheet, and use a Mitutoyo micrometer to measure the thicknesses of the positive electrode sheet and the negative electrode sheet to obtain H0 and h0;

[0181] Secondly, place the battery after cycling 2 times and charging to the fully charged state at 45 ± 2°C for 30 days with an open circuit, then take it out, use a flat plate pressure PPG thickness gauge to measure the thickness of the battery within 5 minutes to obtain T1, and disassemble the battery to obtain the positive electrode sheet and the negative electrode sheet, and use a Mitutoyo micrometer to measure the thicknesses of the positive electrode sheet and the negative electrode sheet to obtain H1 and h1;

[0182] Then, place the battery after being left open circuit at 45 ± 2°C for 30 days at 25.0 ± 2°C for 2 hours. At this time, the body temperature of the battery is 25 ± 2°C. Use a flat plate pressure PPG thickness gauge to measure the thickness of the battery within 10 minutes to obtain T2, and disassemble the battery to obtain the positive electrode sheet and the negative electrode sheet, and use a Mitutoyo micrometer to test the thicknesses of the positive electrode sheet and the negative electrode sheet to obtain H2 and h2;

[0183] Subsequently, place the battery after being left open circuit at 25.0 ± 2°C for 2 hours within 10 minutes at 70 ± 2°C for 24 hours, take it out, use a flat plate pressure PPG thickness gauge to measure the thickness of the battery within 5 minutes to obtain T3, and disassemble the battery to obtain the positive electrode sheet and the negative electrode sheet, and use a Mitutoyo micrometer to measure the thicknesses of the positive electrode sheet and the negative electrode sheet to obtain H3 and h3; place the battery after being left open circuit at 70 ± 2°C for 24 hours at 25.0 ± 2°C for 2 hours. At this time, the body temperature of the lithium-ion battery is 25 ± 2°C. Measure the thickness of the battery within 10 minutes to obtain T4, and disassemble the battery to obtain the positive electrode sheet and the negative electrode sheet, and test the thicknesses of the positive electrode sheet and the negative electrode sheet to obtain H4 and h4.

[0184] The test results are shown in Table 3 - Table 5.

[0185] Table 3

[0186]

[0187]

[0188] Table 4

[0189]

[0190] Table 5

[0191]

[0192]

[0193] 2. Discharge the batteries prepared in the above examples and comparative examples at a rate of 0.5C to 3.0V at 25°C. After standing for 5 minutes, charge them at a rate of 0.7C to 4.4V, and then charge them at a constant voltage of 4.4V until the cut-off current is 0.05C. At this time, the battery is fully charged. Disassemble the battery to obtain the negative electrode sheet. Use a Mitutoyo micrometer to measure the thickness of the negative electrode sheet to obtain T5, and record the thickness of the negative electrode sheet after rolling as T6. Then, the rebound rate (%) of the negative electrode sheet = (T6 - T5) / T5 × 100%. The test results are shown in Table 6.

[0194] Table 6

[0195]

[0196] As can be seen from Tables 3 - 6:

[0197] The rebound rates of the electrode sheets in Examples 1 - 5 are relatively low. From Examples 1, 6 - 13, it can be seen that as the mass content of the silicon-carbon material in the negative active material gradually increases, the rebound rate of the electrode sheet also gradually increases; from Comparative Example 1 and Example 1, it can be seen that the battery of the present invention can effectively reduce the rebound rate of the electrode sheet.

[0198] 3. Test the energy density and cycle performance of the batteries in the above examples and comparative examples:

[0199] 1) Energy density

[0200] At 25 ± 2°C, charge to 4.4V at a rate of 0.5C, then charge at a constant voltage of 4.4V until the cut-off current is 0.05C, stand for 10 minutes, and then discharge to 3.0V at a rate of 0.7C and stand for 10 minutes to obtain the actual capacity (mAh), the plateau voltage (V), measure the length (mm), width (mm), and thickness (mm) of the battery cell. Then, the energy density (Wh / L) = (actual capacity × plateau voltage) / (length × width × thickness) × 1000.

[0201] 2) Cycle performance

[0202] The batteries in the above-mentioned examples and comparative examples were left standing for 10 min at 25°C ± 5°C, discharged at 0.2C to 3.0V, left standing for 10 min, then charged at a rate of 0.7C to 4.4V, and then charged at a constant voltage of 4.4V until the cut-off current was 0.05C, and left standing for 10 min; then discharged at a rate of 1C to 3.3V, and then discharged at a rate of 0.7C to 3V, and left standing for 10 min; cycled 1 circle according to the aforementioned charge-discharge mechanism, and the discharge capacity of the battery was recorded as C0; after cycling 500 circles according to the aforementioned charge-discharge mechanism, the discharge capacity of the battery was recorded as C1, then the capacity retention rate of the battery was C1 / C0×100%.

[0203] 3) Rate performance

[0204] The batteries in the above-mentioned examples and comparative examples were left standing for 10 min at 25°C ± 5°C, discharged at 0.2C to the cut-off voltage of 3.0V, left standing for 10 min, charged at 0.5C to 4.4V in a constant temperature chamber, and then charged at a constant voltage of 4.4V until the cut-off current was 0.05C. At this time, it was in a fully charged state. After leaving it standing for 10 min, it was discharged to the cut-off voltage of 3.0V at rates of 0.2C, 0.5C, 1.0C, and 1.5C respectively, and the discharge capacities at different discharge rates were obtained. Then, the discharge capacity retention rate at 0.2C (%) = discharge capacity at 0.2C / discharge capacity at 0.2C × 100%, the discharge capacity retention rate at 0.5C (%) = discharge capacity at 0.5C / discharge capacity at 0.2C × 100%, the discharge capacity retention rate at 1.0C (%) = discharge capacity at 1.0C / discharge capacity at 0.2C × 100%, and the discharge capacity retention rate at 1.5C (%) = discharge capacity at 1.5C / discharge capacity at 0.2C × 100%.

[0205] The test and calculation results are shown in Table 7.

[0206] Table 7

[0207]

[0208]

[0209] As can be seen from Table 7:

[0210] The batteries in Examples 1 - 14 have higher cycle capacity retention rates and higher rate discharge capacity retention rates compared to the battery in Comparative Example 1, and the energy densities of the batteries in Examples 1 - 14 all remain at a relatively high level. It can be seen from this that the present utility model can significantly improve the stability of the battery in a high-temperature environment, which helps to improve the energy density and service life of the battery.

[0211] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery, characterized in that: The invention comprises a shell and a battery cell located inside the shell, wherein the battery cell comprises a first pole piece, a second pole piece and a diaphragm located between the first pole piece and the second pole piece; The thickness of the battery satisfies Formula 1, (T1-T2) / T0≤0.3% Formula 1 In formula 1, T0 is the thickness of the battery when the battery is fully charged after cycling, in mm; T1 is the thickness of the battery after the battery is placed in an open circuit at 45±2°C for 30 days after cycling and charging to a fully charged state, in mm; T2 is the thickness of the battery after the battery is placed in an open circuit at 45±2°C for 30 days and then placed at 25±2°C for 2 hours, in mm.

2. The battery according to claim 1, characterized in that The battery satisfies Formula 2 and / or Formula 3, (H1-H2) / H0≤0.4% Formula 2 (h1-h2) / h0≤0.2% Formula 3 Among them, H0 is the thickness of the first pole piece when the battery is cycled and charged to a fully charged state, in mm, h0 is the thickness of the second pole piece when the battery is cycled and charged to a fully charged state, in mm, H1 is the thickness of the first pole piece after the battery is cycled and charged to a fully charged state and left in an open circuit at 45±2°C for 30 days, in mm, h1 is the thickness of the second pole piece after the battery is cycled and charged to a fully charged state and left in an open circuit at 45±2°C for 30 days, in mm, H2 is the thickness of the first pole piece after the battery is left in an open circuit at 45±2°C for 30 days and then left at 25±2°C for 2 hours, in mm, h2 is the thickness of the second pole piece after the battery is left in an open circuit at 45±2°C for 30 days and then left at 25±2°C for 2 hours, in mm.

3. The battery according to claim 1 or 2, characterized in that: The battery satisfies Formula 4, (T3-T4) / T0≤0.4% Formula 4 Among them, T3 is the battery thickness after the battery body temperature drops to 25±2℃ and is placed in an open circuit at 70±2℃ for 24 hours, in mm; T4 is the battery thickness after the battery is placed in an open circuit at 70±2℃ for 24 hours and then at 25±2℃ for 2 hours, in mm.

4. The battery according to claim 3, characterized in that The battery satisfies Formula 5 and / or Formula 6, (H3-H4) / H0≤0.6% Formula 5 (h3-h4) / h0≤0.25% Formula 6 Among them, H3 is the thickness of the first pole piece after the battery body temperature drops to 25±2℃ and is left open circuit at 70±2℃ for 24h, in mm, h3 is the thickness of the second pole piece after the battery body temperature drops to 25±2℃ and is left open circuit at 70±2℃ for 24h, in mm, H4 is the thickness of the first pole piece after the battery is left open circuit at 70±2℃ for 24h and then left at 25±2℃ for 2h, in mm, h4 is the thickness of the second pole piece after the battery is left open circuit at 70±2℃ for 24h and then left at 25±2℃ for 2h, in mm.

5. The battery according to claim 4, characterized in that The battery satisfies Formula 7 and / or Formula 8, 1≤((H2-H0) / H0) / ((h2-h0) / h0)≤10 Formula 7 1≤((H4-H0) / H0) / ((h4-h0) / h0)≤10 Equation 8.

6. The battery according to claim 5, characterized in that T0 is 2.0 to 10.0 mm, and / or T1 is 2.0 to 11.0 mm, and / or T2 is 2.0 to 10.5 mm; and / or, H0 is 0.035 to 0.18 mm, and / or, H1 is 0.035 to 0.185 mm, and / or, H2 is 0.035 to 0.183 mm; and / or, h0 is 0.035 to 0.120 mm, and / or, h1 is 0.035 to 0.125 mm, and / or, h2 is 0.035 to 0.123 mm; and / or, T3 is 2.0 to 12.0 mm, and / or, T4 is 2.0 to 11.5 mm; and / or, H3 is 0.035 to 0.190 mm, and / or, H4 is 0.035 to 0.188 mm; And / or, h3 is 0.035 to 0.130 mm, and / or, h4 is 0.035 to 0.128 mm.

7. The battery according to any one of claims 1 to 6, characterized in that: The first electrode sheet comprises a negative electrode active layer and a negative electrode current collector, wherein the negative electrode active layer is disposed on at least one functional surface of the negative electrode current collector; In the thickness direction of the first electrode sheet, from the side close to the negative electrode current collector to the side away from the negative electrode current collector, the negative electrode active layer includes a first region, a second region and a third region distributed in sequence; The cross-sectional porosity of the first zone is smaller than the cross-sectional porosity of the second zone, and / or the cross-sectional porosity of the third zone is smaller than the cross-sectional porosity of the second zone.

8. The battery according to claim 7, characterized in that The cross-sectional porosity of the first zone is 5% to 35%, and / or the cross-sectional porosity of the second zone is 7% to 40%, and / or the cross-sectional porosity of the third zone is 5% to 35%.

9. The battery according to claim 8, characterized in that The first pole piece satisfies the following relationship: (The cross-sectional porosity of the first region+the cross-sectional porosity of the third region) / 2≤the cross-sectional porosity of the second region.

10. The battery according to any one of claims 7 to 9, characterized in that: The thickness ratio of the first zone, the second zone and the third zone is (1-4): (2-8): (1-4).

11. The battery according to claim 10, characterized in that The thickness of the first zone is 0.007-0.021 mm, and / or the thickness of the second zone is 0.015-0.055 mm, and / or the thickness of the third zone is 0.007-0.021 mm.

12. The battery according to any one of claims 1 to 11, characterized in that: The first electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least one functional surface of the negative electrode current collector; The mass percentage of silicon in the negative electrode active layer is not less than 30wt%, and the rebound rate of the first pole piece is not higher than 50%.

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