Battery cell

Abstract

The invention belongs to the field of secondary batteries, and particularly relates to a battery cell, and the charging cut-off voltage of the battery cell is greater than or equal to 4.48 V; the battery cell comprises a roll core, an electrolyte and a membrane shell, a closed accommodating cavity is formed in the membrane shell, and the roll core and the electrolyte are positioned in the membrane shell; the roll core comprises a positive plate, a diaphragm and a negative plate which are stacked and wound; the positive plate comprises a positive current collector and a positive active material layer arranged on the surface of the positive current collector, and the positive active material layer contains lithium titanium aluminum phosphate; along the winding direction, the positive electrode current collector exceeds the positive electrode active material layer, the tail end of the positive electrode active material layer is provided with a termination adhesive tape, a part of the termination adhesive tape extends to the positive electrode current collector, the termination adhesive tape comprises a base material layer and an adhesive layer coated on the surface of the base material layer, and the adhesive layer comprises rubber and / or polyolefin. The battery cell solves the problems of gas production and lithium separation at the tail end adhesive tape position of the lithium aluminum titanium phosphate doped positive plate.

Description

Technical Field

[0001] The present invention belongs to the field of secondary batteries, and particularly relates to an electric core. Background Art

[0002] With the application of lithium batteries in more and more scenarios, the requirements for their safety, low temperature, high energy density, etc. are also increasing. In semi-solid batteries, lithium titanium aluminum phosphate can be used as a cathode coating material or blended in the active material. By cathode coating or blending, the safety, cycle stability, rate performance, and low-temperature performance of the electric core can be improved. This is because lithium titanium aluminum phosphate as a solid electrolyte can induce the cathode capacity to play, enhance the surface structure stability of the cathode, reduce the interfacial impedance, and reduce the contact between the cathode and the electrolyte.

[0003] However, the high content of Ti element in lithium titanium aluminum phosphate is prone to catalyze the electrolyte, resulting in gas generation during the battery cycle, especially at the position where the tape is attached to the tail of the battery cathode plate, which affects the safety and life of the battery. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide an electric core, which solves the problems of easy gas generation and lithium deposition at the position of the termination tape at the tail of the cathode plate doped with lithium titanium aluminum phosphate.

[0005] The present invention provides an electric core, and the charging cut-off voltage of the electric core ≥ 4.48V;

[0006] The electric core includes a wound core, an electrolyte, and a film shell. A sealed accommodation cavity is formed in the film shell, and the wound core and the electrolyte are located in the film shell;

[0007] The wound core includes a cathode plate, a separator, and an anode plate stacked and wound;

[0008] The cathode plate includes a cathode current collector and a cathode active material layer provided on the surface of the cathode current collector, and the cathode active material layer contains lithium titanium aluminum phosphate;

[0009] Along the winding direction, the cathode current collector extends beyond the cathode active material layer. A termination tape is provided at the tail end of the cathode active material layer, and part of the termination tape extends to the cathode current collector. The termination tape includes a substrate layer and an adhesive layer coated on the surface of the substrate layer, and the adhesive layer includes rubber and / or polyolefin.

[0010] Preferably, the substrate layer includes polyethylene terephthalate and / or polyimide;

[0011] And / or, the adhesive layer comprises one or more of natural rubber, isoprene rubber, styrene-butadiene rubber, chloroprene rubber, butyl rubber, nitrile rubber, cis-1,4-polybutadiene rubber, ethylene-propylene-diene monomer rubber, chlorosulfonated polyethylene, chlorinated butyl rubber, polysulfide rubber, acrylate rubber, epichlorohydrin rubber, chlorinated rubber, silicone rubber, ethylene-vinyl acetate rubber, polyisobutylene, epoxy resin, phenolic-nitrile, polyacrylate, polyamide, polyhydroxy ether, polyurethane and epoxy-polyamide.

[0012] Preferably, the following relationship is satisfied among the Ti content in the positive electrode active material layer, the overlapping width of the termination tape and the positive electrode active material layer, and the adhesive layer thickness of the termination tape:

[0013] 0.01 ≤ (L1×h) / A ≤ 0.06 Formula (I);

[0014] In Formula (I), A represents the Ti content in the positive electrode active material layer, in ppm; L1 represents the overlapping width of the termination tape and the positive electrode active material layer, in mm; h represents the adhesive layer thickness of the termination tape, in μm.

[0015] Preferably, the Ti content in the positive electrode active material layer is 1000 - 4000 ppm;

[0016] And / or, the adhesive layer thickness is 2 - 30 μm;

[0017] And / or, the overlapping width of the termination tape and the positive electrode active material layer is 1 - 8 mm.

[0018] Preferably, the electrolyte contains nitrile compounds;

[0019] The following relationship is satisfied between the content of nitrile compounds in the electrolyte and the Ti content in the positive electrode active material layer:

[0020] 0.08×10 -4 ≤ B / A ≤ 1.2×10 -4 Formula (II);

[0021] In Formula (II), A represents the Ti content in the positive electrode active material layer, in ppm; B represents the mass percentage content of nitrile compounds in the electrolyte.

[0022] Preferably, the mass percentage content of nitrile compounds in the electrolyte is 2 - 20%, more preferably 5 - 15%;

[0023] And / or, the nitrile compound includes one or more of glutarodinitrile, adiponitrile, succinonitrile, sebaconitrile, pelargononitrile, dicyanobenzene, terephthalonitrile, pyridine-3,4-dicarbonitrile, 2,5-dicyanopyridine, 2,2,3,3-tetrafluorosuccinonitrile, tetrafluoroterephthalonitrile, 4-tetrahydropyranylidene malononitrile, fumarodinitrile, ethylene glycol bis(propionitrile) ether, 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarbonitrile, 1,3,6-hexanetricarbonitrile, 1,3,5-cyclohexanetricarbonitrile, 1,3,5-benzenetricarbonitrile, 1,2,3-propane trimethyl cyanide, glycerol trinitrile, tris(3-cyanopropyl) phosphate, 1,1,3,3-propane tetramethyl cyanide, 1,2,2,3-tetracyanopropane, 1,2,4,5-tetracyanobenzene, 2,3,5,6-pyrazine tetracarbonitrile, 3-methyl-3-propyl-cyclopropane-1,1,2,2-tetramethyl cyanide, 7,7,8,8-tetracyano-p-benzoquinone dimethane, tetracyanoethylene and 1,4-dicyano-2-butene.

[0024] Preferably, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on the surface of the negative electrode current collector; the negative electrode active material layer contains a silicon material;

[0025] The following relationship is satisfied between the silicon content in the negative electrode active material layer and the Ti content in the positive electrode active material layer:

[0026] 0.15×10 -4 ≤C / A≤2.5×10 -4 Formula (III);

[0027] In Formula (III), A represents the Ti content in the positive electrode active material layer, with the unit ppm; C represents the mass percentage content of silicon in the negative electrode active material layer.

[0028] Preferably, the mass percentage content of silicon in the negative electrode active material layer is 3 to 50%, more preferably 10 to 20%;

[0029] And / or, the silicon material is a silicon-carbon composite material.

[0030] Preferably, the surface of the positive electrode active material layer is provided with a recess;

[0031] The depth of the recess of the positive electrode active material layer is 8 to 40 μm; and / or, the thickness of the positive electrode active material layer is 20 to 60 μm; and / or, the following relationship is satisfied among the depth of the recess of the positive electrode active material layer, the thickness of the positive electrode active material layer, and the Ti content in the positive electrode active material layer:

[0032] 0.08×10 -3 ≤(s×A) / t≤0.4×10 -3 Formula (IV);

[0033] In formula (IV), A represents the Ti content in the positive electrode active material layer, in ppm; s represents the depth of the concave portion of the positive electrode active material layer, in μm; t represents the thickness of the positive electrode active material layer, in μm.

[0034] Preferably, the battery cell has a straight section and arc sections located on both sides of the straight section respectively; the termination tape covers at least one of the arc sections, and both ends of the termination tape extend to the straight section respectively;

[0035] And / or, along the winding direction, the length by which the termination tape extends beyond the positive electrode active material layer is L2, and L2 satisfies: 1 mm ≤ L2 ≤ 30 mm;

[0036] And / or, along the width direction of the positive electrode sheet, the length by which at least one side edge of the termination tape extends beyond the side edge of the positive electrode sheet is L3, and L3 satisfies: 1 mm ≤ L3 ≤ 2.5 mm.

[0037] In a high-voltage system, the electrolyte in the battery cell with the positive electrode sheet doped with lithium titanium aluminum phosphate is more likely to have a side reaction with the adhesive layer of the conventional acrylic termination tape pasted at the tail of the positive electrode sheet, generating a gas containing hydrofluoric acid, causing swelling due to the corrosion of the acrylic termination tape, so that the surface of the termination tape bulges to form a warp (corrugation), that is, exposing the positive electrode active material in this area, thus causing adverse phenomena such as lithium deposition and burrs. Compared with the prior art, the termination tape at the tail of the positive electrode sheet in the battery cell of the present invention uses rubber or polyolefin as the adhesive layer material. Since rubber and polyolefin have stronger acid resistance, the termination tape with rubber or polyolefin as the adhesive layer is less likely to be swollen due to corrosion, and can greatly delay the swelling time, thereby suppressing the problems of gas generation and lithium deposition at the position of the termination tape at the tail of the positive electrode sheet doped with lithium titanium aluminum phosphate in a high-voltage system, and improving the cycle performance of the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to the provided drawings.

[0039] Figure 1 It is a schematic top view structure diagram of the positive electrode sheet with a termination tape pasted at the tail end in an unfolded state provided by an embodiment of the present invention;

[0040] Figure 2 It is a schematic side view structure diagram of the positive electrode sheet with a termination tape pasted at the tail end in an unfolded state provided by an embodiment of the present invention.

[0041] Explanation of reference numerals: 1 is a positive electrode current collector, 2 is a positive electrode active material layer, and 3 is a termination tape. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] The problem of gas generation and lithium deposition at the tail termination tape position of the lithium aluminum titanium phosphate mixed positive electrode sheet under high voltage system is addressed.

[0044] The present invention provides a battery core, comprising: a winding core, an electrolyte and a membrane shell, wherein a sealed accommodating cavity is formed in the membrane shell, and the winding core and the electrolyte are located in the membrane shell;

[0045] The winding core comprises a positive electrode sheet, a separator and a negative electrode sheet which are stacked and wound;

[0046] The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector, wherein the positive electrode active material layer contains lithium aluminum titanium phosphate;

[0047] Along the winding direction, the positive electrode current collector exceeds the positive electrode active material layer, a termination tape is provided at the tail end of the positive electrode active material layer, part of the termination tape extends to the positive electrode current collector, the termination tape comprises a substrate layer and a glue layer coated on the surface of the substrate layer, and the glue layer comprises rubber and / or polyolefin;

[0048] The charging cut-off voltage of the battery cell is ≥4.48 V, for example, 4.48 V, 4.5 V or 4.53 V. The term charging cut-off voltage has a conventional meaning in the art, and generally refers to the maximum voltage value that the battery cell can safely reach during charging.

[0049] In some embodiments, the positive current collector in the positive electrode sheet includes but is not limited to aluminum foil. The positive electrode active material layer includes a positive electrode active material, a conductive agent and a binder; wherein the positive electrode active material includes lithium aluminum titanium phosphate, preferably also includes lithium cobalt oxide (LCO); the conductive agent includes but is not limited to SP conductive agent; the binder includes but is not limited to polyvinylidene fluoride (PVDF); the mass ratio of the positive electrode active material, the conductive agent and the binder is preferably 97: (0.5-2): (1-5), more preferably 97: 1: 2.

[0050] In the battery cell of the present invention, the tail termination tape of the positive electrode sheet uses rubber and polyolefin as the adhesive layer materials. Since rubber and polyolefin have stronger acid resistance, the termination tape with rubber and polyolefin as the adhesive layer is less likely to be corroded and swollen, which can greatly delay the swelling time, thereby suppressing the problems of gas generation and lithium deposition at the position of the tail termination tape of the positive electrode sheet doped with lithium titanium aluminum phosphate, and improving the cycle performance of the battery cell.

[0051] In some embodiments, the adhesive layer materials of the termination tape preferably include one or more of natural rubber, isoprene rubber, styrene-butadiene rubber, chloroprene rubber, butyl rubber, nitrile rubber, cis-butadiene rubber, ethylene-propylene-diene monomer rubber, chlorosulfonated polyethylene, chlorinated butyl rubber, polysulfide rubber, acrylate rubber, epichlorohydrin rubber, chlorinated rubber, silicone rubber, ethylene-vinyl acetate rubber, polyisobutylene, epoxy resin, phenolic-nitrile, polyacrylate, polyamide, polyhydroxy ether, polyurethane, and epoxy-polyamide. Thus, the above preferred adhesive layer materials all have excellent elasticity and flexibility, which can better avoid stress concentration caused by volume changes during the expansion and contraction of the electrode sheet at the termination tape, leading to cracking of the positive electrode active material layer at this position; at the same time, the above preferred adhesive layer materials all have good chemical stability, which can effectively prevent electrolyte corrosion; and the above preferred adhesive layer materials also have good bonding adaptability and can maintain strong adhesion with the positive electrode active material layer.

[0052] In some embodiments, the substrate layer materials of the termination tape preferably include polyethylene terephthalate (PET) and / or polyimide (PI). Thus, the PET substrate layer has high mechanical strength, good corrosion resistance, and can also remain stable at high temperatures; the PI substrate layer has extremely high heat resistance, low thermal expansion coefficient, excellent electrical insulation, and anti-aging properties.

[0053] In some embodiments, the following relationship is satisfied among the Ti content in the positive electrode active material layer, the overlapping width of the termination tape and the positive electrode active material layer, and the adhesive layer thickness of the termination tape:

[0054] 0.01 ≤ (L1 × h) / A ≤ 0.06 Formula (I);

[0055] In Formula (I), A represents the Ti content in the positive electrode active material layer, in ppm; L1 represents the overlapping width of the termination tape and the positive electrode active material layer, in mm; h represents the adhesive layer thickness of the termination tape, in μm.

[0056] The higher the Ti content in the positive electrode active layer, the larger the specific surface area at the burr part of the edge of the pole piece, and the more active sites are in contact with the electrolyte, so it is easier to produce gas, and more termination tape coverage area and adhesive layer coverage thickness are required to prevent the electrolyte from contacting the positive electrode active material at the burr. When it is less than the lower limit of formula (I), the Ti content is too high, or the termination tape coverage area is too small, and the gas production is large; when it is greater than the upper limit of formula (I), the Ti content is too low, or the termination tape is too large, affecting the performance of the battery.

[0057] In some embodiments, the thickness (h) of the termination adhesive layer is obtained by using argon ion grinding to grind the tape cross section and then performing SEM testing. The specific testing method is as follows: discharge the battery to 0% SOC, dissect the battery to obtain the positive electrode sheet, cut off the portion of the positive electrode sheet covered with the termination tape with scissors, put the termination tape together with the positive electrode sheet on an argon ion grinder for polishing, and then put it into the SEM to observe the ground cross section.

[0058] In some embodiments, the width (L1) of the overlap between the tail termination tape and the positive electrode active material is measured using a ruler, and the specific test method is as follows: discharge the battery to 0% SOC, dissect the battery to obtain the positive electrode sheet, unfold and flatten the positive electrode sheet, and then use a ruler to measure the width of the termination tape covering the positive electrode sheet.

[0059] In some embodiments, the Ti content (A) in the positive electrode active material is measured by ICP, and the specific test method is as follows: the battery is discharged to 0% SOC, the positive electrode sheet is disassembled and taken out, and immersed in DMC solvent for 12 hours; then the DMC solvent is used to rinse to remove the lithium salt attached to the positive electrode sheet, and the positive electrode active coating is gently scraped off from the surface of the positive electrode current collector after calcination at 450° C. in a muffle furnace for 3 hours, and the element Ti (in ppm) is measured by ICP-OES. The specific operation method is performed in accordance with GB / T 30902-2014.

[0060] In some embodiments, the (L1×h) / A is preferably 0.02 to 0.04, specifically 0.01, 0.02, 0.03, 0.04, 0.05 or 0.06.

[0061] In some embodiments, on the basis of satisfying the relationship of formula (I), the thickness (h) of the adhesive layer of the termination tape is preferably 2 to 30 μm, specifically 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm or 30 μm. In this way, the above preferred termination tape adhesive layer thickness range can not only ensure the adhesion strength between the termination tape and the pole piece, but also avoid the positive electrode tail burr piercing the termination tape and the diaphragm, and at the same time avoid the termination tape being too thick, resulting in an increase in the thickness of the battery cell and a decrease in flatness. In addition, compared with an excessively thick glue layer, an appropriate glue layer thickness can further weaken the volume expansion amplitude of the glue layer after swelling in the electrolyte, thereby further reducing the adverse effects caused by the swelling of the glue layer.

[0062] In some embodiments, on the basis of satisfying the relationship of formula (I), the overlapping width (L1) of the termination tape and the positive electrode active material layer is preferably 1 to 8 mm, specifically 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, 6.5 mm, 7 mm, 7.5 mm or 8 mm. In this way, the above preferred overlapping width range can effectively avoid the termination tape from covering the positive electrode active material layer for an insufficient length, reduce the risk of the termination tape lifting and exposing the positive electrode active material to cause lithium deposition at the tail of the positive electrode sheet, and avoid the termination tape covering the positive electrode active material layer for too long, resulting in a significant reduction in the effective area of ​​the positive electrode active material layer and excessive loss of positive electrode sheet capacity.

[0063] In some embodiments, on the basis of satisfying the relationship of formula (I), the Ti content (A) of the positive electrode active material layer is preferably 1000-4000ppm, specifically 1000ppm, 1500ppm, 2000ppm, 2500ppm, 3000ppm, 3500ppm or 4000ppm. In the present invention, when the Ti content in the positive electrode active material layer meets the above preferred range, the safety, cycle stability, rate performance and low temperature performance of the battery cell can be improved. This is because lithium aluminum titanium phosphate as a solid electrolyte can induce the positive electrode capacity, enhance the surface structural stability of the positive electrode, reduce the interface impedance, and reduce the contact between the positive electrode and the electrolyte. At the same time, the addition of an appropriate amount of Ti will not increase the electrolyte side reaction and cause serious gas production in the battery cell.

[0064] In some embodiments, the electrolyte contains a lithium salt, and the lithium salt includes but is not limited to LiFP6.

[0065] In some embodiments, the electrolyte preferably further contains nitrile compounds. In the present invention, after adding nitrile compounds to the electrolyte, the cyano group in the nitrile can form a strong interaction with the metal ions on the surface of the positive electrode to form a stable and uniform positive electrode interface film, effectively preventing the direct contact between the electrolyte and the positive electrode, thereby reducing the catalytic effect of the metal ions on the electrolyte, avoiding the oxidative decomposition of the electrolyte, and at the same time enhancing the stability of the positive electrode surface structure, reducing the easy decomposition phase change of the positive electrode material after the voltage is increased.

[0066] In some embodiments, the content of the nitrile compound in the electrolyte and the content of Ti in the positive electrode active material layer preferably satisfy the following relationship:

[0067] 0.08×10 -4 ≤B / A≤1.2×10 -4 Formula (II);

[0068] In formula (II), A represents the Ti content in the positive electrode active material layer, in ppm; B represents the mass percentage of the nitrile compound in the electrolyte.

[0069] When it is less than the lower limit of formula (II), B is too small or A is too large, the content of nitrile compounds in the electrolyte is small, and it is not enough to form a positive electrode interface film, while the Ti element content is high, the positive electrode lacks a stable interface film and the electrolyte forms a barrier, and gas generation is easy to occur; when it is greater than the upper limit of formula (II), B is too large or A is too small, the content of nitrile compounds in the electrolyte is too much, the electrolyte viscosity is increased, the electrolyte conductivity is reduced, and the by-products generated by nitrile decomposition increase, while the Ti element content is too small, the solid electrolyte is small, and the low-temperature performance decreases. Therefore, when the content of nitrile compounds in the electrolyte and the Ti content in the positive electrode active material layer satisfy the relationship of formula (II), the performance of the battery core can be guaranteed and the electrolyte side reaction can be avoided.

[0070] In some embodiments, the mass percentage (B) of nitrile compounds in the electrolyte is measured by a gas chromatograph, and the specific measurement method is as follows: discharge the battery cell to 0% SOC, gradually pressurize the battery cell to 10mPa with a manual hydraulic press, and when the hydraulic press instrument begins to display pressure, use a syringe to puncture a small hole in the battery cell membrane shell, extract the electrolyte from the hole, and then perform gas chromatography on the extracted electrolyte to obtain the mass percentage of the corresponding nitrile compound.

[0071] In some embodiments, the B / A is preferably 0.1×10 -4 ~1×10 -4 , specifically 0.08×10 -4 , 0.1×10 -4 , 0.2×10 -4 , 0.3×10 -4 , 0.4×10-4 , 0.5×10 -4 , 0.6×10 -4 , 0.7×10 -4 , 0.8×10 -4 , 0.9×10 -4 , 1×10 -4 , 1.1×10 -4 or 1.2×10 -4 .

[0072] In some embodiments, on the basis of satisfying the relationship of formula (II), the mass percentage content (B) of the nitrile compound in the electrolyte is preferably 2-20%, more preferably 5-15%, specifically 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%. In the present invention, an appropriate amount of nitrile additives can maintain the stability of the electrolyte, but an excessive amount of nitrile additives will reduce the viscosity of the electrolyte, hinder the migration of lithium ions, increase the internal resistance of the battery, and reduce the rate performance (such as fast charging capability), so the nitrile additives are preferably within the above range.

[0073] In some embodiments, on the basis of satisfying the relationship of formula (II), the nitrile compound preferably includes glutaronitrile, adiponitrile, succinonitrile, sebaconitrile, azelaic acid dicyanobenzene, terephthalonitrile, pyridine-3,4-dinitrile, 2,5-dicyanopyridine, 2,2,3,3-tetrafluorosuccinonitrile, tetrafluoroterephthalonitrile, 4-tetrahydrothiopyranylmalononitrile, butylene dinitrile, ethylene glycol bis(propionitrile) ether, 1,4,5,6-tetrahydro-5,6-dioxy-2,3-pyrazine dicarbonitrile, 1,3,6-hexane trinitrile, One or more of 1,3,5-cyclohexane trinitrile, 1,3,5-benzene tricyano, 1,2,3-propane tricarbonitrile, glycerol trinitrile, tris(3-cyanopropyl) phosphate, 1,1,3,3-propane tetracarbonitrile, 1,2,2,3-tetracyanopropane, 1,2,4,5-tetracyanobenzene, 2,3,5,6-pyrazine tetracarbonitrile, 3-methyl-3-propyl-cyclopropane-1,1,2,2-tetracarbonitrile, 7,7,8,8-tetracyanoquinodimethane, tetracyanoethylene and 1,4-dicyano-2-butene. In this way, the above-mentioned preferred nitrile compounds all have a higher electrochemical window and antioxidant properties, can inhibit the decomposition of the electrolyte at high voltage (such as >4.5V), and are suitable for high energy density batteries; at the same time, the above-mentioned preferred nitrile compounds can be preferentially reduced on the surface of the negative electrode (such as graphite, silicon-based materials) to form a more stable, low-impedance SEI film, effectively reducing the growth of lithium dendrites and continuous consumption of electrolyte; in addition, the above-mentioned preferred nitrile compounds can also effectively stabilize the electrolyte components, inhibit the generation of gases such as CO2 and CH4 during the cycle, and reduce the risk of battery expansion.

[0074] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector; the negative electrode active material layer preferably contains silicon material. In the present invention, the negative electrode sheet doped with silicon can be combined with the positive electrode sheet containing lithium titanium aluminum phosphate to improve the rate and low temperature performance of the battery cell. Specifically: after the negative electrode is doped with silicon, the conductivity of the negative electrode decreases, resulting in an increase in the polarization of the battery cell, and the rate performance decreases significantly at low temperatures. At the same time, the potential of the negative electrode increases, resulting in a corresponding increase in the potential of the positive electrode; and the lithium titanium aluminum phosphate added to the positive electrode can reduce the impedance of the interface between the positive and negative electrode sheets, reduce polarization, improve the rate performance and low temperature performance of the battery, and at the same time maintain the stability of the positive electrode material under a high voltage system, and can even increase the capacity released by the positive electrode material and improve the energy density.

[0075] In some embodiments, the negative electrode current collector in the negative electrode sheet includes but is not limited to carbon-coated copper foil. The negative electrode active material layer includes a negative electrode active material, a conductive agent, an additive and a binder; wherein the negative electrode active material includes but is not limited to a silicon-carbon composite material; the conductive agent includes but is not limited to an SP conductive agent; the additive includes but is not limited to carboxymethyl cellulose lithium (CMC-Li); the binder includes but is not limited to polyacrylic acid (PAA); the mass ratio of the negative electrode active material, conductive agent, additive and binder is preferably 97: (0.1-1): (0.05-0.2): (1-5), and more preferably 97: 0.4: 0.1: 2.5.

[0076] In some embodiments, the silicon content in the negative electrode active material layer and the Ti content in the positive electrode active material layer preferably satisfy the following relationship:

[0077] 0.15×10 -4 ≤C / A≤2.5×10 -4 Formula (III);

[0078] In formula (III), A represents the Ti content in the positive electrode active material layer, in ppm; C represents the mass percentage of silicon in the negative electrode active material layer.

[0079] When it is less than the lower limit of formula (III), it means that C is too small or A is too large. At this time, the amount of silicon added is too small or the amount of Ti added is too large, which will cause the energy density of the battery cell to decrease or the gas production to increase; when it is greater than the upper limit of formula (III), it means that C is too large or A is too small. At this time, the amount of silicon added is too much or the amount of Ti added is too little. In this case, the relative potential of the positive electrode increases, but the additive content that maintains the high voltage stability of the positive electrode is insufficient, resulting in a decrease in the stability of the positive electrode and a decrease in the cycle performance of the battery. Therefore, when the silicon content in the negative electrode active material layer and the Ti content in the positive electrode active material layer satisfy the relationship of formula (III), both the high energy density of the battery cell and the stable cycle can be maintained.

[0080] In some embodiments, the mass percentage (C) of silicon in the negative electrode active material layer is measured according to the following method: weigh M grams of negative electrode active material, heat to 800°C at 5°C / min in an air atmosphere, keep warm for 10 hours, and cool to room temperature to obtain m grams of remaining material, C = m / M×100%.

[0081] In some embodiments, the C / A is preferably 0.5×10 -4 ~1×10 -4 , specifically 0.15×10 -4 , 0.3×10 -4 , 0.5×10 -4 , 0.7×10 -4 , 1×10 -4 , 1.2×10 -4 , 1.5×10 -4 , 1.7×10 -4 , 2×10 -4 , 2.3×10 -4 or 2.5 × 10 -4 .

[0082] In some embodiments, on the basis of satisfying the relationship of formula (III), the mass percentage of silicon in the negative electrode active material layer is preferably 3% to 50%, specifically 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49% or 50%. In the present invention, the above-mentioned preferred silicon content range of the negative electrode active material layer can increase the negative electrode gram capacity while producing appropriate expansion, thereby maximizing the energy density.

[0083] In some embodiments, on the basis of satisfying the relationship of formula (III), the silicon material in the negative electrode active material layer is preferably a silicon-carbon composite material. In this way, the silicon-carbon composite material has a higher gram capacity than graphite, which can improve the energy density of the battery cell, and has good electrical conductivity, which improves the electronic conductivity; and the silicon material in the silicon-carbon composite material is deposited on the skeleton of the carbon material, which also reduces the volume expansion of the silicon material.

[0084] In some embodiments, the positive active material layer of the positive electrode sheet preferably has a concave portion. In the present invention, the positive electrode sheet concave portion can improve the process performance and electrical performance of the positive electrode sheet. Specifically, the positive electrode sheet concave portion changes the transmission channel in the positive electrode active material layer, and dislocation and gaps are generated between the active materials around the concave portion, which is conducive to the infiltration of the electrolyte and the release of the generated gas, and can improve the cycle performance and rate performance of the semi-solid electrolyte battery; moreover, the concave portion can increase the contact area between the positive electrode sheet and the active material, can reduce the contact impedance of the battery, further enhance the low temperature capability of the semi-solid battery, and reduce polarization; in addition, the concave portion can also improve the toughness of the positive electrode sheet, release stress, and prevent the positive electrode sheet from breaking during the winding process.

[0085] In some embodiments, the depth of the recess of the positive electrode active material layer, the thickness of the positive electrode active material layer, and the Ti content in the positive electrode active material layer preferably satisfy the following relationship:

[0086] 0.08×10 -3 ≤s / (t×A)≤0.4×10 -3 Formula (IV);

[0087] In formula (IV), A represents the Ti content in the positive electrode active material layer, in ppm; s represents the depth of the concave portion of the positive electrode active material layer, in μm; and t represents the thickness of the positive electrode active material layer, in μm.

[0088] In some embodiments, appropriate recess depth and Ti content can increase the contact area between the pole piece and the active material, reduce the contact impedance of the battery, further enhance the low temperature capability of the semi-solid battery, and reduce polarization. When the recess depth of the positive electrode active material layer, the thickness of the positive electrode active material layer, and the Ti content in the positive electrode active material layer do not satisfy the relationship of formula (IV), if the recess depth or Ti content of the positive electrode is too high, the contact area is too large, and there are too many Ti reaction sites, which easily leads to an increase in electrolyte side reactions; if the recess depth and Ti content are too low, the process state of the pole piece is not optimal, and the solid electrolyte has low performance improvement.

[0089] In some embodiments, the depth of the recess (s) of the positive electrode active material layer is tested using a 3D profilometer, and the specific testing method is as follows: discharge the battery to 0% SOC, dissect the battery to obtain the positive electrode sheet, cut the positive electrode sheet into a flat sheet, place it under the 3D profilometer, and measure the depth of the recess.

[0090] In some embodiments, the thickness (t) of the positive electrode active material layer is obtained by using argon ions to grind the cross-section of the positive electrode sheet and then performing SEM testing. The specific testing method is as follows: discharge the battery to 0% SOC, dissect the battery to obtain the positive electrode sheet, place the positive electrode sheet on an argon ion grinder for polishing, and then place it in a SEM to observe the ground cross-section.

[0091] In some embodiments, (s×A) / t is preferably 0.11×10 -3 ~0.3×10 -3 , specifically 0.08×10 -3 , 0.1×10 -3 , 0.11×10 -3 , 0.15×10 -3 , 0.2×10 -3 , 0.25×10 -3 , 0.3×10 -3 , 0.35×10 -3 or 0.4×10 -3 .

[0092] In some embodiments, on the basis of satisfying the relationship of formula (IV), the depth of the recess of the positive electrode active material layer is preferably 8 to 40 μm, specifically 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm or 40 μm. In the present invention, the above preferred recess depth range of the positive electrode active material layer can effectively improve the toughness of the positive electrode sheet, improve the wetting, and improve the rate performance; if it is too deep, the thickness of the electrode sheet increases and the energy density decreases.

[0093] In some embodiments, on the basis of satisfying the relationship of formula (IV), the thickness of the positive electrode active material layer is preferably 20 to 60 μm, specifically 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm, 40 μm, 41 μm, 42 μm, 43 μm, 44 μm, 45 μm, 46 μm, 47 μm, 48 μm, 49 μm, 50 μm, 51 μm, 52 μm, 53 μm, 54 μm, 55 μm, 56 μm, 57 μm, 58 μm, 59 μm or 60 μm. In the present invention, the above preferred positive electrode active material layer thickness range can effectively improve the energy density and ensure electrical properties such as cycle, rate, and impedance; if the active layer is too thick, the path of lithium ion migration is too long and the electrical performance is reduced.

[0094] In some embodiments, the battery cell has a straight section and arc sections located on both sides of the straight section; the termination tape covers at least one of the arc sections, and the two ends of the termination tape extend to the straight sections respectively. In the present invention, the starting point and the end point of the termination tape are set at the straight section of the positive electrode sheet, which can reduce the risk of the electrode sheet cracking and breaking. Specifically: the arc of the wound battery cell is where the stress is most concentrated, and the end of the positive electrode sheet is in the outer ring area of ​​the winding core, which is the area where the winding core is subjected to the greatest expansion stress. Therefore, the electrode sheet in the arc section of this area is prone to cracking or even breaking failure during the cycle process. Therefore, the termination tape pasted in this area of ​​the positive electrode sheet should completely cover the arc area, and the starting point and the end point are both in the straight section of the electrode sheet. This can give the electrode sheet in this area a constraint opposite to the expansion stress, thereby reducing the risk of the electrode sheet cracking and breaking.

[0095] In some embodiments, along the winding direction, the length of the termination tape beyond the positive electrode active material layer is L2, and L2 preferably satisfies: 1mm≤L2≤30mm, and L2 can specifically be 1mm, 3mm, 5mm, 7mm, 10mm, 12mm, 15mm, 17mm, 20mm, 23mm, 25mm, 27mm or 30mm. In the present invention, L2 satisfies the above preferred range to prevent the termination tape from falling off, and at the same time avoid the termination tape being too long, exceeding the winding arc, resulting in an increase in the thickness and width of the winding core.

[0096] In some embodiments, along the width direction of the positive electrode sheet, the length of at least one side edge of the termination tape beyond the side edge of the positive electrode sheet is L3, and L3 preferably satisfies: 1mm≤L3≤2.5mm, and L3 can specifically be 1mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm, 1.5mm, 1.6mm, 1.7mm, 1.8mm, 1.9mm, 2mm, 2.1mm, 2.2mm, 2.3mm, 2.4mm, 2.5mm. In the present invention, since the positive electrode sheet extends along the width direction during the cycle, the positive electrode sheet on the outside of the battery cell will be in contact and squeezed with the membrane shell, and the positive electrode sheet will therefore produce wrinkles or cracks. When the width of the termination tape covering the positive electrode sheet exceeds a certain range of the width of the positive electrode sheet, it can effectively prevent the top and bottom of the positive electrode sheet from being squeezed and wrinkled by the membrane shell.

[0097] The present invention will be described in detail below by way of examples. The examples described in the present invention are only a part of the examples of the present invention, rather than all of the examples. Based on the examples in the present invention, all other examples obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0098] The following examples are used to illustrate the lithium ion secondary battery of the present invention.

[0099] The present invention also provides a method for preparing the lithium battery cell described in the above technical solution, comprising the following steps:

[0100] a) coating the positive electrode slurry on the front and back surfaces of the positive electrode current collector, baking and rolling to obtain a positive electrode sheet;

[0101] b) coating the negative electrode slurry on the front and back surfaces of the negative electrode current collector, baking and rolling to obtain a negative electrode sheet;

[0102] There is no order restriction between step a) and step b);

[0103] c) cutting and sheeting the positive electrode sheet and the negative electrode sheet, winding them with the separator, and attaching the termination tape to the designated position of the positive electrode sheet during the winding process to obtain a winding core;

[0104] d) The core is packaged, baked, injected, formed, sealed, sorted and OCV (Open Circuit Voltage) tested to obtain a lithium-ion battery cell.

[0105] For the purpose of greater clarity, the present invention is described in detail with reference to the following examples and comparative examples.

[0106] Example 1

[0107] A lithium battery cell, comprising: a winding core, an electrolyte and a membrane shell, wherein a sealed accommodating cavity is formed in the membrane shell, and the winding core and the electrolyte are located in the membrane shell; the winding core comprises a stacked and wound positive electrode sheet, a separator and a negative electrode sheet. The structure of the positive electrode sheet is as follows Figures 1 to 2 As shown, it includes a positive electrode current collector 1 and a positive electrode active material layer 2 arranged on the front and back surfaces of the positive electrode current collector 1; along the winding direction, the positive electrode current collector 1 exceeds the positive electrode active material layer 2, and a termination tape 3 is provided at the tail end of the positive electrode active material layer 2, and part of the termination tape 3 extends to the positive electrode current collector 1;

[0108] The positive electrode current collector is aluminum foil; the positive electrode active material layer contains positive electrode active material (LCO and lithium aluminum titanium phosphate), conductive agent (SP) and binder (PVDF), the mass ratio of the three is 97:1:2, and the Ti content (A) of the positive electrode active material layer is 2000ppm; the termination tape comprises a substrate layer and a glue layer coated on the surface of the substrate layer, the substrate layer material of the termination tape is PET, and the glue layer material is natural rubber; the glue layer thickness (h) of the termination tape is 6μm, the overlapping width (L1) with the positive electrode active material layer is 5mm, the length (L2) beyond the positive electrode active material layer is 5mm, and the length (L3) beyond the side edge of the positive electrode sheet is 1.5mm; after calculation, (L1×h) / A=0.015, satisfying the relationship of formula (I);

[0109] The thickness (t) of the single side of the positive electrode active material layer on the positive electrode sheet is 45 μm, and the surface of the positive electrode active material layer has a concave portion, and the depth (s) of the concave portion is 20 μm; after calculation, s / (t×A)=0.22×10 -3 , satisfying the relationship of formula (IV);

[0110] The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on the positive and negative surfaces of the negative electrode current collector; the negative electrode current collector is a carbon-coated copper foil; the negative electrode active material layer contains a negative electrode active material (silicon-carbon composite material), a conductive agent (SP), an additive (CMC-Li) and a binder (PAA), the mass ratio of the four being 97:0.4:0.1:2.5, and the silicon mass percentage (C) of the negative electrode active material layer is 10%; after calculation, C / A=0.5×10 -4 , satisfying the relationship of formula (III); the single-sided thickness of the negative electrode active material layer on the negative electrode sheet is 50 μm;

[0111] The winding core has a straight section and arc sections located on both sides of the straight section; the terminating tape covers one of the arc sections, and both ends of the terminating tape extend to the straight section respectively;

[0112] The electrolyte contains LiFP6 and glutaronitrile, wherein the content of LiFP6 is 1 mol / L and the mass percentage content (B) of glutaronitrile is 5%. After calculation, B / A=0.25×10 -4 , satisfying the relationship of formula (II).

[0113] The above lithium battery cell is prepared according to the following steps:

[0114] Step 1: Mix the positive electrode active material (LCO and lithium aluminum titanium phosphate), the conductive agent (SP) and the binder (PVDF) in a mass ratio of 97:1:2, add NMP, stir evenly, and prepare a positive electrode slurry; apply the positive electrode slurry on the front and back surfaces of the aluminum foil, bake, and press the concave part to obtain a positive electrode sheet with a thickness of 100 μm;

[0115] Step 2: Mix the negative electrode active material (silicon-carbon composite material), conductive agent (SP), additive (CMC-Li) and binder (PAA) in a mass ratio of 97:0.4:0.1:2.5, and add deionized water to prepare a negative electrode slurry; apply the negative electrode slurry on the front and back surfaces of the carbon-coated copper foil, and after baking and rolling, obtain a negative electrode sheet with a thickness of 110 μm; a certain position of the negative electrode sheet has a slot of fixed size, and the copper-plated nickel tab is welded in this slot by laser or ultrasonic welding;

[0116] Step 3: After slitting and fabricating the positive and negative electrode sheets, wind them with the separator, and attach the termination tape to the designated position on the positive electrode sheet during the winding process to obtain a wound core;

[0117] Step 4: The wound core is further subjected to encapsulation, baking, liquid injection, formation, secondary encapsulation, sorting, and OCV testing to obtain a lithium-ion battery cell.

[0118] Example 2

[0119] Referring to the lithium battery cell provided in Example 1, the difference is only that the Ti content (A) of the positive active material layer is adjusted to 1000 ppm, and the single-sided thickness (t) of the positive active material layer on the positive electrode sheet is adjusted to 50 μm; after calculation, (L1×h) / A = 0.03, B / A = 0.5×10 -4 , C / A = 1×10 -4 , s / (t×A) = 0.4×10 -3 .

[0120] Example 3

[0121] Referring to the lithium battery cell provided in Example 1, the difference is only that the Ti content (A) of the positive active material layer is adjusted to 4000 ppm, and the adhesive layer thickness (h) of the termination tape is 8 μm; after calculation, (L1×h) / A = 0.01, B / A = 0.125×10 -4 , C / A = 0.25×10 -4 , s / (t×A) = 0.11×10 -3 .

[0122] Example 4

[0123] Referring to the lithium battery cell provided in Example 1, the difference is only that the overlapping width (L1) between the termination tape and the positive active material layer is adjusted to 1 mm, and the adhesive layer thickness (h) of the termination tape is 20 μm; after calculation, (L1×h) / A = 0.01.

[0124] Example 5

[0125] Referring to the lithium battery cell provided in Example 1, the difference is only that the overlapping width (L1) between the termination tape and the positive active material layer is adjusted to 8 mm; after calculation, (L1×h) / A = 0.024.

[0126] Example 6

[0127] Referring to the lithium battery cell provided in Example 1, the difference is only that the adhesive layer thickness (h) of the termination tape is adjusted to 15 μm; after calculation, (L1×h) / A = 0.0375.

[0128] Example 7

[0129] Referring to the lithium battery cell provided in Example 1, the difference is only that the Ti content (A) in the positive active material layer is adjusted to 1500 ppm, the overlapping width (L1) between the termination tape and the positive active material layer is adjusted to 7.5 mm, and the adhesive layer thickness (h) of the termination tape is adjusted to 2 μm; after calculation, (L1×h) / A = 0.01, B / A = 0.33×10 -4 , C / A = 0.67×10 -4 , s / (t×A) = 0.3×10 -3 .

[0130] Example 8

[0131] Referring to the lithium battery cell provided in Example 1, the difference is only that the overlapping width (L1) between the termination tape and the positive active material layer is adjusted to 4 mm, and the adhesive layer thickness (h) of the termination tape is adjusted to 30 μm; after calculation, (L1×h) / A = 0.06.

[0132] Example 9

[0133] Referring to the lithium battery cell provided in Example 1, the difference is only that the mass percentage content (B) of glutaronitrile in the electrolyte is adjusted to 2%; after calculation, B / A = 0.1×10 -4 .

[0134] Example 10

[0135] Referring to the lithium battery cell provided in Example 1, the difference is only that the mass percentage content (B) of glutaronitrile in the electrolyte is adjusted to 15%; after calculation, B / A = 0.75×10 -4 .

[0136] Example 11

[0137] Referring to the lithium battery cell provided in Example 1, the difference is only that the mass percentage content (B) of glutaronitrile in the electrolyte is adjusted to 20%; after calculation, B / A = 1×10 -4 .

[0138] Example 12

[0139] Referring to the lithium battery cell provided in Example 1, the difference is only that the Ti content (A) in the positive active material layer is adjusted to 2500 ppm, and the mass percentage content (B) of glutaronitrile in the electrolyte is adjusted to 2%; after calculation, (L1×h) / A = 0.012, B / A = 0.08×10 -4 , C / A = 0.4×10 -4 , s / (t×A) = 0.178×10 -3 .

[0140] Example 13

[0141] Referring to the lithium battery cell provided in Example 1, the difference is only that the Ti content (A) in the positive electrode active material layer is adjusted to 1500 ppm, and the mass percentage content (B) of glutaronitrile in the electrolyte is adjusted to 18%; after calculation, (L1×h) / A = 0.02, 10000×B / A = 1.2×10 -4 , C / A = 0.67×10 -4 , s / (t×A) = 0.296×10 -3 .

[0142] Example 14

[0143] Referring to the lithium battery cell provided in Example 1, the difference is only that the mass percentage content (C) of silicon in the negative electrode active material layer is adjusted to 3%; after calculation, C / A = 0.15×10 -4 .

[0144] Example 15

[0145] Referring to the lithium battery cell provided in Example 1, the difference is only that the mass percentage content (C) of silicon in the negative electrode active material layer is adjusted to 20%; after calculation, C / A = 1×10 -4 .

[0146] Example 16

[0147] Referring to the lithium battery cell provided in Example 1, the difference is only that the mass percentage content (C) of silicon in the negative electrode active material layer is adjusted to 50%; after calculation, C / A = 2.5×10 -4 .

[0148] Example 17

[0149] Referring to the lithium battery cell provided in Example 1, the difference is only that the single-sided thickness (t) of the positive electrode active material layer on the positive electrode plate is adjusted to 20 μm, and the recess depth (s) of the positive electrode active material layer is adjusted to 16 μm; after calculation, s / (t×A) = 0.4×10 -3 .

[0150] Example 18

[0151] Referring to the lithium battery cell provided in Example 1, the difference is only that the single-sided thickness (t) of the positive electrode active material layer on the positive electrode plate is adjusted to 60 μm; after calculation, s / (t×A) = 0.167×10 -3 .

[0152] Example 19

[0153] Referring to the lithium battery cell provided in Example 1, the difference is only that the depth (s) of the concave portion of the positive electrode active material layer is adjusted to 10 μm; after calculation, s / (t×A) = 0.11×10 -3 .

[0154] Example 20

[0155] Referring to the lithium battery cell provided in Example 1, the difference is only that the single-sided thickness (t) of the positive electrode active material layer on the positive electrode plate is adjusted to 20 μm, and the depth (s) of the concave portion of the positive electrode active material layer is adjusted to 10 μm; after calculation, s / (t×A) = 0.25×10 -3 .

[0156] Example 21

[0157] Referring to the lithium battery cell provided in Example 1, the difference is only that the single-sided thickness (t) of the positive electrode active material layer on the positive electrode plate is adjusted to 50 μm, and the depth (s) of the concave portion of the positive electrode active material layer is adjusted to 8 μm; after calculation, s / (t×A) = 0.08×10 -3 .

[0158] Example 22

[0159] Referring to the lithium battery cell provided in Example 1, the difference is only that the single-sided thickness (t) of the positive electrode active material layer on the positive electrode plate is adjusted to 50 μm, and the depth (s) of the concave portion of the positive electrode active material layer is adjusted to 40 μm; after calculation, s / (t×A) = 0.4×10 -3 .

[0160] Comparative Example 1

[0161] Referring to the lithium battery cell provided in Example 1, the difference is only that the Ti content (A) of the positive electrode active material layer is adjusted to 5000 ppm; after calculation, (L1×h) / A = 0.006, B / A = 0.1×10 -4 , C / A = 0.2×10 -4 , s / (t×A) = 0.089×10 -3 .

[0162] Comparative Example 2

[0163] Referring to the lithium battery cell provided in Example 1, the difference is only that the Ti content (A) of the positive electrode active material layer is adjusted to 450 ppm; after calculation, (L1×h) / A = 0.067, B / A = 1.11×10 -4 , C / A = 2.22×10 -4 , s / (t×A) = 0.987×10 -3 .

[0164] Comparative Example 3

[0165] Referring to the lithium battery cell provided in Example 1, the only difference is that the overlapping width (L1) between the termination tape and the positive active material layer is adjusted to 0.5 mm; after calculation, (L1×h) / A = 0.0015.

[0166] Comparative Example 4

[0167] Referring to the lithium battery cell provided in Example 1, the only difference is that the overlapping width (L1) between the termination tape and the positive active material layer is adjusted to 21 mm; after calculation, (L1×h) / A = 0.063.

[0168] Comparative Example 5

[0169] Referring to the lithium battery cell provided in Example 1, the only difference is that the mass percentage (B) of glutaric nitrile in the electrolyte is adjusted to 1%; after calculation, B / A = 0.05×10 -4 。

[0170] Comparative Example 6

[0171] Referring to the lithium battery cell provided in Example 1, the only difference is that the mass percentage (B) of glutaric nitrile in the electrolyte is adjusted to 25%; after calculation, B / A = 1.25×10 -4 。

[0172] Comparative Example 7

[0173] Referring to the lithium battery cell provided in Example 1, the only difference is that the mass percentage (C) of silicon in the negative active material layer is adjusted to 2%; after calculation, C / A = 0.1×10 -4 。

[0174] Comparative Example 8

[0175] Referring to the lithium battery cell provided in Example 1, the only difference is that the mass percentage (C) of silicon in the negative active material layer is adjusted to 55%; after calculation, C / A = 2.75×10 -4 。

[0176] Comparative Example 9

[0177] Referring to the lithium battery cell provided in Example 1, the only difference is that the depth (s) of the concave part of the positive active material layer is adjusted to 6 μm; after calculation, s / (t×A) = 0.067×10 -3 。

[0178] Comparative Example 10

[0179] Referring to the lithium battery cell provided in Embodiment 1, the difference is only that the depth (s) of the concave portion of the positive electrode active material layer is adjusted to 41 μm; after calculation, s / (t×A) = 0.45×10 -3 .

[0180] Performance Evaluation

[0181] Perform performance tests on the lithium battery cells provided in the above embodiments and comparative examples, specifically including:

[0182] (1) Energy density test: Use a Neware battery tester to charge at 0.2C to the upper limit voltage of 4.5V (cut-off at 0.02C) / discharge at 0.2C to the lower limit voltage, repeat 3 times, and take the discharge energy of the third time as the cell energy Q. Use a 2.5D microscope tester to measure the width W and height H of the cell, and use a PPG thickness tester to measure the full charge thickness L of the cell. Then the energy density is Q / (W×H×L).

[0183] (1) 0°C cycle capacity retention rate: Take the maximum value of the discharge capacities in the first three cycles as the initial capacity R0, and the discharge capacity after 50 cycles is R50. The capacity retention rate is R50 / R0×100%. Cycling conditions: At a temperature of 0°C, constant current charging at 2C until the cut-off voltage of 4.5V, constant voltage charging until the cut-off current of 0.2C, constant current discharging at 0.7C, and cut-off voltage of 3V.

[0184] (2) 0°C cycle expansion rate: Charge the battery before cycling to full charge, measure the thickness B1 of the battery before cycling, after 50 cycles, charge the battery to full charge, and measure the cell thickness B2. The expansion rate = (B2 - B1) / B1. Cycling conditions: At a temperature of 0°C, constant current charging at 2C until the cut-off voltage of 4.5V, constant voltage charging until the cut-off current of 0.2C, constant current discharging at 0.7C, and cut-off voltage of 3V.

[0185] (3) Cell state, observe whether the electrode film shell bulges and generates gas and the state of gas generation.

[0186] For easy comparison, the key parameters of the cells in different embodiments and comparative examples are summarized in Table 1.

[0187] Table 1 Key Parameter Table of Cells

[0188]

[0189]

[0190] The performance test results of the cells in different embodiments and comparative examples are shown in Table 2.

[0191] Table 2 Test Results of Cells

[0192]

[0193] From the comparison between Example 1 and Comparative Examples 1 to 4, it can be seen that when the parameter conditions of the battery cell do not satisfy 0.01 ≤ (L1×h + L2) / A ≤ 0.06, the battery cell will generate more gas and form bulges during the cycle test, indicating that the above-mentioned parameter conditions of the battery cell defined in the present invention can effectively inhibit gas generation and lithium deposition at the position of the termination tape at the tail of the lithium titanium aluminum phosphate-doped positive electrode sheet.

[0194] From the comparison between Example 1 and Comparative Examples 5 to 6, it can be seen that when the parameter conditions of the battery cell do not satisfy 0.08 ≤ 10000×B / A ≤ 1.2, the 0°C cycle capacity retention rate of the battery cell will decrease significantly, and the 0°C cycle expansion will increase significantly, indicating that the above-mentioned parameter conditions of the battery cell defined in the present invention can effectively improve the electrochemical stability of the battery cell doped with lithium titanium aluminum phosphate positive electrode sheet.

[0195] From the comparison between Example 1 and Comparative Examples 7 to 8, it can be seen that when the parameter conditions of the battery cell do not satisfy 0.15 ≤ 10000×C / A ≤ 2.5, the 0°C cycle capacity retention rate of the battery cell will decrease significantly, and the 0°C cycle expansion will increase significantly, indicating that the above-mentioned parameter conditions of the battery cell defined in the present invention can effectively improve the electrochemical stability of the battery cell doped with lithium titanium aluminum phosphate positive electrode sheet.

[0196] From the comparison between Example 1 and Comparative Examples 9 to 10, it can be seen that when the parameter conditions of the battery cell do not satisfy 0.08 ≤ 1000×s / t / A ≤ 0.4, the 0°C cycle capacity retention rate of the battery cell will decrease significantly, and the 0°C cycle expansion will increase significantly, indicating that the above-mentioned parameter conditions of the battery cell defined in the present invention can effectively improve the electrochemical stability of the battery cell doped with lithium titanium aluminum phosphate positive electrode sheet.

[0197] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A battery cell, characterized in that: The charging cut-off voltage of the battery cell is ≥4.48V; The battery core comprises a winding core, an electrolyte and a membrane shell, a sealed accommodating cavity is formed in the membrane shell, and the winding core and the electrolyte are located in the membrane shell; The winding core comprises a positive electrode sheet, a separator and a negative electrode sheet which are stacked and wound; The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on the surface of the positive electrode current collector, wherein the positive electrode active material layer contains lithium aluminum titanium phosphate; Along the winding direction, the positive current collector exceeds the positive active material layer, and a termination tape is provided at the tail end of the positive active material layer. Part of the termination tape extends to the positive current collector, and the termination tape includes a substrate layer and a glue layer coated on the surface of the substrate layer, and the glue layer includes rubber and / or polyolefin.

2. The battery cell according to claim 1, characterized in that: The substrate layer comprises polyethylene terephthalate and / or polyimide; And / or, the adhesive layer includes one or more of natural rubber, isoprene rubber, styrene-butadiene rubber, chloroprene rubber, butyl rubber, nitrile rubber, butadiene rubber, ethylene propylene diene rubber, chlorosulfonated polyethylene, chlorinated butadiene rubber, polysulfide rubber, acrylate rubber, epichlorohydrin rubber, chlorinated rubber, silicone rubber, ethylene-vinyl acetate rubber, polyisobutylene, epoxy resin, phenolic-nitrile, polyacrylate, polyamide, polyhydroxy ether, polyurethane and epoxy-polyamide.

3. The battery cell according to claim 1, characterized in that: The Ti content in the positive electrode active material layer, the overlapping width between the termination tape and the positive electrode active material layer, and the thickness of the termination tape layer satisfy the following relationship: 0.01≤(L1×h) / A≤0.06 Formula (I); In formula (I), A represents the Ti content in the positive electrode active material layer, in ppm; L1 represents the overlapping width between the termination tape and the positive electrode active material layer, in mm; and h represents the thickness of the termination tape layer, in μm.

4. The battery cell according to claim 1, characterized in that: The Ti content of the positive electrode active material layer is 1000 to 4000 ppm; And / or, the thickness of the adhesive layer is 2 to 30 μm; And / or, the overlapping width between the termination tape and the positive electrode active material layer is 1 to 8 mm.

5. The battery cell according to claim 1, characterized in that: The electrolyte contains nitrile compounds; The content of the nitrile compound in the electrolyte and the content of Ti in the positive electrode active material layer satisfy the following relationship: 0.08×10 -4 ≤B / A≤1.2×10 -4 Formula (II); In formula (II), A represents the Ti content in the positive electrode active material layer, in ppm; B represents the mass percentage of the nitrile compound in the electrolyte.

6. The battery cell according to claim 5, characterized in that: The mass percentage of nitrile compounds in the electrolyte is 2 to 20%, preferably 5 to 15%; And / or, the nitrile compound includes glutaronitrile, adiponitrile, succinonitrile, sebaconitrile, azelaic acid dicyanobenzene, terephthalonitrile, pyridine-3,4-dicarbonitrile, 2,5-dicyanopyridine, 2,2,3,3-tetrafluorosuccinonitrile, tetrafluoroterephthalonitrile, 4-tetrahydrothiopyranylmalononitrile, butylene dicarbonitrile, ethylene glycol bis(propionitrile) ether, 1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazine dicarbonitrile, 1,3,6-hexane tricarbonitrile, 1,3,5-cyclohexane tricarbonitrile , 1,3,5-benzenetricyanide, 1,2,3-propanetricarboxylate, glycerol trinitrile, tris(3-cyanopropyl)phosphate, 1,1,3,3-propanetetracarbonitrile, 1,2,2,3-tetracyanopropane, 1,2,4,5-tetracyanobenzene, 2,3,5,6-pyrazinetetracarbonitrile, 3-methyl-3-propyl-cyclopropane-1,1,2,2-tetracarbonitrile, 7,7,8,8-tetracyanoquinodimethane, tetracyanoethylene and 1,4-dicyano-2-butene.

7. The battery cell according to claim 1, characterized in that: The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector; the negative electrode active material layer contains silicon material; The silicon content in the negative electrode active material layer and the Ti content in the positive electrode active material layer satisfy the following relationship: 0.15×10 -4 ≤C / A≤2.5×10 -4 Formula (III); In formula (III), A represents the Ti content in the positive electrode active material layer, in ppm; C represents the mass percentage of silicon in the negative electrode active material layer.

8. The battery cell according to claim 7, characterized in that: The mass percentage of silicon in the negative electrode active material layer is 3 to 50%, preferably 10 to 20%; And / or, the silicon material is a silicon-carbon composite material.

9. The battery cell according to claim 1, characterized in that: The surface of the positive electrode active material layer is provided with a concave portion; The depth of the concave portion of the positive electrode active material layer is 8 to 40 μm; and / or, the thickness of the positive electrode active material layer is 20 to 60 μm; and / or, the depth of the concave portion of the positive electrode active material layer, the thickness of the positive electrode active material layer and the Ti content in the positive electrode active material layer satisfy the following relationship: 0.08×10 -3 ≤s / (t×A)≤0.4×10 -3 Formula (IV); In formula (IV), A represents the Ti content in the positive electrode active material layer, in ppm; s represents the depth of the concave portion of the positive electrode active material layer, in μm; and t represents the thickness of the positive electrode active material layer, in μm.

10. The battery cell according to claim 1, characterized in that: The battery cell has a straight section and arc sections located on both sides of the straight section; the termination tape covers at least one of the arc sections, and both ends of the termination tape extend to the straight section respectively; and / or, along the winding direction, the length of the termination tape beyond the positive electrode active material layer is L2, and L2 satisfies: 1 mm ≤ L2 ≤ 30 mm; And / or, along the width direction of the positive electrode sheet, the length of at least one side edge of the termination tape beyond the side edge of the positive electrode sheet is L3, and L3 satisfies: 1mm≤L3≤2.5mm.

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