A battery cell and a battery

Abstract

The present invention relates to the technical field of batteries and discloses a battery cell and a battery, wherein the battery cell comprises a negative electrode plate, a separator and a positive electrode plate; the negative electrode plate comprises a negative electrode current collector and a negative electrode active material coating; the positive electrode plate comprises a positive electrode current collector and a positive electrode active material coating; the separator comprises a substrate, a first coating and a second coating; wherein the porosity of the first coating is A and the thickness of the first coating is aμm, the porosity of the second coating is B and the thickness of the second coating is bμm, the porosity of the negative electrode active material coating is C and the thickness of the negative electrode active material coating is cμm, the porosity of the positive electrode active material coating is D and the thickness of the positive electrode active material coating is dμm; by limiting 0.8≤[(Dd+Bb) / (b+d)] / [(Aa+Cc) / (a+c)]≤1.2, the porosities on both sides of the substrate of the separator are made to be relatively close, thereby improving the cycle performance of the battery cell and ensuring the stability and reliability of the battery during long-term use.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a battery cell and a battery. Background Art

[0002] Throughout the development of lithium-ion batteries, optimizing the performance of battery cells has always been a core research direction. As a key component of batteries, the performance of battery cells directly determines important indicators such as battery energy density, cycle life, and safety.

[0003] As a crucial component of the battery cell, the diaphragm not only isolates the positive and negative electrodes and prevents short circuits, but also shoulders the critical responsibilities of electrolyte storage and ion conduction. However, in the current design and manufacturing process of battery cells, the problem of balancing the porosity on both sides of the diaphragm substrate has not been effectively addressed. A large difference in porosity on both sides of the diaphragm substrate will lead to an imbalance in the adsorption and retention capacity of the coatings on both sides for the electrolyte. One side may have excessive porosity, resulting in excessive electrolyte adsorption, while the other side may have insufficient electrolyte infiltration due to low porosity, which seriously affects the uniform distribution of the electrolyte within the battery cell. This uneven electrolyte distribution will further cause ion transport obstacles. During the battery's charge and discharge process, lithium ions cannot be smoothly and evenly transferred between the two sides of the diaphragm, resulting in a disruption in the consistency of the electrochemical reactions within the battery cell. This not only reduces the energy conversion efficiency of the battery cell, but also seriously affects the cycle performance of the battery cell. As the number of charge and discharge cycles increases, the battery cell performance deteriorates, and the battery's stability and reliability decrease significantly.

[0004] Existing technical means have limitations in regulating the porosity distribution on both sides of the diaphragm, making it difficult to achieve precise control of the electrolyte distribution and ion transport environment inside the battery cell. Therefore, it is urgent to develop a technology that can effectively balance the porosity on both sides of the diaphragm, ensure the balanced electrolyte retention, and thereby improve the cycle performance and stability of the battery cell. This has important practical significance for promoting the development and application of lithium-ion battery technology. Summary of the Invention

[0005] Aiming to solve at least one of the technical problems existing in the prior art, the present invention aims to provide a battery cell and a battery, wherein the battery cell can ensure the stability and reliability of the battery during long-term use.

[0006] In order to achieve the above-mentioned purpose, in the first aspect, the present invention provides a battery cell, which comprises a negative electrode sheet, a separator and a positive electrode sheet stacked in sequence; the negative electrode sheet comprises a negative electrode collector and a negative electrode active material coating, and the negative electrode active material coating is applied to the side of the negative electrode collector facing the separator; the positive electrode sheet comprises a positive electrode collector and a positive electrode active material coating, and the positive electrode active material coating is applied to the side of the positive electrode collector facing the separator; the separator comprises a substrate, a first coating and a second coating, and the first coating is applied to the substrate facing the negative electrode One side of the electrode sheet is connected to the negative electrode active material coating, and the second coating is applied to the side of the substrate away from the first coating and is connected to the positive electrode active material coating; wherein the porosity of the first coating is A, the thickness of the first coating is aμm, the porosity of the second coating is B, the thickness of the second coating is bμm, the porosity of the negative electrode active material coating is C, the thickness of the negative electrode active material coating is cμm, the porosity of the positive electrode active material coating is D, the thickness of the positive electrode active material coating is dμm, and the following conditions are met:

[0007] 0.8≤[(Dd+Bb) / (b+d)] / [(Aa+Cc) / (a+c)]≤1.2.

[0008] In some embodiments, 0.25≤C / A≤0.67.

[0009] In some embodiments, 0.11 ≤ D / B ≤ 0.43.

[0010] In some embodiments, 60%≤A≤80%; 0.5 μm≤a≤3 μm.

[0011] In some embodiments, 70%≤B≤90%; 0.5 μm≤b≤5 μm.

[0012] In some embodiments, 20%≤C≤40%; 50.5 μm≤c≤54 μm.

[0013] In some embodiments, 10%≤D≤30%; 42 μm≤d≤46 μm.

[0014] In some embodiments, the pore size of the first coating layer is E μm, the pore size of the second coating layer is F μm, and the pore size of the substrate is G μm, satisfying:

[0015] 0.1≤E≤2, 0.3≤F≤4, 0.02≤G≤0.08, F>E>G.

[0016] In some embodiments, the air permeability of the first coating is Js / 100cc, and the air permeability of the second coating is Ks / 100cc, satisfying:

[0017] 5≤J≤70, 5≤K≤50, J≥K.

[0018] In some embodiments, the substrate comprises one or more of polyethylene, polypropylene, polyimide, and polyethylene terephthalate;

[0019] The first coating layer is composed of a first organic polymer and a first inorganic material;

[0020] The second coating layer is composed of a second organic polymer and a second inorganic material;

[0021] The first organic polymer comprises one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyacrylonitrile, polyetherimide, polyamide, meta-aramid, para-aramid, polymethyl methacrylate, polyethylene, styrene-butadiene rubber and polyacrylate;

[0022] The first inorganic material is one or more of aluminum oxide, magnesium oxide, silicon oxide, titanium dioxide, zirconium dioxide, zinc oxide, barium sulfate, boron nitride, aluminum nitride, magnesium nitride, tin dioxide, magnesium hydroxide, boehmite, zeolite and calcium carbonate;

[0023] The second organic polymer comprises one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyacrylonitrile, polyetherimide, polyamide, meta-aramid, para-aramid, polymethyl methacrylate, polyethylene, styrene-butadiene rubber and polyacrylate;

[0024] The second inorganic material is one or more of aluminum oxide, magnesium oxide, silicon oxide, titanium dioxide, zirconium dioxide, zinc oxide, barium sulfate, boron nitride, aluminum nitride, magnesium nitride, tin dioxide, magnesium hydroxide, boehmite, zeolite and calcium carbonate.

[0025] In some embodiments, the mass ratio of the first organic polymer to the first inorganic material is (0-9.5):1; the mass ratio of the second organic polymer to the second inorganic material is (0-9.5):1.

[0026] In some embodiments, the first inorganic material includes first inorganic particles, and the second inorganic material includes second inorganic particles; wherein the average particle size of the first inorganic particles under an electron microscope is H μm, and the average particle size of the second inorganic particles under an electron microscope is 1 μm, and the following conditions are satisfied:

[0027] 0.2≤H≤0.8, 0.4≤I≤1.5,I≥H.

[0028] In a second aspect, the present invention further provides a battery, comprising the battery cell described in any one of the above items, and further comprising a shell and an electrolyte, wherein the battery cell and the electrolyte are both disposed in the shell.

[0029] In a third aspect, the present invention further provides a method for preparing a battery according to any one of the above items, comprising the following steps:

[0030] Preparation of positive electrode sheet: lithium cobalt oxide, acetylene black and polyvinylidene fluoride are thoroughly stirred and mixed in an N-methylpyrrolidone solvent system, and then coated on the positive electrode current collector, dried, cold pressed and slit to obtain the positive electrode sheet;

[0031] Preparation of negative electrode sheet: artificial graphite, acetylene black, binder styrene butadiene rubber, and thickener sodium carboxymethyl cellulose are thoroughly stirred and mixed in a deionized water solvent system, and then coated on the negative electrode current collector, dried, cold pressed, and slit to obtain the negative electrode sheet;

[0032] Prepare the diaphragm: apply the first coating layer on one side of the substrate and apply the second coating layer on the other side of the substrate;

[0033] Preparation of electrolyte: A solution prepared by mixing lithium salt with a non-aqueous organic solvent is used as the electrolyte;

[0034] Obtaining a battery: stacking the negative electrode sheet, the separator, and the positive electrode sheet in sequence and then making a battery cell according to a winding process or a lamination process, placing the battery cell in a shell, injecting the electrolyte into the shell and encapsulating it to obtain a battery.

[0035] In some embodiments, in the step of preparing the positive electrode sheet, the mass ratio of the lithium cobaltate, the acetylene black, and the polyvinylidene fluoride is 95:3:2.

[0036] In some embodiments, in the step of preparing the negative electrode sheet, the mass ratio of the artificial graphite, the acetylene black, the binder styrene-butadiene rubber, and the thickener sodium carboxymethyl cellulose is 96:1:1.5:1.5.

[0037] In some embodiments, in the step of preparing the electrolyte, the mass ratio of the lithium salt to the non-aqueous organic solvent is 8:92.

[0038] In some embodiments, the non-aqueous organic solvent is prepared from the following raw materials in parts by weight: 20 parts of ethylene carbonate, 30 parts of diethyl carbonate, 20 parts of propylene carbonate, 28 parts of propyl propionate and 2 parts of vinylene carbonate.

[0039] Compared with the prior art, the embodiment of the present invention provides a battery cell, which has the following beneficial effects: by limiting the condition of 0.8≤[(Dd+Bb) / (b+d)] / [(Aa+Cc) / (a+c)]≤1.2, the porosity on both sides of the substrate of the diaphragm can be made to be relatively close, thereby making the porosity on both sides of the substrate evenly distributed, and further ensuring that the adsorption and retention capabilities of the coatings on both sides of the substrate for the electrolyte are consistent, which helps to maintain the balance of the electrolyte retention volume of the coatings on both sides of the substrate; the balance of the retention volume can stabilize the ion transport environment inside the battery cell, and further avoid ion transport barriers caused by uneven distribution of electrolyte on both sides of the diaphragm, which helps to improve the cycle performance of the battery cell and ensure the stability and reliability of the battery during long-term use. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a structural schematic diagram of a battery cell provided by an embodiment of the present invention.

[0041] In the figure, 1, negative electrode plate; 11, negative electrode current collector; 12, negative electrode active material coating;

[0042] 2. Positive electrode sheet; 21. Positive electrode current collector; 22. Positive electrode active material coating;

[0043] 3. Diaphragm; 31. Substrate; 32. First coating; 33. Second coating. DETAILED DESCRIPTION

[0044] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0045] In the description of the present invention, it should be understood that the terms "length", "width", "thickness", "up", "down", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0046] The terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the quantity of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features.

[0047] In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," "fixed," etc. should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0048] In the present invention, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Furthermore, a first feature being "above," "above," and "above" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature may include the first feature being directly below or obliquely below the second feature, or may simply mean that the first feature is lower in level than the second feature.

[0049] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as commonly understood by technicians in the technical field to which this application belongs; the terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0050] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments.

[0051] First aspect

[0052] like Figure 1 As shown, an embodiment of the present invention provides a battery cell, which includes a negative electrode sheet 1, a separator 3 and a positive electrode sheet 2 stacked in sequence.

[0053] The negative electrode plate 1 includes a negative electrode collector 11 and a negative electrode active material coating 12, and the negative electrode active material coating 12 is coated on the side of the negative electrode collector 11 facing the separator 3; the positive electrode plate 2 includes a positive electrode collector 21 and a positive electrode active material coating 22, and the positive electrode active material coating 22 is coated on the side of the positive electrode collector 21 facing the separator 3; the separator 3 includes a substrate 31, a first coating 32 and a second coating 33, the first coating 32 is coated on the side of the substrate 31 facing the negative electrode plate 1 and is connected to the negative electrode active material coating 12, and the second coating 33 is coated on the side of the substrate 31 away from the first coating 32 and is connected to the positive electrode active material coating 22.

[0054] Among them, the porosity of the first coating 32 is A, the thickness of the first coating 32 is aμm, the porosity of the second coating 33 is B, the thickness of the second coating 33 is bμm, the porosity of the negative electrode active material coating 12 is C, the thickness of the negative electrode active material coating 12 is cμm, the porosity of the positive electrode active material coating 22 is D, and the thickness of the positive electrode active material coating 22 is dμm, satisfying: 0.8≤[(Dd+Bb) / (b+d)] / [(Aa+Cc) / (a+c)]≤1.2.

[0055] Based on this technical solution, by limiting the condition of 0.8≤[(Dd+Bb) / (b+d)] / [(Aa+Cc) / (a+c)]≤1.2, the porosity on both sides of the substrate 31 can be made relatively close, thereby achieving a balanced distribution of the porosity on both sides of the substrate 31, thereby ensuring that the adsorption and retention capabilities of the coatings on both sides of the substrate 31 tend to be consistent, which helps to maintain the balance of the electrolyte retention volume of the coatings on both sides of the substrate 31; the balance of the electrolyte retention volume can stabilize the ion transport environment inside the battery cell, thereby avoiding ion transport barriers caused by uneven distribution of electrolyte on both sides of the diaphragm 3, helping to improve the cycle performance of the battery cell and ensure the stability and reliability of the battery during long-term use.

[0056] In the present invention, the thickness testing method of the first coating layer 32, the second coating layer 33, the negative electrode active material coating layer 12, and the positive electrode active material coating layer 22 is as follows: the first coating layer 32 is subjected to argon ion polishing to obtain a cross section of the first coating layer 32, the cross section morphology of the first coating layer 32 along the thickness direction is observed using a field emission scanning electron microscope (Philips, XL-30 model) and a scanning electron microscope photograph is taken, and the thickness a of the first coating layer 32 is measured using the scanning electron microscope.

[0057] The second coating 33 was subjected to argon ion polishing to obtain a cross section of the second coating 33. The cross-sectional morphology of the second coating 33 along the thickness direction was observed using a field emission scanning electron microscope (Philips, XL-30 model) and a scanning electron microscope photograph was taken. The thickness b of the second coating 33 was measured using the scanning electron microscope.

[0058] The negative electrode active material coating 12 was subjected to argon ion polishing to obtain a cross section of the negative electrode active material coating 12. The cross-sectional morphology of the negative electrode active material coating 12 along the thickness direction was observed using a field emission scanning electron microscope (Philips, XL-30 model) and a scanning electron microscope photograph was taken. The thickness c of the negative electrode active material coating 12 was measured using the scanning electron microscope.

[0059] The positive electrode active material coating 22 was subjected to argon ion polishing to obtain a cross section of the positive electrode active material coating 22. The cross-sectional morphology of the positive electrode active material coating 22 along the thickness direction was observed using a field emission scanning electron microscope (Philips, XL-30 model) and a scanning electron microscope photograph was taken. The thickness d of the positive electrode active material coating 22 was measured using a scanning electron microscope.

[0060] In some specific embodiments of the present invention, the negative electrode current collector 11 is copper foil, and the positive electrode current collector 21 is aluminum foil.

[0061] In some specific embodiments of the present invention, the first coating 32 is an organic polymer coating, and the second coating 33 is one or more of a ceramic coating and an organic polymer coating.

[0062] The appropriate porosity of the positive electrode, negative electrode and separator 3 of a lithium-ion battery is of great significance for improving the energy density of the battery; the pores can accommodate more electrolyte, which allows ions to be transmitted more smoothly during the charge and discharge process, thereby helping to improve the energy density of the battery; however, the impact of porosity on battery performance is multifaceted; excessively high porosity of the positive and negative electrodes may cause the electrode structure to become loose, thereby reducing the mechanical strength of the battery. During the use of the battery, the battery performance may be easily degraded due to the instability of the electrode structure; on the contrary, excessively low porosity of the positive, negative electrode and separator 3 will limit the penetration of the electrolyte and the transmission of ions, seriously affecting the normal performance of the battery, making it impossible for the battery to reach an ideal working state during the charge and discharge process.

[0063] In some specific embodiments of the present invention, 0.25≤C / A≤0.67. By limiting the porosity D of the positive active material coating 22 of the positive electrode plate 2 and the porosity B of the second coating 33 of the separator 3 to 0.11≤D / B≤0.43, the porosity of the positive electrode can be controlled within a suitable ratio range. Within this ratio range, the positive electrode plate 2 can accommodate more electrolyte without compromising mechanical strength by virtue of its suitable pore structure, providing sufficient ion transport medium for the electrochemical reaction, thereby helping to improve the energy density of the battery, while ensuring the stability of the plate structure and avoiding the problem of loose structure caused by excessive porosity. At the same time, limiting 0.11≤D / B≤0.43 also helps to improve the cycle performance of the battery cell during the charge and discharge process and extend the battery life.

[0064] In some specific embodiments of the present invention, 0.11≤D / B≤0.43. By limiting the porosity C of the negative electrode active material coating 12 of the negative electrode plate 1 and the porosity A of the first coating 32 of the separator 3 to 0.25≤C / A≤0.67, the porosity of the negative electrode can be controlled within an appropriate ratio range. Within this ratio range, the negative electrode plate can fully absorb the electrolyte without compromising the mechanical strength by virtue of the appropriate pore structure, ensuring smoother insertion and extraction of lithium ions in the negative electrode region, thereby helping to improve the energy density of the battery and ensure the stability of the plate structure, avoiding the problem of loose structure caused by excessive porosity. At the same time, limiting 0.25≤C / A≤0.67 also helps to improve the cycle performance of the battery cell during the charge and discharge process, thereby extending the battery life.

[0065] In some specific embodiments of the present invention, 60%≤A≤80%. Limiting the porosity A of the first coating 32 of the separator 3 to 60%≤A≤80% can construct an ideal channel for the distribution and transmission of the electrolyte in the negative electrode region. This porosity range not only ensures that the coating has sufficient pore space, allowing the electrolyte to fully penetrate and closely contact the negative electrode active material coating 12, creating good conditions for the insertion and extraction of lithium ions, but also avoids the fragility of the coating structure caused by excessively high porosity.

[0066] In some specific embodiments of the present invention, 0.5 μm ≤ a ≤ 3 μm. Limiting the thickness a of the first coating layer 32 to 0.5 μm ≤ a ≤ 3 μm allows the first coating layer 32 of the separator 3 to ensure effective electrolyte transport while not excessively increasing the length of the ion migration path, thereby improving the lithium ion conduction efficiency in the negative electrode region and optimizing the electrochemical reaction kinetics of the negative electrode.

[0067] In some specific embodiments of the present invention, 70%≤B≤90%. The porosity B of the second coating 33 of the diaphragm 3 is limited to 70%≤B≤90%, creating an excellent environment for the penetration and distribution of the electrolyte in the positive electrode area; this porosity range ensures that the coating has sufficient pore volume to fully absorb the electrolyte, promoting its close fit with the positive electrode active material coating 22, and providing a rich ion source for the insertion and extraction of lithium ions in the positive electrode; at the same time, it avoids the problem of loose coating structure caused by excessive porosity, and ensures the structural stability of the coating in high potential and strong oxidizing environment.

[0068] In some specific embodiments of the present invention, 0.5 μm ≤ b ≤ 5 μm. Limiting the thickness b of the second coating layer 33 of the separator 3 to 0.5 μm ≤ b ≤ 5 μm allows the second coating layer 33 of the separator 3 to ensure effective electrolyte transmission while not excessively increasing the path length of ion migration, thereby improving the conduction efficiency of lithium ions in the positive electrode region and optimizing the electrochemical reaction kinetics of the positive electrode.

[0069] In some specific embodiments of the present invention, 20% ≤ C ≤ 40%. The porosity C of the negative electrode active material coating 12 is limited to 20% ≤ C ≤ 40%. This range ensures that the negative electrode active material coating 12 has a suitable pore structure. On the one hand, sufficient pores allow the electrolyte to fully penetrate, providing ample channels for the insertion and extraction of lithium ions, promoting the efficient electrochemical reaction. On the other hand, a reasonable porosity avoids the loose electrode structure caused by excessive pores, ensuring the structural stability of the negative electrode active material coating 12 during the charge and discharge process.

[0070] In some specific embodiments of the present invention, 50.5 μm ≤ c ≤ 54 μm. Limiting the thickness c of the negative electrode active material coating 12 to 50.5 μm ≤ c ≤ 54 μm optimizes the migration path of lithium ions within the coating while maintaining the negative electrode active material loading. A suitable thickness neither reduces the storage capacity of the active material due to excessive thinness, thereby affecting the battery capacity, nor increases the diffusion distance of lithium ions due to excessive thickness, thereby reducing the battery's charge and discharge performance. This effectively improves the electrochemical reaction efficiency in the negative electrode region and enhances the battery's charge and discharge capabilities.

[0071] In some specific embodiments of the present invention, 10%≤D≤30%. The porosity D of the positive electrode active material coating 22 is limited to 10%≤D≤30%, which constructs an ideal microstructure for the positive electrode region; on the one hand, the moderate porosity ensures that the electrolyte can fully infiltrate the coating, providing sufficient transmission channels for lithium ions to be embedded during charging and released during discharge, greatly promoting the efficient conduct of the electrochemical reaction; on the other hand, the reasonable number of pores avoids the loosening of the electrode structure due to excessive pores, ensuring that the positive electrode active material coating 22 can still maintain a stable structure in the complex environment of high potential and strong oxidation, thereby ensuring the reliability of the battery cell during the charge and discharge cycle.

[0072] In some specific embodiments of the present invention, 42 μm ≤ d ≤ 46 μm. Limiting the thickness d of the positive electrode active material coating 22 to a range of 42 μm ≤ d ≤ 46 μm optimizes the migration path of lithium ions within the coating while ensuring sufficient active material loading to maintain high battery capacity. The appropriate thickness avoids the problem of insufficient active material storage and limited battery capacity due to excessive thinness, while also preventing the increased lithium ion diffusion distance due to excessive thickness, thereby avoiding a decrease in battery charge and discharge performance, effectively improving the electrochemical reaction efficiency in the positive electrode region, and significantly enhancing the battery's charge and discharge performance.

[0073] In some specific embodiments of the present invention, the pore size of the first coating 32 is E μm, the pore size of the second coating 33 is F μm, and the pore size of the substrate 31 is G μm, satisfying: 0.1≤E≤2, 0.3≤F≤4, 0.02≤G≤0.08, F>E>G.

[0074] By limiting the pore size E of the first coating 32 to 0.1≤E≤2μm, the pore size F of the second coating 33 to 0.3≤F≤4μm, and the pore size G of the substrate 31 to 0.02≤G≤0.08μm and satisfying the relationship F>E>G, the pore blockage problem can be effectively avoided; specifically, the larger coating pore size allows the electrolyte to penetrate and transmit more smoothly between the diaphragm 3 and the electrode active material coating during the charge and discharge cycle of the battery cell; the migration path of lithium ions is guaranteed, avoiding the obstruction of ion transmission due to pore blockage, and improving the cycle performance of the battery cell.

[0075] By limiting 0.1≤E≤2, 0.3≤F≤4, 0.02≤G≤0.08 and F>E>G, a good fit can be formed between the first coating 32, the second coating 33 and the substrate; the larger coating pore size combined with the relatively small substrate 31 pore size ensures that the coating can fully absorb and store the electrolyte, providing a sufficient ion source for the electrochemical reaction, and utilizes the smaller pore size of the substrate 31 to maintain the basic barrier function of the diaphragm to prevent short circuits between the positive and negative electrodes; this collaborative working mode optimizes the overall performance of the diaphragm, ensuring that the battery cell achieves efficient energy conversion while operating safely and stably.

[0076] Optionally, E can be any value satisfying 0.1≤E≤2, such as 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, etc., and is not limited here.

[0077] Optionally, F can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, or any other value that satisfies 0.3≤E≤4, and is not limited here.

[0078] Optionally, G can be any value such as 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, etc. that satisfies 0.02≤G≤0.08, and is not limited here.

[0079] In the present invention, the pore size of the first coating 32, the pore size of the second coating 33, and the pore size of the substrate 31 can be measured by the following method: using a TESCAN VEGA3 scanning electron microscope, in secondary electron imaging mode, an accelerating voltage of 20 kV, a magnification of 5000 times, and a scanning range of 25 μm*25 μm, 50 micropores on the surface of the coating (or substrate) are randomly selected within this range and the sizes of the micropores are taken. The pore size of the micropore is calculated from the starting point to the end point of the micropore (the starting point to the longest end point of the micropore), and the average of the 50 micropore sizes is the average pore size.

[0080] In some specific embodiments of the present invention, the air permeability of the first coating 32 is Js / 100cc, and the air permeability of the second coating 33 is Ks / 100cc, satisfying the following conditions: 5≤J≤70, 5≤K≤50, and J≥K.

[0081] Since lower coating permeability indicates higher porosity, the permeability J of the first coating 32 is limited to 5≤J≤70s / 100cc, and the permeability K of the second coating 33 is limited to 5≤K≤50s / 100cc with J≥K, ensuring the coatings have appropriate porosity. The higher porosity allows the first and second coatings 32 and 33 to fully absorb electrolyte, providing ample ion transport media for the electrochemical reactions within the battery cell. By matching the permeability J of the first coating 32 with the permeability K of the second coating 33 to J≥K, the electrolyte environment on both sides of the separator is relatively balanced, reducing ion transport barriers caused by significant differences between the two sides. This creates a stable environment for the electrochemical reactions within the battery cell, improves the cycling stability of the battery cell, and extends the battery's service life.

[0082] Optionally, J can be any value such as 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, etc. that satisfies 5≤J≤70, and is not limited here.

[0083] Optionally, K can be any value such as 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, etc. that satisfies 5≤K≤50, and is not limited here.

[0084] The air permeability value can be obtained by testing as follows: first, place the substrate on a test instrument (Asahi Seiko air permeability tester), squeeze 100ml of gas from one air chamber to another at a constant pressure (e.g., 0.05 MPa), and record the time it takes for the gas to pass through as S1. Then, measure the substrate with the coating membrane in the same manner, and record the time it takes for the gas to pass through as S2. The coating air permeability value S = S2-S1. For example, a substrate is coated with the first coating 32 and tested in the same manner, and the gas passage time is S1. 21 , then the air permeability of the first coating 32 is S 21 -S1; The substrate 31 is coated with a second coating 33 and tested by the above method to obtain a gas passage time of S 22 , then the air permeability of the second ceramic layer is S 22 -S1.

[0085] In some specific embodiments of the present invention, the substrate 31 includes but is not limited to one or more of polyethylene, polypropylene, polyimide, and polyethylene terephthalate.

[0086] The first coating layer 32 is composed of a first organic polymer and a first inorganic material.

[0087] The second coating layer 33 is composed of a second organic polymer and a second inorganic material.

[0088] In some specific embodiments of the present invention, the first organic polymer may be one or more including but not limited to polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyacrylonitrile, polyetherimide, polyamide, meta-aramid, para-aramid, polymethyl methacrylate, polyethylene, styrene-butadiene rubber and polyacrylate.

[0089] In some specific embodiments of the present invention, the first inorganic material may be one or more including but not limited to aluminum oxide, magnesium oxide, silicon oxide, titanium dioxide, zirconium dioxide, zinc oxide, barium sulfate, boron nitride, aluminum nitride, magnesium nitride, tin dioxide, magnesium hydroxide, boehmite, zeolite and calcium carbonate.

[0090] In some specific embodiments of the present invention, the second organic polymer may be one or more including but not limited to polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyacrylonitrile, polyetherimide, polyamide, meta-aramid, para-aramid, polymethyl methacrylate, polyethylene, styrene-butadiene rubber and polyacrylate.

[0091] In some specific embodiments of the present invention, the second inorganic material may be one or more including but not limited to aluminum oxide, magnesium oxide, silicon oxide, titanium dioxide, zirconium dioxide, zinc oxide, barium sulfate, boron nitride, aluminum nitride, magnesium nitride, tin dioxide, magnesium hydroxide, boehmite, zeolite and calcium carbonate.

[0092] In some specific embodiments of the present invention, the mass ratio of the first organic polymer to the first inorganic material is (0-9.5):1; the mass ratio of the second organic polymer to the second inorganic material is (0-9.5):1.

[0093] In some specific embodiments of the present invention, the first inorganic material includes first inorganic particles, and the second inorganic material includes second inorganic particles; wherein the average particle size of the first inorganic particles is H μm, and the average particle size of the second inorganic particles is I μm, satisfying: 0.2≤H≤0.8, 0.4≤I≤1.5, I≥H.

[0094] The larger the particle size of the inorganic particles in the coating, the easier it is to increase the porosity of the coating; by limiting the average particle size H of the first inorganic particles to 0.2≤H≤0.8μm, and the average particle size I of the second inorganic particles to 0.4≤I≤1.5μm and limiting I≥H, from the perspective of the difference between the positive and negative electrode reactions, the positive electrode reaction is more complex; during charging, lithium ions are released from the positive electrode, and the process involves complex redox reactions, which have high requirements for electrolyte consumption and ion transfer rate; the second inorganic particles with larger particle size construct a richer and larger pore network in the second coating 33, which can store more electrolyte and continuously supply lithium ions to the positive electrode area to meet its high demand for ion transfer; while the negative electrode reaction is relatively simple, the pore structure formed by the first inorganic particles with smaller particle size in the first coating 32 can meet the negative electrode's needs for electrolyte adsorption and ion transfer, avoid problems such as the shedding of negative electrode active materials due to excessive pores, and ensure the stability of the negative electrode structure.

[0095] In the present invention, the average particle size of the inorganic particles can be tested by the following method: using a TESCAN VEGA3 scanning electron microscope, mode secondary electron imaging, acceleration voltage 20kV, magnification 5000 times, scanning range 25μm*25μm, randomly selecting 50 particles within the range to measure the size of the particles, calculating the particle size from the starting point to the end point of the particle (from the starting point to the longest end point of the particle), and the average size of the 50 particles is the average particle size.

[0096] Second aspect

[0097] The present invention also provides a battery, which includes any one of the above-mentioned battery cells, and further includes a shell and an electrolyte, wherein the battery cell and the electrolyte are both arranged in the shell.

[0098] The third aspect

[0099] The present invention also provides a method for preparing any of the above batteries, comprising the following steps:

[0100] Preparation of positive electrode sheet 2: lithium cobalt oxide, acetylene black, and polyvinylidene fluoride are thoroughly stirred and mixed in an N-methylpyrrolidone solvent system, and then coated on the positive electrode current collector 21, dried, cold pressed, and cut into strips to obtain positive electrode sheet 2;

[0101] Preparation of negative electrode sheet 1: artificial graphite, acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose are thoroughly stirred and mixed in a deionized water solvent system, and then coated on the negative electrode current collector 11. After drying, cold pressing, and slitting, a negative electrode sheet 1 is obtained;

[0102] Preparation of the diaphragm 3: applying a first coating 32 on one side of the substrate 31 and applying a second coating 33 on the other side of the substrate 31;

[0103] Preparation of electrolyte: A solution prepared by mixing lithium salt with a non-aqueous organic solvent is used as the electrolyte;

[0104] Obtaining a battery: stacking the negative electrode sheet 1, the separator 3, and the positive electrode sheet 2 in sequence and then making a battery cell according to a winding process or a lamination process, placing the battery cell in a shell, injecting the electrolyte into the shell and encapsulating it to obtain a battery.

[0105] Six examples and six comparative examples of batteries were obtained using the aforementioned battery preparation method. In the positive electrode sheet 2 preparation step, the mass ratio of lithium cobalt oxide, acetylene black, and polyvinylidene fluoride was 95:3:2. In the negative electrode sheet 1 preparation step, the mass ratio of artificial graphite, acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose was 96:1:1.5:1.5. In the electrolyte preparation step, the mass ratio of lithium salt to non-aqueous organic solvent was 8:92. The non-aqueous organic solvent was composed of the following raw materials in parts by weight: 20 parts ethylene carbonate, 30 parts diethyl carbonate, 20 parts propylene carbonate, 28 parts propyl propionate, and 2 parts vinylene carbonate. In the battery preparation step, the negative electrode sheet 1, separator 3, and positive electrode sheet 2 were stacked in sequence and then wound to form a battery cell.

[0106] The batteries of the six embodiments and the six comparative examples differ only in the values ​​of A, a, B, b, C, c, D, and d. Specific data of the six embodiments and the six comparative examples are shown in Table 1 below:

[0107]

[0108] Table 1

[0109] According to the specific data in Table 1, the C / A, D / B and [(Dd+Bb) / (b+d)] / [(Aa+Cc) / (a+c)] of Examples 1-6 and Comparative Examples 1-6 are shown in Table 2 below:

[0110]

[0111] Table 2

[0112] As can be seen from Table 2, Examples 1-6 all meet the following three conditions: 0.25≤C / A≤0.67, 0.11≤D / B≤0.43, and 0.8≤[(Dd+Bb) / (b+d)] / [(Aa+Cc) / (a+c)]≤1.2.

[0113] Comparative Example 1 does not satisfy the two conditions of 0.11≤D / B≤0.43 and 0.8≤[(Dd+Bb) / (b+d)] / [(Aa+Cc) / (a+c)]≤1.2.

[0114] Comparative Examples 2 and 6 do not satisfy the condition of 0.8≤[(Dd+Bb) / (b+d)] / [(Aa+Cc) / (a+c)]≤1.2.

[0115] Comparative Examples 3 and 4 do not satisfy the condition of 0.25≤C / A≤0.67.

[0116] Comparative Example 5 does not satisfy the two conditions of 0.25≤C / A≤0.67 and 0.8≤[(Dd+Bb) / (b+d)] / [(Aa+Cc) / (a+c)]≤1.2.

[0117] The room temperature cycle performance test method of the battery is as follows: in an environment of 25°C, the first charge and discharge are carried out, constant current and constant voltage charging is performed at a charging current of 0.1C (i.e. the current value that completely discharges the theoretical capacity within 10 hours) until the upper limit voltage is 4.3V, and then constant current discharge is performed at a discharge current of 1C until the final voltage is 3V, and the discharge capacity of the first cycle is recorded; then 100 charge and discharge cycles are carried out, and the discharge capacity of the 100th cycle is recorded.

[0118] The cycle capacity retention rate of the 200th cycle = (discharge capacity of the 200th cycle / discharge capacity of the first cycle) × 100%; the cycle capacity retention rate of the 400th cycle = (discharge capacity of the 400th cycle / discharge capacity of the first cycle) × 100%; the cycle capacity retention rate of the 600th cycle = (discharge capacity of the 600th cycle / discharge capacity of the first cycle) × 100%; the cycle capacity retention rate of the 800th cycle = (discharge capacity of the 800th cycle / discharge capacity of the first cycle) × 100%.

[0119] The test samples were set as five groups of parallel samples, and the final test results were calculated as the average value of the five groups of parallel samples.

[0120] The above-mentioned room temperature cycle performance test method was used to test the batteries provided in Examples 1-6 and Comparative Examples 1-6. The specific test structure is shown in Table 3 below:

[0121]

[0122] Table 3

[0123] It can be seen from Tables 1 to 3 that when the battery cells meet the three conditions of 0.25≤C / A≤0.67, 0.11≤D / B≤0.43 and 0.8≤[(Dd+Bb) / (b+d)] / [(Aa+Cc) / (a+c)]≤1.2, the cycle performance of the battery cells is significantly better, and the battery has higher stability and reliability during long-term use.

[0124] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.

Claims

1. A battery cell, characterized in that: It comprises a negative electrode sheet (1), a separator (3) and a positive electrode sheet (2) stacked in sequence; The negative electrode plate (1) comprises a negative electrode current collector (11) and a negative electrode active material coating (12), wherein the negative electrode active material coating (12) is coated on a side of the negative electrode current collector (11) facing the separator (3); The positive electrode plate (2) comprises a positive electrode current collector (21) and a positive electrode active material coating (22), wherein the positive electrode active material coating (22) is coated on a side of the positive electrode current collector (21) facing the separator (3); The separator (3) comprises a substrate (31), a first coating (32) and a second coating (33), wherein the first coating (32) is coated on a side of the substrate (31) facing the negative electrode plate (1) and connected to the negative electrode active material coating (12), and the second coating (33) is coated on a side of the substrate (31) facing away from the first coating (32) and connected to the positive electrode active material coating (22); The porosity of the first coating (32) is A, the thickness of the first coating (32) is a μm, the porosity of the second coating (33) is B, the thickness of the second coating (33) is b μm, the porosity of the negative electrode active material coating (12) is C, the thickness of the negative electrode active material coating (12) is c μm, the porosity of the positive electrode active material coating (22) is D, the thickness of the positive electrode active material coating (22) is d μm, the pore size of the first coating (32) is E μm, the pore size of the second coating (33) is F μm, and the pore size of the substrate (31) is G μm, satisfying the following: 0.8≤[(Dd+Bb) / (b+d)] / [(Aa+Cc) / (a+c)]≤1.2; 60%≤A≤80%; 0.5μm≤aμm≤3μm; 70%≤B≤90%; 0.5μm≤bμm≤5μm; 20%≤C≤40%;50.5μm≤cμm≤54μm; 10%≤D≤30%;42μm≤dμm≤46μm; 0.1≤E≤2, 0.3≤F≤4, 0.02≤G≤0.08, F>E>G.

2. The battery cell according to claim 1, characterized in that 0.25≤C / A≤0.

67.

3. The battery cell according to claim 1, characterized in that 0.11≤D / B≤0.

43.

4. The battery cell according to claim 1, characterized in that The air permeability of the first coating (32) is Js / 100cc, and the air permeability of the second coating (33) is Ks / 100cc, satisfying the following conditions: 5≤J≤70, 5≤K≤50, and J≥K.

5. The battery cell according to claim 1, characterized in that The substrate (31) includes one or more of polyethylene, polypropylene, polyimide, and polyethylene terephthalate; The first coating (32) is composed of a first organic polymer and a first inorganic material; The second coating (33) is composed of a second organic polymer and a second inorganic material; The first organic polymer comprises one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyacrylonitrile, polyetherimide, polyamide, meta-aramid, para-aramid, polymethyl methacrylate, polyethylene, styrene-butadiene rubber and polyacrylate; The first inorganic material is one or more of aluminum oxide, magnesium oxide, silicon oxide, titanium dioxide, zirconium dioxide, zinc oxide, barium sulfate, boron nitride, aluminum nitride, magnesium nitride, tin dioxide, magnesium hydroxide, boehmite, zeolite and calcium carbonate; The second organic polymer comprises one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyacrylonitrile, polyetherimide, polyamide, meta-aramid, para-aramid, polymethyl methacrylate, polyethylene, styrene-butadiene rubber and polyacrylate; The second inorganic material is one or more of aluminum oxide, magnesium oxide, silicon oxide, titanium dioxide, zirconium dioxide, zinc oxide, barium sulfate, boron nitride, aluminum nitride, magnesium nitride, tin dioxide, magnesium hydroxide, boehmite, zeolite and calcium carbonate.

6. The battery cell according to claim 5, characterized in that The mass ratio of the first organic polymer to the first inorganic material is (0-9.5):1; The mass ratio of the second organic polymer to the second inorganic material is (0-9.5):

1.

7. The battery cell according to claim 5, characterized in that The first inorganic material includes first inorganic particles, and the second inorganic material includes second inorganic particles; The average particle size of the first inorganic particles is H μm, and the average particle size of the second inorganic particles is I μm, satisfying the following conditions: 0.2≤H≤0.8, 0.4≤I≤1.5, and I≥H.

8. A battery, characterized in that: The invention comprises the battery cell according to any one of claims 1 to 7, and further comprises a shell and an electrolyte, wherein the battery cell and the electrolyte are both arranged in the shell.

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