Lithium ion cylindrical battery, preparation method thereof and power utilization device

Abstract

The invention discloses a cylindrical lithium ion battery, a preparation method thereof and a power utilization device, and relates to the technical field of lithium batteries. The cylindrical lithium ion battery provided by the invention is provided with the positive pole piece of the positive active material layer with a specific surface Ni / F normalized mass ratio range, the reaction degrees of different positions in a roll core of the cylindrical lithium ion battery and electrolyte are reflected, and the surface Ni / F normalized mass ratio of the positive pole piece is adjusted within the range limited by the invention; the side reaction degree of the positive electrode material and electrolyte is improved, and a crystal structure is protected, so that the cycle performance and the safety performance of the battery are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular, to a lithium-ion cylindrical battery, a preparation method thereof, and an electrical device using the same. Background Art

[0002] With the increasing prominence of environmental and energy issues, the use of lithium-ion batteries (LIBs) as secondary clean energy sources has become increasingly widespread. However, the safety issues and cycle stability of the batteries have become key factors restricting their development. During the charge and discharge process of the battery, side reactions between the electrolyte and the positive and negative electrode materials can lead to capacity attenuation and shortened lifespan. In addition, the thermal stability problem of the battery in a high-temperature environment is also an important factor affecting its safety performance.

[0003] Currently, it is urgent to improve the degree of side reactions between the positive electrode material and the electrolyte and enhance the cycle performance of the battery.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a lithium-ion cylindrical battery, a preparation method thereof, and an electrical device using the same, aiming to improve the degree of side reactions between the positive electrode material and the electrolyte and enhance the cycle performance of the battery.

[0006] The present invention is implemented as follows:

[0007] In a first aspect, the present invention provides a lithium-ion cylindrical battery, including a cylindrical core formed by winding a positive electrode sheet, a negative electrode sheet, and a separator. Three different points are selected at intervals of 1 / 4 within the range from the center to the edge of the cylindrical core in the radial direction, and the positions of the three points all correspond to the positive electrode sheet. The three points are marked as K1, K2, and K3;

[0008] After the cylindrical core is unfolded, three positive electrode sheet segments are cut out on the positive electrode sheet with the marked K1, K2, and K3 as the centers;

[0009] On the positive electrode sheet segment corresponding to K1, three test regions are selected at intervals of 1 / 4 in the height direction. The Ni / F normalized mass ratios of the corresponding electrode surface of the three test regions are respectively named a1, a2, and a3. The Ni / F normalized mass ratio at K1 of the cylindrical core is defined as A1, and A1 = (a1 + a2 + a3) / 3;

[0010] On the positive electrode sheet segment corresponding to K2, three test regions are selected at intervals of 1 / 4 in the height direction. The Ni / F normalized mass ratios of the corresponding electrode surface of the three test regions are respectively named b1, b2, and b3. The Ni / F normalized mass ratio at K2 of the cylindrical core is defined as A2, and A2 = (b1 + b2 + b3) / 3;

[0011] Select three test regions at intervals of 1 / 4 in the height direction of the positive electrode segment corresponding to K3. Name the Ni / F normalized mass ratios of the surfaces of the electrode foils corresponding to the three test regions as c1, c2, and c3 respectively, and define the Ni / F normalized mass ratio at the cylindrical core K3 as A3, and A3 = (c1 + c2 + c3) / 3;

[0012] A1, A2, and A3 satisfy:

[0013] (A1 + A2 + A3) / 3 ≤ 10, 0.1 ≤ |A1 - A2| + |A2 - A3| + |A1 - A3| ≤ 4.

[0014] In an alternative embodiment, A1, A2, and A3 satisfy: (A1 + A2 + A3) / 3 ≤ 9.5, 0.1 ≤ |A1 - A2| + |A2 - A3| + |A1 - A3| ≤ 3.5.

[0015] In an alternative embodiment, the widths of the three positive electrode segments cut are all 3 cm - 5 cm;

[0016] The three test regions selected on the positive electrode segments corresponding to K1, K2, and K3 are all square regions with side lengths of 0.5 cm - 2.0 cm;

[0017] The Ni / F normalized mass ratios of the surfaces of the electrode foils corresponding to the three test regions satisfy:

[0018] |a1 - a2| + |a2 - a3| + |a1 - a3| ≤ 3;

[0019] |b1 - b2| + |b2 - b3| + |b1 - b3| ≤ 3;

[0020] |c1 - c2| + |c2 - c3| + |c1 - c3| ≤ 3;

[0021] The Ni / F normalized mass ratio of the surface of the electrode foil corresponding to the test region is the average of the Ni / F normalized mass ratios of the two surfaces on both sides of the current collector. Name the difference between the Ni / F normalized mass ratios of the surfaces of the electrode foils on both sides of the current collector as Δx, and it satisfies Δx ≤ 1; preferably, Δx ≤ 0.85.

[0022] In an alternative embodiment, the positive active material on the positive electrode foil includes a first positive active material and a second positive active material. The first positive active material is polycrystalline large particles, and the second positive active material is single-crystalline small particles;

[0023] Among them, the particle size of the first positive active material satisfies: 8.5 μm < D50 < 15 μm, 18 μm < Dmax < 30 μm;

[0024] The particle size of the second positive electrode active material satisfies: 2.0 μm < D50 < 5 μm, 7 μm < Dmax < 15 μm;

[0025] In the positive electrode active material, the volume ratio of the first positive electrode active material is 20% - 50%, and the volume ratio of the second positive electrode active material is 50% - 80%;

[0026] Preferably, in the positive electrode active material, the volume ratio of the first positive electrode active material is 20% - 40%, and the volume ratio of the second positive electrode active material is 60% - 80%.

[0027] In an alternative embodiment, both the first positive electrode active material and the second positive electrode active material are at least one of lithium nickel cobalt manganate and lithium nickel cobalt aluminate;

[0028] Preferably, the chemical formulas of both the first positive electrode active material and the second positive electrode active material are LiNi x Co y M z N s O2;

[0029] Among them, M is Mn or Al;

[0030] N represents a doping element, and N is selected from at least one of Al, Co, Ta, Ti, Nb, Zr, B, W, Mg, Te, Ca, Fe, Mo, Na, K, La, Ga, F, Cl, S, B, and N;

[0031] 0.7 ≤ x < 1, 0 < y < 0.3, 0 < z < 0.1, s = 1 - x - y - z.

[0032] In an alternative embodiment, the lithium-ion cylindrical battery further includes an electrolyte, the electrolyte includes a lithium salt, an organic solvent, and an additive, and the mass ratio of the additive in the electrolyte is 0 - 5%, preferably 0.2% - 4.0%;

[0033] Preferably, the additive is selected from at least one of ethylene carbonate, dimethyl carbonate, fluoroethylene carbonate, lithium borate, vinylene sulfate, and lithium bis(trifluoromethanesulfonyl)imide;

[0034] Preferably, the organic solvent is a mixed solvent formed by ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate, and the volume ratio of ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate is 1:(0.5 - 1.5):(0.5 - 1.5);

[0035] Preferably, the lithium salt is LiPF6.

[0036] In an alternative embodiment, the separator includes a base film, a ceramic coating is provided on one side of the base film, and a PVDF coating is provided on the other side;

[0037] Preferably, the base film is a PE film with a thickness of 8 μm - 10 μm, the thickness of the ceramic coating is 0.5 μm - 2.0 μm, and the thickness of the PVDF coating is 0.5 μm - 2.0 μm;

[0038] Preferably, the air permeability of the separator is 70 s / 100 mL - 150 s / 100 mL.

[0039] In a third aspect, the present invention provides a method for preparing a lithium-ion cylindrical battery according to any one of the foregoing embodiments, including: providing a positive electrode sheet, a negative electrode sheet, and a separator, winding the positive electrode sheet, the negative electrode sheet, and the separator to form a cylindrical core, and injecting an electrolyte into a battery case;

[0040] Among them, the preparation process of the positive electrode sheet includes: mixing a first positive electrode active material and a second positive electrode active material to obtain a mixed active material, and using the mixed active material to prepare a positive electrode sheet; wherein, the first positive electrode active material is polycrystalline large particles, and the second positive electrode active material is single crystal small particles; in the mixed active material, the volume ratio of the first positive electrode active material is 20% - 50%, and the volume ratio of the second positive electrode active material is 50% - 80%.

[0041] In an alternative embodiment, the particle size of the first positive electrode active material satisfies: 8.5 μm < D50 < 15 μm, 18 μm < Dmax < 30 μm; the particle size of the second positive electrode active material satisfies: 2.0 μm < D50 < 5 μm, 7 μm < Dmax < 15 μm;

[0042] Preferably, the process of preparing the positive electrode sheet includes: mixing the mixed active material, a conductive agent, and a binder in a mass ratio of (94% - 98%):(1% - 3%):(1% - 3%), and homogenizing to obtain a positive electrode slurry, coating the positive electrode slurry on both sides of a positive electrode current collector, and drying;

[0043] Preferably, the electrolyte includes a lithium salt, a solvent, and an additive, and the mass ratio of the additive in the electrolyte is 0 - 5%, more preferably 0.2% - 4.0%; the additive is selected from at least one of ethylene carbonate, dimethyl carbonate, fluoroethylene carbonate, lithium borate, ethylene sulfate, and lithium bis(trifluoromethanesulfonyl)imide.

[0044] In a fourth aspect, the present invention provides an electrical device, including a lithium-ion cylindrical battery according to any one of the foregoing embodiments or a lithium-ion cylindrical battery prepared by the preparation method according to any one of the foregoing embodiments.

[0045] The present invention has the following beneficial effects: The positive electrode tab of the lithium-ion cylindrical battery provided by the present invention has a positive electrode active material layer with a specific surface Ni / F normalized mass ratio range, which reflects the reaction degree between different positions in the lithium-ion cylindrical battery core and the electrolyte. Adjusting the surface Ni / F normalized mass ratio of the positive electrode tab within the range defined by the present invention is beneficial to improving the side reaction degree between the positive electrode material and the electrolyte, protecting the crystal structure, and thus enhancing the cycle performance and safety performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0047] Figure 1 Schematic diagram of the positions of the cylindrical cores K1, K2, and K3;

[0048] Figure 2 Schematic diagram of the positive electrode tab corresponding to the position of K1;

[0049] Figure 3 Schematic diagram of the structure of the cylindrical battery after assembly. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer are all conventional products that can be obtained through commercial purchase.

[0051] An embodiment of the present invention provides a lithium-ion cylindrical battery, including a cylindrical core formed by winding a positive electrode tab, a negative electrode tab, and a separator, as Figure 1 shown. Three different points are selected at intervals of 1 / 4 within the range from the center to the edge of the cylindrical core in the radial direction, and the positions of the three points all correspond to the positive electrode tab in the height direction. The three points are marked as K1, K2, and K3.

[0052] As Figure 2 shown, after the cylindrical core is unfolded, three positive electrode tabs with a certain width are cut out on the positive electrode tab with the marked K1, K2, and K3 as the centers respectively, and then points are taken on the three positive electrode tabs to test the surface Ni / F normalized mass ratio. The specific steps are as follows:

[0053] Select three test areas at intervals of 1 / 4 in the height direction of the positive electrode segment corresponding to K1. Name the normalized mass ratios of Ni / F on the electrode surface corresponding to the three test areas as a1, a2, and a3 respectively. Define the normalized mass ratio of Ni / F at the cylindrical core K1 as A1, and A1 = (a1 + a2 + a3) / 3, where |a1 - a2| + |a2 - a3| + |a1 - a3| ≤ 3. That is to say, A1 is equal to the average value of a1, a2, and a3, and the differences between a1, a2, and a3 are very small. Due to the relatively high group margin of the all-pole-ear lithium-ion cylindrical battery, under high-rate discharge conditions, the electrochemical reaction is relatively intense, resulting in differences in the values of the normalized mass ratios of Ni / F at different heights. Therefore, it is necessary to select appropriate test areas at different heights. The all-pole-ear lithium-ion cylindrical battery means that an empty foil area is left at one end in the width direction of the positive electrode sheet, and after being flattened or cut and stacked, a positive electrode ear layer is formed. An empty foil area is left at one end in the width direction of the negative electrode sheet, and after being flattened or cut and stacked, a negative electrode ear layer is formed. Such a design can reduce the internal resistance value by more than 70%. The internal resistance value of the battery is between 1 and 5 milliohms, greatly improving the charge and discharge performance of the all-pole-ear cylindrical lithium-ion battery.

[0054] Similarly, select three test areas at intervals of 1 / 4 in the height direction of the positive electrode segment corresponding to K2. Name the normalized mass ratios of Ni / F on the electrode surface corresponding to the three test areas as b1, b2, and b3 respectively. Define the normalized mass ratio of Ni / F at the cylindrical core K2 as A2, and A2 = (b1 + b2 + b3) / 3, where |b1 - b2| + |b2 - b3| + |b1 - b3| ≤ 3. That is to say, A2 is equal to the average value of b1, b2, and b3, and the differences between b1, b2, and b3 are very small.

[0055] Similarly, select three test areas at intervals of 1 / 4 in the height direction of the positive electrode segment corresponding to K3. Name the normalized mass ratios of Ni / F on the electrode surface corresponding to the three test areas as c1, c2, and c3 respectively. Define the normalized mass ratio of Ni / F at the cylindrical core K3 as A3, and A3 = (c1 + c2 + c3) / 3; |c1 - c2| + |c2 - c3| + |c1 - c3| ≤ 3. That is to say, A3 is equal to the average value of c1, c2, and c3, and the differences between c1, c2, and c3 are very small.

[0056] The above-measured A1, A2, and A3 satisfy:

[0057] (A1 + A2 + A3) / 3 ≤ 10, 0.1 ≤ |A1 - A2| + |A2 - A3| + |A1 - A3| ≤ 4.

[0058] It should be noted that Ni comes from the positive active material on the positive electrode tab, and F mainly comes from the binder and electrolyte on the positive electrode tab. During the charge and discharge process, the electrolyte and binder will decompose into fluorinated products (HF, LiF). Therefore, the Ni / F on the surface of the positive electrode tab can reflect the degree of side reactions at the interface. The smaller the value of the normalized mass ratio of Ni / F on the tab surface, the better. A smaller value indicates that the interface of the positive electrode material is more stable. If the value of (A1 + A2 + A3) / 3 is greater than 10, it means that the decomposition products of the electrolyte and binder corrode the interface of the positive electrode material more severely. The closer the values of A1, A2, and A3 are, the better, indicating good consistency of electrolyte infiltration inside and outside the core. If the value of |A1 - A2| + |A2 - A3| + |A1 - A3| is greater than 4, the infiltration effect of the electrolyte does not reach the ideal state. By controlling the reaction degree between different positions in the lithium-ion cylindrical battery core and the electrolyte, adjusting the normalized mass ratio of Ni / F on the surface of the positive electrode material within this range is beneficial to improving the degree of side reactions at the interface of the positive electrode material, protecting the crystal structure, and thus enhancing the cycle performance and safety performance of the battery.

[0059] Specifically, the value of (A1 + A2 + A3) / 3 can be 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 9.5, 10.0, etc. The value of |A1 - A2| + |A2 - A3| + |A1 - A3| can be 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, etc. The normalized mass ratio of Ni / F on the tab surface is obtained through EDS testing, detecting the characteristic X-rays emitted by the test sample excited by the electron beam, and distinguishing different elements through the X-ray energy.

[0060] In a preferred embodiment, A1, A2, and A3 satisfy: (A1 + A2 + A3) / 3 ≤ 9.5, 0.1 ≤ |A1 - A2| + |A2 - A3| + |A1 - A3| ≤ 3.5. By further optimizing the values of A1, A2, and A3, the high-temperature cycle stability of the cylindrical battery can be further improved.

[0061] In some embodiments, the widths of the three cut positive electrode tab segments are all 3 cm - 5 cm, such as 3 cm, 4 cm, 5 cm, and the height of the positive electrode tab segment is equal to the height of the entire positive electrode tab. The three test areas selected on the positive electrode tab segments corresponding to K1, K2, and K3 can all be square areas with side lengths of 0.5 cm - 2.0 cm, such as side lengths of 0.5 cm, 1.0 cm, 1.5 cm, 2.0 cm, etc., such as a 1×1 cm square area.

[0062] Furthermore, the normalized mass ratio of Ni / F on the surface of the electrode corresponding to the test area is the average of the normalized mass ratios of Ni / F on the surfaces on both sides of the current collector. The difference in the normalized mass ratio of Ni / F on the surfaces of the electrodes (on the surfaces of the positive active material particles) on both sides of the current collector is named Δx, and it satisfies Δx ≤ 1, preferably Δx ≤ 0.85, that is, the test values on both surfaces are relatively close, indicating better wetting effect of the electrolyte. The value of Δx can be 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, etc.

[0063] In some embodiments, the positive active material on the positive electrode includes a first positive active material and a second positive active material. The first positive active material is polycrystalline large particles, and the second positive active material is single-crystalline small particles of the first positive active material; wherein, the particle size of the first positive active material satisfies: 8.5 μm < D50 < 15 μm, 18 μm < Dmax < 30 μm; the particle size of the second positive active material satisfies: 2.0 μm < D50 < 5 μm, 7 μm < Dmax < 15 μm. In the positive active material, the volume ratio of the first positive active material is 20% - 50%, preferably 20% - 40%; the volume ratio of the second positive active material is 50% - 80%, preferably 60% - 80%.

[0064] It should be noted that the positive active material of the present invention includes two components, polycrystalline large particles and single-crystalline small particles. The mixing of single-crystalline small particles and polycrystalline large particles can achieve higher tap density and better cycle stability performance. The synergistic effect of the two can exhibit excellent rate performance and cycle life on the basis of ensuring the capacity of the positive electrode material.

[0065] Specifically, a "single crystal particle" refers to a particle composed of a single crystal. Different from polycrystalline particles, there are no grain boundaries inside single crystal particles, which have higher structural integrity and stability. Polycrystalline large particles are formed by the aggregation of single crystal particles and have a relatively large particle size. The D50 of the first positive electrode active material can be 9.0μm, 10.0μm, 11.0μm, 12.0μm, 13.0μm, 14.0μm, etc.; the maximum particle diameter Dmax of the first positive electrode active material can be 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, etc. The D50 of the second positive electrode active material can be 2.5μm, 3.0μm, 3.5μm, 4.0μm, 4.5μm, etc.; the maximum particle diameter Dmax of the second positive electrode active material can be 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, etc. In the positive electrode active material, the volume ratio of the first positive electrode active material can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc.; the volume ratio of the second positive electrode active material can be 80%, 75%, 70%, 65%, 60%, 55%, 50%, etc.

[0066] In some embodiments, both the first positive electrode active material and the second positive electrode active material are at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminate, and can be any one or several of the above. The types of the first positive electrode active material and the second positive electrode active material can be the same or different. The chemical formulas of the first positive electrode active material and the second positive electrode active material can both be LiNi x Co y M z N s O2; where M is Mn or Al, and M can be any one of the above; N represents a doping element, and N is selected from at least one of Al, Co, Ta, Ti, Nb, Zr, B, W, Mg, Te, Ca, Fe, Mo, Na, K, La, Ga, F, Cl, S, B, and N. The doping element N can be any one or several of the above. The introduction of metal doping elements can effectively improve the structural stability of the ternary positive electrode material. The values of each subscript in the chemical formula are: 0.7 ≤ x < 1, such as 0.70, 0.80, 0.90, 0.95, etc.; 0 < y < 0.3, such as 0.05, 0.10, 0.15, 0.20, 0.25, etc.; 0 < z < 0.1, such as 0.01, 0.03, 0.05, 0.08, 0.09, etc.; s = 1 - x - y - z, that is, x + y + z + s = 1.

[0067] In some embodiments, the lithium-ion cylindrical battery further includes an electrolyte, which includes a lithium salt, an organic solvent, and an additive. The mass ratio of the additive in the electrolyte is 0-5%, and the mass ratio of the additive in the electrolyte can be 0.1%, 0.2%, 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, etc., preferably 0.2%-4.0%. The additive is selected from at least one of ethylene carbonate, dimethyl carbonate, fluoroethylene carbonate, lithium borate, vinylene sulfate, and lithium bis(trifluoromethanesulfonyl)imide. The additive can be any one or several of the above.

[0068] Further, the organic solvent is a mixed solvent formed by ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate, and the volume ratio of ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate is 1:(0.5-1.5):(0.5-1.5), such as 1:0.5:0.5, 1:1.0:1.0, 1:1.5:1.5, etc. The lithium salt can be LiPF6, but is not limited thereto.

[0069] It should be noted that through the optimization of the electrolyte formula and the regulation of the introduction and content ratio of different additives, on the one hand, a more stable passivation film is formed on the material surface, which can prevent the dissolution of transition metal ions in the high-nickel ternary cathode material; on the other hand, the subsequent decomposition of the electrolyte can be inhibited, ensuring the electrochemical stability of the electrolyte, thereby improving the cycle life and safety performance of the battery.

[0070] In some embodiments, the separator includes a base film, with a ceramic coating provided on one side of the base film and a PVDF coating provided on the other side to form a composite separator. The base film can be a PE film with a thickness of 8μm-10μm, and the specific thickness can be 8μm, 9μm, 10μm, etc.; the thickness of the ceramic coating is 0.5μm-2.0μm, such as 0.5μm, 1.0μm, 1.5μm, 2.0μm, etc., and the thickness of the PVDF coating is 0.5μm-2.0μm, such as 0.5μm, 1.0μm, 1.5μm, 2.0μm, etc. The air permeability of the separator is 70s / 100mL-150s / 100mL, such as 70s / 100mL, 100s / 100mL, 120s / 100mL, 150s / 100mL, etc.

[0071] The embodiment of the present invention also provides a preparation method of a lithium-ion cylindrical battery, including: providing a positive electrode plate, a negative electrode plate, and a separator, winding the positive electrode plate, the negative electrode plate, and the separator to form a cylindrical core, loading it into a battery case and injecting an electrolyte, and then performing the sealing and formation processes to obtain a cylindrical battery.

[0072] Among them, the preparation process of the positive electrode sheet includes: mixing the first positive electrode active material and the second positive electrode active material to obtain a mixed active material, and using the mixed active material to prepare the positive electrode sheet; wherein, the first positive electrode active material is polycrystalline large particles, and the second positive electrode active material is single crystal small particles; in the mixed active material, the volume ratio of the first positive electrode active material is 20%-50%, and the volume ratio of the second positive electrode active material is 50%-80%. The positive electrode active material contains two components, polycrystalline large particles and single crystal small particles. The mixing of single crystal small particles and polycrystalline large particles can achieve a higher compaction density and better cycle stability. The synergistic effect of the two can exhibit excellent rate performance and cycle life on the basis of ensuring the capacity of the positive electrode material.

[0073] In a preferred embodiment, the particle size of the first positive electrode active material satisfies: 8.5μm < D50 < 15μm, 18μm < Dmax < 30μm; the particle size of the second positive electrode active material satisfies: 2.0μm < D50 < 5μm, 7μm < Dmax < 15μm. It is appropriate that the particle sizes of the first positive electrode active material and the second positive electrode active material meet the above requirements, which can further improve the capacity and rate performance of the battery.

[0074] Furthermore, the process of preparing the positive electrode sheet includes: mixing the mixed active material, the conductive agent, and the binder in a mass ratio of (94%-98%):(1%-3%):(1%-3%), and homogenizing to obtain a positive electrode slurry. The positive electrode slurry is coated on both sides of the positive electrode current collector and dried. The type of the positive electrode current collector is not limited, and the coating process and the drying process can refer to the existing preparation process of the positive electrode sheet of the cylindrical battery. The mass ratio of the mixed active material, the conductive agent, and the binder can be 94%:3.0%:3.0%, 95%:2.5%:2.5%, 96%:2.0%:2.0%, 97%:1.5%:1.5%, 98%:1.0%:1.0%, etc.

[0075] Furthermore, the electrolyte includes a lithium salt, a solvent, and an additive. The specific components are referred to the above description in the specification and will not be repeated here.

[0076] The embodiment of the present invention also provides an electrical device, including the lithium-ion cylindrical battery provided by the embodiment of the present invention, and using the lithium-ion cylindrical battery for power supply. The form of the electrical device is not limited, such as it can be an electronic device, an electric vehicle, etc.

[0077] The features and performance of the present invention will be further described in detail below in conjunction with the embodiments.

[0078] Example 1

[0079] This embodiment provides a preparation method of a lithium-ion cylindrical battery, and the steps are as follows:

[0080] (1) Preparation method of the positive electrode sheet

[0081] The positive electrode sheet includes a positive current collector aluminum foil and positive active material layers coated on both sides of the current collector. Among them, calculated by mass percentage, the positive active material layer includes 96% lithium nickel cobalt aluminate, 2% polyvinylidene fluoride (PVDF) binder, and 2% Super-P (conductive carbon black) conductive agent. The above substances are added to the solvent NMP and stirred to obtain a positive electrode slurry with a solid content of 68%. It is coated on both sides of the aluminum foil with a thickness of 12 μm, and the coating areal density is 13.6 mg / cm -2 , and after drying, rolling, and slitting, the positive electrode sheet is obtained.

[0082] Among them, the chemical formula of lithium nickel cobalt aluminate is LiNi 0.8 Co 0.1 Al 0.1 O2, and its preparation process is as follows: The first positive active material and the second positive active material are mixed to obtain a mixed active material. The particle size D50 of the first positive active material is 12 μm, and Dmax is 26 μm; the particle size D50 of the second positive active material is 3 μm, and Dmax is 8 μm. 80% by volume of the first positive active material polycrystalline large particles and 20% by volume of the second positive active material single crystal small particles are mixed.

[0083] (2) Preparation method of the negative electrode sheet

[0084] The negative electrode sheet includes a negative current collector copper foil and negative active material layers coated on both sides of the current collector. Among them, calculated by mass percentage, the negative electrode coating includes 96% negative active material, 1.0% conductive agent (Super-P), 1.0% thickening agent (CMC), and 2% binder (SBR). The above materials are added to deionized water as the solvent and stirred to obtain a negative electrode slurry with a solid content of 40%. It is coated on both sides of the copper foil with a thickness of 15 μm, and the coating areal density is 7.8 mg / cm -2 , and after drying, rolling, and slitting, the negative electrode sheet is obtained.

[0085] Among them, the negative active material is graphite + 3 wt% carbon silicon, the mass ratio of carbon to silicon in carbon silicon is 10:3, and the mass ratio of carbon silicon to graphite is 3:100.

[0086] (3) Preparation of the electrolyte

[0087] The lithium salt LiPF6 is dissolved in an organic solvent. The organic solvent is prepared by mixing ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate in a volume ratio of 1:1:1. The additive content is 0.2% - 5%, and finally an electrolyte with a lithium salt concentration of 1 mol / L is prepared.

[0088] (4) Preparation of separator (high-porosity separator)

[0089] Provide a base film: The material of the base film is PE, and the thickness of the base film is 9 μm.

[0090] Coat a ceramic material (aluminum oxide) on one side of the base film, and after drying, form a ceramic coating with a thickness of 1 μm.

[0091] Coat PVDF on the other side of the base film to form a PVDF coating with a thickness of 1 μm.

[0092] After testing: The air permeability of the separator is 110 s / 100 mL.

[0093] (5) Assembly

[0094] After cutting and die-cutting the positive electrode plate and the negative electrode plate, the positive electrode plate, the negative electrode plate and the separator are wound by a winding machine to form a 21700 cylindrical battery core. As Figure 3 shown, perform the cutting and stacking of the positive electrode tab and the negative electrode tab on the core, then respectively weld the positive current collector and the negative current collector to the core, then weld the negative current collector to the steel shell, place an insulating sheet above the positive current collector, and weld the positive current collector to the cap. Then complete the processes of grooving, liquid injection, sealing, film covering, formation, etc. to obtain a cylindrical battery.

[0095] Examples 2 - 10

[0096] The specific preparation process is substantially the same as that of Example 1, except that some parameters are different. For details, see Table 1.

[0097] Comparative Examples 1 - 7

[0098] The specific preparation process is substantially the same as that of Example 1, except that some parameters are different. For details, see Table 1.

[0099] Table 1 Other relevant parameters of Examples 1 - 9 and Comparative Examples 1 - 7

[0100]

[0101]

[0102] As can be seen from Table 1, the electrolytes in Comparative Examples 1 - 2 do not contain additives, the dosage of additives in Comparative Examples 4 - 7 is relatively large; the volume fraction of polycrystalline large particles in Comparative Examples 6 - 7 is relatively small.

[0103] Test the normalized mass ratio of Ni / F on the surface of the positive electrode plate after discharging for each example and comparative example:

[0104] At 25 °C, the battery is discharged at a constant current of 0.1C until it reaches the cut-off voltage of 2.5V. Subsequently, the steel shell of the fully discharged battery is removed. Three points are taken from the inside to the outside in the radial direction of the core and marked as K1, K2, and K3. At the positions corresponding to K1, K2, and K3 on the core, after the core is unfolded, three positive electrode plates with a width of 4 cm are cut from the positive electrode plate with the marked K1, K2, and K3 as the center points respectively. At three positions a1, a2, and a3 in the height direction of the positive electrode plate corresponding to K1, 1×1 cm square areas are taken respectively. Then, after the electrode plate is cleaned, EDS testing is carried out, and the normalized mass ratios of Ni / F on the surface of the electrode plate corresponding to the three square areas are named a1, a2, and a3 respectively. The normalized mass ratio of Ni / F at K1 of the core is defined as A1, and A1 = (a1 + a2 + a3) / 3, |a1 - a2| + |a2 - a3| + |a1 - a3| ≤ 3; similarly, the three 1×1 cm square areas in the height direction of the positive electrode plate corresponding to K2 are named b1, b2, and b3 respectively, A2 = (b1 + b2 + b3) / 3, and |b1 - b2| + |b2 - b3| + |b1 - b3| ≤ 3; the three 1×1 cm square areas in the height direction of the positive electrode plate corresponding to K3 are named c1, c2, and c3 respectively, A3 = (c1 + c2 + c3) / 3, and |c1 - c2| + |c2 - c3| + |c1 - c3| ≤ 3.

[0105] Cleaning of the positive electrode plate: To prevent the fluorine-containing organic solvents adhering to the surface of the disassembled positive electrode plate from affecting the results of EDS elemental analysis, before performing EDS testing on the positive electrode plate, the positive electrode plate needs to be cleaned. The specific operation is as follows: Place the disassembled positive electrode plate in a DMC (dimethyl carbonate) solution and soak it for at least 30 minutes to remove the electrolyte and other impurities on the electrode plate, and then air dry it for more than 30 minutes to ensure that the DMC solvent completely volatilizes.

[0106] Testing method for the normalized mass ratio of Ni / F in the surface active material layer of the positive electrode plate: Prepare a cleaned 1×1 cm positive electrode plate, randomly select a range with 20 - 40 polycrystalline large particles for elemental analysis, perform area scanning in this selected area using EDS, select 3 different areas for area scanning, and calculate the average value. This average value is used as the normalized mass ratio of Ni / F of the surface active material of the 1×1 cm positive electrode plate. Through testing, a1, a2, and a3 are 3.64, 4.57, and 4.20 respectively; b1, b2, and b3 are 4.81, 5.92, and 5.63 respectively; c1, c2, and c3 are 4.70, 5.72, and 4.17 respectively.

[0107] The relevant data of A1, A2, and A3 involved in Examples 1 - 10 and Comparative Examples 1 - 7 are as follows in Table 2:

[0108] Table 2 Relevant data of A1, A2, and A3 involved in Examples 1-10 and Comparative Examples 1-7

[0109]

[0110] As can be seen from Table 2, the value of (A1 + A2 + A3) / 3 in Comparative Examples 1-6 is greater than 10, and the value of ∣A1 - A2∣ + ∣A2 - A3∣ + ∣A1 - A3∣ in Comparative Example 7 is greater than 4, both of which do not meet the value limitations of the above two parameters in the present invention.

[0111] Test the rate performance and the passing rate of the thermal box test of the cylindrical batteries prepared in Tests 1-10 and Comparative Examples 1-7:

[0112] 1. Rate performance test

[0113] Take a cylindrical battery provided by the embodiment or comparative example of the present invention. Its positive electrode material is a ternary material, and the voltage window is 2.5 - 4.2V. For different positive electrode materials, the voltage window needs to be adjusted accordingly. Place the battery in an incubator at 25°C for more than 4h and conduct tests according to the following steps: (1) Constant current discharge the battery to 2.5V cutoff at 0.1C and let it stand for 10min; (2) Constant current charge the battery to 4.2V cutoff at 0.1C, then constant voltage charge it to 0.01C cutoff and let it stand for 10min; (3) Constant current discharge the battery to 2.5V cutoff at 0.1C and let it stand for 10min, and read the capacity value C0 at this time; (4) Constant current charge the battery to 4.2V at 0.1C, then constant voltage charge it to 0.01C cutoff and let it stand for 10min; (5) Constant current discharge the battery to 2.5V cutoff at 0.5C and let it stand for 10min; (6) Constant current charge the battery to 4.2V at 0.1C, then constant voltage charge it to 0.01C cutoff and let it stand for 10min; (7) Constant current discharge the battery to 2.5V cutoff at 1C and let it stand for 10min; (8) Constant current charge the battery to 4.2V at 0.1C, then constant voltage charge it to 0.01C cutoff and let it stand for 10min; (9) Constant current discharge the battery to 2.5V cutoff at 2C and let it stand for 10min; (10) Constant current charge the battery to 4.2V at 0.1C, then constant voltage charge it to 0.01C cutoff and let it stand for 10min; (11) Constant current discharge the battery to 2.5V cutoff at 3C and let it stand for 10min; (12) Constant current charge the battery to 4.2V at 0.1C, then constant voltage charge it to 0.01C cutoff and let it stand for 10min; (13) Constant current discharge the battery to 2.5V cutoff at 4C and let it stand for 10min; (14) Constant current charge the battery to 4.2V at 0.1C, then constant voltage charge it to 0.01C cutoff and let it stand for 10min; (15) Constant current discharge the battery to 2.5V cutoff at 5C and let it stand for 10min; (16) Constant current charge the battery to 4.2V at 0.1C, then constant voltage charge it to 0.01C cutoff and let it stand for 10min; (17) Constant current discharge the battery to 2.5V cutoff at 6C and let it stand for 10min; (18) Constant current charge the battery to 4.2V at 0.1C, then constant voltage charge it to 0.01C cutoff and let it stand for 10min; (19) Constant current discharge the battery to 2.5V cutoff at 8C and let it stand for 10min; (20) Obtain the rate performance of a single battery, that is, the capacity retention rate, through the ratio of the discharge capacity at each rate to the discharge capacity of the first discharge.

[0114] 2. Thermal Chamber Test

[0115] Take a fresh battery, place it in an incubator at 25°C for more than 4 hours, and perform tests according to the following steps: (1) Constantly discharge the battery at 0.1C until it cuts off at 2.5V, and let it stand for 5 minutes; (2) Constantly charge the battery at 0.2C until it cuts off at 4.2V, and then constantly charge it at a constant voltage until it cuts off at 0.05C, and let it stand for 5 minutes; (3) Put the battery into the incubator, set the heating rate to 5K / min, heat it up to 130°C, and keep it for 1 hour, then stop heating and let it cool down naturally to below 30°C; (4) If the battery does not catch fire or emit smoke, it is considered to pass, otherwise it fails. Test at least 5 batteries and record the passing rate.

[0116] The relevant data of the capacity retention rate and the passing rate of the hot box test involved in Examples 1-9 and Comparative Examples 1-7 are shown in Table 3 below:

[0117] Table 3 Relevant data of the capacity retention rate and the passing rate of the hot box test for Examples 1-7 and Comparative Examples 1-4

[0118]

[0119]

[0120] As can be seen from Table 3, the cylindrical batteries provided by the examples have significantly higher capacity retention rates, better electrochemical performance, and can all pass the hot box test.

[0121] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, various changes and modifications can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A lithium-ion cylindrical battery, characterized in that: A cylindrical winding core is formed by winding a positive electrode sheet, a negative electrode sheet and a separator, and three different points are selected every 1 / 4 from the center to the edge of the cylindrical winding core in the radial direction, and the positions of the three points all correspond to the positive electrode sheet, and the three points are marked as K1, K2 and K3; After unfolding the cylindrical winding core, three positive electrode segments are cut from the positive electrode sheet with the marked K1, K2 and K3 as the center respectively; Three test areas are selected at intervals of 1 / 4 in the height direction of the positive electrode segment corresponding to K1, and the normalized Ni / F mass ratios of the electrode surface corresponding to the three test areas are named a1, a2 and a3 respectively, and the normalized Ni / F mass ratio at the cylindrical winding core K1 is defined as A1, and A1 = (a1 + a2 + a3) / 3; Three test areas are selected at intervals of 1 / 4 in the height direction of the positive electrode segment corresponding to K2, and the normalized Ni / F mass ratios of the electrode surface corresponding to the three test areas are named b1, b2 and b3 respectively, and the normalized Ni / F mass ratio at the cylindrical winding core K2 is defined as A2, and A2 = (b1 + b2 + b3) / 3; Three test areas are selected at intervals of 1 / 4 in the height direction of the positive electrode segment corresponding to K3, and the normalized Ni / F mass ratios of the electrode surface corresponding to the three test areas are named c1, c2 and c3 respectively, and the normalized Ni / F mass ratio at the cylindrical winding core K3 is defined as A3, and A3 = (c1 + c2 + c3) / 3; A1, A2 and A3 meet the following requirements: (A1+A2+A3) / 3≤10, 0.1≤∣A1-A2∣+∣A2-A3∣+∣A1-A3∣≤4.

2. The lithium-ion cylindrical battery according to claim 1, characterized in that: A1, A2 and A3 satisfy: (A1+A2+A3) / 3≤9.5, 0.1≤|A1-A2|+|A2-A3|+|A1-A3|≤3.

5.

3. The lithium ion cylindrical battery according to claim 1 or 2, characterized in that: The width of the three cut positive electrode segments is 3 cm to 5 cm; The three test areas selected on the positive electrode segments corresponding to K1, K2 and K3 are all square areas with a side length of 0.5 cm-2.0 cm; The normalized mass ratio of Ni / F on the electrode surface corresponding to the three test areas satisfies: |a1-a2|+|a2-a3|+|a1-a3|≤3; |b1-b2|+|b2-b3|+|b1-b3|≤3; |c1-c2|+|c2-c3|+|c1-c3|≤3; The normalized Ni / F mass ratio of the electrode surface corresponding to the test area is the average value of the normalized Ni / F mass ratio of the surface on both sides of the current collector. The difference in the normalized Ni / F mass ratio of the electrode surfaces on both sides of the current collector is named Δx, and satisfies Δx≤1; preferably Δx≤0.

85.

4. The lithium-ion cylindrical battery according to claim 1, characterized in that: The positive electrode active material on the positive electrode plate includes a first positive electrode active material and a second positive electrode active material, wherein the first positive electrode active material is a large polycrystalline particle, and the second positive electrode active material is a small single crystal particle; Wherein, the particle size of the first positive electrode active material satisfies: 8.5 μm<D50<15 μm, 18 μm<Dmax<30 μm; The particle size of the second positive electrode active material satisfies: 2.0 μm<D50<5 μm, 7 μm<Dmax<15 μm; In the positive electrode active material, the volume proportion of the first positive electrode active material is 20%-50%, and the volume proportion of the second positive electrode active material is 50%-80%; Preferably, in the positive electrode active material, the volume proportion of the first positive electrode active material is 20%-40%, and the volume proportion of the second positive electrode active material is 60%-80%.

5. The lithium-ion cylindrical battery according to claim 4, characterized in that: The first positive electrode active material and the second positive electrode active material are at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide; Preferably, the chemical formula of the first positive electrode active material and the second positive electrode active material are both LiNi x Co y M z N s O2; Wherein, M is Mn or Al; N represents a doping element, and N is selected from at least one of Al, Co, Ta, Ti, Nb, Zr, B, W, Mg, Te, Ca, Fe, Mo, Na, K, La, Ga, F, Cl, S, B and N; 0.7≤x<1, 0<y<0.3, 0<z<0.1, s=1-xyz.

6. The lithium-ion cylindrical battery according to claim 1, characterized in that: The lithium-ion cylindrical battery further comprises an electrolyte, wherein the electrolyte comprises a lithium salt, an organic solvent and an additive, wherein the additive accounts for 0-5% by mass in the electrolyte, preferably 0.2%-4.0%; Preferably, the additive is selected from at least one of ethylene carbonate, dimethyl carbonate, fluoroethylene carbonate, lithium borate, vinyl sulfate and lithium bis(trifluoromethanesulfonyl)imide; Preferably, the organic solvent is a mixed solvent formed by ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, and the volume ratio of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate is 1:(0.5-1.5):(0.5-1.5); Preferably, the lithium salt is LiPF6.

7. The lithium-ion cylindrical battery according to claim 1, characterized in that: The diaphragm comprises a base membrane, a ceramic coating is provided on one side of the base membrane, and a PVDF coating is provided on the other side; Preferably, the base film is a PE film with a thickness of 8 μm-10 μm, the ceramic coating has a thickness of 0.5 μm-2.0 μm, and the PVDF coating has a thickness of 0.5 μm-2.0 μm; Preferably, the air permeability of the diaphragm is 70s / 100mL-150s / 100mL.

8. A method for preparing a lithium ion cylindrical battery according to any one of claims 1 to 7, characterized in that: include: Providing a positive electrode sheet, a negative electrode sheet and a separator, winding the positive electrode sheet, the negative electrode sheet and the separator into a cylindrical winding core, placing the cylindrical winding core into a battery housing and injecting an electrolyte; The preparation process of the positive electrode plate includes: mixing a first positive electrode active material and a second positive electrode active material to obtain a mixed active material, and using the mixed active material to prepare a positive electrode plate; wherein the first positive electrode active material is large polycrystalline particles, and the second positive electrode active material is small single crystal particles; in the mixed active material, the volume proportion of the first positive electrode active material is 20%-50%, and the volume proportion of the second positive electrode active material is 50%-80%.

9. The preparation method according to claim 8, characterized in that: The particle size of the first positive electrode active material satisfies: 8.5 μm<D50<15 μm, 18 μm<Dmax<30 μm; the particle size of the second positive electrode active material satisfies: 2.0 μm<D50<5 μm, 7 μm<Dmax<15 μm; Preferably, the process of preparing the positive electrode sheet comprises: mixing the mixed active material with the conductive agent and the binder in a mass ratio of (94%-98%): (1%-3%): (1%-3%), homogenizing to obtain a positive electrode slurry, coating the positive electrode slurry on both sides of the positive electrode current collector, and drying; Preferably, the electrolyte comprises a lithium salt, a solvent and an additive, the mass proportion of the additive in the electrolyte is 0-5%, more preferably 0.2%-4.0%; the additive is selected from at least one of ethylene carbonate, dimethyl carbonate, fluoroethylene carbonate, lithium borate, vinyl sulfate and lithium bis(trifluoromethanesulfonyl)imide.

10. An electrical device, characterized in that: It comprises the lithium ion cylindrical battery described in any one of claims 1 to 7 or the lithium ion cylindrical battery prepared by the preparation method described in any one of claims 8 to 9.

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