A lithium-ion battery

Abstract

This invention relates to the field of battery technology, specifically to a lithium-ion battery. The lithium-ion battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode comprises a ternary material, which includes a doping element M, wherein M includes one or more of Al, Mg, Ti, Fe, W, V, and Mo. The negative electrode comprises a silicon-carbon material, the median particle size Dv50 of which is 5 μm–30 μm. In the Raman spectrum of the silicon-carbon material, the particle size is located at 470 cm⁻¹. ‑1 -480cm ‑1 The intensity of the first characteristic peak is I1, located at 507 cm⁻¹. ‑1 -517cm ‑1 The intensity of the second characteristic peak is I2, located at 1330 cm⁻¹. ‑1 -1350cm ‑1 The intensity of the third characteristic peak is I3, then I3 > Max[I1, I2]; the electrolyte includes chain carbonates and cyclic carbonates, and the weight ratio of chain carbonates to cyclic carbonates is 1-8. The lithium-ion battery of the present invention can improve the problem of current collector breakage at the positive electrode, improve the cycle performance and safety performance of the battery, and extend the battery's service life.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery, in particular to a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries are widely used in portable electronic devices, electric vehicles and energy storage systems, and their service life and safety are crucial to these applications. Currently, aluminum foil plays an important role in lithium ion batteries as a positive current collector (i.e., a current conductor of the positive electrode), which mainly functions to effectively conduct electricity and support the positive electrode material. At the same time, silicon has been widely used in negative electrodes in recent years due to its high specific capacity. However, when both aluminum foil and silicon negative electrode material exist in the battery system, the severe expansion of the silicon negative electrode material during the cycling process can cause the aluminum foil to break, thereby affecting the service life and safety of the lithium ion battery. SUMMARY

[0003] It has been found through research that in the ternary / silicon negative electrode system of a lithium ion battery, under the condition of deep discharge at a large current, the rapid expansion of the silicon negative electrode causes the aluminum foil to repeatedly bear a certain pressure, which can cause the aluminum foil to break, leading to internal short circuit, increased resistance, capacity decay, and even safety hazards in the battery. The phenomenon of aluminum foil breakage is usually manifested as the appearance of cracks or peeling on the surface of the aluminum foil, which not only affects the electrical performance of the battery, but also can lead to a shortened service life and reduced safety of the battery.

[0004] To solve the problem of aluminum foil breakage, the present application provides a lithium ion battery (hereinafter referred to as a battery), which improves the stability of ternary materials and silicon-carbon materials by the synergistic cooperation of chain carbonates and cyclic carbonates in the electrolyte and ternary materials in the positive electrode sheet and silicon-carbon materials in the negative electrode sheet, reduces the expansion rate of the battery, thereby reducing the impact of expansion on the positive current collector, avoiding breakage of the positive current collector (such as aluminum foil), and improving the wettability of the electrolyte in the positive electrode sheet and the negative electrode sheet, so that the reactions in the ternary materials and silicon-carbon materials proceed uniformly, avoiding excessive local reactions that can cause the electrochemical performance and cycle performance of the lithium ion battery to decline, reducing the shedding or expansion of ternary materials and silicon-carbon materials during the charging and discharging process of the lithium ion battery, thereby improving the problem of positive current collector breakage, improving the cycle performance and safety performance of the battery, and prolonging the service life of the battery.

[0005] The present application provides a lithium ion battery, wherein the lithium ion battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, the positive electrode sheet comprises a ternary material, the ternary material comprises a doping element M, M comprises one or more of Al, Mg, Ti, Fe, W, V and Mo; the negative electrode sheet comprises a silicon-carbon material, the median particle size Dv50 of the silicon-carbon material is 5-30 μm, in the Raman spectrum of the silicon-carbon material, the peak intensity ratio of D band and G band is 0.5-1.5, and the peak intensity ratio of G band and 2D band is 0.5-1.5. -1 -480cm -1the intensity of the first characteristic peak is I1, located at 507 cm -1 -517 cm -1 the intensity of the second characteristic peak is I2, located at 1330 cm -1 -1350 cm -1 the intensity of the third characteristic peak is I3, and I3>Max[I1, I2];

[0006] The electrolyte comprises a chain carbonate and a cyclic carbonate, the ratio of the weight of the chain carbonate to the weight of the cyclic carbonate is 1-8, and the sum of the percentage of the chain carbonate in the total mass of the electrolyte and the percentage of the cyclic carbonate in the total mass of the electrolyte is 20%-75%.

[0007] Compared with the prior art, the technical scheme has at least the following advantages:

[0008] The silicon-carbon material in the lithium ion battery has high structural stability and low volume expansion rate, the high proportion of chain ester significantly reduces the overall viscosity of the electrolyte, improves the electrode wettability, and the electrolyte has high wettability and high lithium ion migration rate, can fully wet the silicon-carbon material and the ternary material, makes the reaction in the silicon-carbon material and the ternary material uniform, reduces the falling or expansion of the ternary material and the silicon-carbon material in the battery charging and discharging process, and the cyclic carbonate in the electrolyte can also form an SEI film on the surface of the silicon-carbon material, reduce the volume expansion of the silicon-carbon material, and the doping element M in the ternary material can also reduce the dissolution of transition metal ions in the ternary material, reduce the damage of the transition metal ions to the SEI film, thereby further reducing the volume expansion of the silicon-carbon material, and overcoming the problem of positive electrode current collector breakage, improving the cycle stability and safety performance of the lithium ion battery, and prolonging the service life of the lithium ion battery.

[0009] Other features and advantages of the present application will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 Fig. 1 shows a structure schematic diagram of a winding type battery cell in an embodiment of the present application.

[0011] Figure 2 Fig. 3 shows a Raman spectrum of a silicon-carbon material in an embodiment of the present application.

[0012] Figure 3 Fig. 5 shows a top view of a positive electrode sheet in an embodiment of the present application.

[0013] Figure 4 Fig. 7 shows a top view of a negative electrode sheet in an embodiment of the present application. DETAILED DESCRIPTION

[0014] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and explanatory in nature and are not intended to limit the application. In this document, data ranges include the endpoints unless otherwise indicated.

[0015] The present application provides a lithium ion battery, wherein the lithium ion battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, the positive electrode sheet comprises a ternary material, the ternary material comprises a doping element M, M comprises one or more of Al, Mg, Ti, Fe, W, V and Mo; the negative electrode sheet comprises a silicon-carbon material, the median particle size Dv50 of the silicon-carbon material is 5-30 μm, in the Raman spectrum of the silicon-carbon material, the intensity of the first characteristic peak located at 470 cm -1 -480cm -1 is I1, the intensity of the second characteristic peak located at 507 cm -1 -517cm -1 is I2, and the intensity of the third characteristic peak located at 1330 cm -1 -1350cm -1 is I3, then I3>Max[I1, I2];

[0016] The electrolyte comprises a chain carbonate and a cyclic carbonate, the ratio of the weight of the chain carbonate to the weight of the cyclic carbonate is 1-8; a higher proportion of chain ester significantly reduces the overall viscosity of the electrolyte, improves the electrode wettability, reduces the polarization, thereby improves the energy density and the cycle stability, while an appropriate amount of cyclic carbonate can still maintain the formation of stable SEI film to prevent the peeling of the silicon-based negative electrode. This proportion can balance the high-temperature safety and cycle stability of the battery.

[0017] The sum of the percentage of the chain carbonate in the total weight of the electrolyte and the percentage of the cyclic carbonate in the total weight of the electrolyte is 20%-75% (for example, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or 75%), which ensures the total content of the chain carbonate and the cyclic carbonate in the electrolyte, which can effectively dissolve the lithium salt and ensure good ionic conductivity.

[0018] The median particle size Dv50 of the silicon-carbon material can be 5-30 μm (for example, 5 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm or 30 μm). Controlling the median particle size Dv50 of the silicon-carbon material in the above range can ensure that the reaction in the silicon-carbon material is more uniform, avoid the peeling or expansion of the silicon-carbon material caused by excessive local reaction, and thereby improve the cycle stability of the battery.

[0019] In this invention, the median particle size Dv50 can be obtained by testing with a laser particle size analyzer.

[0020] like Figure 2 As shown, in the Raman spectrum of the silicon-carbon material, the value located at 470 cm⁻¹ -1 -480cm -1 (For example, 470cm) -1 471cm -1 472cm -1 473cm -1 474cm -1 475cm -1 476cm -1 477cm -1 478cm -1 479cm -1 Or 480cm -1 The intensity of the first characteristic peak is I1, located at 507 cm⁻¹. -1 -517cm -1 (For example, 507cm) -1 508cm -1 509cm -1 510cm -1 511cm -1 512cm -1 513cm -1 514cm -1 515cm -1 516cm -1 Or 517cm -1 The intensity of the second characteristic peak is I2, located at 1330 cm⁻¹. -1 -1350cm -1 (For example, 1330cm) -1 1332cm -1 1335cm -1 1338cm -1 1340cm -1 1342cm -1 1345cm -1 1348cm -1 Or 1350cm -1 If the intensity of the third characteristic peak of the silicon-carbon material is I3, then I3 > Max[I1, I2]. The silicon in the silicon-carbon material is dispersed within the carbon-based material. When the Raman spectrum of the silicon-carbon material satisfies I3 > Max[I1, I2], the silicon in the silicon-carbon material is dispersed in an amorphous state within the carbon-based material, thereby forming a porous structure with pores on the interior and surface of the silicon-carbon material. This porous structure can provide buffer space for the expansion of silicon, thus reducing the volume expansion of the silicon-carbon material.

[0021] Max[I1, I2] is the intensity of the greater of I1 and I2, for example, I3 > Max[I1, I2] means that I3 is greater than the intensity of the greater of I1 and I2, for example, when the intensity of the greater of I1 and I2 is I1, then I3 > I1, and when the intensity of the greater of I1 and I2 is I2, then I3 > I2.

[0022] The ratio of the weight of the chain carbonate to the weight of the cyclic carbonate can be 1-8 (e.g., 1, 2, 3, 4, 5, 6, 7, or 8). Controlling the ratio of the weight of the chain carbonate to the weight of the cyclic carbonate in the above range can maintain a high electrochemical window and a high dielectric constant of the electrolyte, improve the wettability and lithium ion migration rate of the electrolyte, enable the electrolyte to fully penetrate into the pores between the ternary materials of the positive electrode sheet and the pores between the silicon-carbon materials of the negative electrode sheet, improve the ion transmission inside the electrode sheet, reduce the battery impedance, and improve the charge-discharge efficiency of the battery.

[0023] The lithium ion battery of the present application includes an electrolyte of a chain carbonate and a cyclic carbonate satisfying the above weight relationship, a ternary material including a doping element M, and a silicon-carbon material satisfying the above median particle size range and the characteristic peak in the Raman spectrum satisfying the above relationship, at which time the reactions in the silicon-carbon material and the ternary material proceed uniformly and the stability of the SEI film is maintained, the risk of the ternary material and the silicon-carbon material falling off or swelling during the charge-discharge process of the battery is reduced, the problem of the positive current collector breaking is improved, the safety and cycle stability of the battery are improved, and the service life of the lithium ion battery is extended.

[0024] In the present application, by controlling the weight relationship of the chain carbonate and the cyclic carbonate, the intensity of the characteristic peak in the Raman spectrum of the silicon-carbon material, the median particle size, and the doping element M in the ternary material, the cycle performance and safety performance of the lithium ion battery have been improved compared with the prior art, and the service life is extended. In order to further improve the effect, one or more of the technical features can be further optimized.

[0025] In an example, the median particle size Dv50 of the silicon-carbon material is 6-12 μm.

[0026] In an example, the silicon-carbon material includes a carbon matrix and a silicon material in the pores of the carbon matrix.

[0027] In an example, the ratio c of the weight of the chain carbonate to the weight of the cyclic carbonate is 2-5.

[0028] According to one specific embodiment, the median particle size Dv50 of the silicon-carbon material is 6μm-12μm, and the weight ratio c of the chain carbonate to the cyclic carbonate is 2-5.

[0029] In one example, based on the total weight of the ternary material, the weight content p% of the dopant element M is 0.01%-5% (e.g., 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%). The dopant element M in the ternary material can improve its structural stability. Controlling the weight content of the dopant element M within the above range can further improve the stability of the ternary material, reduce the dissolution of transition metal ions in the ternary material, thereby reducing the damage of transition metal ions to the negative electrode interface, thus improving the stability of the negative electrode, reducing the rapid expansion of the negative electrode, avoiding the problem of band breakage in the positive electrode current collector caused by the rapid expansion of the positive electrode, and improving the cycle stability and safety of lithium ions.

[0030] In one example, the weight content p% of the dopant element M is 0.1%-3% based on the total weight of the ternary material.

[0031] In one example, the average particle size d of the silicon-carbon material is 6μm-12μm, the weight ratio c of the chain carbonate to the cyclic carbonate is 2-5, and based on the total weight of the ternary material, the weight content p% of the dopant element M is 0.1%-3%, and the dopant element M includes one or more of Al, Mg, Ti, Fe, W, V and Mo.

[0032] like Figure 2 As shown, in the Raman spectrum of the silicon-carbon material, the value at 1590 cm⁻¹ is... -1 -1610cm -1 (For example, 1590cm) -1 1592cm -1 1595cm -1 1598cm -1 1600cm -1 1602cm -1 1605cm -1 1608cm -1 Or 1610cm -1 If the intensity of the fourth characteristic peak of ) is I4, then I4 > Max[I1, I2].

[0033] In an example, the silicon-carbon material satisfies the following relationship formula simultaneously: p = (I1+I3) / (I2+I4), 0.65≤p≤2.4 (for example, 0.65, 0.8, 1, 1.3, 1.5, 1.8, 2, 2.3 or 2.4). When the silicon-carbon material satisfies the above, the crystal form of the silicon-carbon material is better, which is conducive to reducing the volume expansion of the silicon-carbon material. When p<0.0.65, the crystallinity of the silicon-carbon material is too high, and the surface of the silicon-carbon material is prone to appear crystal silicon, so that the expansion of silicon cannot be inhibited, which is easy to cause the battery to extrude the film shell, and then cause the damage or damage problem of the corner of the battery; when p>2.4, the defect degree of the silicon-carbon material is too high, and the specific surface area is large, which increases the side reaction of the silicon-carbon material, and there may be a situation that part of the carbon-based material is not completely carbonized, thereby affecting the initial efficiency and cycle performance of the battery.

[0034] In an example, the silicon-carbon material satisfies the following relationship formula simultaneously: I3>Max[I1, I2], and I4>Max[I1, I2], p = (I1+I3) / (I2+I4), 0.65≤p≤2.4.

[0035] In the present application, the Raman spectrum of the silicon-carbon material can be obtained by a conventional test method in the art, for example, using a Thermo Fisher Raman spectrometer, and the test wave number range is 400cm -1 -4000cm -1 .

[0036] In an example, the ternary material includes nickel elements, cobalt elements and manganese elements. Among them, the nickel element can improve the capacity of the ternary material and the energy density of the positive plate, so that the energy storage of the lithium ion battery is larger. The cobalt element can improve the stability of the lithium ion battery, prolong the cycle life of the lithium ion battery, and improve the overall performance of the lithium ion battery. The atomic radius of the manganese element is large, which can play a supporting role in the skeleton of the positive plate during the charging and discharging process, thereby improving the structural stability of the ternary material, improving the safety of the lithium ion battery, prolonging the service life of the lithium ion battery, and also reducing the cost of the ternary material.

[0037] In an example, the ternary material includes nickel elements, cobalt elements and manganese elements, and the ternary material further includes a doping element M, and the doping element M includes one or more of Al, Mg, Ti, Fe, W, V and Mo.

[0038] In an example, the mole percentage N% of the manganese element in the ternary material is 2%≤N≤30% (e.g., 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, or 30%). Controlling the mole percentage N% of the manganese element in the ternary material in the above range, during the charging and discharging process of the lithium ion battery, as the lithium ions are extracted and inserted, the manganese element with a larger atomic radius is combined with oxygen, reducing the precipitation of active oxygen in the ternary material, reducing the side reaction of the electrolyte with active oxygen, reducing the generation of HF, and further reducing the risk of corrosion of the aluminum foil by HF. In addition, the manganese element can also maintain the structural stability of the positive electrode to reduce overcharging, which can cause excessive alloying reaction of the silicon material with lithium ions, exacerbating the volume expansion of the silicon material, and reducing overcharging can reduce the pressure on the aluminum foil caused by the long-term and rapid expansion of the silicon negative electrode.

[0039] When N>30%, the mole content of the manganese element in the ternary material is high, thereby affecting the power output and charging and discharging performance of the lithium ion battery, and the capacity of the ternary material is reduced, thereby reducing the energy density of the lithium ion battery. In order to keep the energy density of the lithium ion battery unchanged, the volume of the lithium ion needs to be increased, and accordingly the thickness of the positive electrode sheet will also increase, which reduces the de-intercalation kinetics of the lithium ion; the high content of manganese element migrates with the positive electrode oxygen ions, the longitudinal Mn-O bond will gradually elongate, and the horizontal Mn-O bond will shorten, thereby making the linear MnO2 arrangement elongate along the axial direction, resulting in Jahn-Teller distortion. Jahn-Teller distortion will bring about severe structural changes to the ternary material, accelerating the destruction and deactivation of the ternary material structure, and increasing the risk of aluminum foil strip breakage. When M<2%, the mole content of the manganese element in the ternary material is too low, which reduces the structural stability of the ternary material, reduces the safety of the lithium ion battery, and shortens the cycle life of the lithium ion battery. When a large amount of lithium ions are extracted from the positive electrode, excessive alloying reaction occurs between the silicon negative electrode and the excess lithium ions, not only increasing the negative electrode expansion, but also causing irreversible loss of capacity.

[0040] In an example, the mole percentage N% of the manganese element in the ternary material is 5%≤N≤20%.

[0041] In the present application, the mole percentage of the manganese element in the ternary material refers to the ratio of the moles of manganese element to the sum of the moles of all elements in the ternary material.

[0042] In an example, the ternary material includes a single crystal structure and a polycrystalline structure.

[0043] In one example, the average particle size of the ternary material with the single-crystal structure is 1 μm-7 μm (e.g., 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, or 7 μm). Controlling the average particle size of the single-crystal structure within this range can improve the mechanical strength of the ternary material while providing a larger specific surface area, thereby promoting faster lithium-ion diffusion and increasing the energy density of the lithium-ion battery.

[0044] In one example, the average particle size of the ternary material with the single-crystal structure is 2 μm-5 μm.

[0045] In this invention, the average particle size can be obtained by testing Dv50, for example, using a laser particle size analyzer.

[0046] In one example, the weight ratio of the single-crystal ternary material to the polycrystalline ternary material is (1-20):1 (e.g., 1:1, 5:1, 10:1, 15:1, or 20:1). By controlling the weight ratio of the single-crystal ternary material to the polycrystalline ternary material within the above range, the overall specific surface area of ​​the ternary material is larger, and the volume change of the single-crystal ternary material is smaller during battery cycling. When the proportion of single-crystal structure in the ternary material is larger, it can ensure the orderly insertion and extraction of lithium ions under high-rate charge and discharge, and the overall volume of the ternary material will not undergo drastic expansion and contraction. This results in uniform stress on the aluminum foil in the battery, reducing the risk of aluminum foil breakage.

[0047] In one example, the weight ratio of the ternary material with the single-crystal structure to the weight of the ternary material with the polycrystalline structure is (2-10):1.

[0048] In one example, the lithium-ion battery cell has a wound structure, the positive electrode includes a first positive electrode surface and a second positive electrode surface, the first positive electrode surface is located on the side of the positive electrode near the center of the cell, and the second positive electrode surface is located on the side of the positive electrode away from the center of the cell, and the cell includes a positive electrode tab.

[0049] like Figure 1 and Figure 3 As shown, the positive electrode 1 includes a first positive electrode surface 11 and a second positive electrode surface 12. The first positive electrode surface 11 is located on the side of the positive electrode closer to the center of the cell, and the second positive electrode surface 12 is located on the side of the positive electrode away from the center of the cell.

[0050] Due to the lithium ion battery including the ternary material, the internal resistance of the lithium ion battery is slightly larger, if the conventional tab structure (for example, the tab is located at the starting position of the cell winding or at the tail of the cell winding) is adopted, under high rate discharge, the internal current density of the lithium ion battery is larger, which can further increase the internal resistance of the lithium ion battery with ternary material, causing the release of electric energy in the form of heat, causing the lithium ion battery to heat obviously, and the chemical reaction rate in the lithium ion battery will also be improved, and the energy release in the reaction process will also cause heat generation. Based on the special performance of the lithium ion battery including the ternary material, the tab in the application is placed at the middle position in the width direction of the cell, for example, the tab is placed in the middle position of the first positive electrode surface along the length direction of the positive electrode sheet. With such a structure, the current can be more evenly distributed on the tab of the lithium ion battery, thereby improving the charge and discharge efficiency of the lithium ion battery, reducing the uneven flow of current on the tab, and also reducing the internal resistance of the lithium ion battery, reducing local overheating, improving the heat dissipation performance of the lithium ion battery, and improving the overall performance and safety performance of the lithium ion battery.

[0051] In the application, the middle position means the position between the N / 3th fold and the 2*N / 3th fold of the cell. For example, when the cell has 18 folds, the tab can be located between the 6th fold and the 12th fold.

[0052] In an example, the positive electrode coating on the first positive electrode surface is a first positive electrode coating, and the positive electrode coating on the second positive electrode surface is a second positive electrode coating, and the thickness of the second positive electrode coating is greater than the thickness of the first positive electrode coating. When the positive tab is arranged at the middle position of the first positive electrode surface along the length direction of the positive electrode sheet, the current at the positive tab of the first positive electrode surface is in a peak state for a long time, causing the lithium ions in the area near the positive tab to be rapidly stripped, which can easily cause lithium precipitation. In order to improve the problem of lithium precipitation of the corresponding negative electrode in the area near the positive tab, the first positive electrode coating and the second positive electrode coating are coated on the first positive electrode surface and the second positive electrode surface respectively, and the thickness of the second positive electrode coating is greater than the thickness of the first positive electrode coating, which can reduce the impedance of the electrolyte and the positive electrode interface, increase the diffusion path of lithium ions, and enable the lithium ions to migrate to the negative electrode in an orderly manner, thereby reducing the risk of lithium precipitation. Since the thickness of the first positive electrode coating is small, the stress generated during the charging and discharging process is small, which can reduce the mechanical damage of the ternary material due to volume change, improve the durability of the electrode, thereby improving the charge and discharge performance of the lithium ion battery and prolonging the service life of the lithium ion battery.

[0053] In one example, the second positive electrode coating has a thickness that is 1 pm to 20 pm different from the thickness of the first positive electrode coating (e.g., 1 pm, 3 pm, 5 pm, 8 pm, 10 pm, 13 pm, 15 pm, 18 pm, or 20 pm). The positive electrode cathode and anode faces are configured to enable the CB value of the lithium ion battery to be within a suitable range, which enables a concentration gradient to form during lithium ion deintercalation, and the lithium ions to diffuse toward the anode and then intercalate into the anode under the influence of the concentration gradient and electric field, which reduces the risk of lithium plating.

[0054] In one example, the second positive electrode coating has a thickness that is 2 pm to 15 pm different from the thickness of the first positive electrode coating.

[0055] In one example, the first positive electrode coating has a thickness of 20 pm to 150 pm (e.g., 20 pm, 30 pm, 40 pm, 50 pm, 60 pm, 70 pm, 80 pm, 90 pm, 100 pm, 110 pm, 120 pm, 130 pm, 140 pm, or 150 pm).

[0056] In one example, the second positive electrode coating has a thickness of 20 pm to 150 pm (e.g., 20 pm, 30 pm, 40 pm, 50 pm, 60 pm, 70 pm, 80 pm, 90 pm, 100 pm, 110 pm, 120 pm, 130 pm, 140 pm, or 150 pm).

[0057] In one example, the second positive electrode coating has a thickness that is 1 pm to 20 pm different from the thickness of the first positive electrode coating, the first positive electrode coating has a thickness of 20 pm to 150 pm, and the second positive electrode coating has a thickness of 20 pm to 150 pm.

[0058] In one example, the second positive electrode coating has a thickness that is 2 pm to 15 pm different from the thickness of the first positive electrode coating, the first positive electrode coating has a thickness of 20 pm to 150 pm, and the second positive electrode coating has a thickness of 20 pm to 150 pm.

[0059] In one example, the ternary material includes a first ternary material and a second ternary material.

[0060] In one example, the first positive electrode coating includes a first ternary material, a first positive electrode conductive agent, and a first positive electrode binder.

[0061] In one example, the first positive electrode conductive agent includes at least one of conductive carbon black (Super P), acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, and metal powder.

[0062] In an example, the first cathode binder includes at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose, styrene butadiene rubber, polytetrafluoroethylene, and polyethylene oxide.

[0063] In an example, the first ternary material has a weight content of 95-98.5% (e.g., 95%, 96%, 97%, 98%, or 98.5%) and the first cathode conductive agent has a weight content of 0.5-3% (e.g., 0.5%, 1%, 1.5%, 2%, 2.5%, or 3%) and the first cathode binder has a weight content of 0.5-3% (e.g., 0.5%, 1%, 1.5%, 2%, 2.5%, or 3%) based on the total weight of the first cathode coating.

[0064] In an example, the first ternary material has a weight content of 96-98% and the first cathode conductive agent has a weight content of 0.7-2% and the first cathode binder has a weight content of 0.7-2% based on the total weight of the first cathode coating.

[0065] In an example, the second cathode coating includes a second ternary material, a second cathode conductive agent, and a second cathode binder.

[0066] In an example, the second cathode conductive agent includes at least one of conductive carbon black (Super P), acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, and metal powder.

[0067] In an example, the second cathode binder includes at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose, styrene butadiene rubber, polytetrafluoroethylene, and polyethylene oxide.

[0068] In an example, the second ternary material has a weight content of 95-98.5% (e.g., 95%, 96%, 97%, 98%, or 98.5%) and the second cathode conductive agent has a weight content of 0.5-3% (e.g., 0.5%, 1%, 1.5%, 2%, 2.5%, or 3%) and the second cathode binder has a weight content of 0.5-3% (e.g., 0.5%, 1%, 1.5%, 2%, 2.5%, or 3%) based on the total weight of the second cathode coating.

[0069] In an example, the second ternary material has a weight content of 96-98% and the second cathode conductive agent has a weight content of 0.7-1.5% and the second cathode binder has a weight content of 0.7-2% based on the total weight of the second cathode coating.

[0070] In an example, the negative tab includes a first negative surface and a second negative surface, the first negative surface is located at a side of the negative tab far away from the center of the battery cell, the second negative surface is located at a side of the negative tab close to the center of the battery cell, the negative coating layer located at the first negative surface is a first negative coating layer, the negative coating layer located at the second negative surface is a second negative coating layer, the thickness of the second negative coating layer > the thickness of the first negative coating layer. In order to ensure that the negative tab and the positive tab have a higher degree of fit, thereby avoiding the occurrence of lithium precipitation problem, the present application controls the size relationship between the thickness of the first negative coating layer and the thickness of the second negative coating layer, makes the CB of the lithium ion battery more reasonable, thereby the lithium ion battery will not exist overcharge phenomenon (if the lithium ion battery exists overcharge phenomenon, the volume expansion of the silicon-carbon material will be larger), thereby reducing the influence of the volume expansion of the silicon-carbon material on the positive current collector, avoiding the positive current collector breaking.

[0071] As shown in Figure 1 and Figure 4 , the negative tab 2 includes a first negative surface 21 and a second negative surface 22, the first negative surface 21 is located at a side of the negative tab far away from the center of the battery cell, the second negative surface 22 is located at a side of the negative tab close to the center of the battery cell.

[0072] In an example, the difference between the thickness of the second negative coating layer and the thickness of the first negative coating layer is 1 μm-20 μm (for example, 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, or 20 μm). The design of the positive and negative surfaces of the negative material (such as graphite or other alloys) can reduce the thickness of the positive and negative of the negative single foil area (the single foil area is the area where the negative active layer is only on one side of the negative current collector surface), increase the rate of lithium ion deintercalation, reduce the accumulation of lithium ions during charging, and reduce the risk of lithium precipitation. Moreover, the reduction of the thickness of the positive and negative reduces the polarization phenomenon during charging and discharging, improves the migration rate of lithium ions, reduces the expansion and contraction of materials (including silicon-carbon materials and graphite materials) during charging and discharging, reduces mechanical stress, and prolongs the cycle life.

[0073] In an example, the difference between the thickness of the second negative coating layer and the thickness of the first negative coating layer is 3 μm-15 μm.

[0074] In an example, the thickness of the first negative coating layer is 30 μm-160 μm.

[0075] In an example, the thickness of the second negative coating layer is 30 μm-160 μm.

[0076] In an example, the difference between the thickness of the second negative electrode coating and the thickness of the first negative electrode coating is 1 pm to 20 pm, and the thickness of the first negative electrode coating is 30 pm to 160 pm, and the thickness of the second negative electrode coating is 30 pm to 160 pm.

[0077] In an example, the difference between the thickness of the second negative electrode coating and the thickness of the first negative electrode coating is 3 pm to 15 pm, and the thickness of the first negative electrode coating is 30 pm to 160 pm, and the thickness of the second negative electrode coating is 30 pm to 160 pm.

[0078] In an example, the difference between the thickness of the second positive electrode coating and the thickness of the first positive electrode coating is 1 pm to 20 pm, and the thickness of the first positive electrode coating is 20 pm to 150 pm, and the thickness of the second positive electrode coating is 20 pm to 150 pm, and the difference between the thickness of the second negative electrode coating and the thickness of the first negative electrode coating is 1 pm to 20 pm, and the thickness of the first negative electrode coating is 30 pm to 160 pm, and the thickness of the second negative electrode coating is 30 pm to 160 pm.

[0079] In an example, the difference between the thickness of the second positive electrode coating and the thickness of the first positive electrode coating is 2 pm to 15 pm, and the thickness of the first positive electrode coating is 20 pm to 150 pm, and the thickness of the second positive electrode coating is 20 pm to 150 pm, and the difference between the thickness of the second negative electrode coating and the thickness of the first negative electrode coating is 3 pm to 15 pm, and the thickness of the first negative electrode coating is 30 pm to 160 pm, and the thickness of the second negative electrode coating is 30 pm to 160 pm.

[0080] In an example, the silicon-carbon material includes a first silicon-carbon material and a second silicon-carbon material.

[0081] In an example, the first negative electrode coating includes a first silicon-carbon material, a first graphite material, a first negative electrode conductive agent, and a first negative electrode binder.

[0082] In an example, the first graphite material includes artificial graphite and / or natural graphite.

[0083] In an example, the first negative electrode conductive agent includes at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, and metal powder.

[0084] In an example, the first negative electrode binder includes at least one of styrene butadiene rubber, sodium carboxymethyl cellulose, polyacrylic acid, polyvinyl alcohol, and polyvinylidene fluoride.

[0085] In an example, the first silicon-carbon material has a weight content of 3-40% (e.g., 3%, 5%, 8%, 10%, 13%, 15%, 18%, 20%, 30%, or 40%), the first graphite material has a weight content of 59-96% (e.g., 59%, 65%, 70%, 73%, 75%, 78%, 80%, 83%, 85%, 88%, 90%, 93%, or 96%), the first negative electrode conductive agent has a weight content of 0.5-2.5% (e.g., 0.5%, 1%, 1.5%, 2%, or 2.5%), and the first negative electrode binder has a weight content of 0.5-6% (e.g., 0.5%, 1%, 2%, 3%, 4%, 5%, or 6%) based on the total weight of the first negative electrode coating.

[0086] In an example, the first silicon-carbon material has a weight content of 5-25%, the first graphite material has a weight content of 72.8-92.8%, the first negative electrode conductive agent has a weight content of 1-2%, and the first negative electrode binder has a weight content of 1.2-5% based on the total weight of the first negative electrode coating.

[0087] In an example, the second negative electrode coating includes a second silicon-carbon material, a second graphite material, a second negative electrode conductive agent, and a second negative electrode binder.

[0088] In an example, the second graphite material includes artificial graphite and / or natural graphite.

[0089] In an example, the second negative electrode conductive agent includes at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, and metal powder.

[0090] In an example, the second negative electrode binder includes at least one of styrene butadiene rubber, sodium carboxymethyl cellulose, polyacrylic acid, polyvinyl alcohol, and polyvinylidene fluoride.

[0091] In an example, the second silicon-carbon material has a weight content of 3-40% (e.g., 3%, 5%, 8%, 10%, 13%, 15%, 18%, 20%, 30%, or 40%), the second graphite material has a weight content of 59-96% (e.g., 59%, 65%, 70%, 73%, 75%, 78%, 80%, 83%, 85%, 88%, 90%, 93%, or 96%), the second negative electrode conductive agent has a weight content of 0.5-2.5% (e.g., 0.5%, 1%, 1.5%, 2%, or 2.5%), and the second negative electrode binder has a weight content of 0.5-6% (e.g., 0.5%, 1%, 2%, 3%, 4%, 5%, or 6%) based on the total weight of the second negative electrode coating.

[0092] In an example, the weight content of the second silicon-carbon material is 5-25%, the weight content of the second graphite material is 72.8-92.8%, the weight content of the second negative electrode conductive agent is 1-2%, and the weight content of the second negative electrode binder is 1.2-5%, based on the total weight of the second negative electrode coating.

[0093] In an example, the battery cell includes a negative electrode tab, the negative electrode tab being located at a middle position of the first negative electrode surface along a length direction of the negative electrode sheet.

[0094] In an example, the lithium ion battery further includes a separator and an electrolyte.

[0095] The electrolyte can be a conventional electrolyte in the art, for example, the electrolyte includes a lithium salt, an organic solvent, and an additive.

[0096] In an example, the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluoro oxalate borate (LiDFOB), lithium bisfluorosulfonylimide (LiTFSI), lithium bis-trifluoromethylsulfonylimide, lithium difluorobisoxalate phosphate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methide, and lithium bis(trifluoromethylsulfonyl)imide.

[0097] In an example, the organic solvent includes a cyclic carbonate and a chain carbonate.

[0098] In an example, the cyclic carbonate includes ethylene carbonate (EC) and / or propylene carbonate (PC).

[0099] In an example, the chain carbonate includes diethyl carbonate (DEC) and / or ethyl methyl carbonate (EMC).

[0100] In an example, the organic solvent further includes one or more of propyl propionate (PP), ethyl propionate (EP), ethyl butyrate (EB), and ethyl acetate (EA).

[0101] In an example, the additive includes one or more of fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), 1,3-propene sultone (PST), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), succinonitrile (SN), vinyl sulfate, and 1,3,6-hexane trinitrile (HTCN).

[0102] In an example, the weight content of the lithium salt is 12%-21%, the weight content of the organic solvent is 54%-70%, and the weight content of the additive is 15%-25%, based on the total weight of the electrolyte.

[0103] The separator can be a conventional separator in the art, for example, the separator comprises a substrate, a ceramic layer on one or both surfaces of the substrate, and a glue layer on the surface of the substrate and / or the surface of the ceramic layer.

[0104] In an example, the substrate comprises one or more of PP and PE.

[0105] In an example, the ceramic layer comprises inorganic particles and a separator binder.

[0106] In an example, the inorganic particles comprise alumina.

[0107] In an example, the separator binder comprises PVDF and PMMA.

[0108] In an example, the weight content of the inorganic particles is 90%-99% and the weight content of the separator binder is 1%-10%, based on the total weight of the ceramic layer.

[0109] In an example, the glue layer comprises one or more of polyvinylidene fluoride (PVDF) and polymethyl methacrylate (PMMA).

[0110] In an example, the lithium ion battery is a lithium ion secondary battery.

[0111] The present application will be described in detail below by way of examples. The examples described in the present application are only a part of the examples of the present application, rather than all the examples. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0112] The following examples are used to illustrate the lithium ion battery of the present application.

[0113] Example 1

[0114] (1) Negative electrode sheet

[0115] A first silicon-carbon material (median particle size Dv50 of 10 μm), a first graphite material (including artificial graphite), a first negative electrode conductive agent Super P, and a first negative electrode binder (weight ratio of butadiene-styrene rubber (SBR) to sodium carboxymethyl cellulose (CMC) of 1:1) were dispersed in a proper amount of deionized water in a weight ratio of 5:92:1:2, and fully stirred to form a uniform first negative electrode slurry. The first negative electrode slurry was coated on one side surface of a negative electrode current collector copper foil to form a first negative electrode coating layer.

[0116] The second silicon-carbon material (median particle size Dv50 of 10 μm), the second graphite material (including artificial graphite), the second negative electrode conductive agent Super P, and the second negative electrode binder (the weight ratio of SBR to CMC is 1:1) are dispersed in a proper amount of deionized water at a weight ratio of 5:92:1:2, and uniformly stirred to form a second negative electrode slurry. The second negative electrode slurry is coated on the other side surface of the negative electrode current collector copper foil to form a second negative electrode coating. Then, the second negative electrode coating is dried, rolled, cut, washed, and pasted with an ear rubber to obtain a negative electrode sheet.

[0117] wherein the carbonization temperature of the carbon matrix of the silicon-carbon material is 950℃ and the deposition temperature of the silicon material is 500℃, I1 in the Raman spectrum is 1000, I2 is 500, I3 is 3000, I4 is 3000, I3>Max[I1, I2] and I4>Max[I1, I2] are satisfied, and ρ=(I1+I3) / (I2+I4)=1.14.

[0118] (2) the positive electrode sheet

[0119] The first ternary material (ternary lithium material, the doping element M is Al, the weight content of the doping element in the ternary material is 0.5%, the mole percentage of manganese element in the ternary material is 5%, and the crystal structure of the ternary material is single crystal and polycrystal, and the weight ratio of the single crystal structure to the polycrystal structure is 7:1), the first positive electrode conductive agent (Super P), and the first positive electrode binder (polyvinylidene fluoride (PVDF)) are dispersed in a proper amount of N-methyl pyrrolidone (NMP) at a weight ratio of 98:1.2:0.8, and uniformly stirred to form a first positive electrode slurry. The first positive electrode slurry is coated on one side surface of the positive electrode current collector aluminum foil to form a first positive electrode coating.

[0120] The second ternary material (ternary lithium material, the doping element M is Al, the weight content of the doping element in the ternary material is 0.5%, the mole percentage of manganese element in the ternary material is 5%, and the crystal structure of the ternary material is single crystal and polycrystal, and the weight ratio of the single crystal structure to the polycrystal structure is 7:1), the second positive electrode conductive agent (Super P), and the second positive electrode binder (polyvinylidene fluoride (PVDF)) are dispersed in a proper amount of N-methyl pyrrolidone (NMP) at a weight ratio of 98:1.2:0.8, and uniformly stirred to form a second positive electrode slurry. The second positive electrode slurry is coated on the other side surface of the positive electrode current collector aluminum foil to form a second positive electrode coating. Then, the second positive electrode coating is dried, rolled, cut, washed, and pasted with an ear rubber to obtain a positive electrode sheet.

[0121] (3) the electrolyte

[0122] In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the chain carbonate, cyclic carbonate and organic solvent were mixed uniformly, then the fully dried lithium salt was quickly added thereto, the additive was added, and stirring was performed for 10 h to allow the electrolyte to be fully dissolved. The lithium salt was lithium hexafluorophosphate, 15 parts by weight; the organic solvent was 75 parts by weight, wherein the chain carbonate was 55 parts by weight (the weight ratio of DEC to EMC was 5:1); the cyclic carbonate was 20 parts by weight (the weight ratio of EC to PC was 1:1); and the additive was 1,3-propane sultone 3 parts by weight, vinyl sulfate 1 part by weight and fluoroethylene carbonate 6 parts by weight, for a total of 10 parts by weight.

[0123] (4) Lithium ion battery

[0124] The positive electrode sheet of step (2), the negative electrode sheet of step (1) and the separator were stacked in the order of positive electrode sheet, separator and negative electrode sheet, and then were wound to obtain a battery cell. The battery cell was placed in an outer packaging aluminum foil, and the electrolyte of step (3) was injected into the outer packaging. After vacuum packaging, standing, formation, shaping, sorting and other processes, a lithium ion battery was obtained.

[0125] The first efficiency of charging and discharging was 95%, and the thickness expansion rate of high-temperature cycle was 12.2%.

[0126] Example 2

[0127] (1) Negative electrode sheet: refer to Example 1.

[0128] (2) Positive electrode sheet: refer to Example 1, except that the doping element M in the ternary material was Ti, the weight content of the doping element in the ternary material was 4.3%, the molar percentage of manganese element in the ternary material was 20%, and the crystal structure of the ternary material was single crystal and polycrystal, and the weight ratio of single crystal structure to polycrystal structure was 7:1. Both the first ternary material and the second ternary material used the above ternary material.

[0129] (3) Electrolyte: refer to Example 1, except that the lithium salt was lithium hexafluorophosphate, 15 parts by weight; the organic solvent was 75 parts by weight, wherein the chain carbonate was 65 parts by weight (the weight ratio of DEC to EMC was 5:1); the cyclic carbonate was 10 parts by weight (the weight ratio of EC to PC was 1:1); and the additive was 1,3-propane sultone 3 parts by weight, vinyl sulfate 1 part by weight and fluoroethylene carbonate 6 parts by weight, for a total of 10 parts by weight.

[0130] (4) Lithium ion battery: refer to Example 1.

[0131] Example 3 group

[0132] This group of examples is used to illustrate the effect when the ratio of the weight of the chain carbonate to the weight of the cyclic carbonate is changed.

[0133] Example 3a

[0134] Example 3a is conducted with the difference that the weight content of the chain carbonate in the electrolyte is 50%, the weight content of the cyclic carbonate is 25%, and the ratio of the weight of the chain carbonate to the weight of the cyclic carbonate is 2.

[0135] Example 3b

[0136] Example 3b is conducted with the difference that the weight content of the chain carbonate in the electrolyte is 62.5%, the weight content of the cyclic carbonate is 12.5%, and the ratio of the weight of the chain carbonate to the weight of the cyclic carbonate is 5.

[0137] Example 3c

[0138] Example 3c is conducted with the difference that the weight content of the chain carbonate in the electrolyte is 37.5%, the weight content of the cyclic carbonate is 37.5%, and the ratio of the weight of the chain carbonate to the weight of the cyclic carbonate is 1.

[0139] Example 3d

[0140] Example 3d is conducted with the difference that the weight content of the chain carbonate in the electrolyte is 66.6%, the weight content of the cyclic carbonate is 8.4%, and the ratio of the weight of the chain carbonate to the weight of the cyclic carbonate is 7.9.

[0141] Example 4 group

[0142] This group of examples is used to illustrate the effect when the Raman spectrum of the silicon-carbon material is changed by changing the carbonization temperature of the carbon matrix and the deposition temperature of the silicon material.

[0143] Example 4a

[0144] This group of examples is conducted according to Example 1 with the difference that the Raman spectrum of the silicon-carbon material is adjusted by changing the carbonization temperature of the carbon matrix to 800°C and the deposition temperature of the silicon material to 400°C, as shown in Table 1-1. The initial charge-discharge efficiency of Example 4a is 95%.

[0145] Example 4b

[0146] This group of examples is conducted according to Example 1 with the difference that the Raman spectrum of the silicon-carbon material is adjusted by changing the carbonization temperature of the carbon matrix to 900°C and the deposition temperature of the silicon material to 420°C, as shown in Table 1-1.

[0147] Example 4c

[0148] This set of examples was performed according to example 1, except that the Raman spectrum of the silicon-carbon material was adjusted by changing the carbonization temperature of the carbon matrix to 1000 °C and the deposition temperature of the silicon material to 450 °C, see table 1-1.

[0149] Example 4d

[0150] This set of examples was performed according to example 1, except that the Raman spectrum of the silicon-carbon material was adjusted by changing the carbonization temperature of the carbon matrix and the deposition temperature of the silicon material, see table 1-1.

[0151] Example 4e

[0152] This set of examples was performed according to example 1, except that the Raman spectrum of the silicon-carbon material was adjusted by changing the carbonization temperature of the carbon matrix to 1100 °C and the deposition temperature of the silicon material to 550 °C, see table 1-1.

[0153] Table 1-1

[0154]

[0155] * indicates same as example 1.

[0156] Example 5 set

[0157] This set of examples is used to illustrate the effect when the doping element M in the ternary material is changed.

[0158] Example 5a

[0159] This was performed according to example 1, except that the doping element M in the ternary material was Mg.

[0160] Example 5b

[0161] This was performed according to example 1, except that the doping element M in the ternary material was Fe.

[0162] Example 5c

[0163] This was performed according to example 1, except that the doping element M in the ternary material was W.

[0164] Example 6 set

[0165] This set of examples is used to illustrate the effect when the weight content P of the doping element M in the ternary material is changed.

[0166] Example 6a

[0167] This was performed according to example 1, except that the weight content of the doping element M in the ternary material was 0.01%.

[0168] Example 6b

[0169] Example 6b was performed as in Example 1 except that the weight content of the doping element M in the ternary material was 0.1%.

[0170] Example 6c

[0171] Example 6c was performed as in Example 1 except that the weight content of the doping element M in the ternary material was 3%.

[0172] Example 6d

[0173] Example 6d was performed as in Example 1 except that the weight content of the doping element M in the ternary material was 5%.

[0174] Example 7 group

[0175] This group of examples is used to illustrate the effect when the weight ratio of the ternary material of single crystal structure to the ternary material of polycrystal structure is changed.

[0176] Example 7a

[0177] Example 7a was performed as in Example 1 except that the weight ratio of the ternary material of single crystal structure to the ternary material of polycrystal structure was 1:1. Among them, the thickness expansion rate of high temperature cycle was 13.6%.

[0178] Example 7b

[0179] Example 7b was performed as in Example 1 except that the weight ratio of the ternary material of single crystal structure to the ternary material of polycrystal structure was 2:1. Among them, the thickness expansion rate of high temperature cycle was 14.1%.

[0180] Example 7c

[0181] Example 7c was performed as in Example 1 except that the weight ratio of the ternary material of single crystal structure to the ternary material of polycrystal structure was 10:1. Among them, the thickness expansion rate of high temperature cycle was 16.5%.

[0182] Example 7d

[0183] Example 7d was performed as in Example 1 except that the ternary material was all of single crystal structure. Among them, the thickness expansion rate of high temperature cycle was 20.3%.

[0184] Example 7e

[0185] Example 7e was performed as in Example 1 except that the ternary material was all of polycrystal structure. Among them, the thickness expansion rate of high temperature cycle was 12.6%.

[0186] Example 8 group

[0187] This group of examples is used to illustrate the effect when the thickness of the first positive electrode coating and the thickness of the second positive electrode coating are changed.

[0188] This group of examples is performed according to Example 1, except that the thickness of the first positive electrode coating and the thickness of the second positive electrode coating are changed, as shown in Table 1-2.

[0189] Example 9 group

[0190] This group of examples is used to illustrate the effect when the thickness of the first negative electrode coating and the thickness of the second negative electrode coating are changed.

[0191] This group of examples is performed according to Example 1, except that the thickness of the first negative electrode coating and the thickness of the second negative electrode coating are changed, as shown in Table 1-2.

[0192] Table 1-2

[0193]

[0194] Comparative Example 1

[0195] According to Example 1, except that the weight content of the chain carbonate in the electrolyte is 35%, the weight content of the cyclic carbonate is 40%, and the ratio of the weight of the chain carbonate to the weight of the cyclic carbonate is 0.88.

[0196] Comparative Example 2

[0197] According to Example 1, except that the weight content of the chain carbonate in the electrolyte is 68%, the weight content of the cyclic carbonate is 7%, and the ratio of the weight of the chain carbonate to the weight of the cyclic carbonate is 9.71.

[0198] Comparative Example 3

[0199] According to Example 1, except that the Raman spectrum of the silicon-carbon material is adjusted by adjusting the carbonization temperature of the carbon matrix in the silicon-carbon material and the deposition temperature of the silicon material, the carbonization temperature is 1300°C, and the deposition temperature is 600°C, as shown in Table 1-3.

[0200] Comparative Example 4

[0201] According to Example 1, except that there is no doping element in the ternary material.

[0202] Table 1-3

[0203]

[0204] * indicates the same as Example 1.

[0205] Test Example

[0206] 1. High temperature cycle performance and belt breaking condition test

[0207] (1) The lithium ion battery was placed at 45°C, charged at 1C constant current to 4.42V, then converted to 0.7C to the upper limit voltage (4.45V), then charged at 4.45V constant voltage to 0.05C, and the thickness of the battery at this time was measured as the initial thickness H0; then discharged at 0.7C constant current to 3V, and the discharge capacity at this time was recorded as the initial discharge capacity C0, and rested for 5 minutes;

[0208] (2) According to step 1, cycle 700T, record the discharge capacity of cycle 700T as C1 and thickness as H1.

[0209] Capacity retention rate: C = (C1 / C0) x 100%, thickness expansion rate = [(H1-H0) / H0] x 100%.

[0210] The battery after 700T cycle was disassembled to observe the aluminum foil belt breaking condition. Among them, if the positive plate is complete without cracks, the result is represented by no belt breaking, if there is a slight crack in the first fold of the outermost core, and the inner layer of the positive plate has no crack, the result is represented by slight belt breaking, if there are cracks in the outermost and inner layer of the core, the result is represented by belt breaking.

[0211] 3. Furnace temperature test

[0212] The full battery (100% SOC) obtained after battery charge and discharge was placed in an oven, and the oven was subjected to a temperature rising process at 5°C / min, and the temperature was raised to 140°C for 1 hour. If fire or explosion occurs, it is not passed, and if no fire or explosion occurs, it is passed. A total of 10 batteries were tested, and the result was represented by the furnace temperature pass rate. The furnace temperature pass rate = (the number of times the furnace temperature passes / 10) x 100%.

[0213] The results are recorded in Table 2.

[0214]

[0215]

[0216] As can be seen from Table 2, by comparing the comparative examples and the examples, it can be seen that the belt breaking condition of the lithium ion battery of the examples is significantly reduced, the high temperature cycle capacity retention rate is significantly improved, and the furnace temperature performance is significantly improved, which shows that by matching the silicon-carbon material, the electrolyte and the ternary material, the problem of positive current collector belt breaking is improved, and the cycle performance and safety performance of the battery are improved.

[0217] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including that each technical feature is combined in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A lithium-ion battery, characterized by, The lithium ion battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, the positive electrode sheet comprises a ternary material, the ternary material comprises a doping element M, M comprises one or more of Al, Mg, Ti, Fe, W, V and Mo; The negative electrode sheet comprises a silicon-carbon material, a median particle size Dv50 of the silicon-carbon material is 5-30 mu m, in a Raman spectrum of the silicon-carbon material, an intensity of a first characteristic peak located at 470 cm -1 -480 cm -1 is I1, an intensity of a second characteristic peak located at 507 cm -1 -517 cm -1 is I2, an intensity of a third characteristic peak located at 1330 cm -1 -1350 cm -1 is I3, then I3>Max[I1, I2]; in the Raman spectrum of the silicon-carbon material, an intensity of a fourth characteristic peak located at 1590 cm -1 -1610 cm -1 is I4, then I4>Max[I1, I2], the silicon-carbon material simultaneously satisfies the following relationship: p=(I1+I3) / (I2+I4), 0.65<=p<=2.4; The electrolyte comprises a chain carbonate and a cyclic carbonate, the ratio of the weight of the chain carbonate to the weight of the cyclic carbonate is 1-8, and the sum of the percentage of the chain carbonate in the total mass of the electrolyte and the percentage of the cyclic carbonate in the total mass of the electrolyte is 20%-75%.

2. The lithium-ion battery of claim 1, wherein, The weight content p% of the doping element M is 0.01%-5% based on the total weight of the ternary material; And / or, the median particle size Dv50 of the silicon-carbon material is 6-12 μm; And / or, the ratio of the weight of the chain carbonate to the weight of the cyclic carbonate is 2-5.

3. The lithium-ion battery of claim 2, wherein, The weight content p% of the doping element M is 0.1%-3% based on the total weight of the ternary material.

4. The lithium-ion battery of claim 1, wherein, The ternary material comprises nickel element, cobalt element and manganese element, and the mole percentage N of the manganese element in the ternary material is 2%≤N≤30%; And / or, the ternary material comprises a single-crystal structure ternary material, and the average particle size of the single-crystal structure ternary material is 1-7 μm; And / or, the ternary material comprises a single-crystal structure and a polycrystal structure, and the ratio of the weight of the single-crystal structure ternary material to the weight of the polycrystal structure ternary material is (1-20):

1.

5. The lithium-ion battery of claim 4, wherein, The average particle size of the single-crystal structure ternary material is 2-5 μm.

6. The lithium-ion battery of claim 1, wherein, The lithium ion battery has a winding structure, the positive electrode sheet comprises a first positive electrode surface and a second positive electrode surface, the first positive electrode surface is located on the side of the positive electrode sheet close to the center of the battery cell, the second positive electrode surface is located on the side of the positive electrode sheet away from the center of the battery cell, and the battery cell comprises a positive electrode tab.

7. The lithium-ion battery of claim 6, wherein, The positive electrode coating on the first positive electrode surface is a first positive electrode coating, the positive electrode coating on the second positive electrode surface is a second positive electrode coating, and the thickness of the second positive electrode coating is greater than the thickness of the first positive electrode coating.

8. The lithium-ion battery of claim 7, wherein, The difference between the thickness of the second positive electrode coating and the thickness of the first positive electrode coating is 1-20 μm; And / or, the thickness of the first positive electrode coating is 20-150 μm; And / or, the thickness of the second positive electrode coating is 20-150 μm.

9. The lithium-ion battery of claim 8, wherein, The difference between the thickness of the second positive electrode coating and the thickness of the first positive electrode coating is 2-15 μm.

10. The lithium-ion battery of any one of claims 1-9, wherein, The negative electrode sheet comprises a first negative electrode surface and a second negative electrode surface, the first negative electrode surface is located on the side of the negative electrode sheet away from the center of the battery cell, the second negative electrode surface is located on the side of the negative electrode sheet close to the center of the battery cell, the negative electrode coating on the first negative electrode surface is a first negative electrode coating, the negative electrode coating on the second negative electrode surface is a second negative electrode coating, and the thickness of the second negative electrode coating is greater than the thickness of the first negative electrode coating.

11. The lithium-ion battery of claim 10, wherein, The difference between the thickness of the second negative electrode coating and the thickness of the second negative electrode coating is 1-20 μm; And / or, the thickness of the first negative electrode coating is 30-160 μm; And / or, the thickness of the second negative electrode coating is 30 μm - 160 μm.

12. The lithium-ion battery of claim 11, wherein, The difference between the thickness of the second negative electrode coating and the thickness of the second negative electrode coating is 3 μm - 15 μm.

Images