battery

Abstract

The application relates to the field of batteries, in particular to a battery. The battery comprises a negative electrode sheet and an electrolyte; the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer located on at least one side surface of the negative electrode current collector; the negative electrode active material layer comprises a negative electrode active material, the negative electrode active material comprises a silicon-based material, the content of silicon is A, unit: weight percent, based on the total weight of the negative electrode active material layer; the negative electrode active material layer has a recess on the surface, the depth of the recess is B, unit: mu m, the width of the recess is C, unit: mu m, and the interval of the recess is D, unit: mm; the electrolyte comprises 1,3-propylene sulfite, the mass percentage of the 1,3-propylene sulfite in the total mass of the electrolyte is E, unit: %; and 0.05<=C / (A*E*B*D)<=100 is met. The battery of the application not only has a high energy density, but also can significantly improve the problem of the damage angle crack of the outer film shell in the later stage of the battery cycle.

Description

TECHNICAL FIELD

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

[0002] In recent years, lithium ion batteries are widely used in digital, energy storage, power, military aerospace, communication equipment and other fields. And with the development of the diversification of electronic devices and the diversification of their functions, people's demand for the endurance of electronic devices is also getting higher and higher. Therefore, improving the energy density of lithium ion batteries is the current research hotspot. Using silicon-containing materials as battery negative active materials is one of the effective means to improve the energy density of lithium ion batteries. However, as the silicon content in the negative active material increases, the problem of damage and angular cracking of the outer film shell in the later stage of battery cycle is becoming increasingly serious, which directly affects the cycle life of the battery.

[0003] Therefore, it is of great significance to improve the energy density of lithium ion batteries while improving the problem of damage and angular cracking of the outer film shell in the later stage of battery cycle. SUMMARY

[0004] The purpose of the present application is to overcome the problem of damage and angular cracking of the outer film shell in the later stage of cycle of the silicon-doped battery with high energy density in the prior art, and to provide a battery. The battery of the present application not only has high energy density, but also can significantly improve the problem of damage and angular cracking of the outer film shell in the later stage of battery cycle.

[0005] The present application provides a battery, which comprises a negative electrode sheet and an electrolyte; the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer located on at least one side surface of the negative electrode current collector; the negative electrode active material layer comprises a negative electrode active material, the negative electrode active material comprises a silicon-based material, and the content of silicon is A based on the total weight of the negative electrode active material layer, with the unit being weight %; the negative electrode active material layer has a recess on the surface, the depth of the recess is B, with the unit being μm, the width of the recess is C, with the unit being μm, and the pitch of the recess is D, with the unit being mm; the electrolyte comprises 1,3-propylene sulfite, and the mass percentage of 1,3-propylene sulfite in the total mass of the electrolyte is E, with the unit being %; and 0.05≤C / (A×E×B×D)≤100 is satisfied.

[0006] Compared with the prior art, the present application has at least the following advantages:

[0007] (1) The battery of the present application not only has high energy density, but also can improve the problem of damage and angular cracking of the outer film shell in the later stage of battery cycle, and has excellent sealing performance after cycle;

[0008] (2) The battery of the present application has excellent cycle performance, high-temperature and high-humidity storage performance, and low-temperature discharge performance.

[0009] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as exactly that endpoint. Any values that fall within common BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 A cross-sectional view of a negative electrode sheet in an example of the present application is shown.

[0011] Figure 2 A scanning electron microscope (SEM) image of a negative electrode sheet in an example of the present application is shown.

[0012] Figure 3 A schematic view of the width of a groove in an example of the present application is shown.

[0013] Figure 4 A schematic view of the pitch of a groove in an example of the present application is shown. DETAILED DESCRIPTION

[0014] The specific embodiments of the present application are described in detail below. It should be understood that the detailed description and specific examples described herein are intended to illustrate the application and not limit the scope of the application.

[0015] The silicon-containing battery in the related art often has the problem of corner cracking of the outer film shell in the later stage of the cycle. The inventors of the present application found through a large number of experiments that the reasons for the above problem can be as follows: 1. As the silicon-containing battery is cycled, the volume expansion of silicon becomes larger and larger, thereby breaking the outer film shell; 2. As the lithium is deintercalated / intercalated from the negative electrode sheet, the probability of side reactions between the negative electrode sheet and the electrolyte is increased, which increases the gas production, thereby causing the outer film shell to crack; 3. On the one hand, the volume expansion of silicon causes a certain degree of extrusion to the negative electrode current collector, and on the other hand, the corrosion of the electrolyte to the negative electrode current collector destroys the crystal structure of the negative electrode current collector, which is thinned and more easily stretched, and the above two aspects both cause the negative electrode current collector to be stretched, thereby piercing the outer film shell and causing the outer film shell to crack. Based on the above three reasons, the inventors have conducted a large number of targeted researches and found that improving the electrolyte or improving the structure of the negative electrode sheet can improve the above problems to a certain extent. This is because the electrolyte, as an important component of the battery, not only can transport Li +The additive can also form a film on the negative electrode, which can inhibit the volume expansion of the negative electrode sheet and protect the negative electrode sheet. Similarly, the negative electrode sheet is an important component of the battery, and modification of the structure of the negative electrode sheet can alleviate the expansion of the negative electrode sheet. Based on this, the inventors of the present application propose the following solutions.

[0016] The present application provides a battery, which can include a negative electrode sheet and an electrolyte. The negative electrode sheet can include a negative electrode current collector and a negative electrode active material layer located on at least one side surface of the negative electrode current collector; the negative electrode active material layer can include a negative electrode active material, which can include a silicon-based material, and the content of silicon is A (unit: wt%) based on the total weight of the negative electrode active material layer; the surface of the negative electrode active material layer can have a recess. As shown in Figure 1 As shown in FIG. 1, the negative electrode sheet includes a negative electrode current collector 1 and a negative electrode active material layer 2 located on both side surfaces of the negative electrode current collector 1, and the surface of the negative electrode active material layer 2 has a recess 3. Figure 2 As shown in FIG. 2, the surface of the negative electrode active material layer has a recess.

[0017] The depth of the recess can be B (unit: μm), the width of the recess can be C (unit: μm), and the pitch of the recess can be D (unit: mm). The electrolyte can include 1,3-propylene sulfite (PST), and the mass percentage of the 1,3-propylene sulfite in the total mass of the electrolyte is E (unit: %). A, B, C, D and E satisfy: 0.05≤C / (A×E×B×D)≤100, for example, 0.05, 0.1, 0.5, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100.

[0018] The recess provided on the surface of the negative plate is beneficial to the infiltration of the electrolyte to the negative active material layer, improves the capacity release of the battery, and improves the energy density. Moreover, the recess can provide a certain buffer space for the volume expansion of the silicon-based material. The PST in the electrolyte can form a stable protective film on the negative electrode, which not only has a certain inhibitory effect on the volume expansion of the silicon-based material, but also has a protective effect on the negative plate. The protective effect is reflected in: on the one hand, it can reduce the probability of occurrence of side reactions between the electrolyte and the negative active material; on the other hand, it can reduce the corrosion of the electrolyte to the negative current collector, thereby reducing the dissolution of metal ions (such as copper ions) in the negative current collector, and having a certain inhibitory effect on the extension problem of the negative current collector during the battery cycle. However, the use of negative plates with recesses alone or the use of electrolyte with PST often cannot effectively solve the problem of the broken corner cracking of the outer film shell in the later stage of the battery cycle. The use of negative plates with recesses in combination with electrolyte with PST can further improve the problem of the broken corner cracking of the outer film shell in the later stage of the battery cycle compared to the use of one of the two alone, which may be because PST can avoid the local infiltration phenomenon of the negative plate caused by the presence of the recess, make the electrolyte more evenly distributed in the negative plate, improve the infiltration effect of the negative plate as a whole, and form a highly homogeneous phase in the negative plate, thereby improving the structural stability of the negative plate. However, the improvement effect is not obvious, and the reason may be that: first, the negative plate and the electrolyte mutually influence and restrict each other, which is specifically reflected in: as the inner surface area of the recess on the negative plate increases, the wettability of the electrolyte to the negative active material layer also increases, at this time, the probability of side reactions between the electrolyte and the negative active material layer and the corrosion of the electrolyte to the negative current collector will also increase, which requires adding more PST in the electrolyte to provide stronger binding force to alleviate the above problems, but too much PST will increase the battery impedance and lithium precipitation, which will seriously affect the cycle performance of the battery; second, the negative plate and the electrolyte have a certain restrictive relationship with the content of silicon: in order to improve the energy density of the battery, it is necessary to increase the content of silicon in the negative active material layer, and when the content of silicon increases, the volume expansion of the negative plate will also increase, on the one hand, the volume of the recess needs to be increased to provide more buffer space to alleviate the volume expansion of the negative plate; on the other hand, more PST needs to be added to form a protective film with stronger strength to inhibit the volume expansion of the silicon-based material and protect the negative plate from being damaged by the electrolyte. Therefore, it is necessary to regulate the relationship between the content of silicon A in the negative active material layer, the size (depth B, width C and spacing D) of the recess, and the content of 1,3-propane sultone E in the electrolyte, so that the three are compatible, thereby effectively improving the problem of the broken corner cracking of the outer film shell in the later stage of the battery cycle on the basis of improving the energy density of the battery.When C / (A x E x B x D) is small (for example, less than 0.05), the negative plate has a large amount of liquid storage, which may cause the negative plate to soften and the separator to be raised, resulting in broken bridge and lithium analysis, and seriously affecting the electrical performance of the battery; when C / (A x E x B x D) is large (for example, greater than 100), the electrolyte is not enough to infiltrate the negative plate, and the inhibition of the side reaction is not in place, and the performance of the protective negative plate cannot be optimized.

[0019] In an example, 0.1≤C / (A x E x B x D)≤45.

[0020] In an example, 0.15≤C / (A x E x B x D)≤17.

[0021] In the present application, the calculation of "C / (A x E x B x D)" only uses the numerical part of A, B, C, D and E, and the unit does not participate in the operation, for example, in Example 1, C / (A x E x B x D) = 80 / (5 x 0.2 x 10 x 0.8) = 10.

[0022] In the present application, the content A of silicon in the negative active material layer can be obtained by conventional methods in the art, for example, by using thermal gravimetric analysis, and the specific method is as follows: after discharging the battery to 0% SOC, the negative plate is disassembled and taken out, and is treated at 400℃ for 2h (under nitrogen atmosphere), so that the negative active material layer is peeled off from the negative current collector, and the negative active material is collected; a thermal gravimetric analyzer (such as TGA550 thermal gravimetric analyzer) is used, the sample amount for testing is 5mg-15mg, and the temperature is raised from room temperature (25℃) to 900℃ at a rate of 10℃ / min under air or oxygen atmosphere, and is kept at 900℃ for 40min, so that the non-silicon components in the negative active material layer are volatilized, and at the same time, the silicon is fully oxidized to silicon dioxide; taking the weight percentage at the end of the whole test process as the basis, dividing by the molar mass of silicon dioxide, and multiplying by the molar mass of silicon, the content A of silicon in the negative active material layer can be obtained (unit: wt%).

[0023] In the present application, the depth of the recess refers to the maximum value of the vertical distance from any point in the recess to the surface of the negative active material layer. The depth of the recess can be tested by conventional means in the art, for example, a 3D microscope.

[0024] In the present application, the recess can include a recess hole, or a groove.

[0025] In an example, the recess includes a groove.

[0026] In an example, the recess is a groove.

[0027] In the present invention, the positive projection of the groove on the negative electrode active material layer may include two long sides, and the width of the groove refers to the average distance from one long side to the other long side in the length direction or width direction of the negative electrode active material layer. Figure 3 The figure shows the width of the groove in an embodiment of the present invention, wherein Figure 3 (a)- Figure 3 The two long sides of the groove in (c) are straight lines. Figure 3 The two long sides of the groove in (d) are curved. Figure 3 (a) and Figure 3 In (b), the two long sides are arranged in parallel. Therefore, in the length direction of the negative electrode sheet, the distance from any point on one long side to the other long side is equal. In this case, the width of the groove is the distance d from any point on one long side to the other long side in the length direction or width direction of the negative electrode sheet. Figure 3 In (c), the two long sides of the groove are straight lines, but they are not parallel. Therefore, the distance from any point on one long side to the other long side is not equal. In this case, the width of the groove can be averaged. That is, on one long side, based on the length of the side, 50 points are selected at equal distances (that is, the distance between each point is equal, so the selection of points can make the calculation result more accurate), and the width d corresponding to each point is measured. The average value is used to obtain the width of the groove. Figure 3 In (d), the two long sides are curved. Therefore, the distance from any point on one long side to the other long side is not equal. In this case, the width of the groove can also be averaged, that is, 50 points are randomly selected on one long side (due to the Figure 3 In (d), the two long sides are curved and do not exist. Figure 3 (c) The relationship between the two long sides, therefore, 50 points can be randomly selected for measurement), and the width d corresponding to each point is measured, and the average is taken to obtain the width of the groove. The groove width can be measured by conventional means in the art, such as SEM or 3D microscopy.

[0028] In the present invention, the spacing of the grooves refers to the average distance between the two adjacent long sides of two adjacent grooves on the negative electrode active material layer in the length direction or width direction of the negative electrode sheet. Figure 4 The figure shows the spacing of the grooves in an embodiment of the present invention, wherein Figure 4 (a) is the case where two adjacent long sides are straight and parallel. Figure 4 (b) is the case where two adjacent long sides are straight lines and not parallel. Figure 4 (c) is the case where two adjacent long sides are curved. Figure 4In (a), the two adjacent long sides are straight and parallel, so that the distance from any point on one long side to the other long side is equal in the length direction, and the pitch of the grooves is the distance D from any point on one long side to the other long side in the length direction; in Figure 4 In (b), the two adjacent long sides are straight but not parallel, so that the distance from any point on one long side to the other long side is not equal, and the pitch of the grooves can be the average value, i.e. 50 points are selected at equal intervals on one long side based on the length of the long side (i.e. the distance between each point is equal, so that the selected points can make the calculation result more accurate), the width D corresponding to each point is measured, and the average value is taken to obtain the pitch of the grooves; in Figure 4 In (c), the two adjacent long sides are curved, so that the distance from any point on one long side to the other long side is not equal, and the pitch of the grooves can also be the average value, i.e. 50 points are selected at equal intervals on one long side (since Figure 4 In (c), the two long sides are curved, and there is no Figure 4 In (b), the relationship between the two long sides is random, so that 50 points can be measured at random), the width D corresponding to each point is measured, and the average value is taken to obtain the pitch of the grooves. The pitch of the grooves can be tested by conventional means in the art, such as SEM or 3D microscope.

[0029] In the present application, the manufacturing method of the grooves is not particularly limited as long as the purpose of the present application can be achieved. For example, the manufacturing method of the grooves can include at least one of laser etching processing, mechanical processing and pore-forming agent processing.

[0030] In an example, the manufacturing method of the grooves includes laser etching processing. The width and depth of the grooves increase with the increase of the power of the laser; different groove pitches can be obtained by adjusting the processing rate of the laser or the running speed of the negative plate. Therefore, the width, depth and pitch of the grooves can be adjusted by adjusting the power, processing rate of the laser and running speed of the negative plate.

[0031] In the present application, the shape of the grooves is not particularly limited, and the shape of the cross section of the grooves in the thickness direction of the negative plate can be rectangular or conical.

[0032] In the present application, the percentage E of the mass of the 1,3-propene sulfite in the total mass of the electrolyte can be tested by conventional methods in the art, such as gas chromatography-mass spectrometry (GC-MS).

[0033] In the present application, the silicon-based material can include at least one of nano-silicon, silicon alloy, silicon oxide (SiOx, 0

[0034] In an example, the silicon-based material comprises silicon-carbon.

[0035] In an example, the silicon-carbon comprises a material in which silicon particles are located in a porous carbon skeleton.

[0036] In the present application, the negative active material can further comprise a carbon-based material. The carbon-based material can comprise at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon and hard carbon.

[0037] In an example, the negative active material comprises a silicon-based material and artificial graphite.

[0038] The inventors of the present application have found that, under the premise that C / (A x E x B x D) has a certain range, when B, C and D are within a certain range, on the one hand, it can be more conducive to improving the local infiltration of the electrolyte to the negative active material layer, improving the infiltration of the electrolyte to the negative plate as a whole, making the distribution of the electrolyte in the negative plate more uniform, and forming a highly homogeneous phase inside the negative plate, thereby further improving the capacity of the battery; on the other hand, it can improve the volume expansion of the negative plate. When the depth B of the recess is within a certain range, not only can the infiltration of the electrolyte to the negative active material be improved, thereby improving the embedding and de-embedding speed of lithium ions and the kinetic performance of the negative plate; but also the utilization rate of the negative active material can be improved, thereby improving the energy density of the battery. When the width C of the recess and the pitch D of the recess are within a certain range, the adhesion performance between the negative plate and the separator will not be affected. If the width is too large and the pitch is too small, the adhesion between this position and the separator is relatively weak, and the problem of lithium precipitation caused by poor interface adhesion is likely to occur; if the width is too small and the pitch is too large, the electrolyte cannot be absorbed and lithium ions cannot be quickly accommodated, which can also cause the problem of lithium precipitation.

[0039] In the present application, B can be 5 μm-50 μm, for example 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm or 50 μm. C can be 40 μm-200 μm, for example 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm or 200 μm. D can be 0.5 mm-5 mm, for example 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm or 5 mm.

[0040] In an example, B is 10 μm-30 μm.

[0041] In an example, C is 80 μm-150 μm.

[0042] In an example, D is 0.8mm-2mm.

[0043] When A is within a certain range, the energy density of the battery can be improved under the premise that C / (A×E×B×D) is within a certain range.

[0044] In the present application, A can be 0.8wt%-25wt%, for example, 0.8wt%, 1wt%, 1.5wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 20wt% or 25wt%.

[0045] In an example, A is 1.2wt%-20wt%.

[0046] In an example, A is 3wt%-15wt%.

[0047] When E is within a certain range, the probability of side reactions between the electrolyte and the negative active material can be reduced without significantly adversely affecting the impedance of the battery, and the corrosion of the electrolyte to the negative current collector can be reduced, thereby avoiding the fracture of the pole piece (especially the pole piece in the bending area of the roll core) caused by the corrosion effect, and also reducing the stress concentration problem of the negative pole piece, thereby further improving the protection of the negative pole piece.

[0048] In the present application, E can be 0.1%-5%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%.

[0049] In an example, E is 0.2%-3%.

[0050] 1,3-propane sultone (PS) can assist in strengthening the protective film formed by 1,3-propylene sultone, and the use of the two together can further improve the inhibition of volume expansion of silicon-based materials and the protection of the negative pole piece.

[0051] In the present application, the electrolyte can also include 1,3-propane sultone. The mass of the 1,3-propane sultone accounts for F(%) of the total mass of the electrolyte, 0.5%≤F≤6%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5% or 6%.

[0052] In an example, 1%≤F≤4%.

[0053] In the present application, the mass percentage F of 1,3-propane sultone in the total mass of the electrolyte can be tested by a method conventional in the art, such as gas chromatography-mass spectrometry (GC-MS).

[0054] When E / F is within a certain range, the synergistic effect of the two can be played to a more optimal level, at which the chain length of the polymerized monomers formed after the ring-opening polymerization of PS and PST is longer and more stable, a more flexible and stronger protective film can be formed, the occurrence of side reactions and the corrosion of the electrolyte to the negative current collector are inhibited to inhibit the angular cracking of the outer film shell in the later stage of battery cycling; the sealing performance of the battery after cycling is improved, thereby preventing water vapor from entering and improving the cycle stability of the battery and the storage performance under high temperature and high humidity conditions. When E / F is too small (e.g., less than 0.02), the synergistic effect of the two cannot be effectively played; when E / F is too large (e.g., greater than 6), the protective film formed by the two has a large impedance, which will deteriorate the low-temperature performance of the battery.

[0055] In the present application, 0.02≤E / F≤6, for example, 0.02, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, or 6.

[0056] In an example, 0.05≤E / F≤3.

[0057] The inventors of the present application found that when the battery is cycled 1000 times at 25℃, the elongation of the negative electrode sheet within a certain range can further improve the angular cracking of the outer film shell in the later stage of battery cycling.

[0058] In the present application, the elongation of the negative electrode sheet when the battery is cycled 1000 times at 25℃ can be 2%-5%, for example, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%.

[0059] In an example, the elongation of the negative electrode sheet when the battery is cycled 1000 times at 25℃ is 2%-4%.

[0060] In the present application, the elongation of the negative electrode sheet can be tested by a method conventional in the art, specifically as follows: disassemble the battery, take out the negative electrode sheet, cut into a strip with a length of 60mm±5mm and a width of 15mm±0.25mm, and use a tensile testing machine to perform a tensile test at a gauge length of 30mm and a speed of 30mm / min.

[0061] In the present application, the negative current collector can include a copper foil.

[0062] In the present application, the negative active material layer can further include a negative electrode conductive agent and a negative electrode binder. The negative electrode conductive agent can include at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, carbon fiber, and carbon nanotube including at least one of single-walled carbon nanotube and multi-walled carbon nanotube, and carbon fiber. The negative electrode binder can include at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose, styrene butadiene rubber, polytetrafluoroethylene, and polyethylene oxide.

[0063] In the present application, the content of the negative active material can be 80-99.8% by weight (for example, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 99, or 99.8% by weight) based on the total weight of the negative active material layer, the content of the negative electrode conductive agent can be 0.1-10% by weight (for example, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5, or 0.1% by weight), and the content of the negative electrode binder can be 0.1-10% by weight (for example, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5, or 0.1% by weight).

[0064] In the present application, the electrolyte can further include at least one of a nitrile compound, a sulfur-containing compound, and a carbonate compound. The nitrile compound can include at least one of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, glycerol trinitrate, ethoxy-pentafluorophosphazene, 1,2,3,4,5-penta(2-cyanoethoxy)pentane, tris(cyanoethyl)phosphate, and 1,3,6-hexanetrinitrile. The sulfur-containing compound can include at least one of vinyl sulfide and vinylene sulfide. The carbonate compound can include at least one of ethylene carbonate, fluoroethylene carbonate, and vinylene ethylene carbonate.

[0065] The nitrile compound can be complexed on the surface of the positive electrode sheet, coordinated, and protect the positive electrode sheet. The carbonate compound can be reduced on the surface of the negative electrode to form a protective film. The sulfur-containing compound can improve the protection effect on the positive electrode sheet and the negative electrode sheet.

[0066] In the present application, the electrolyte can further include an organic solvent. The organic solvent can include at least one of a carbonate, a carboxylate, and a fluoroether. The carbonate can include at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, and methyl propyl carbonate. The carboxylate can include at least one of ethyl propionate (EP) and propyl propionate (PP). The fluoroether can include 1,1,2,3-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0067] In the present application, the electrolyte can further include a lithium salt. The lithium salt can include at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bisfluorosulfonylimide, and lithium hexafluorophosphate (LiPF6). The content of the lithium salt in the electrolyte can be 10-20% by weight, for example, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20% by weight.

[0068] In the present application, the battery can further include a positive electrode sheet. The positive electrode sheet can include a positive electrode current collector and a positive electrode active material layer located on at least one side surface of the positive electrode current collector, and the positive electrode active material layer can include a positive electrode active material.

[0069] In an example, the positive electrode active material includes lithium cobalt oxide and / or lithium cobalt oxide doped and / or coated with at least two elements among Al, Mg, Mn, Cr, Ti, Zr, Y, La, and B.

[0070] In an example, the positive electrode active material includes a material having a chemical formula of Li a Co b M 1 c1 M 2 c2 M 3 c3 M 4 c4 O2, wherein 0.9≤a≤1.05 (for example, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.01, 1.02, 1.03, 1.04, or 1.05), 0.8≤b≤1.2 (for example, 0.8, 0.9, 1, 1.1, or 1.2), 0≤c1≤0.1 (for example, 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1), 0≤c2≤0.1 (for example, 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1), 0≤c3≤0.1 (for example, 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1), 0≤c4≤0.1 (for example, 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1), M 1 , M 2 , M 3 , and M 4 each independently include at least one of Al, Mg, Mn, Cr, Ti, Zr, Y, La, and B.

[0071] In an example, 0.01 < c1 < 0.1.

[0072] In an example, 0.005 < c2 < 0.1.

[0073] In an example, 0.01 < c2 < 0.1.

[0074] In the present application, the positive electrode active material layer can further include a positive electrode conductive agent and a positive electrode binder. The positive electrode conductive agent can include at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, carbon fiber, and carbon nanotube (including at least one of single-walled carbon nanotube and multi-walled carbon nanotube), and carbon fiber. The positive electrode binder can include at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene butadiene rubber, polytetrafluoroethylene, and polyethylene oxide.

[0075] In the present application, the content of the positive electrode active material can be 80-99.8% by weight (for example, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 99, or 99.8% by weight) based on the total weight of the positive electrode active material layer, the content of the positive electrode conductive agent can be 0.1-10% by weight (for example, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5, or 0.1% by weight), and the content of the positive electrode binder can be 0.1-10% by weight (for example, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5, or 0.1% by weight).

[0076] In an example, the battery has a charge cut-off voltage of 4.48 V or more.

[0077] In an example, the battery is a lithium ion battery.

[0078] In the present application, the battery can further include a separator. The separator can be selected from separators conventionally used in the art, for example, including at least one of a polyethylene film and a polypropylene film.

[0079] In the present application, the battery can further include an outer film case. The outer film case can include, for example, an aluminum plastic film. The thickness of the outer film case can be 50 μm-150 μm, for example, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, or 150 μm.

[0080] In an example, the thickness of the outer film case is 85 μm-115 μm.

[0081] The inventor of the present application finds that when the thickness of the outer film shell is within a certain range, the problem of the outer film shell breaking and angular cracking in the later stage of battery cycle can be further improved, and the outer film shell within the thickness range has better corrosion resistance to electrolyte, which is beneficial to reduce the occurrence of side reactions, reduce the corrosion of electrolyte, reduce gas production, and improve safety.

[0082] In the present application, the battery can include the outer film shell and the battery core; the battery core is contained in the outer film shell; the battery core includes the positive electrode sheet, the separator and the negative electrode sheet; the positive electrode sheet, the separator and the negative electrode sheet can be sequentially stacked in the order of positive electrode sheet, separator, negative electrode sheet, or the positive electrode sheet, the separator and the negative electrode sheet can be wound and arranged to form flat areas and bending areas. The electrolyte is injected into the battery core to obtain the battery.

[0083] In an example, the battery is a soft package battery.

[0084] In the present application, the battery can be a laminated soft package battery or a wound soft package battery. When the battery is a wound soft package battery, the effect of improving the breaking and angular cracking of the outer film shell is more obvious.

[0085] In an example, the battery is a lithium ion battery.

[0086] In an example, the battery is a lithium ion secondary battery.

[0087] The present application can improve the breaking of the battery in the later stage of cycle by regulating the relationship between the content of silicon in the negative active material layer, the size of the recess and the content of 1,3-propylene sulfite in the electrolyte, so that the battery has a higher energy density, improves the sealing performance of the battery, prevents water vapor from entering, and improves the cycle stability, low temperature discharge performance and storage performance under high temperature and high humidity conditions.

[0088] It should be noted that the "first", "second" and the like in the present application only represent the different substances or usage methods, and do not represent the order difference.

[0089] The present application will be described in detail by the following examples. The examples described in the present application are only a part of the examples of the present application, not all 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.

[0090] In the following examples, the materials used are commercially available analytical pure unless otherwise specified.

[0091] The following examples are used to illustrate the battery of the present application.

[0092] Example 1

[0093] Prepare the battery according to the following method:

[0094] (1) Preparation of positive electrode sheet

[0095] Mix the positive electrode active material (lithium cobaltate LiCo 0.977 Al 0.015 Mg 0.005 Mn 0.003 O2), positive electrode binder (PVDF) and positive electrode conductive agent (acetylene black) in a mass ratio of 97.2:1.3:1.5, add N-methyl pyrrolidone (NMP), and stir under the action of a vacuum stirrer until the mixed system becomes a positive electrode slurry with uniform fluidity; uniformly coat the positive electrode slurry on an aluminum foil with a thickness of 12 μm; dry, roll, and cut the coated aluminum foil to obtain a positive electrode sheet.

[0096] (2) Preparation of negative electrode sheet

[0097] Mix the negative electrode active material (combination of silicon-carbon and artificial graphite, with a mass ratio of silicon-carbon to artificial graphite being 1:9), negative electrode conductive agent (combination of single-walled carbon nanotubes (SWCNT) and conductive carbon black (SP), with a mass ratio of single-walled carbon nanotubes to conductive carbon black being 0.1:1), and negative electrode binder (combination of carboxymethyl cellulose sodium (CMC-Na) and styrene-butadiene rubber (SBR), with a mass ratio of carboxymethyl cellulose sodium to styrene-butadiene rubber being 1:2) in a mass ratio of 95.9:1.1:3 to prepare a negative electrode slurry by a wet process; uniformly coat the negative electrode slurry on both sides of a copper foil with a thickness of 6 μm; after drying, rolling, die cutting, and cold pressing the coated copper foil, etch grooves on the surface of the negative electrode active material layer by laser processing, and then perform slitting, cutting, and welding of the negative electrode tabs to obtain a negative electrode sheet, wherein A, B, C, and D are shown in Table 1.

[0098] (3) Preparation of electrolyte

[0099] In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), mix EC, PC, PP, and EP in a mass ratio of 1:1:2:1, slowly add 15% LiPF6, 10% fluoroethylene carbonate, and 2% 1,3,6-hexanetricarbonitrile based on the total mass of the electrolyte, and then add PST and PS (the addition amount of PST to PS is shown in Table 1), and stir uniformly to obtain an electrolyte.

[0100] (4) Preparation of battery

[0101] The positive electrode sheet prepared in step (1), a separator (a polyethylene-based film with a thickness of 5 μm, on both sides of which a composite layer of titanium oxide with a thickness of 1 μm and polyvinylidene-hexafluoropropylene copolymer is coated), and the negative electrode sheet prepared in step (2) are wound to obtain a bare battery cell; the bare battery cell is placed in an aluminum plastic film (with a thickness of 105 μm), and the electrolyte prepared in step (3) is injected into the dried bare battery cell, which is subjected to processes such as vacuum packaging, standing, formation, shaping, sorting, and the like to obtain a battery.

[0102] Example 2

[0103] Example 1 is followed, except that the size of the groove and the content of PST and PS in the electrolyte are changed, as shown in Table 1, the thickness of the aluminum plastic film is changed (the aluminum plastic film with a thickness of 105 μm is replaced with an aluminum plastic film with a thickness of 113 μm), and the positive electrode active material is changed (LiCo 0.977 Al 0.015 Mg 0.005 Mn 0.003 O2 is replaced with LiCo 0.96 Al 0.015 Mg 0.015 Mn 0.01 O2) of the same mass.

[0104] Example 3

[0105] Example 1 is followed, except that the size of the groove and the content of PST and PS in the electrolyte are changed, as shown in Table 1, the thickness of the aluminum plastic film is changed (the aluminum plastic film with a thickness of 105 μm is replaced with an aluminum plastic film with a thickness of 95 μm), and the positive electrode active material is changed (LiCo 0.977 Al 0.015 Mg 0.005 Mn 0.003 O2 is replaced with LiCo 0.98 Al 0.01 Mg 0.01 O2) of the same mass.

[0106] Example 4

[0107] Example 1 is followed, except that the size of the groove and the content of PST and PS in the electrolyte are changed, as shown in Table 1, the thickness of the aluminum plastic film is changed (the aluminum plastic film with a thickness of 105 μm is replaced with an aluminum plastic film with a thickness of 88 μm), and the positive electrode active material is changed (LiCo 0.977 Al 0.015 Mg 0.005 Mn 0.003 O2 is replaced with LiCo 0.95 Al 0.02 Mg 0.015 Mn0.015 O2).

[0108] Example 5 group

[0109] The examples in this group are used to verify the effect of the change of C / (A x E x B x D).

[0110] The examples in this group are performed according to Example 1, except that the size of the groove and the content of PST and PS in the electrolyte are changed, as shown in Table 1.

[0111] Example 6 group

[0112] The examples in this group are used to verify the effect of the change of A.

[0113] The examples in this group are performed according to Example 1, except that A is changed by adjusting the mass ratio of silicon carbon to artificial graphite, as shown in Table 1.

[0114] Example 7 group

[0115] The examples in this group are used to verify the effect of the change of B and C.

[0116] The examples in this group are performed according to Example 1, except that B and C are changed, as shown in Table 1.

[0117] Example 8 group

[0118] The examples in this group are used to verify the effect of the change of D.

[0119] The examples in this group are performed according to Example 1, except that D is changed, as shown in Table 1.

[0120] Example 9 group

[0121] The examples in this group are used to verify the effect of the change of E.

[0122] The examples in this group are performed according to Example 1, except that E is changed, as shown in Table 1.

[0123] Example 10 group

[0124] The examples in this group are used to verify the effect of the change of F or E / F.

[0125] The examples in this group are performed according to Example 1, except that E and / or F are changed, as shown in Table 1.

[0126] Example 11 group

[0127] The examples in this group are used to verify the effect of the change of the nitrile compound or the carbonate compound in the electrolyte.

[0128] The present examples are performed according to Example 1, except that the composition of the electrolyte is changed, specifically:

[0129] Example 11a, in an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), EC, PC, PP and EP are mixed uniformly according to the mass ratio of 1:1:2:1, 15% LiPF6 and 2% 1,3,6-hexanetricarbonitrile based on the total mass of the electrolyte are slowly added, then PST and PS (the PST PS addition amount is shown in Table 1) are added, and stirred uniformly to obtain the electrolyte;

[0130] Example 11b, in an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), EC, PC, PP and EP are mixed uniformly according to the mass ratio of 1:1:2:1, 15% LiPF6 and 10% fluoroethylene carbonate based on the total mass of the electrolyte are slowly added, then PST and PS (the PST PS addition amount is shown in Table 1) are added, and stirred uniformly to obtain the electrolyte.

[0131] Example 12

[0132] According to Example 1, except that the negative active material is replaced by the same mass of (a combination of SiO and artificial graphite, wherein the mass ratio of SiO to artificial graphite is 1:11.7).

[0133] Example 13

[0134] According to Example 1, except that in step (4), the positive electrode sheet, the separator and the negative electrode sheet are stacked in the order of positive electrode sheet, separator, negative electrode sheet, and separator to obtain the bare battery cell.

[0135] Comparative Example 1

[0136] According to Example 1, except that the size of the groove and the content of PST and PS in the electrolyte are changed, specifically see Table 1.

[0137] Comparative Example 2

[0138] According to Example 1, except that the surface of the negative electrode sheet has no groove.

[0139] Comparative Example 3

[0140] According to Example 1, except that no PST is added in the electrolyte.

[0141] Comparative Example 4

[0142] According to Example 13, except that the size of the groove and the content of PST and PS in the electrolyte are changed, specifically see Table 1.

[0143] Note: The silicon carbon used in the above examples and comparative examples is the following material: silicon particles are located in a porous carbon skeleton.

[0144] Table 1

[0145]

[0146]

[0147] Note: “*” in Table 1 indicates that the corresponding parameter value is the same as that in Example 1; “ / ” indicates that it does not exist.

[0148] Test Case

[0149] (1) 25℃ cycle test

[0150] The batteries prepared in the examples and comparative examples were placed in a (25±2)°C environment and allowed to stand for 2-3 hours. When the battery body reached (25±2)°C, they were charged at a 1.5C constant current with a cutoff current of 0.05C. After the battery was fully charged, it was left for 5 minutes and then discharged at a 0.7C constant current to a cutoff voltage of 3.0V. The highest discharge capacity of the first three cycles was recorded as the initial capacity Q. When the cycle reached 1000 times, the last discharge capacity Q1 of the battery was recorded. Whether the aluminum-plastic film of the battery body was broken and the elongation of the negative electrode sheet were tested were also checked. The results are recorded in Table 2, where capacity retention (%) = Q1 / Q×100%.

[0151] (2) 35-day storage test at 60°C high temperature and high humidity

[0152] The batteries prepared in the examples and comparative examples were discharged at 0.5C, left for 5 minutes, and charged at 0.7C. The cycle was repeated twice, and the second discharge capacity was taken as the initial capacity Q2. The fully charged batteries were left in an open circuit at (60±2)°C and 90%-95% humidity for 35 days, and then left in an open circuit at room temperature for 2 hours to test the cooling thickness. The batteries were discharged at a constant current of 0.5C to 3.0V, which was recorded as the residual capacity. The batteries were then charged at 0.7C, left for 5 minutes, and then tested. Discharge at 0.5C was performed three times in this cycle. The highest capacity was recorded as the recovered capacity Q3. The recovery capacity retention rate of the battery after high temperature and high humidity storage and whether the battery produced gas were calculated. The results are recorded in Table 2, where capacity retention rate (%) = Q3 / Q2 × 100%. When the thickness change rate of the battery is less than 10%, it is "no gas production"; when the thickness change rate of the battery is 10%-15% (including the two end points), it is "gas production"; and when the thickness change rate of the battery is greater than 15%, it is "serious gas production".

[0153] (3) -10℃ low temperature discharge test

[0154] The battery prepared from the example and the comparative example was subjected to 10 charge-discharge cycles at room temperature at a rate of 0.7C, then charged to full state at a rate of 0.7C, and the charge capacity Q4 was recorded; the battery in full state was left to stand at -10℃ for 4h, then discharged to 3V at a rate of 0.4C, and the discharge capacity Q5 was recorded, and the low-temperature discharge capacity retention rate was calculated according to the following formula: capacity retention rate (%) = Q5 / Q4 x 100%, and the results were recorded in Table 2.

[0155] Note: the upper limit voltage of the above test examples was 4.5V.

[0156] Table 2

[0157]

[0158]

[0159] As can be seen from Table 2, the battery of the present application has C / (AxExBxD) in a specific range, which can significantly improve the problem of the outer film shell breakage and corner cracking in the later stage of battery cycle compared with Comparative Example 1 and Comparative Example 4; the battery of the present application has a recess on the surface of the negative active material layer, which significantly improves the cycle performance and improves the problem of the outer film shell breakage and corner cracking in the later stage of battery cycle compared with Comparative Example 2; the battery of the present application includes PST in the electrolyte, which also significantly improves the cycle performance and improves the problem of the outer film shell breakage and corner cracking in the later stage of battery cycle compared with Comparative Example 3.

[0160] 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 the combination of various technical features in any other suitable manner, and 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 battery, characterized in that: The battery comprises a negative electrode sheet and an electrolyte; The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector; the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material. Based on the total weight of the negative electrode active material layer, the silicon content is A, and A is 0.8 wt%-25 wt%; The negative electrode active material layer has a concave portion on its surface, the depth of the concave portion is B, B is 5 μm-50 μm, the width of the concave portion is C, C is 40 μm-200 μm, and the spacing between the concave portions is D, D is 0.5 mm-5 mm; The electrolyte includes 1,3-propylene sultone, the mass of the 1,3-propylene sultone accounts for a percentage E of the total mass of the electrolyte, and E is 0.1%-5%; Satisfies 0.05≤C / (A×E×B×D)≤100.

2. The battery according to claim 1, wherein 0.1≤C / (A×E×B×D)≤45.

3. The battery according to claim 2, wherein 0.15≤C / (A×E×B×D)≤17.

4. The battery according to claim 1 or 2, wherein B is 10μm-30μm; and / or, C is 80 μm-150 μm; And / or, D is 0.8mm-2mm.

5. The battery according to claim 1 or 2, wherein A is 3% to 15% by weight; and / or, E is 0.2%-3%; And / or, the silicon-based material includes at least one of nano-silicon, silicon alloy, silicon oxygen and silicon carbon.

6. The battery according to claim 5, wherein The silicon-based material includes silicon carbon.

7. The battery according to claim 6, wherein The silicon carbon comprises the following materials: silicon particles are located in a porous carbon framework.

8. The battery according to claim 1 or 2, wherein The electrolyte also includes 1,3-propane sultone.

9. The battery according to claim 8, wherein The percentage of the mass of the 1,3-propane sultone to the total mass of the electrolyte is F, in %, and 0.5%≤F≤6%.

10. The battery according to claim 9, wherein 1%≤F≤4%。 11. The battery according to claim 9, wherein 0.02≤E / F≤6.

12. The battery according to claim 11, wherein 0.05≤E / F≤3.

13. The battery according to claim 1 or 2, wherein When the battery is cycled 1000 times at 25° C., the elongation of the negative electrode sheet is 2%-5%.

14. The battery according to claim 13, wherein When the battery is cycled 1000 times at 25° C., the elongation of the negative electrode sheet is 2%-4%.

15. The battery according to claim 1 or 2, wherein The electrolyte further includes at least one of a nitrile compound, a sulfur-containing compound, and a carbonate compound.

16. The battery according to claim 15, wherein The nitrile compound includes at least one of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, glycerol trinitrile, ethoxypentafluorophosphazene, 1,2,3,4,5-penta(2-cyanoethoxy)pentane, tris(cyanoethyl) phosphate and 1,3,6-hexane trinitrile.

17. The battery according to claim 15, wherein The sulfur-containing compound includes at least one of vinyl sulfate and vinylene sulfate.

18. The battery according to claim 15, wherein The carbonate compound includes at least one of ethylene carbonate, fluoroethylene carbonate, and vinylethylene carbonate.

19. The battery according to claim 1 or 2, wherein The battery further includes a positive electrode sheet, which includes a positive electrode current collector and a positive electrode active material layer located on at least one side of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material.

20. The battery according to claim 19, wherein The positive electrode active material includes a chemical formula of Li a Co b M 1 c1 M 2 c2 M 3 c3 M 4 c4 O2 substances, where 0.9≤a≤1.05, 0.8≤b≤1.2, 0≤c1≤0.1, 0≤c2≤0.1, 0≤c3≤0.1, 0≤c4≤0.1, M 1 、M 2 、M 3 and M 4 Each independently includes at least one of Al, Mg, Mn, Cr, Ti, Zr, Y, La and B.

21. The battery according to claim 1 or 2, wherein The charging cut-off voltage of the battery is 4.48V or above.

22. The battery according to claim 21, wherein The battery is a lithium-ion secondary battery.

23. The battery according to claim 1 or 2, wherein The battery comprises an outer film shell and a battery core, wherein the battery core is accommodated in the outer film shell; the battery core comprises a positive electrode sheet, a diaphragm and the negative electrode sheet; the positive electrode sheet, the diaphragm and the negative electrode sheet are stacked in sequence.

24. The battery according to claim 23, wherein The outer film shell comprises an aluminum-plastic film.

25. The battery according to claim 23, wherein The thickness of the outer membrane shell is 50 μm-150 μm.

26. The battery according to claim 25, wherein The thickness of the outer membrane shell is 85 μm-115 μm.

Images