A battery

Abstract

The application relates to the technical field of batteries, in particular to a battery. The battery comprises a diaphragm and an electrolyte, the electrolyte comprises a first additive and a second additive, the structural formula of the first additive is, the structural formula of the second additive is, wherein R1, R2 and R3 each independently comprises an unsubstituted or halogen-substituted C1-C6 alkyl; the mass content of the first additive is w 1 % and the mass content of the second additive is w 2 % based on the total mass of the electrolyte; the diaphragm comprises a base film and a functional coating layer, the functional coating layer is located on at least one side surface of the base film; the functional coating layer comprises functional particles, the functional particles comprise lithium aluminum titanium phosphate and / or lithium lanthanum titanate, the total thickness of the functional coating layer in the diaphragm is d 1 , unit: mu m; w 1 , w 2 and d 1 satisfy: 0.1 <= (w 1 +w 2 ) / d 1 <=10. The battery has good high-temperature storage, high-temperature cycle performance, hot box performance and low-temperature performance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a battery. Background Technology

[0002] With the rapid development of electric vehicles, mobile devices, and energy storage systems, higher demands are being placed on the performance and safety of lithium batteries. However, improving battery energy density and performance is difficult while simultaneously maintaining high and low temperature performance. The operating voltage of cathode materials is increasing. When the voltage exceeds 4.5V, lithium cobalt oxide materials may undergo irreversible phase transitions or release lattice oxygen, leading to structural collapse. Furthermore, the electrolyte on the cathode surface is easily oxidized and decomposed, generating an excessively thick solid electrolyte layer. At high temperatures, the phase transition or lattice oxygen release of lithium cobalt oxide accelerates, further compromising material stability. This also exacerbates electrolyte side reactions, causing battery swelling or even thermal runaway. Additionally, it accelerates the damage to the CEI film, leading to rapid electrolyte consumption, triggering more side reactions, and resulting in the loss of significant amounts of active materials and electrolyte. This can lead to lithium plating, rapid capacity decay, and even battery safety issues. Therefore, optimizing the electrolyte composition to form a stable interfacial film at the cathode interface improves the battery's high-temperature cycle performance. However, improved high-temperature cycle performance is often accompanied by deterioration in low-temperature performance. Therefore, providing a battery that can balance high and low temperature performance is crucial. Summary of the Invention

[0003] The purpose of this invention is to overcome the aforementioned problems in the prior art and to propose a battery that optimizes the electrolyte composition to include a first additive and a second additive and adjusts their content, while simultaneously using a separator coated with a solid electrolyte functional coating, thereby enabling the battery to achieve both high and low temperature performance.

[0004] Under high voltage, the positive electrode active material is prone to irreversible phase transitions, leading to structural collapse. Simultaneously, side reactions between the positive electrode and electrolyte intensify, causing battery gas production and transition metal dissolution at the positive electrode. These problems are further exacerbated under high-temperature conditions. The first additive is a sulfur-containing additive with a unique structure. Its introduction promotes the formation of an organic interface film rich in alkyl lithium carbonate on the positive electrode surface, improving the interface stability under high pressure, delaying the phase transition of the positive electrode active material under high voltage, and enhancing the structural stability of the positive electrode. The second additive is a phosphazene compound that further reduces the dissolution of transition metals in the positive electrode active material. It has a complexing effect on transition metals, thus preventing transition metal ions from damaging the positive electrode interface film or depositing on the negative electrode, affecting the structural stability of the negative electrode. The combination of the first and second additives effectively improves the high-temperature performance of the battery, but at low temperatures, it increases the viscosity of the electrolyte, reduces its fluidity, and decreases the migration rate of lithium ions in the electrolyte, thus degrading the low-temperature performance of the battery. To further improve the low-temperature performance of the battery, a separator with a functional coating containing a solid electrolyte is used. The solid electrolyte has high ionic / electronic conductivity, and the functional coating containing the solid electrolyte can form a porous conductive network, which improves the migration efficiency of lithium ions in the electrolyte under low-temperature conditions, alleviates the problem of increased polarization caused by low temperature, and thus improves the low-temperature performance of the battery.

[0005] Based on this, the present invention proposes the following technical solution: This invention provides a battery comprising a separator and an electrolyte, wherein the electrolyte comprises a first additive and a second additive, and the first additive has the following structural formula: The structural formula of the second additive is R1, R2, and R3 each independently comprise unsubstituted or halogen-substituted C1-C6 alkyl groups; Based on the total mass of the electrolyte, the mass content of the first additive is w. 1 %, the mass content of the second additive is w 2 % The diaphragm includes a base membrane and a functional coating, wherein the functional coating is located on at least one side surface of the base membrane; The functional coating comprises functional particles, including lithium aluminum titanium phosphate and / or lithium lanthanum titanate, and the total thickness of the functional coating in the separator is d. 1 The unit is μm; w 1 w 2 and d 1 Satisfy: 0.1≤(w) 1 +w 2 ) / d 1 ≤10.

[0006] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art: (1) The battery of the present invention improves the high-temperature cycle stability of the battery by optimizing the electrolyte composition to include a first additive and a second additive.

[0007] (2) The battery of the present invention improves the migration efficiency of lithium ions in the electrolyte and improves the low-temperature performance of the battery by combining an electrolyte and a separator with a functional coating containing a solid electrolyte.

[0008] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0009] Figure 1 The diagram shown is a cross-sectional schematic of the diaphragm in one embodiment of the present invention.

[0010] Figure 2 The image shown is a SEM image of the functional coating of the diaphragm of the present invention. Detailed Implementation

[0011] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0012] This invention provides a battery comprising a separator and an electrolyte, wherein the electrolyte comprises a first additive and a second additive, and the first additive has the following structural formula: The structural formula of the second additive is R1, R2, and R3 each independently comprise unsubstituted or halogen-substituted C1-C6 alkyl groups; Based on the total mass of the electrolyte, the mass content of the first additive is w. 1 %, the mass content of the second additive is w 2 % The diaphragm includes a base membrane and a functional coating, wherein the functional coating is located on at least one side surface of the base membrane; The functional coating comprises functional particles, including lithium aluminum titanium phosphate and / or lithium lanthanum titanate, and the total thickness of the functional coating in the separator is d. 1 The unit is μm; w 1 w 2 and d1 Satisfy: 0.1≤(w) 1 +w 2 ) / d 1 ≤10 (e.g., 0.1, 0.2, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5 or 10).

[0013] In this invention, R1, R2, and R3 each independently comprise an unsubstituted or halogen-substituted C1-C6 alkyl group. It is understood that "C1-C6 alkyl group" refers to an alkyl group containing one to six carbon atoms.

[0014] In this invention, the C1-C6 alkyl group includes at least one of methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, tert-pentyl, and hexyl.

[0015] In this invention, the "halogen-substituted C1-C6 alkyl group" includes at least one of F, Cl, Br, and I.

[0016] In this invention, the total thickness of the functional coatings in the diaphragm is the sum of the thicknesses of all functional coatings in the diaphragm. When a functional coating is provided on one side of the base membrane, the total thickness of the functional coatings in the diaphragm is the thickness of the functional coating on that side, and the thickness of the functional coating on that side satisfies 0.1 ≤ (w 1 +w 2 ) / d 1 ≤10; When coatings are applied to both sides of the base membrane, the total thickness of the functional coatings in the diaphragm is the sum of the thicknesses of the functional coatings on both sides, and the sum of the thicknesses of the functional coatings on both sides satisfies 0.1≤(w 1 +w 2 ) / d 1 ≤10.

[0017] The introduction of a first additive and a second additive into the electrolyte involves two steps. The first additive is a sulfur-containing additive with a special structure that can form a stable CEI film on the surface of the positive electrode. This CEI film contains not only inorganic components such as Li₂SO₃ and Li₂SO₄, but also organic components such as alkyl lithium carbonate. This not only improves the interfacial stability of the positive electrode but also repairs the CEI film during cycling, thereby mitigating side reactions from other additives and solvents in the electrolyte and improving the battery's high-temperature cycling performance. The second additive is a phosphazene compound containing three cyano groups. These cyano groups can complex with transition metal ions dissolved from the positive electrode, reducing their accumulation at the negative electrode. This reduces the catalytic effect on the electrolyte solvent, mitigating electrolyte side reactions and improving the battery's high-temperature cycling performance and thermal safety. Furthermore, the second additive can also form a film at the positive electrode, further reducing electrolyte side reactions. Therefore, the introduction of the first and second additives into the electrolyte can synergistically promote the formation of a stable and dense CEI film at the positive electrode, alleviate battery swelling or even thermal runaway caused by electrolyte side reactions, improve interface stability, delay the irreversible phase transition of the lithium cobalt oxide positive electrode, and inhibit the dissolution of transition metals in the positive electrode, thereby improving the structural stability of the battery under high voltage and high temperature.

[0018] However, while both the first and second additives can improve the high-temperature performance of the high-voltage system, they degrade the low-temperature performance of the battery. This is because the viscosity of the electrolyte increases and its fluidity decreases at low temperatures, hindering the smooth migration of lithium ions and leading to the degradation of the battery's low-temperature performance. To further improve these issues, the structure and composition of the separator are further optimized by using a separator with a functional coating mainly composed of solid electrolyte functional particles (such as LATP and / or LLTO). This utilizes the high ionic / electronic conductivity of the solid electrolyte to improve the lithium-ion migration rate under low-temperature conditions. The separator with the functional coating not only isolates the positive and negative electrodes but also provides an additional lithium-ion transport path, reducing the overall battery impedance. This is because the viscosity of the liquid electrolyte increases and the ion migration rate decreases at low temperatures, while the presence of the functional coating containing the solid electrolyte can circumvent the resistance of the high-viscosity electrolyte and directly promote lithium-ion migration. + This facilitates the transport of electrolytes, thereby mitigating the problem of increased polarization caused by low temperatures. Furthermore, the functional coating containing solid electrolytes has a porous structure, providing storage space for the electrolyte, increasing the electrolyte retention capacity of the membrane, and preventing the interruption of ion transport pathways due to localized electrolyte depletion under low-temperature conditions.

[0019] Meanwhile, the functional particles in the functional coating contain Ti and / or Al elements, which will dissolve Ti under the action of the electrolyte. 4+ and / or Al 3+ Ti 4+ Or Al 3+It catalyzes the decomposition of the first additive, enabling it to preferentially oxidize on the surface of the solid electrolyte to form a protective layer, thereby improving the structural stability of the solid electrolyte; the second additive, as a phosphazene compound, has cyano groups that can react with the Ti released from the solid electrolyte. 4+ And Co that dissociates at the positive extreme 3+ Complexation serves two purposes: firstly, it reduces the accumulation of metal ions on the negative electrode surface, thereby decreasing the catalytic reduction of the electrolyte by transition metal ions at the negative electrode; secondly, the second additive complexes Ti... 4+ Furthermore, a stable interfacial film can be formed on the positive electrode surface, reducing side reactions between the electrolyte and the positive electrode. The complexed Ti elements adhere to the particle surface of the positive electrode active material, further enhancing the lithium-ion insertion / extraction rate of the positive electrode active material (such as LCO), improving the low-temperature rate performance of the battery, and stabilizing the positive electrode structure. This improves the battery's cycle stability at 45℃ and storage performance at 60℃. Under low-temperature conditions, due to the increased viscosity of the electrolyte, Li... + The migration rate decreases, but the solid electrolyte particles coated on the membrane surface can shorten the lithium-ion migration distance. Simultaneously, the presence of the functional coating can partially circumvent the limitations of the electrolyte's low fluidity, directly promoting the migration of Li-ions. + The transmission further alleviates the problem of increased polarization caused by low temperature.

[0020] Regulation (w) 1 +w 2 ) / d 1 Within a suitable range, the first and second additives in the electrolyte can work synergistically with the functional coating in the separator to balance the battery's high-temperature stability, high-temperature storage performance, and low-temperature rate performance; when (w 1 +w 2 ) / d 1 <0.1 indicates that the functional coating thickness is too high while the amount of the first and second additives in the electrolyte is insufficient. The first additive is too small to form a protective layer on the solid electrolyte surface through oxidation. This results in insufficient structural stability of the solid electrolyte under high voltage and in the electrolyte, leading to the dissociation of Ti. 4+ and / or Al 3+ However, the content of the second additive with complexing effect in the electrolyte is too low, insufficient to simultaneously complex the functional coating and the transition metal dissolved from the positive electrode, and excessive Ti... 4+ Under high voltage, side reactions occur with the electrolyte, leading to Ti... 4+ Reduction increases interfacial impedance and causes transition metal elements dissolved from the solid electrolyte and positive electrode active material to migrate to the negative electrode, damaging the negative electrode SEI film and negatively impacting the battery's high-temperature stability; when (w 1 +w 2 ) / d 1>10. At this point, the functional coating thickness is too low and the amount of the first and second additives in the electrolyte is too high. While the fluidity of the electrolyte decreases at low temperatures, the improvement of the lithium-ion transport rate by the solid electrolyte is insufficient to compensate for the decrease in the migration rate of lithium ions at low temperatures caused by the excessive viscosity of the electrolyte. This is not conducive to further improving the low-temperature rate performance of the battery.

[0021] In some embodiments, the functional coating is located only on one side of the base film, wherein the functional coating is directed toward the positive electrode side. When the first additive and the second additive participate in the formation of the CEI film, the first additive and the second additive are consumed more on the surface of the positive electrode. The functional coating is directed toward the positive electrode side, which can provide a channel for the rapid transfer of lithium ions to the positive electrode side at low temperatures, avoid the interruption of the lithium ion transport pathway caused by the consumption of electrolyte on the positive electrode side under low temperature conditions, and further improve the low temperature performance of the battery.

[0022] In some embodiments, the functional particles in the functional coating account for 50%-99% by weight (e.g., 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 99%).

[0023] In one embodiment, the functional particle comprises LATP.

[0024] In this invention, by using LATP as a functional particle, the special crystal structure of LATP gives it a three-dimensional ion channel, which provides a fast channel for the efficient transfer of lithium ions at low temperatures, further alleviating the problem of increased polarization caused by low temperature and improving the low temperature performance of the battery.

[0025] In one embodiment, the functional particle includes LLTO. At low temperatures, the kinetic energy of lithium ion migration is lower. LLTO can reduce the low-temperature transition energy barrier of lithium ions, and in a low-temperature environment, it builds a channel that is easier for lithium ions to cross, thereby further alleviating the problem of increased polarization caused by low temperature and improving the low-temperature performance of the battery.

[0026] In one embodiment, the functional particles include LATP and LLTO.

[0027] In some embodiments, the functional particles comprise 30%-99% by weight in the functional coating.

[0028] In some embodiments, 0.5 ≤ (w 1 +w 2 ) / d 1 ≤8.

[0029] In this invention, the mass content of the first additive is w based on the total mass of the electrolyte. 1 %, w1 The percentage ranges from 0.1% to 3.5%, for example, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, or 3.5%.

[0030] In this invention, the mass content of the second additive is w based on the total mass of the electrolyte. 2 %, w 2 It ranges from 0.1% to 3%, for example, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.5%, 2%, 2.5%, or 3%.

[0031] In this invention, the total thickness of the functional coating is d. 1 The unit is μm, d 1 It is 0.5-3 (e.g., 0.5, 0.6, 0.8, 1, 1.5, 2, 2.5 or 3).

[0032] According to one specific implementation, w 1 The value is 0.1-3.5, w 2 0.1-3, d 1 The value is 0.5-3, and the battery satisfies: 0.1 ≤ (w 1 +w 2 ) / d 1 ≤10.

[0033] According to one specific implementation, w 1 The value is 0.1-3.5, w 2 0.1-3, d 1 The value is 0.5-3, and the battery satisfies: 0.5≤(w 1 +w 2 ) / d 1 ≤8.

[0034] In this invention, w 1 It ranges from 1% to 3%, for example, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, or 3%.

[0035] In this invention, w 2 It ranges from 0.5% to 2%, for example, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, or 2%.

[0036] In this invention, w 1 and w 2 It can be obtained by conventional testing methods in the field, such as by gas chromatography or gas chromatography coupled with mass spectrometry.

[0037] In this invention, the thickness of the diaphragm is d. 2 The unit is μm, d 2 It is 4-15 (e.g., 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15).

[0038] In this invention, d 1 and d 2 Satisfy: D=d 1 / d 2 D is 0.05-0.4, for example, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.12, 0.15, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, 0.32, 0.35, 0.38 or 0.4.

[0039] In this invention, by limiting the proportion of the functional coating thickness to the total thickness of the separator within a suitable range, both high ionic conductivity and high-temperature stability can be achieved. When D > 0.4, the functional coating thickness is too high, the proportion of solid electrolyte in the separator increases, and the high-temperature stability is insufficient, leading to increased interfacial impedance and aggravated electrolyte side reactions. When D < 0.05, the functional coating thickness is too low, the proportion of solid electrolyte in the separator decreases, the improvement effect on ionic conductivity is not significant, and it is not conducive to improving the low-temperature performance of the battery.

[0040] In this invention, d 1 and d 2 The membrane can be obtained using conventional testing methods in this field, such as scanning electron microscopy (SEM). Specifically, the membrane is removed from the battery cell, and the membrane is selected from the head, tail, or superanode region of the cell, where it is not bonded to the electrode, thus obtaining a membrane with a relatively complete functional coating. The membrane is cleaned with anhydrous ethanol to remove electrolyte and residual lithium salt, and then placed in a 40°C vacuum oven to dry and remove the solvent, obtaining the test sample. A high-magnification image of the cross-section of the obtained sample is captured using SEM. After magnification to a certain degree, the base film and functional coating are distinguished by the interface. The thickness of the membrane and the functional coating are measured at 10 different points, and the average value is taken to obtain d. 1 and d 2 .

[0041] According to one specific implementation, d 1 It is 0.5-3, d 2 For 4-15, d 1 and d 2 Satisfy: D=d 1 / d 2 D is 0.05-0.4.

[0042] In this invention, the second additive comprises at least one of the following structural formulas: (Equation 1-1) (Equation 1-2) (Equation 1-3) (Equation 1-4) (Equation 1-5) (Equations 1-6).

[0043] In this invention, the electrolyte further includes a first solvent, the first solvent having the following structural formula: R1', R2', R3' and R4' each independently include C1-C5 alkyl substituents and / or halogens.

[0044] In one embodiment, the first solvent comprises at least one of the following structural formulas: (Equation 2-1) (Equation 2-2) (Equation 2-3) (Equation 2-4) (Equation 2-5) (Equation 2-6) and (Equation 2-7).

[0045] In this invention, based on the total mass of the electrolyte, the content of the first solvent is w. 3 w 3 It ranges from 1% to 15%, for example, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.5%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 14%, or 15%.

[0046] In one embodiment, w 3 It is 5%-10%.

[0047] Compared to commonly used straight-chain carboxylic esters (such as propyl propionate or ethyl propionate), the first solvent has stronger antioxidant capacity and a higher boiling point, effectively reducing the risk of gas generation under high voltage and high temperature conditions. Furthermore, due to its branched structure, the first solvent reduces side reactions with transition metal ions, thereby improving the battery's high-temperature cycle performance and thermal performance. The branched structure of the first solvent also reduces intermolecular forces, resulting in a lower electrolyte viscosity at low temperatures, which can improve the performance of Li... + The increased migration rate promotes electrolyte wetting at the interface between the separator and the electrode, and enhances the separator's electrolyte retention, thereby improving the battery's low-temperature performance. Simultaneously, the steric effect of the branched structure can also weaken the influence of Li on the electrolyte's performance. + The coordination effect of Li accelerates + The desolvation process reduces polarization and improves the low-temperature performance of the battery.

[0048] In this invention, w 3 It can be obtained by conventional testing methods in the field, such as by gas chromatography or gas chromatography coupled with mass spectrometry.

[0049] In this invention, the contact angle between the functional coating and the test electrolyte is 5°-40° (e.g., 5°, 6°, 8°, 10°, 12°, 14°, 16°, 20°, 25°, 30°, 35° or 40°). The test electrolyte is composed of lithium hexafluorophosphate, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC). The concentration of lithium hexafluorophosphate is 1 mol / L, and the volume ratio of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate is 1:1:1.

[0050] In one embodiment, the contact angle between the functional coating and the test electrolyte is 10°-35°.

[0051] When the contact angle between the functional coating and the test electrolyte is within the above range, it indicates that the surface energy of the functional coating is high, allowing the electrolyte to spread rapidly and penetrate into the membrane pores, ensuring sufficient contact between the electrode and the electrolyte. At low temperatures, although the viscosity of the electrolyte increases, good wettability prevents localized electrolyte drying due to insufficient wetting, reducing interfacial impedance. The electrolyte can fully fill the porous structure of the functional coating, forming continuous ion transport channels to compensate for the decrease in the electrolyte's own ionic conductivity at low temperatures. A low contact angle ensures that the electrolyte uniformly covers the electrode surface, allowing sulfur-containing additives or nitrile additives (such as the first and second additives) to decompose at low temperatures, forming a dense and highly ionicly conductive interfacial film on the electrode surface, reducing Li... + This reduces diffusion resistance, thereby further improving the battery's low-temperature performance.

[0052] In this invention, the contact angle between the functional coating and the test electrolyte is obtained using conventional testing methods in the art, such as by measuring with a contact angle meter, specifically as follows: Using a pipette, 3 μL of test electrolyte (EC:EMC:DMC mass ratio of 1:1:1, lithium hexafluorophosphate 1 mol / L) is drawn, and a single drop of electrolyte is slowly squeezed out, allowing it to fall freely onto the surface of the functional coating. At the instant the droplet contacts the surface (typically within 1-3 seconds), a clear side view of the droplet is captured using a high-speed camera on the contact angle meter. Measurements are taken at least three times at different locations on the same sample, and at least three different functional coating samples are prepared for measurement, with the average value and standard deviation recorded.

[0053] In this invention, the average particle size of the functional particles is 0.05μm-5μm, for example, 0.05μm, 0.06μm, 0.08μm, 0.1μm, 0.2μm, 0.4μm, 0.6μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 5μm.

[0054] In this invention, the average particle size of the functional particles can be measured using the following methods: For example, in an SEM image of the functional coating surface, arbitrarily select a 100μm × 100μm area, identify and randomly select 100 functional particles, and draw a rectangle or square with the smallest area completely surrounding each particle (i.e., a rectangle or square tangent to the four sides of the particle's edge). The arithmetic mean of the length of the long side and the short side of the rectangle, or the length of any side of the square, is the particle size of that single functional particle. If the number of functional particles in a single image is insufficient, multiple images can be taken until the number of observed functional particles accumulates to 100. The arithmetic mean of the particle sizes of these 100 functional particles is then calculated, which is the average particle size of the functional particles. Alternatively, before preparing the functional coating, the average particle size of the functional particles can be obtained by measuring them using a laser particle size analyzer after thorough stirring.

[0055] In one embodiment, the average particle size of the functional particles is 0.1 μm-4 μm.

[0056] In this invention, the functional particles are lithium aluminum titanium phosphate. Based on the total mass of the functional coating, the content of element Al is c(Al), the content of Ti is c(Ti), and 12%≤c(Al)+c(Ti)≤40%, for example, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38% or 40%.

[0057] In one embodiment, 15% ≤ c(Al) + c(Ti) ≤ 36%.

[0058] In this invention, w 3 / [c(Al)+c(Ti)] is 0.08-1, for example, 0.08, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95 or 1.

[0059] In one embodiment, w 3 / [c(Al)+c(Ti)] is 0.12-0.8.

[0060] Al derived from functional coatings 3+It can catalyze the formation of a stable CEI film at the positive electrode by the first additive; in addition, Al 3 + It can also adsorb HF in the electrolyte, reducing the corrosion of the CEI film on the positive electrode surface by HF, thereby inhibiting the dissolution of Co from the positive electrode; while Ti derived from the functional coating 4+ This can remove reactive oxygen species (such as O2) from the electrolyte. - O2 2− This reduces the concentration of reactive oxygen species, effectively suppresses the occurrence of electrolyte side reactions, and further improves the battery's high-temperature cycle stability, high-temperature storage performance, and thermal box performance. Combined with the high antioxidant and low viscosity characteristics of the first solvent in the electrolyte, it can suppress the oxidation side reactions that occur in the electrolyte, thereby further improving the battery's 45℃ cycle stability, 60℃ high-temperature storage performance, and 130℃ thermal box performance.

[0061] By further limiting w 3 / [c(Al)+c(Ti)] allows it to improve the synergistic effect between the functional coating and the first solvent within a suitable range, when w 3 / [c(Al)+c(Ti)]<0.08, at this point, on the one hand, the content of the first solvent in the electrolyte is too low, weakening its antioxidant capacity and failing to effectively suppress oxidation side reactions; on the other hand, the content of Al and Ti elements in the functional coating is too high, leading to the dissolution of Al... 3+ and Ti 4+ A large amount of [amount] may further catalyze the generation of side reactions, thus preventing further improvement in the battery's high-temperature cycling, high-temperature storage performance, and high-temperature safety performance; when w 3 / [c(Al)+c(Ti)]>1, at this point the content of elements Al and Ti in the functional coating is too low, which is not conducive to further improving the lithium-ion transport capability between the positive and negative electrodes at low temperatures, and is not conducive to further improving the low-temperature performance of the battery.

[0062] In this invention, c(Al) and c(Ti) can be obtained by conventional testing methods in the art, for example, by removing the separator from the cell to obtain a test sample, or by directly using the functional coating prepared during the separator preparation process as a test sample, taking a high-magnification image of the functional coating cross-section in the thickness direction of the separator using SEM, selecting 10 different regions to determine the content of Al and Ti using an energy dispersive spectroscopy (EDS) analyzer, and taking the average value as c(Al) and c(Ti).

[0063] In this invention, the electrolyte further includes lithium salt additives and ethylene carbonate (EC).

[0064] In this invention, based on the total mass of the electrolyte, the mass content of the lithium salt additive is 12%-25%, for example, 12%, 13%, 14%, 15%, 16%, 18%, 20%, 22%, 24% or 25%.

[0065] In this invention, based on the total mass of the electrolyte, the mass content of the ethylene carbonate (EC) is 0%-10%, for example, 0%, 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0066] EC is a commonly used carbonate solvent that can form an SEI film on the negative electrode side. However, its oxidation stability is insufficient under high voltage and high temperature systems. Adding large amounts increases the risk of high-temperature gas generation in the battery, which is detrimental to further improvement of the battery's high-temperature safety and stability. Using an electrolyte without EC can alleviate the above problems and significantly improve the high-temperature gas generation issue. The amount of EC added can be selected within the range of 0%-10%, and the appropriate content should be selected according to the specific electrolyte composition to ensure film formation effect on the negative electrode while improving the high-temperature gas generation problem of the battery.

[0067] In this invention, the mass content of EC in the electrolyte can be obtained by conventional testing methods in the art, such as by gas chromatography or gas chromatography coupled with mass spectrometry.

[0068] In this invention, the battery further includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material, the positive electrode active material includes lithium cobalt oxide, the lithium cobalt oxide includes a doping element Q, Q includes at least one selected from Al, Mg, Ti, Zr, Y, La and W.

[0069] Lithium cobalt oxide (LCO) exhibits excellent energy density and good cycle stability as a cathode material. However, at voltages above 4.5V, the LCO cathode undergoes an irreversible phase transition, releasing lattice oxygen and causing structural collapse. High temperatures accelerate this phase transition and lattice oxygen release, further compromising structural stability. Under high temperature and pressure, the electrolyte undergoes accelerated oxidation and decomposition, generating gases such as CO2, leading to battery swelling and even thermal runaway. The electrode interface film is damaged and repeatedly regenerated, further accelerating electrolyte consumption and resulting in active lithium loss. This can lead to lithium plating and capacity decay. When the LCO cathode is combined with the electrolyte system and separator of this invention, the first and second additives enhance the stability of the CEI film on the cathode surface and complex transition metal ions in the system, reducing electrolyte side reactions and thus improving the structural stability of the LCO cathode under high voltage and high temperature. The separator with a solid electrolyte functional coating improves ion migration efficiency at low temperatures, enhances CEI film stability, and reduces the concentration of active oxygen in the electrolyte. This strategy can delay or suppress the irreversible phase transition and structural collapse of lithium cobalt oxide cathodes under high voltage and high temperature, improve the overall cycle stability, storage performance and thermal performance of the battery at high temperature, and take into account low temperature performance.

[0070] In this invention, the battery further includes a negative electrode sheet, which comprises a negative electrode active material, including silicon-carbon material and / or graphite. The graphite includes artificial graphite and / or natural graphite.

[0071] In one embodiment, the negative electrode active material includes silicon-carbon material.

[0072] In one embodiment, the negative electrode active material includes graphite.

[0073] In one embodiment, the negative electrode active material includes silicon-carbon material and graphite.

[0074] In this invention, the negative electrode active material may further include at least one of mesophase carbon microspheres, soft carbon, hard carbon, nano-silicon particles, and silicon-oxygen materials.

[0075] The first and second additives in the electrolyte can form a stable and dense SEI film at the negative electrode interface. Due to the special structure of the first additive, the SEI film contains not only inorganic components such as Li₂SO₃ and Li₂SO₄, but also potentially organic components such as alkyl lithium carbonate. This not only improves the stability of the negative electrode interface but also repairs the SEI film and alleviates side reactions between the electrolyte and the negative electrode. The second additive contains cyano groups, which can complex transition metal ions (such as Co) in the electrolyte. 3 +The first solvent helps prevent transition metals from dissolving and migrating to the negative electrode, which could damage the SEI film and hinder the improvement of the battery's high-temperature performance. The first solvent also promotes the wetting effect of the electrolyte on the separator, improving its electrolyte retention and thus enhancing the battery's low-temperature performance. The solid electrolyte functional coating in the separator provides a fast channel for lithium-ion transport under low-temperature conditions, promoting lithium-ion migration between the positive and negative electrodes, reducing migration resistance and interfacial impedance, and further optimizing the battery's low-temperature performance.

[0076] In this invention, the charging cutoff voltage of the battery is greater than or equal to 4.5V, for example, 4.5V, 4.6V, 4.7V, 4.8V, 4.9V, 5V, 5.1V, 5.2V, 5.3V, 5.4V, 5.5V, 5.6V, 5.7V, 5.8V, 5.9V, or 6V.

[0077] In this invention, the diaphragm further includes an adhesive layer located on the outer surface of the functional coating and / or the surface of the base film.

[0078] In one embodiment, such as Figure 1 As shown, the diaphragm includes a base membrane, an adhesive layer, and a functional coating. The functional coating 12 is located on one side surface of the base membrane 11, and the adhesive layer 13 is located on the outer surface of the functional coating 12 and the other side surface of the base membrane 11.

[0079] In one embodiment, the diaphragm includes a base membrane, an adhesive layer, and a functional coating, wherein the functional coating is located on one side surface of the base membrane, and the adhesive layer is located on the outer surface of the functional coating.

[0080] In one embodiment, the diaphragm includes a base membrane, an adhesive layer, and a functional coating, wherein the functional coating is located on one side surface of the base membrane, and the adhesive layer is located on the other side surface of the base membrane.

[0081] In one embodiment, the functional coating is located on both sides of the base film, and the adhesive layer is located on the outer surface of the functional coating.

[0082] In some embodiments, the thickness of the adhesive layer is d. 3 d 3 The value is 0.5-5 (e.g., 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5), and the unit is μm.

[0083] In this invention, d 3 This can be obtained through conventional testing methods in the field, such as by scanning electron microscopy (SEM) with reference to d. 1 and d 2 The test method was obtained.

[0084] In this invention, the adhesive layer comprises a polymer, the polymer comprising at least one of p-phenylenediamine terephthalamide, polyisophthalamide terephthalamide, fluoropolymers, acrylate polymers, phenolic resins, modified phenolic resins, polyimides, furanyl-modified polyamides, modified phenolic resins, and modified polyimides.

[0085] In this invention, the acrylate polymers include one or more of the following: polymethyl methacrylate, polybutyl acrylate, acrylate monomer-acrylonitrile copolymer, acrylate monomer-ethylene copolymer, acrylate monomer-acrylonitrile-ethylene copolymer, styrene-acrylate monomer-acrylonitrile copolymer, ethylhexyl acrylate-methyl methacrylate copolymer, butyl acrylate-methyl methacrylate copolymer, methyl acrylate-N,N-dimethylacrylamide copolymer, ethyl acrylate-2-(diethylamino)ethyl acrylate copolymer, ethyl acrylate-N,N-diethylacrylamide copolymer, and ethyl acrylate-2-(diethylamino)ethyl acrylate.

[0086] In this invention, the acrylate monomers include one or more of methyl acrylate, methyl methacrylate, ethyl acrylate, butyl acrylate, ethyl methacrylate, n-propyl acrylate, octyl acrylate, isooctyl acrylate, octadecyl acrylate, isobutyl acrylate, cyclohexyl acrylate, and 2-hydroxyethyl acrylate.

[0087] In one embodiment, the fluoropolymer includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene modified and copolymer thereof, polyvinylidene fluoride-trichloroethylene, polyvinylidene fluoride-chlorotrifluoroethylene, acrylic acid-vinylidene fluoride copolymer and acrylonitrile-vinylidene fluoride copolymer.

[0088] In one embodiment, the furanyl-modified polyamide is a polymer containing a five-membered furan ring and an amide group.

[0089] In other instances, the furanyl-modified polyamide has the structure shown in formula (I). Equation (I), where m is an integer from 5 to 100 (e.g., 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100), n is an integer from 5 to 100 (e.g., 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100), and Ar 1 Selected from and At least one of them, Ar 2 Selected from at least one of the following groups: , , , , , , , , , , , , , , , and .

[0090] In this invention, the adhesive layer may further include additives, which include at least one of polyvinyl alcohol, styrene-butadiene rubber, ethylene-vinyl acetate copolymer, sodium carboxymethyl cellulose, polyvinylpyrrolidone, and styrene-acrylic latex.

[0091] In this invention, the base film comprises at least one of polyethylene, propylene, polyimide, polyacrylonitrile, and polyethersulfone.

[0092] In this invention, the puncture strength of the base membrane is 150gf-600gf, for example, 150gf, 160gf, 170gf, 180gf, 200gf, 220gf, 250gf, 300gf, 350gf, 400gf, 450gf, 500gf, 550gf or 600gf.

[0093] In one embodiment, the puncture strength of the base membrane is 180gf-500gf.

[0094] Adjusting the puncture strength of the base membrane within a suitable range helps improve the safety performance of the battery and avoids short circuits between the positive and negative electrodes caused by damage to the separator under external force. For example, when the negative electrode uses silicon-carbon material, the large volume expansion during battery cycling can cause the separator to puncture.

[0095] In this invention, the puncture strength of the base film can be obtained by conventional testing methods in the art: disassemble the battery, remove the separator, remove the coating on the surface of the base film, and when the coating residue on the surface of the base film is less than 5%, it is considered as obtaining a test sample of the base film. Alternatively, the original base film without coating can be used as a test sample. A test sample of 50mm×50mm is cut arbitrarily from the test sample. The test sample is laid flat in the fixture of the universal tensile testing machine and clamped. The puncture strength test item is selected, and puncture is performed at a rate of (100±10)mm / min. The puncture strength test result is read from the test report. The test is repeated 3 times and the average value is taken as the puncture strength of the base film.

[0096] In this invention, the average pore size of the base film is 20nm-60nm, for example, 20nm, 22nm, 24nm, 26nm, 28nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm or 60nm.

[0097] In one embodiment, the average pore size of the base film is 30nm-50nm.

[0098] When the average pore size of the base film is within the above range, it can ensure that the base film has high electrolyte wetting performance and ion transport performance, which, together with the functional coating on the surface, can improve the high and low temperature performance of the battery.

[0099] It is understood that the average pore size of the base film refers to the pore structure that the base film has at the microscopic level, and the pore size corresponding to the cumulative proportion of pores being 50% in the pore size distribution diagram obtained by arranging the pore sizes of the substrate layer from large to small.

[0100] In this invention, the average pore size of the base film can be obtained by conventional testing methods in the art, such as by measuring it with a mercury porosimeter from PMI.

[0101] In some embodiments, the functional coating comprises 30%-99% functional particles (e.g., 30%, 32%, 34%, 36%, 38%, 40%, 45%, 50%, 60%, 70%, 80%, 90%, or 99%), 0%-50% filler particles (e.g., 0%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 40%, or 50%), and 1%-10% polymer binder (e.g., 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%).

[0102] In this invention, the filler particles are selected from at least one of alumina, boehmite, magnesium hydroxide, silicon dioxide, magnesium oxide, boron nitride, 1,3,5-triazine-2,4,6-triamine, melamine cyanurate, melamine thiocyanate, 4-amino-2,6-dihydroxypyrimidine, uracil, cytosine, guanine, 2-mercaptobenzimidazole, 2-mercapto-5-methylbenzimidazole, 2-mercapto-5-methoxybenzimidazole, 2-mercapto-5-ethoxybenzimidazole, 2-mercapto-5-hydroxybenzimidazole, 2-mercapto-5-aminobenzimidazole, 2-mercapto-5-chlorobenzimidazole, 2-mercapto-5-sulfonic acid benzimidazole, 2-mercapto-5-carboxybenzimidazole, and 2-mercapto-5-nitrobenzimidazole. The polymer binder is selected from at least one of the following: polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyimide, polyacrylonitrile, poly(meth)acrylate, aramid resin, poly(meth)acrylic acid, styrene-butadiene rubber (SBR), polyvinyl alcohol, polyvinyl acetate, carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (CMC-Na), carboxyethyl cellulose, polyacrylamide, phenolic resin, epoxy resin, waterborne polyurethane, ethylene-vinyl acetate copolymer, multi-component acrylic copolymer, lithium polystyrene sulfonate, waterborne silicone resin, nitrile-polyvinyl chloride blend, styrene-acrylic latex, pure styrene latex, etc., and blends and copolymers derived from the aforementioned polymer modifications.

[0103] In this invention, the electrolyte further includes a second solvent, which comprises carbonates and / or carboxylic acid esters. The carbonate is selected from at least one of the following fluorinated or unsubstituted solvents: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; the carboxylic acid ester is selected from at least one of the following solvents: propyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, ethyl propionate, n-propyl propionate, methyl butyrate, ethyl butyrate, and n-ethyl butyrate.

[0104] In this invention, the electrolyte further includes a third additive, which is selected from at least one of the following: vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, vinyl sulfate, succinate, glutaronitrile, adiponitrile, heptaonitrile, octanoic acid, sebaconitrile, 1,3,6-hexanetrionitrile, glycerol trionitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,3-propanesulfonic acid lactone, and propenyl-1,3-sulfonic acid lactone.

[0105] In some embodiments, the base film includes a first surface and a second surface opposite to each other, the first surface being disposed facing the positive electrode and the second surface being disposed facing the negative electrode, the first surface including the functional coating and the adhesive layer, the functional coating being located between the base film and the adhesive layer.

[0106] In some embodiments, the second surface may include the functional coating or may not include the functional coating and the adhesive layer. When the second surface includes the functional coating, the functional coating is located between the adhesive layer and the base film. When the second surface does not include the functional coating, the adhesive layer is located on the outer surface of the base film.

[0107] It should be noted that the numerical designations such as "first" and "second" in this invention are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0108] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0109] In the following examples, unless otherwise specified, all materials used are commercially available analytical grade.

[0110] The following examples illustrate the lithium-ion secondary battery of the present invention.

[0111] Example 1 Lithium-ion secondary batteries are prepared according to the following method: (1) Preparation of positive electrode The positive electrode active material (lithium cobalt oxide containing doped elements Al and Mg), positive electrode binder (polyvinylidene fluoride 500), and positive electrode conductive agent (conductive carbon black: carbon nanotubes (mass ratio) = 1:1) were mixed in N-methylpyrrolidone (NMP) solvent at a weight ratio of 96:2:2 and continuously stirred under the action of a stirrer to form a uniform and flowing positive electrode slurry. Subsequently, the positive electrode slurry was coated on both sides of the positive electrode current collector (aluminum foil), and then dried, rolled, and slit to obtain the desired positive electrode sheet.

[0112] (2) Preparation of negative electrode Graphite, silicon carbide material, negative electrode conductive agent (conductive carbon black: carbon nanotubes (mass ratio) = 1:1), sodium carboxymethyl cellulose, and negative electrode binder (styrene-butadiene rubber: polyacrylic acid (mass ratio) = 1:1) were mixed in an aqueous solvent at a weight ratio of 92:5:1:0.5:1.5 and continuously stirred under the action of a stirrer to form a homogeneous and fluid negative electrode slurry. Subsequently, the slurry was coated on both sides of the negative electrode current collector (copper foil), and then dried, rolled, and slit to obtain the negative electrode sheet.

[0113] (3) Electrolyte preparation In an argon-filled glove box (moisture <1ppm, oxygen <1ppm), the following solvents—propyl propionate:ethyl propionate:propylene carbonate—are mixed in a volume ratio of 1:1:1. Then, 8.5% of the first solvent (Formula 2-1, w) based on the total mass of the electrolyte is slowly added. 3 It contains 8.5% ethylene carbonate, 6.8% ethylene carbonate, and 2.5% of the first additive (w). 1 The second additive is 2.5% (w / 1%), and 1% (Formula 1-1, w / 1%). 2 The desired lithium-ion battery electrolyte was obtained by stirring 18.5% LiPF6 and 2% adiponitrile evenly.

[0114] (4) Preparation of functional coatings and diaphragms Lithium aluminum titanium phosphate (LATP, functional particles), polyvinylidene fluoride-hexafluoropropylene, polyvinyl alcohol, and deionized water were uniformly mixed in a mass ratio of 22.2:0.7:0.1:77 to obtain a first mixed slurry. The first mixed slurry was coated onto one side of a polyethylene film using a microgravure plate and dried in a multi-section oven at 60°C to obtain a functional coating. Subsequently, polyvinylidene fluoride (PVDF) was added to DMAC and stirred thoroughly until dissolved. Alumina was then added and stirred until evenly dispersed to obtain a second mixed slurry with a solid content of 10%. Based on the total mass of solids in the second mixed slurry, the mass percentage of PVDF was 62% and the mass percentage of alumina was 38%. The second mixed slurry was coated onto the surfaces of the base film and the functional coating using a gravure roller. After drying in a multi-section oven at 60°C, an adhesive layer was formed, thus obtaining the desired diaphragm. The thickness of the functional coating was 1.8 μm (d). 1 The membrane thickness is 8.8 μm (d = 1.8). 2 The contact angle between the functional coating and the test electrolyte is 22.5°, the average particle size of the functional particles is 0.75 μm, the c(Al)+c(Ti) ratio is 22.5%, the puncture strength of the base film is 403 gf, and the average pore size of the base film is 46 nm.

[0115] (5) Preparation of lithium-ion batteries The prepared positive electrode sheet, separator, and negative electrode sheet are stacked and wound to obtain an electrode assembly, which is then subjected to electrolyte injection, vacuum sealing, room temperature settling, and high-temperature formation processes to obtain the desired lithium-ion battery, where D=d 1 / d 2 =1.8 / 8.8=0.2, (w 1 +w 2 ) / d 1 =(2.5+1) / 1.8=1.94, w 3 / [c(Al)+c(Ti)]=8.5% / 22.5%=0.38, the charging cut-off voltage of the battery is 4.53V, and the functional coating of the separator is used on the side facing the positive electrode.

[0116] Example 2 This embodiment group is carried out with reference to Embodiment 1, except that the functional coating of the separator is used on the side facing the negative electrode.

[0117] Example 3 This embodiment is based on Example 1, except that the functional coating is located on both sides of the base film, the adhesive layer is located on the surface of the functional coating, and the thickness of the functional coating on one side is 0.9 μm (d). 1 (1.8).

[0118] Example 4 group This set of examples is used to illustrate when D=d 1 / d 2 The impact of changes.

[0119] This embodiment group is based on Embodiment 1, except that D=d 1 / d 2 Changes have occurred; see Table 1 for details.

[0120] Table 1 Example 5 group This set of examples illustrates the effects of changing the specific selection of the second additive.

[0121] Example 5-1 This embodiment is based on Embodiment 1, except that the second additive is of Formula 1-3.

[0122] Example 5-2 This embodiment is based on Embodiment 1, except that the second additive is of Formula 1-6.

[0123] Example 6 group This set of examples is used to illustrate when (w) 1 +w 2 ) / d 1 The effects of changes.

[0124] This embodiment group is carried out with reference to Embodiment 1, except that (w 1 +w 2 ) / d 1 Changes have occurred; see Table 2 for details.

[0125] Table 2 Example 7 group This set of examples illustrates how, based on the total mass of the electrolyte, the content w of the first solvent... 3 The effects of changes.

[0126] This embodiment group is carried out with reference to Example 1, except that the content of the first solvent w is based on the total mass of the electrolyte. 3 The changes have been made; please refer to Table 3 for details.

[0127] Table 3 Example 8 group This set of examples illustrates the effects of changes in at least one of the following: the contact angle of the functional coating and the test electrolyte, the puncture strength of the base film, and the average pore size of the base film.

[0128] This embodiment group is based on Embodiment 1, except that at least one of the following is changed: the contact angle of the functional coating and the test electrolyte, the puncture strength of the base film, and the average pore size of the base film. See Table 4 for details.

[0129] Table 4 Example 9 group This set of examples is used to illustrate when w 3 The effects of changes in / [c(Al)+c(Ti)].

[0130] This set of examples is based on Example 1, except that the content of the first solvent in the electrolyte is adjusted, and the content of LATP in the functional coating is changed. In Examples 9-2 and 9-4, melamine trithiocyanate (filler particles) is used to replace part of the LATP, resulting in w 3 The value of / [c(Al)+c(Ti)] changes; see Table 5 for details.

[0131] Table 5 Example 10 group This set of examples illustrates the effects of changes in the mass content of ethylene carbonate based on the total mass of the electrolyte.

[0132] Example 10-1 This embodiment is based on Example 1, except that the electrolyte does not contain ethylene carbonate.

[0133] Example 10-2 This embodiment is based on Example 1, except that the mass content of ethylene carbonate is 9.7% based on the total mass of the electrolyte.

[0134] Example 10-3 This embodiment is based on Example 1, except that the mass content of ethylene carbonate is 13% based on the total mass of the electrolyte.

[0135] Comparative Example 3 This embodiment group is based on Embodiment 1, except that the functional particles are replaced with equal parts by mass of aluminum oxide.

[0136] Comparative Example 4 This embodiment group is based on Example 1, except that the electrolyte does not contain the first additive.

[0137] Comparative Example 5 This embodiment group is carried out with reference to Example 1, except that the electrolyte does not contain a second additive.

[0138] Test case The batteries prepared in the examples and comparative examples were subjected to the following performance tests, and the test results are shown in Table 6: (1) Storage test at 60℃: Under a constant temperature environment of 25℃, the battery charge was adjusted to 50% SOC, and the initial thickness T of the battery was tested. 1 The battery was charged at a constant current and constant voltage of 0.7C to the upper limit voltage of 4.53V, with a cutoff current of 0.05C, and then discharged at 0.5C to 3V. The fully charged battery was then stored at a constant temperature of 60℃, and the thermal thickness expansion was monitored every 7 days. The final thermal thickness T of the battery was measured at 70 days of storage or when the thermal thickness expansion exceeded 20%. 2 The thickness expansion rate of a lithium battery stored at 60℃ = (T 2 -T 1 ) / T 1 ×100%.

[0139] (2) 0℃ 300T cycle test: The obtained batteries were placed in a constant temperature environment of 0℃ for 2-3 hours. When the battery body reached (0±2)℃, the battery was charged at a constant current and constant voltage of 0.3C to 4.53V, with a cutoff current of 0.05C. After the battery was fully charged, it was left to rest for 10 minutes, and then discharged at a constant current of 0.5C to the cutoff voltage of 3V. The highest discharge capacity of the first 3 cycles was recorded as the initial capacity Q. 1 When the cycle reaches 300T, record the battery's last discharge capacity Q. 2 The capacity retention rate during 0℃ cycling is as follows: Capacity retention rate (%) = Q 2 / Q 1 ×100%.

[0140] (3) 45℃ 500T cycle test: The battery was placed in a constant temperature environment of 45℃ and left to stand for 2 hours. It was then charged at a constant current and constant voltage of 0.7C to 4.53V, with a cutoff current of 0.05C. After fully charging, the battery was left to rest for 10 minutes, and then discharged at a constant current of 0.5C to the cutoff voltage of 3V. The highest discharge capacity of the first three cycles was recorded as the initial capacity Q. 3 The battery was cycled according to the above charge and discharge mode for 500 cycles, and the discharge capacity Q of the battery after 500 cycles was recorded. 4 The capacity retention rate during 45℃ cycling is as follows: Capacity retention rate (%) = Q 4 / Q 3 ×100%.

[0141] (4) -20℃ 0.2C discharge test: The resulting battery was placed in a constant temperature environment of 25℃ and discharged to 3V at 0.2C, then charged to 4.53V at a constant current and constant voltage of 0.7C, with a cutoff current of 0.05C. After the battery was fully charged, it was allowed to stand for 5 minutes, and then discharged again at a constant current of 0.2C to the cutoff voltage of 3.0V. The initial capacity Q of the battery was recorded. 5 The battery was then charged to 4.53V using a constant current and constant voltage of 0.7C, with a cutoff current of 0.05C to fully charge it. The fully charged battery was then placed in a -20℃ environment for 4 hours. Once the battery surface temperature reached ambient temperature, it was discharged to 3V using a 0.2C rate, and the battery discharge capacity was recorded as Q. 6 Then the low-temperature discharge capacity retention rate = Q 6 / Q 5 ×100%.

[0142] (5) 130℃ hot box test: After the battery in the example was fully charged at a constant current and constant voltage of 0.5C, it was placed in a constant temperature chamber and heated at an initial temperature of 20℃±5℃. The temperature was increased to 130℃±2℃ at a rate of (5℃±2℃) / min and maintained at this temperature for 30 minutes before the test ended. The judgment criterion was that the battery did not catch fire or explode within 30 minutes and was considered to have passed. 20 samples were tested. The number of batteries that passed the 130℃ hot chamber test was recorded as X, and the result was recorded as "X / 20".

[0143] Table 6 As shown in Table 6, by comparing the comparative example and the embodiment, the embodiment shows improved capacity retention at 45℃, reduced storage expansion rate at 60℃, increased pass rate in the 130℃ hot box test, improved capacity retention at 0℃, and improved discharge retention at -20℃. This indicates that by controlling the relationship between the weight content of the first additive, the second additive, and the total thickness of the separator functional coating, the battery satisfies the relationship: 0.1 ≤ (w 1 +w 2 ) / d 1 ≤10 can improve the high-temperature cycle stability of the battery, while improving the migration efficiency of lithium ions in the electrolyte, thereby improving the high-temperature cycle capacity retention rate of the battery, increasing the pass rate of the 130℃ hot box test, reducing the high-temperature storage expansion rate, and improving the low-temperature cycle capacity retention rate and low-temperature discharge retention rate of the battery, so that the battery can take into account both high and low temperature performance.

[0144] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A battery, characterized in that, The battery includes a separator and an electrolyte, the electrolyte including a first additive and a second additive, the first additive having the following structural formula: The structural formula of the second additive is R1, R2, and R3 each independently comprise unsubstituted or halogen-substituted C1-C6 alkyl groups; Based on the total mass of the electrolyte, the mass content of the first additive is w. 1 %, the mass content of the second additive is w 2 % The diaphragm includes a base membrane and a functional coating, wherein the functional coating is located on at least one side surface of the base membrane; The functional coating comprises functional particles, including lithium aluminum titanium phosphate and / or lithium lanthanum titanate, and the total thickness of the functional coating in the separator is d. 1 The unit is μm; w 1 w 2 and d 1 Satisfy: 0.1≤(w) 1 +w 2 ) / d 1 ≤10.

2. The battery according to claim 1, wherein, 0.5≤(w 1 +w 2 ) / d 1 ≤8; And / or, w 1 The percentage ranges from 0.1% to 3.5%. And / or, w 2 The percentage is 0.1%-3%; And / or, d 1 It is 0.5-3; And / or, the thickness of the diaphragm is d. 2 The unit is μm, d 1 and d 2 Satisfy: D=d 1 / d 2 D is 0.05-0.

4.

3. The battery according to claim 2, wherein, w 1 It is 1%-3%; And / or, w 2 It ranges from 0.5% to 2%; And / or, d 2 It is 4-15; And / or, D is 0.08-0.

35.

4. The battery according to any one of claims 1-3, wherein, The second additive includes at least one of the following structural formulas: (Equation 1-1) (Equation 1-2) (Equation 1-3) (Equation 1-4) (Equation 1-5) (Equations 1-6).

5. The battery according to any one of claims 1-3, wherein, The electrolyte further includes a first solvent, the first solvent having the following structural formula: R1', R2', R3' and R4' each independently include C1-C5 alkyl substituents and / or halogens; Preferably, based on the total mass of the electrolyte, the content of the first solvent is w. 3 w 3 It ranges from 1% to 15%; Preferably, the first solvent comprises at least one of the following structural formulas: (Equation 2-1) (Equation 2-2) (Equation 2-3) (Equation 2-4) (Equation 2-5) (Equation 2-6) and (Equation 2-7); More preferably, w 3 It is 5%-10%.

6. The battery according to any one of claims 1-3, wherein, The contact angle between the functional coating and the test electrolyte is 5°-40°. The test electrolyte is composed of lithium hexafluorophosphate, ethylene carbonate, methyl ethyl carbonate and dimethyl carbonate. The concentration of lithium hexafluorophosphate is 1 mol / L, and the volume ratio of ethylene carbonate, methyl ethyl carbonate and dimethyl carbonate is 1:1:

1. And / or, the average particle size of the functional particles is 0.05 μm-5 μm; Preferably, the contact angle between the functional coating and the test electrolyte is 10°-35°; Preferably, the average particle size of the functional particles is 0.1 μm-4 μm.

7. The battery according to any one of claims 1-3, wherein, The functional particles are lithium aluminum titanium phosphate. Based on the total mass of the functional coating, the content of element Al is c(Al), the content of Ti is c(Ti), and 12%≤c(Al)+c(Ti)≤40%; preferably, 15%≤c(Al)+c(Ti)≤36%. And / or, w 3 / [c(Al)+c(Ti)] is 0.08-1; preferably, w 3 / [c(Al)+c(Ti)] is 0.12-0.

8.

8. The battery according to any one of claims 1-3, wherein, The electrolyte also includes lithium salt additives and ethylene carbonate; And / or, based on the total mass of the electrolyte, the mass content of the lithium salt additive is 12%-25%; And / or, based on the total mass of the electrolyte, the mass content of the ethylene carbonate is 0%-10%.

9. The battery according to any one of claims 1-3, wherein, The battery further includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material, the positive electrode active material includes lithium cobalt oxide, the lithium cobalt oxide includes a doping element Q, and Q includes at least one selected from Al, Mg, Ti, Zr, Y, La and W; And / or, the battery further includes a negative electrode sheet, the negative electrode sheet including a negative electrode active material, the negative electrode active material including silicon-carbon material and / or graphite; And / or, the charging cut-off voltage of the battery is greater than or equal to 4.5V.

10. The battery according to any one of claims 1-3, wherein, The diaphragm further includes an adhesive layer, which is located on the outer surface of the functional coating and / or the surface of the base film; And / or, the puncture strength of the base membrane is 150gf-600gf; And / or, the average pore size of the base film is 20nm-60nm; Preferably, the puncture strength of the base membrane is 180gf-500gf; Preferably, the average pore size of the base film is 30nm-50nm.

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