Lithium-ion battery

Abstract

A lithium-ion battery. A negative electrode sheet of the battery comprises a negative electrode current collector and a negative electrode active material layer provided on at least one side surface of the negative electrode current collector, the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises a silicon-carbon material; and an open pore volume of the silicon-carbon material is denoted as x mm3 / g, x satisfying: 0.1≤x≤100. An electrolyte comprises a compound A, and on the basis of the total mass of the electrolyte, the mass ratio of the compound A is denoted as y%; and the chemical formula of the compound A is as shown in formula I and / or formula II, wherein R1, R2, R3, and R4 independently comprise F, a Cl-substituted or unsubstituted hydrocarbon group having 1-8 carbon atoms, or a hydrocarbonoxy group, at least one of R1 and R2 contains F, at least one of R3 and R4 contains F, and x and y satisfy 0.05<y / x≤120. The fast charging performance of the battery can be improved, the thermal safety performance of the battery can be enhanced, and the cycle life of the battery can be prolonged.

Description

A lithium-ion battery Technical Field

[0001] This disclosure relates to the technical field of lithium-ion batteries, and specifically to a lithium-ion battery. Background Technology

[0002] With the world's unwavering pursuit of carbon neutrality, green transportation and the utilization of renewable energy have become crucial issues of our time. Lithium-ion batteries, as efficient, environmentally friendly, and renewable energy storage devices, are gradually becoming a core component in this transformation. The widespread adoption of electric vehicles, electric bicycles, and energy storage devices all rely on the support of lithium-ion batteries. However, with the continuous expansion of application areas and the rapid growth of the market, fast-charging technology and safety of lithium-ion batteries have become a focus of industry attention. Summary of the Invention

[0003] The purpose of this disclosure is to overcome the aforementioned problems in the prior art and to provide a lithium-ion battery that, by adjusting the pore volume of the silicon-carbon material and the mass ratio of compound A to satisfy a specific relationship, can improve the battery's fast-charging performance and cycle performance, and enhance the battery's thermal safety performance.

[0004] To achieve the above objectives, this disclosure provides a lithium-ion battery, the battery comprising a positive electrode, a negative electrode, and an electrolyte;

[0005] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, which includes a silicon-carbon material. The pore volume of the silicon-carbon material is denoted as x mm. 3 / g; x satisfies: 0.1≤x≤100;

[0006] The electrolyte includes compound A, and the mass percentage of compound A based on the total mass of the electrolyte is denoted as y%. The chemical formula of compound A is shown in Formula I and / or Formula II.

[0007] Formula I: Formula II: Among them, R1, R2, R3, and R4 independently include hydrocarbon groups or hydrocarbon oxy groups with 1-8 carbon atoms that are substituted or unsubstituted with F or Cl, and at least one of R1 and R2 contains F, and at least one of R3 and R4 contains F;

[0008] x and y satisfy: 0.05 < y / x ≤ 120.

[0009] The adoption of the above-described technical solution in this disclosure has the following beneficial effects:

[0010] (1) The lithium-ion battery provided in this disclosure can improve the fast charging performance, thermal safety performance and cycle life of the battery by adjusting the pore volume of silicon-carbon material and the mass ratio of compound A to satisfy a specific relationship.

[0011] (2) The lithium-ion battery provided in this disclosure can suppress the breakage of the negative electrode current collector caused by the expansion of the negative electrode when the mass ratio of fluoroethylene carbonate in the electrolyte, the mass ratio of silicon in the negative electrode active material, and the tensile strength of the negative electrode current collector are further adjusted to meet a specific relationship, thereby further improving the thermal safety performance of the battery.

[0012] (3) The lithium-ion battery provided in this disclosure further provides a linear recessed region on the negative electrode active material layer. When the width of the linear recessed region is adjusted to a specific range, the stress caused by the volume expansion of the silicon-containing negative electrode material can be dispersed, thereby improving the cycle life of the battery.

[0013] (4) The lithium-ion battery provided in this disclosure, when compound B is added to the electrolyte and the mass ratio of compound B is adjusted to a specific range, can suppress the formation of lithium dendrites, reduce the risk of battery thermal runaway, and improve battery cycle life.

[0014] The endpoints and any values ​​of the ranges disclosed in this disclosure are not limited to the precise ranges or values, and should be understood to include values ​​close to those ranges or values. For numerical ranges, endpoint values ​​of various ranges, endpoint values ​​of 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. In this document, unless otherwise specified, data ranges include endpoints. Attached Figure Description

[0015] Figure 1 shows a schematic diagram of the structure of the negative electrode active material layer in an example of this disclosure.

[0016] Figure labels: 1. Linear depression region; 2. Pits; 3. Negative electrode active material layer. Detailed Implementation

[0017] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0018] Unless otherwise defined, all scientific and technical terms used in this disclosure have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure relates.

[0019] In this disclosure, the terms "battery," "lithium battery," "lithium-ion battery," and "lithium-ion secondary battery" all have the same meaning and refer to lithium-ion secondary batteries, which typically include electrode components (e.g., positive electrode, negative electrode, and separator), a container (housing) housing the electrode components, and an electrolyte.

[0020] In this disclosure, the term "open pore volume" refers to the volume of pores in the internal pore structure of a silicon-carbon material that are connected to the outside, excluding the volume of closed pores that are not connected to the outside.

[0021] In this disclosure, the term "hydrocarbon group" refers to a group formed by replacing hydrogen atoms in a hydrocarbon with other groups (such as alkyl, halogen, hydroxyl, nitro, etc.).

[0022] In this disclosure, the term "alkoxy group" or "alkoxy group" refers to a group formed by attaching a hydrocarbon group to an oxygen atom.

[0023] This disclosure provides a lithium-ion battery, the battery comprising a positive electrode, a negative electrode, and an electrolyte;

[0024] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, which includes a silicon-carbon material. The pore volume of the silicon-carbon material is denoted as x mm. 3 / g; x satisfies: 0.1≤x≤100;

[0025] The electrolyte includes compound A, and the mass percentage of compound A based on the total mass of the electrolyte is denoted as y%. The chemical formula of compound A is shown in Formula I and / or Formula II.

[0026] Formula I: Formula II: Among them, R1, R2, R3, and R4 independently include alkyl groups or alkyloxy groups with 1 to 8 carbon atoms that are substituted or unsubstituted with F or Cl, preferably alkyl groups or alkyloxy groups with 4 or 6 carbon atoms, and at least one of R1 and R2 contains F, and at least one of R3 and R4 contains F.

[0027] x and y satisfy: 0.05 < y / x ≤ 120.

[0028] According to the embodiments of this disclosure, the value of y / x can be, for example, 0.055, 0.06, 0.07, 0.08, 0.09, 0.1, 0.5, 1, 5, 10, 20, 40, 60, 80, 100, 110, 115, 116, 117, 118, 119, 120, or any point value within the range of the above pairs of point values.

[0029] According to embodiments of this disclosure, the pore volume x of the silicon-carbon material satisfies: 0.1 ≤ x ≤ 100; the pore volume of the silicon-carbon material can be, for example, 0.1 mm. 3 / g, 0.3mm 3 / g, 0.5mm 3 / g, 1mm 3 / g, 5mm 3 / g, 10mm 3 / g, 20mm 3 / g, 30mm 3 / g, 40mm 3 / g, 50mm 3 / g, 60mm 3 / g, 70mm 3 / g, 80mm 3 / g, 90mm 3 / g, 95mm 3 / g, 100mm 3 / g or any point value within the range formed by the above pairs of point values, preferably 1≤x≤70.

[0030] According to embodiments of this disclosure, the hydrocarbon group having 1-8 carbon atoms includes, but is not limited to, alkyl groups having 1-8 carbon atoms, alkenyl groups having 1-8 carbon atoms, and 1-6 alkynyl groups having 1-8 carbon atoms; the hydroxyl group having 1-8 carbon atoms includes, but is not limited to, alcohol hydroxyl groups having 1-8 carbon atoms, ether groups having 1-8 carbon atoms, aldehyde groups having 1-8 carbon atoms, and ketone groups having 1-8 carbon atoms.

[0031] Silicon-carbon materials undergo significant volume expansion during battery charging and discharging. This not only causes cracks in the structure of the negative electrode active material, affecting the rapid transport of lithium ions, but also exacerbates the side reactions between the negative electrode active material and the electrolyte, generating more water and acid products that further intensify the side reactions, making the battery more susceptible to thermal runaway or explosion.

[0032] The silicon-carbon material disclosed herein has an open-pore structure with a certain range of open-pore volume, which can buffer the volume expansion of the silicon-carbon material during charging and discharging, reduce the structural damage of the negative electrode material caused by volume changes, reduce the occurrence of side reactions, and improve battery safety performance. Furthermore, the silicon-carbon material provides more lithium storage sites, resulting in lower diffusion resistance of lithium ions within the negative electrode material and a higher rate of lithium ion extraction and insertion at the battery negative electrode, thus improving the battery's charging and discharging efficiency and fast-charging performance. Adding compound A to the electrolyte, where compound A is a cyclic carbonate and / or linear carboxylic acid ester with low viscosity and high fluidity, allows compound A to effectively fill the open-pore structure of the silicon-carbon material, increasing the rate of lithium ion insertion. The protective film formed by compound A on the negative electrode surface extends into the open-pore structure of the silicon-carbon material, effectively suppressing the expansion of the silicon-carbon material and reducing negative electrode expansion. It also isolates the silicon-carbon material from acids, moisture, oxygen, or other substances generated by side reactions in the battery, reducing further contact between the silicon-carbon material and side reaction products, thus preventing rapid heat accumulation. Moreover, the high fluidity of compound A allows for timely heat dissipation from the negative electrode, improving the battery's thermal safety performance. The silicon-carbon material and compound A work synergistically to effectively improve the battery's fast-charging performance and cycle life, and enhance battery safety.

[0033] According to embodiments of this disclosure, x and y satisfy the condition: 0.1 < y / x ≤ 100. Further satisfying the above range for x and y can further enhance the synergistic effect between the pore volume of the silicon-carbon material and compound A, further improve the battery's fast-charging performance, and enhance the battery's thermal safety performance.

[0034] According to the embodiments of this disclosure, adjusting the pore volume of the silicon-carbon material to satisfy 0.1≤x≤100 avoids the situation where the pore volume of the silicon-carbon material is too large when x>100, making the battery negative electrode more susceptible to external environmental factors such as moisture and oxygen. These environmental factors can exacerbate side reactions, produce harmful substances or gases, and affect the safety performance of the battery. Moreover, when the pore volume of the silicon-carbon material is within the above range, it can mitigate the volume change of silicon particles during charging and discharging, reduce the structural damage of the negative electrode material caused by volume changes, reduce the risk of material pulverization and peeling, and thus further improve the cycle life of the battery.

[0035] According to the embodiments of this disclosure, the open-pore volume of silicon-carbon materials can be determined using a low-temperature nitrogen adsorption method, specifically including the following steps: pulverizing the silicon-carbon material into powder, adding approximately 1g of sample to a sample tube, weighing the sample and sample tube, and recording the weight as m1; placing the sample tube in a degassing station for degassing treatment, and after degassing, weighing the sample tube to obtain the mass of the degassed sample, and recording it as m2; using a Tri Star II specific surface area analyzer for testing, inputting the measured sample mass data (m1, m2), starting the instrument to measure the sample, and the analyzer will automatically perform isothermal adsorption and desorption analysis, calculating the specific surface area and open-pore volume of the silicon-carbon material by measuring the amount of nitrogen adsorbed on the sample surface.

[0036] According to embodiments of this disclosure, the mass percentage y of compound A satisfies: 5≤y≤30, that is, the mass percentage of compound A can be, for example, 5%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, or any value within the range of the above two-to-one values. Further adjusting the mass percentage of compound A to meet the above-mentioned range can avoid the following: when y < 5, the content of compound A in the electrolyte is too low, resulting in high electrolyte viscosity and impedance, low lithium ion migration rate, insufficient film formation of compound A on the negative electrode surface, and unstable interfacial film structure, which cannot adequately prevent side reactions at the negative electrode, causing rapid heat accumulation and the generation of more gas, leading to battery thermal runaway or explosion safety issues. Conversely, when y > 30, the content of compound A in the electrolyte is too high, reducing the proportion of other effective components, which is detrimental to lithium ion transport and storage in the electrolyte, leading to reduced battery capacity. It can also easily lead to the formation of an excessively thick SEI film on the electrode surface, increasing interfacial impedance, hindering lithium ion migration, and degrading the battery's charge-discharge performance at high rates. Adjusting the mass percentage of compound A to meet the above-mentioned range can improve the battery's charge-discharge efficiency and enhance its thermal safety performance.

[0037] According to embodiments of this disclosure, compound A represented by formula I includes at least one of the following compounds:

[0038] According to embodiments of this disclosure, compound A represented by formula II includes at least one of the following compounds:

[0039] According to embodiments of this disclosure, compound A comprises the compound shown in Formula I and the compound shown in Formula II, with a mass ratio of 1:(1-4), for example, 1:1, 1:2, 1:3, 1:4, or any value within the range of the aforementioned pairs. Further adjusting the mass ratio of the compound shown in Formula I and the compound shown in Formula II to satisfy the aforementioned range, the higher electrochemical window of compound A (Formula II) can improve the stability of the electrolyte at high voltages, while compound A (Formula I) is relatively easier to form a film on the electrode surface, providing protection for the electrode. The combined use of both can further improve the battery's high-voltage resistance, enhance its thermal safety, and also improve its charge / discharge efficiency and cycle life.

[0040] According to embodiments of this disclosure, compound A is a combination of I-2 and II-1. Extensive experimental research has revealed that when compound A is selected as a combination of I-2 and II-1, and their mass ratio is in the range of 1:(1-4), compound A can better exert its function, further improving the fast-charging performance and safety performance of the battery.

[0041] According to embodiments of this disclosure, the sphericity of the silicon-carbon material is 0.5-1. For example, the sphericity of the silicon-carbon material can be any value within the range of 0.5, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.86, 0.88, 0.90, 0.92, 0.94, 0.96, 0.98, 0.99, 0.999, 1, or any value within the range of any pair of values ​​mentioned above. The sphericity of the silicon-carbon material can affect the flatness and burrs on the surface of the negative electrode. Limiting the sphericity of the silicon-carbon material within the above range can promote the uniform deposition of lithium ions on the negative electrode, improving the fast-charging performance and safety performance of the battery.

[0042] According to embodiments of this disclosure, the method for testing sphericity Q may include the following steps: analyzing the image of each particle in a SEM photograph of the composite material at a certain magnification (e.g., 2500x) using image processing software (such as Image Pro Plus) to obtain the perimeter and area of ​​each particle, calculating the perimeter equivalent radius r1 and area equivalent radius r2 of each particle respectively, then the sphericity S of each particle is S = r2 / r1, and calculating the average value of the measured sphericity of each particle to obtain the average sphericity of the silicon-carbon composite material.

[0043] According to embodiments of this disclosure, the Dv10 of the silicon-carbon material is 1μm-10μm. For example, the Dv10 of the silicon-carbon material can be 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, or any value within the range of any two of the above values, preferably 1μm-8μm. Further adjusting the Dv10 of the silicon-carbon material to meet the above range can optimize the specific surface area of ​​the silicon-carbon material, increase the effective reaction interface of the silicon-carbon material, and is beneficial to improving the energy density and cycle life of the battery; at the same time, it improves the electrode structure, increases the lithium-ion transport efficiency, further improves the charge and discharge efficiency of the battery, and enhances the fast-charging performance of the battery.

[0044] According to embodiments of this disclosure, the silicon-carbon material includes a dopant element M, which includes at least one of K, Ca, and Na. Preferably, the content of the dopant element M is 100ppm-10000ppm, and the content of the dopant element M can be, for example, 100ppm, 200ppm, 300ppm, 500ppm, 1000ppm, 2000ppm, 4000ppm, 6000ppm, 8000ppm, 10000ppm, or any value within the range of any two of the above values. Further adjusting the content of the dopant element in the silicon-carbon material to meet the above range can improve the electronic conductivity of the positive electrode active material, increase the lithium-ion transport efficiency between particles of the negative electrode active material, stabilize the material structure, reduce the formation of lattice defects, reduce the internal resistance of the silicon-carbon material, reduce heat generation, and improve the thermal safety performance of the battery.

[0045] According to embodiments of this disclosure, the dopant content of the silicon-carbon material can be determined using EDS (Energy Dispersive X-ray Spectroscopy) testing; and / or using ICP (Inductively Coupled Plasma) testing.

[0046] This research has found that silicon-carbon materials possess a certain pore volume, which can alleviate the volume change of silicon particles during charging and discharging to some extent, reducing material structure damage caused by volume changes. However, excessively large pore volumes in silicon-carbon materials can exacerbate the negative electrode side reactions, affecting battery safety performance. Therefore, relying solely on adjusting the pore volume of silicon-carbon materials to alleviate negative electrode volume expansion has limited effect. Moreover, as the silicon content in the negative electrode material increases, the volume expansion of the negative electrode material will generate significant stress on the negative electrode current collector, causing it to fracture and increasing the risk of battery thermal runaway. Therefore, to further alleviate the volume expansion of the negative electrode material, this disclosure further proposes:

[0047] According to embodiments of this disclosure, the tensile strength of the negative electrode current collector is denoted as σMPa; σ satisfies: 450≤σ≤750. The tensile strength of the negative electrode current collector can be, for example, 450MPa, 475MPa, 500MPa, 525MPa, 550MPa, 575MPa, 600MPa, 625MPa, 650MPa, 675MPa, 700MPa, 725MPa, 750MPa, or any value within the range of any two of the above values. Conventional negative electrode current collectors in the art have tensile strengths between 300MPa and 450MPa; this disclosure uses a negative electrode current collector with high tensile strength.

[0048] Based on the condition that x and y satisfy 0.05 < y / x ≤ 120, this disclosure further selects a negative electrode current collector with tensile strength satisfying the above range. During battery charging and discharging, this current collector can better withstand the mechanical stress generated by the volume expansion of the negative electrode material, reducing battery thermal runaway caused by deformation or breakage of the negative electrode current collector. Furthermore, a negative electrode current collector with high tensile strength can achieve a more uniform stress distribution when facing the stress generated by the volume change of the electrode material during charging and discharging, reducing stress concentration in the contact area between the electrode and the negative electrode current collector. This avoids adhesion failure and peeling of the negative electrode active material caused by stress concentration, further improving the battery's cycle life.

[0049] According to embodiments of this disclosure, a high-tensile-strength negative electrode current collector is used as a high-strength copper foil, or a coating that improves tensile strength is applied to the surface of the copper foil. Exemplarily, the coating includes, but is not limited to, one or more of Cr2O3, graphite, and polyimide coatings.

[0050] According to embodiments of this disclosure, the thickness of the negative electrode current collector is 2μm-10μm, for example, it can be 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, or any value within the range of any two of the above values, preferably 3μm-8μm. Further adjusting the thickness of the negative electrode current collector to meet the above range helps to reduce the electrode thickness, thereby reducing the overall volume and weight of the battery and increasing the energy density of the battery.

[0051] According to the embodiments of this disclosure, the method for testing the tensile strength of the negative electrode current collector specifically includes the following steps: cutting the current collector into strips of 15mm ± 0.2mm; using a WD-D3 type electronic universal testing machine with a 50mm gap between the upper and lower clamps, clamping both ends of the current collector with the clamps respectively, starting the test at a speed of 100mm / min until the test stops, and recording the tensile strength (breaking strength) σ; taking the average of 3 tests with an error not exceeding 10% as the tensile strength of the negative electrode current collector.

[0052] As the silicon content in the negative electrode material increases, the expansion problem becomes more pronounced. This not only generates significant stress on the current collector, increasing the risk of battery thermal runaway, but also causes the SEI film on the electrode surface to rupture, leading to continuous electrolyte consumption to form a new SEI film. Furthermore, because the electrolyte is in direct contact with the negative electrode, continuous side reactions occur between the negative electrode material and the electrolyte, resulting in a rapid decrease in battery capacity. To further reduce electrolyte side reactions, optimize battery cycle performance, and improve battery thermal safety, this disclosure further proposes:

[0053] According to embodiments of this disclosure, the silicon content in the negative electrode active material is denoted as m%; the electrolyte includes fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate based on the total mass of the electrolyte is denoted as n%; m, n, and σ satisfy: 10 < (n + σ) / m ≤ 500. Exemplarily, the value of (n + σ) / m can be, for example, 10.1, 10.5, 11, 13, 15, 20, 50, 100, 150, 200, 250, 300, 350, 400, 450, 470, 490, 495, 500, or any value within the range of any two of the above values. The fluoroethylene carbonate in the electrolyte can form an effective solid electrolyte interphase (SEI) film on the electrode surface, reducing the rapid decrease in battery capacity caused by side reactions. Further adjustments to m, n, and σ satisfy the above relationship: the higher the silicon content m, the greater the negative electrode volume expansion. The content n of fluoroethylene carbonate and the tensile strength σ of the negative electrode current collector also need to be increased accordingly, i.e., n+σ increases, in order to alleviate the problems of electrolyte side reactions caused by increased negative electrode expansion and battery corner cracking caused by stress on the current collector. Therefore, fluoroethylene carbonate and the tensile strength of the negative electrode current collector work together to further improve the thermal safety problem caused by the volume expansion of silicon negative electrode and improve the cycle life of the battery.

[0054] According to the embodiments of this disclosure, the silicon content percentage m satisfies: 1 < m ≤ 50. The silicon content percentage can be, for example, 1.001%, 1.01%, 1.05%, 1.1%, 1.5%, 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 46%, 47%, 48%, 49%, 50%, or any value within the range of any two of the above values. Further adjusting the silicon content percentage to satisfy the above range avoids excessively high silicon content when m > 50. This prevents more significant volume changes in the silicon-containing anode material during charge and discharge, leading to particle breakage of the anode material, separation of the anode active material from the current collector, and the formation of an unstable solid electrolyte interphase (SEI) film. The rupture of the SEI film results in continuous consumption of the electrolyte, significantly affecting the cycle stability and performance of the battery.

[0055] According to embodiments of this disclosure, the silicon content in the negative electrode active material can be tested using thermogravimetric analysis (TGA), for example, using a Shimadzu DTG-60 TGA analyzer. The specific steps include: taking a 5mg sample, using air as the atmosphere, heating from room temperature to 900℃ at a rate of 10℃ / min and holding at that temperature for 40min, and determining the final weight percentage N after the entire test. The relationship between the silicon content H and N is: H = 7N / 15.

[0056] According to the embodiments of this disclosure, the mass percentage n of fluoroethylene carbonate satisfies: 0 < n ≤ 20. The mass percentage of fluoroethylene carbonate can be, for example, 0.001%, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 5%, 10%, 15%, 16%, 17%, 18%, 19%, 20%, or any value within the range of any two of the above values. Further adjusting the mass percentage of fluoroethylene carbonate to satisfy the above range can avoid situations where n > 20, resulting in excessive fluoroethylene carbonate content in the electrolyte, leading to an overly thick SEI film that hinders lithium ion migration and reduces battery fast-charging performance; and can also avoid the risk of excessive fluoroethylene carbonate decomposing to generate gas and release heat, leading to increased internal battery pressure and thermal runaway.

[0057] To further disperse the stress caused by the volume expansion of the silicon-containing anode material and improve the cycle life of the battery, in some embodiments, a linear recessed region is provided on the anode active material layer. The width of the linear recessed region is 50μm-200μm, and can be, for example, 50μm, 75μm, 100μm, 125μm, 150μm, 175μm, 200μm, or any value within the range of any two of the above values. Further adjusting the width of the linear recessed region on the anode active material layer to meet the above range not only provides space for anode expansion and reduces the pressure on the anode current collector, but also increases the contact area between the anode material and the electrolyte, increases lithium-ion transport efficiency, improves the electrolyte retention capacity of the battery, and thus improves the cycle performance of the battery.

[0058] According to embodiments of this disclosure, the depth of the linear recessed region is 3μm-45μm. For example, the depth of the linear recessed region can be any value within the range of 3μm, 5μm, 8μm, 9μm, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm, 22μm, 24μm, 26μm, 28μm, 30μm, 32μm, 34μm, 36μm, 38μm, 40μm, 42μm, 44μm, 45μm, or any value within the range of the aforementioned values. Further adjusting the depth of the linear recessed region to satisfy the above range can optimize the lithium-ion transport path, reduce the local current density on the negative electrode surface, reduce polarization, thereby improving the battery's fast-charging performance, reducing lithium plating, and increasing cycle life.

[0059] According to an embodiment of this disclosure, as shown in FIG1, a linear recessed region 1 is provided on the negative electrode active material layer 3 of the negative electrode sheet, and a plurality of spaced pits 2 are provided in the linear recessed region 1. The width of the linear recessed region 1 is the size of the linear recessed region along the width direction of the negative electrode sheet.

[0060] In this disclosure, the depth of the linear recessed region is the vertical distance from the surface of the negative electrode active material layer to the bottom of the linear recessed region; the depth of the linear recessed region is less than the thickness of the negative electrode active material layer, and the linear recessed region does not penetrate the negative electrode active material layer.

[0061] According to the embodiments of this disclosure, the linear recessed areas are arranged in a uniformly spaced manner, or the arrangement can be adjusted according to actual needs, such as partially uniformly spaced and partially non-uniformly spaced.

[0062] This disclosure reveals that while the aforementioned silicon-carbon anode material can provide more lithium storage sites, the complex pore structure and diffusion paths of lithium ions within the material during rapid and repeated lithium ion extraction and insertion lead to uneven lithium ion concentration distribution during high-rate charge and discharge, resulting in lithium dendrite formation. This not only causes loss of active materials and accelerated capacity reduction but also raises safety concerns. To further address these issues, this disclosure proposes:

[0063] According to embodiments of this disclosure, the electrolyte further includes compound B, the chemical formula of which is shown in Formula III:

[0064] Among them, X1, X2, and X3 are independent. Furthermore, at least one of X1, X2, and X3 contains an S group, and A1, A2, and A3 are independently selected from alkyl groups connected by O, S, or C.

[0065] In this disclosure, the C-connected alkyl group refers to any one of A1, A2, and A3, where C is directly connected to an adjacent C and X (any one of X1, X2, and X3), for example, formula III-9.

[0066] In this disclosure, the C-linked alkyl group is an alkyl group having 1-3 carbon atoms, such as methyl, ethyl, and propyl.

[0067] According to embodiments of this disclosure, the mass percentage of compound B, based on the total mass of the electrolyte, is 0.1%-5%. For example, the mass percentage of compound B can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any value within the range of any two of the above values. Further addition of compound B to the electrolyte, and adjusting the mass percentage of compound B to meet the above range, allows compound B to participate in the formation of a protective film on the negative electrode surface containing micropores or channels. These micropores or channels provide additional transport paths for lithium ions, and the micropores or channels of the protective film may communicate with the openings in silicon carbon, further reducing the diffusion barrier, promoting uniform deposition of lithium ions, thereby improving battery fast charging and cycle life.

[0068] According to embodiments of this disclosure, compound B includes at least one of the following compounds:

[0069] According to embodiments of this disclosure, compound B, represented by Formula III-1, is preferred.

[0070] According to embodiments of this disclosure, the electrolyte further includes nitrile compounds; the mass percentage of the nitrile compounds, based on the total mass of the electrolyte, is 0.1%-7%, and the mass percentage of the nitrile compounds can be, for example, 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, or any value within the range of any pair of values ​​mentioned above. When nitrile compounds are added to the electrolyte and further adjusted to meet the above range, the nitrile compounds exhibit strong oxidation resistance, which can improve the electrochemical window of the electrolyte, thereby improving the high-voltage resistance of the electrolyte, reducing side reactions under high voltage, and enhancing the safety performance of the battery.

[0071] In this disclosure, the types of nitrile compounds are not specifically limited. Exemplarily, the nitrile compounds may be selected from at least one of mononitrile additives, dinitrile additives, and trinitrile additives. The mononitrile additives include, but are not limited to, at least one of benzonitrile, p-toluenenitrile, and 3,5-difluorobenzonitrile. The dinitrile additives include, but are not limited to, at least one of adiponitrile (AND), succinate (SN), and ethylene glycol bis(propionitrile) ether. The trinitrile additives include, but are not limited to, at least one of 1,3,6-hexanetrionitrile (HTCN), 1,2,6-hexanetrionitrile, and 1,2,3-tris(2-acrylonitrile ethoxy)propane.

[0072] According to embodiments of this disclosure, the electrolyte further includes sulfonic acid compounds; the mass percentage of the sulfonic acid compounds, based on the total mass of the electrolyte, is 0.1%-5%, and the mass percentage of the sulfonic acid compounds can be, for example, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or any value within the range of any two of the above values. When sulfonic acid compounds are added to the electrolyte and further adjusted to meet the above range, the sulfonic acid compounds can undergo a reduction reaction on the negative electrode surface during battery charging and discharging, especially during the first charge, to form a stable SEI film. This SEI film can inhibit the co-intercalation and reductive decomposition of solvent molecules in the electrolyte at the negative electrode, thereby reducing the generation of side reactions and improving the thermal safety performance of the battery.

[0073] In this disclosure, the types of sulfonic acid compounds are not specifically limited. For example, the sulfonic acid compounds may be selected from sulfonate additives. The sulfonate additives include, but are not limited to, 1,3-propanesulfonolactone, 1-propene-1,3-sulfonolactone, 5-methyloxathiapentane 2,2-dioxide, 1,3-propenesulfonolactone, 2,4-butanesulfonolactone, 1,4-butanesulfonolactone, 1,3-butanesulfonolactone, and fluoro1,3-propanesulfonolactone.

[0074] The technical solutions of this disclosure will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this disclosure.

[0075] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0076] The present disclosure is described in detail below with reference to specific embodiments, which are intended to understand rather than limit the present disclosure.

[0077] Example 1-1

[0078] 1) Preparation of positive electrode sheet

[0079] Lithium cobalt oxide (LiCoO2), polyvinylidene fluoride (PVDF), super P (SP), and carbon nanotubes (CNT) were mixed in a mass ratio of 96:2:1.5:0.5. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until it formed a uniform and fluid positive electrode slurry. The positive electrode slurry was then uniformly coated onto both surfaces of an aluminum foil. The coated aluminum foil was dried, and then rolled and slit to obtain the desired positive electrode sheet.

[0080] 2) Preparation of negative electrode sheet

[0081] Artificial graphite, silicon-carbon composite material, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP), and single-walled carbon nanotubes (SWCNTs) were mixed in a mass ratio of 74.5:20:2.5:1.5:1:0.5, and deionized water was added. The mixture was stirred in a vacuum mixer to obtain a negative electrode active slurry. The negative electrode active slurry was uniformly coated on both surfaces of the negative electrode current collector (tensile strength 500 MPa). The coated copper foil was dried at room temperature and then transferred to an 80°C oven for 10 hours. After cold pressing and slitting, the negative electrode sheet was obtained.

[0082] The preparation steps of the negative electrode current collector are as follows: First, a copper sulfate electrolyte is prepared. Then, in the electrolytic cell of the foil forming machine, the copper sulfate electrolyte, under the action of direct current, causes copper ions to gain electrons and deposits a foil (copper) with a thickness of 6μm on the surface of the cathode roller. After the continuous rotation of the cathode roller, the copper foil is continuously peeled off. The copper foil is then immersed in an electroplating tank containing chromium plating solution. A chromium protective layer with a thickness of 5nm is plated on the surface of the copper foil through an electrochemical reaction. Subsequently, a graphite carbon layer with a thickness of 6nm is coated on the surface of the copper foil by spraying to obtain a negative electrode current collector with a tensile strength of 500MPa.

[0083] 3) Preparation of electrolyte

[0084] In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), EC, PC, DEC, and PP were mixed uniformly in a mass ratio of 10:20:20:50. Then, 15% of compounds of formula I-2 and II-6 (with a mass ratio of 1:1) based on the total mass of the electrolyte were added and mixed uniformly. Next, 14 wt% of fully dried LiPF6 based on the total mass of the electrolyte, 10% of fluoroethylene carbonate based on the total mass of the electrolyte, and 1% of ADN, 1.5% of SN, 2.5% of HTCN, and 3% of 1,3-propanesulfonyl lactone based on the total mass of the electrolyte were added. After thorough mixing, the electrolyte was tested for moisture and free acid and found to be within acceptable limits to obtain the desired electrolyte.

[0085] 4) Battery fabrication

[0086] The positive electrode sheet from step 1), the negative electrode sheet from step 2), and the separator are stacked in the order of positive electrode sheet, separator, and negative electrode sheet, and then wound to obtain a battery cell. The battery cell is placed in an outer packaging aluminum foil, and the electrolyte from step 3) is injected into the outer packaging. After vacuum sealing, settling, formation, shaping, and sorting, a lithium-ion battery is obtained. The charge / discharge range of the battery disclosed in this invention is 3.0-4.53V.

[0087] 5) Test the battery

[0088] i) 25℃ 4C cycle test

[0089] The batteries obtained in the examples and comparative examples were discharged at 25°C with a current of 0.5C to 3.0V. They were then charged at a constant current of 5C to a voltage of 4.53V, followed by constant voltage charging at 4.53V to a current of 0.05C. After resting for 5 minutes, they were discharged at a constant current of 5C to a voltage of 3.0V, completing one charge-discharge cycle. The discharge capacity of week 1 was measured as x mAh, and the discharge capacity of week N was measured as y mAh. The capacity of week N was divided by the capacity of week 1 to obtain the cycle capacity retention rate R = y / x. The number of battery cycles was recorded when the capacity retention rate reached 80%.

[0090] ii) Hot box performance test

[0091] At room temperature, the batteries obtained in the examples and comparative examples were charged to 4.53V at a constant current of 1C, left to stand for 60 minutes, and their appearance was inspected and photographed. Then, the temperature was increased to 132℃±2℃ at a rate of 3℃ / min±2℃ / min and held for 60 minutes. The samples were observed; those that did not leak, smoke, ignite, or explode were considered to have passed the test. Ten samples were tested for each example or comparative example, and the pass rate of the hot-box performance test was recorded.

[0092] iii) Cyclic corner crack test

[0093] First, observe whether the four corners of the battery show signs of cracking after cyclic testing (25℃ 4C cycle test). If no obvious cracks are found, use a 3D profilometer to scan the battery and observe whether there are cracks at the four corners of the internal core to determine if corner cracks exist. Ten samples are tested for each embodiment or comparative example, and the probability of corner cracks is recorded.

[0094] iv) Battery lithium plating test

[0095] The batteries that had undergone cycling (25°C 4C cycle test) were recharged (under the same charging conditions as the 25°C 4C cycle test), and then dissected to observe whether lithium plating occurred at the negative electrode interface. Ten samples were tested for each example or comparative example, and the probability of lithium plating was recorded.

[0096] Examples 1-2 and Comparative Examples 1-2 were performed in accordance with Example 1-1, with the main differences shown in Table 1. In Example 1, the pore volume of the silicon-carbon material was changed; in Example 2, the mass percentage of compound A in the electrolyte was changed. In Comparative Example 1, the mass percentage of compound A in the electrolyte was too small, not meeting the formula range. In Comparative Example 2, compound A was not introduced into the electrolyte.

[0097] Table 1

[0098] Note: " / " indicates that the corresponding parameter was not tested.

[0099] As can be seen from Table 1, this disclosure can improve the fast charging performance, thermal safety performance and cycle life of the battery by adjusting the pore volume of the silicon-carbon material and the mass ratio of compound A in the electrolyte.

[0100] Example 3 was performed in accordance with Examples 1-1, with the main differences shown in Table 2. In Example 3, the type of compound A was changed.

[0101] Table 2

[0102] As can be seen from Table 2, compound A that satisfies the structure of Formula I can play a similar role. When compound A of Formula I and compound A of Formula II are used in combination, the battery can have better thermal safety performance.

[0103] Examples 4-6 were performed in accordance with Examples 1-1, with the main differences shown in Table 3. Specifically, Example 4 varied the tensile strength of the negative electrode current collector. Example 5 varied the silicon content in the negative electrode active material. Example 6 varied the mass percentage of fluoroethylene carbonate (FEC) in the electrolyte.

[0104] Table 3

[0105] Note: " / " indicates that the corresponding parameter was not tested.

[0106] As can be seen from Table 3, by adjusting the mass ratio of fluoroethylene carbonate in the electrolyte, the mass ratio of silicon in the negative electrode active material, and the tensile strength of the negative electrode current collector, this disclosure can suppress corner cracks caused by negative electrode expansion, reduce lithium plating, and further improve battery thermal safety and enhance battery thermal safety performance.

[0107] Example 7 was performed in accordance with Example 1-1, with the main differences shown in Table 4. In Example 7, compound B was further introduced into the electrolyte, and the mass percentage of compound B was changed, based on Example 1-1.

[0108] Table 4

[0109] As can be seen from Table 3, by further adding compound B to the electrolyte and adjusting the mass ratio of compound B in the electrolyte, this disclosure can suppress lithium dendrite formation, reduce lithium plating, and improve battery cycle life and thermal safety performance.

[0110] Example 8 was performed in accordance with Examples 7-1, with the main differences shown in Table 5. In Example 8, the type of compound B was changed.

[0111] Table 5

[0112] As can be seen from Table 5, compound B, which satisfies the structure of Formula III, can play a similar role, improving the cycle life and thermal safety performance of the battery and reducing lithium plating.

[0113] Example 9 was performed in accordance with Examples 7-1, with the main differences shown in Table 6. In Example 9, a linear recessed region was further formed on the negative electrode active material layer of the negative electrode sheet. The specific operation steps were as follows: A continuous laser was used to form an arc-shaped groove on the surface of the negative electrode active layer of the obtained negative electrode sheet, parallel to the width direction of the negative electrode sheet. The spacing between adjacent grooves was 2 mm, the width of the groove was 100 μm, and the depth of the groove was 15 μm.

[0114] Table 6

[0115] As can be seen from Table 6, by further setting a linear recessed region in the negative electrode active material layer, this disclosure can increase the contact area between the negative electrode material and the electrolyte, thereby improving the cycle life of the battery.

[0116] Example 10 was performed in accordance with Example 1-1, with the main differences shown in Table 7. In Example 10, the mass ratio of nitrile compounds and / or sulfonic acid compounds in the electrolyte was changed, while the mass ratio of ADN, SN, and HTCN was the same as in Example 1-1.

[0117] Table 7

[0118] Note: " / " indicates that the corresponding parameter was not tested.

[0119] As can be seen from Table 7, this disclosure can improve the fast charging performance, thermal safety performance and cycle life of the battery by adjusting the mass ratio of nitrile compounds and sulfonic acid compounds in the electrolyte.

[0120] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0121] The above description is merely a preferred embodiment of this disclosure and is not intended to limit this disclosure. Any modifications or equivalent substitutions made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. A lithium-ion battery, characterized in that, The battery includes a positive electrode, a negative electrode, and an electrolyte; The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, which includes a silicon-carbon material. The pore volume of the silicon-carbon material is denoted as x mm. 3 / g; x satisfies: 0.1≤x≤100; The electrolyte includes compound A, and the mass percentage of compound A based on the total mass of the electrolyte is denoted as y%. The chemical formula of compound A is shown in Formula I and / or Formula II. Among them, R1, R2, R3, and R4 independently include hydrocarbon groups or hydrocarbon oxy groups with 1-8 carbon atoms that are substituted or unsubstituted with F or Cl, and at least one of R1 and R2 contains F, and at least one of R3 and R4 contains F; x and y satisfy: 0.05 < y / x ≤ 120.

2. The lithium-ion battery according to claim 1, characterized in that, x and y satisfy: 0.1 < y / x ≤ 100.

3. In the lithium-ion battery according to claim 1 or 2, x satisfies: 1 ≤ x ≤ 70; And / or, y satisfies: 5≤y≤30.

4. The lithium-ion battery according to any one of claims 1-3, characterized in that, Compound A represented by Formula I includes at least one of the following compounds:

5. The lithium-ion battery according to any one of claims 1-4, characterized in that, Compound A, represented by Formula II, includes at least one of the following compounds:

6. The lithium-ion battery according to any one of claims 1-5, characterized in that, The compound A comprises the compound shown in Formula I and the compound shown in Formula II, with a mass ratio of 1:(1-4).

7. The lithium-ion battery according to any one of claims 1-6, characterized in that, The tensile strength of the negative electrode current collector is denoted as σMPa; σ satisfies: 450≤σ≤750; Preferably, the thickness of the negative electrode current collector is 2μm-10μm.

8. The lithium-ion battery according to any one of claims 1-7, characterized in that, In the negative electrode active material, the content of silicon element is recorded as m%. The electrolyte includes fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate based on the total mass of the electrolyte is denoted as n%. m, n, and σ satisfy: 10 < (n + σ) / m ≤ 500.

9. The lithium-ion battery according to claim 8, characterized in that, m satisfies: 1 < m ≤ 50; And / or, n satisfies: 0.1 < n ≤ 20.

10. The lithium-ion battery according to any one of claims 1-9, characterized in that, The sphericity of the silicon-carbon material is 0.5-1; And / or, the Dv10 of the silicon-carbon material is 1μm-10μm.

11. The lithium-ion battery according to any one of claims 1-10, characterized in that, The silicon-carbon material includes a doping element M, and the doping element M includes at least one of K, Ca, and Na. Preferably, the content of the dopant element M is 100ppm-10000ppm.

12. The lithium-ion battery according to any one of claims 1-11, characterized in that, The electrolyte also includes compound B, the chemical formula of which is shown in Formula III: Among them, X1, X2, and X3 are independent. Furthermore, at least one of X1, X2, and X3 contains an S group, and A1, A2, and A3 are independently selected from alkyl groups connected by O, S, or C. Preferably, the mass percentage of compound B is 0.1%-5% based on the total mass of the electrolyte.

13. The lithium-ion battery according to claim 12, characterized in that, Compound B includes at least one of the following compounds:

14. The lithium-ion battery according to any one of claims 1-13, characterized in that, A linear recessed region is provided on the negative electrode active material layer, and the width of the linear recessed region is 50μm-200μm. Preferably, the depth of the linear depression region is 3μm-45μm.

15. The lithium-ion battery according to any one of claims 1-14, characterized in that, The electrolyte also includes nitrile compounds; the mass percentage of nitrile compounds is 0.1%-7% based on the total mass of the electrolyte. And / or, the electrolyte further includes sulfonic acid compounds; the sulfonic acid compounds account for 0.1%-5% of the total mass of the electrolyte.

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