Secondary batteries and battery packs

Abstract

The present application discloses a secondary battery and a battery pack, in which a negative electrode active material layer is disposed on a current collector of a negative electrode sheet, the negative electrode active material layer including a negative electrode active material, and the non-Faraday specific capacity of the negative electrode sheet is set to 50 nF / g to 250 nF / g, thereby ensuring the number of electrochemically active sites on the surface of the negative electrode sheet, favoring the contact between the negative electrode sheet and an electrolyte, accelerating the speed of ion-electron conduction, and reducing the resistance of charge transfer, effectively improving the charging rate performance of the secondary battery, and improving the current density of the negative electrode sheet, thereby improving the energy density of the secondary battery, thereby providing the secondary battery with excellent kinetic performance and cycle performance.

Description

[Technical Field]

[0001] This application claims priority from a Chinese patent application bearing application number 202211179117.1 and entitled "Secondary Battery and Battery Pack" filed with the China Patent Office on September 26, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to the field of battery technology, and more particularly to secondary batteries and battery packs. [Background technology]

[0003] With the rapid development of electric vehicles and digital electronic products, secondary batteries with higher power density, energy density, and fast charging / discharging are required for application in the electric vehicle and related electronic product fields. For electric vehicles, the energy density and charging time of secondary batteries, such as lithium-ion batteries, are two important technical indicators. While adopting high-capacity batteries can achieve the maximum driving distance, it has a significant impact on fast charging performance.

[0004] Therefore, it is necessary to provide a secondary battery that can achieve both high energy density and high-speed charging performance. Summary of the Invention [Problem to be solved by the invention]

[0005] The present application provides a secondary battery and a battery pack, in which the non-faradayian specific capacitance of the negative electrode sheet is 50nF / g to 250nF / g, thereby ensuring a sufficient number of electrochemically active sites on the surface of the negative electrode sheet, favoring the contact between the negative electrode sheet and the electrolyte, accelerating the ionic and electronic conduction rate, reducing the resistance of charge transfer, and effectively improving the charging performance of the secondary battery, as well as improving the current density of the negative electrode sheet, and improving the energy density of the secondary battery, thereby endowing the secondary battery with excellent kinetic and cycling performance, and having good application prospects. [Means for solving the problem]

[0006] A first aspect of the present application provides a secondary battery, the secondary battery including a positive electrode sheet, an electrolyte, and a separator, and further including a negative electrode sheet, the negative electrode sheet including 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 including a negative electrode active material, the negative electrode active material including graphite, wherein the negative electrode sheet has a non-faraday specific capacity of Cdl nF / g, where 50≦Cdl≦250.

[0007] In some embodiments, the negative electrode active material layer has a resistance of R mΩ, and 4≦0.1×Cdl−R≦24.

[0008] In some embodiments, the numerical range for R is 1≦R≦15.

[0009] In some embodiments, the porosity P of the negative electrode sheet is 20% to 40%.

[0010] In some embodiments, the coating weight of the negative electrode active material layer on one surface of the negative electrode current collector is CW mg / cm 2 and 7≦CW≦12.

[0011] In some embodiments, the bulk density of the negative electrode active material is 1 g / cm 3 ~2.5g / cm 3 is.

[0012] In some embodiments, the negative electrode active material has a granular dispersity of 1.5-5.

[0013] In some embodiments, the electrolyte comprises a sulfur-containing additive, and the sulfur-containing additive comprises at least one of formulas (1)-(5). [ka]

[0014] In some embodiments, the sulfur-containing additive is A% by weight of the electrolyte, where 0.05≦Cdl×A%≦12.5.

[0015] In some embodiments, the sulfur-containing additive is A % by weight of the electrolyte, where 0.01≦A≦5.

[0016] In addition, a second aspect of the present application further provides a battery pack, which includes the above secondary battery. [Effects of the Invention]

[0017] Provided is a secondary battery and a battery pack, in which the secondary battery comprises a negative electrode active material layer disposed on a current collector of a negative electrode sheet, the negative electrode active material layer comprising a negative electrode active material, and the non-Faraday specific capacity of the negative electrode sheet is 50 nF / g to 250 nF / g, thereby ensuring a sufficient number of electrochemically active sites on the surface of the negative electrode sheet, favoring contact between the negative electrode sheet and an electrolyte, accelerating the rate of ionic and electronic conduction, and reducing the resistance of charge transfer, effectively improving the charging performance of the secondary battery, and also improving the current density of the negative electrode sheet, thereby improving the energy density of the secondary battery, thereby providing the secondary battery with excellent kinetic performance and cycle performance, and having good application prospects. [Brief explanation of the drawings]

[0018] [Figure 1] 1 shows a cyclic voltammogram of the negative electrode sheet produced in Example 1 of the present application at a scan rate of 0.1 mv / s. [Figure 2] 1 is a linear scan voltammogram of the negative electrode sheet prepared in Example 1 of the present application in a potential range of 2.6 V to 2.7 V and a scan rate of 0.1 mv / s. [Figure 3] 1 is a fitting curve showing a scatter diagram of scan rate versus current density for the negative electrode sheet produced in Example 1 of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present application provides a secondary battery and a battery pack. In order to clarify and clarify the purpose, technical idea, and effects of the present application, the present application will be described in more detail below by giving examples with reference to the drawings. It should be understood that the specific examples described in this specification are merely for the purpose of explaining the present application and are not intended to limit the present application.

[0020] In one example of the present application, a secondary battery is provided, and the secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte, and a housing.

[0021] I, negative electrode sheet

[0022] 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 including a negative electrode active material, and the negative electrode active material includes graphite.

[0023] The negative electrode sheet may be a single-sided or double-sided sheet. When the negative electrode sheet is a single-sided sheet, the negative electrode active material layer is disposed on one surface of the negative electrode current collector. When the negative electrode sheet is a double-sided sheet, the negative electrode active material layer is disposed on both surfaces of the negative electrode current collector. The negative electrode sheet may have both a single-sided negative electrode sheet region and a double-sided negative electrode sheet region at the same time.

[0024] The non-Faraday specific capacity Cdl of the negative electrode sheet is as follows:

[0025] The non-Faradaic specific capacitance of the negative electrode sheet is Cdl nF / g, where Cdl is in the range of 50≦Cdl≦250. Specifically, Cdl may be any of 50, 70, 80, 140, 160, 180, 200, 205, 210, and 250, or any range consisting of any two of these numbers. The faradaic reaction in a battery is a process in which the oxidation state of the active material changes, and charge passes through a double charge layer and transfers through the electrode interface into the active material. The non-Faradaic reaction is a reaction in which charge is accumulated and released by the physical adsorption and desorption of ions on the electrode surface, without charge transfer across the electrode interface. The non-Faradaic specific capacitance value Cdl nF / g indicates the number of electrochemically active sites on the negative electrode sheet. Within a certain range, increasing Cdl increases the number of electrochemically active sites, which is beneficial for the contact between the negative electrode active material and the electrolyte, accelerating the ionic and electronic conduction rate, reducing the charge transfer resistance, and effectively improving the charge multiplier performance of the secondary battery. In some embodiments, when 80≦Cdl≦250 and the non-Faraday specific capacity value of the negative electrode sheet is within the above range, the overall performance of the secondary battery is further improved.

[0026] In some embodiments, when 80≦Cdl≦200 and the non-Faraday specific capacity value of the negative electrode sheet is in the above range, the overall performance of the secondary battery is well balanced, and the overall performance of the secondary battery is better.

[0027] The resistance R of the negative electrode active material layer is as follows:

[0028] In some embodiments, the relationship between R and Cdl is 4≦0.1×Cdl−R≦24. When the negative electrode sheet satisfies this relationship, the ion transport path of the negative electrode sheet is shorter, facilitating electrochemical reactions and achieving high-rate discharge performance. Furthermore, when the negative electrode sheet satisfies this relationship, the electrolyte wettability, surface resistance, and high-rate charge / discharge performance of the negative electrode sheet are all appropriate, and expansion of the negative electrode sheet during cycling can be reduced.

[0029] In some embodiments, the relationship between R and Cdl is 4≦0.1×Cdl−R≦14. When the negative electrode sheet satisfies the above relationship, the internal structure of the negative electrode sheet can be further optimized, and the overall performance of the secondary battery can be improved.

[0030] In some embodiments, the resistance of the negative electrode active material layer is R mΩ, and R is in the range of 1≦R≦15. Specifically, R may be 1, 3, 4, 6, 8, 10, 12, or 15, or a range consisting of any two of these numbers. Electronic conduction characteristics primarily affect the rechargeability of a secondary battery. Key factors affecting the conductivity of a negative electrode sheet of a secondary battery include the interface between the negative electrode current collector and the negative electrode active material layer, the distribution of the conductive agent, and the contact state between granules. Adjusting the sheet resistance of the negative electrode sheet (the resistance of the negative electrode active material layer) can optimize the material performance of the negative electrode sheet.

[0031] In some embodiments, the value of R is in the range of 2≦R≦11. When the value of R is within this range, the conductive network within the negative electrode sheet is more complete, resulting in better overall performance of the secondary battery. Furthermore, enabling the secondary battery to accept a larger charging current is an important technology for achieving high-speed charging of the secondary battery, and this requires a sufficiently small polarization resistance of the battery itself. In this application, the resistance R of the negative electrode active material layer of the negative electrode sheet is limited to 1 mΩ≦R≦15 mΩ, and 4≦0.1×Cdl−R≦24. That is, by sufficiently reducing the sheet resistance, the polarization resistance of the secondary battery itself is sufficiently small, and the number of active sites for electrochemical reactions is within a preferred range, resulting in better overall performance of the secondary battery.

[0032] In the examples of the present application, the resistance R of the negative electrode active material layer was tested as follows.

[0033] The negative electrode sheet has an area of ​​1540.25 mm 2The negative electrode sheet is cut into circular sheets, and the cut negative electrode sheet is placed in the center of the probe of a sheet resistance meter. The negative electrode sheet is then tested using the sheet resistance meter to obtain the measured resistance of the negative electrode active material layer of the negative electrode sheet. The selected 10 negative electrode sheet samples are each measured using the sheet resistance meter, and the average resistance of the negative electrode active material layer of the obtained 10 measured negative electrode sheets is then calculated to obtain the resistance of the negative electrode active material layer.

[0034] The porosity P of the negative electrode sheet is as follows:

[0035] In some embodiments, the porosity P of the negative electrode sheet is 20% to 40%, and specifically, P may be any one of 20%, 25%, 28%, 30%, 35%, and 40%, or any two of these ranges. The more the porosity of the negative electrode sheet is within the above range and the more pore structures there are, the more the contact area between the electrode and the electrolyte is increased, and the shorter the lithium ion transport path is, realizing rapid wetting of the electrolyte, providing a smooth charge transport path at the solid-liquid interface, reducing the diffusion barrier, allowing lithium ions to be rapidly absorbed and released onto the surface of the negative electrode material, accelerating the reaction kinetics, reducing polarization on the negative electrode surface, and making the current distribution more uniform. This allows more negative electrode active material to simultaneously absorb and release Li during high-rate charging. + By taking part in the adoption of this material, it can effectively avoid lithium deposition on the surface of the negative electrode, and at the same time provide sufficient active sites for electrochemical reactions in the electrochemical process, accelerate the non-Faraday reaction process of the negative electrode, and favor the transfer of electrons and ions between the solid and liquid phases, improving the kinetics of the electrochemical reaction and ultimately improving the multiplication performance of the material.

[0036] The porosity of the negative electrode sheet is P = (V1 - V2) / V1 × 100%, where V1 is the apparent volume of the sample and V2 is the actual volume of the sample. The test method can refer to GB / T33052-2016 Porosity Measurement Method.

[0037] The coating weight CW of the negative electrode active material layer is as follows.

[0038] In some embodiments, the coating weight of the negative electrode active material layer on one surface of the negative electrode current collector is CW mg / cm 2 where 7≦CW≦12, and specifically, CW may be any one of 7, 9, 9.5, 10, 11, and 12, or a range consisting of any two of these numbers. When the non-Faraday specific capacitance value Cdl of the negative electrode sheet is 50 to 250 nF / g and the coating weight of the negative electrode active material layer is within the above range, the energy density of the negative electrode is ensured while ensuring sufficient diffusion of the electrolyte into the negative electrode sheet. This reduces excessive consumption of electrolyte for film formation and excessive consumption of lithium ions, and also reduces polarization in the thickness direction of the negative electrode sheet, preventing lithium deposition on the negative electrode surface during high-speed charging, ensuring the cycle life and initial efficiency of the secondary battery. When the coating weight of the negative electrode active material layer is 7 mg / cm 2 ~12mg / cm 2 Within this range, the transition distance of lithium ions in the negative electrode sheet is relatively short, resulting in a decrease in charge transfer resistance, which is beneficial to improving the power performance of the battery, and at the same time, improving the current density of the sheet and the energy density of the battery.

[0039] Furthermore, a change in coating weight changes the physical contact between the granules in the negative electrode active material layer, which changes the pore spaces between the granules in the negative electrode active material layer. Because a non-Faradaic reaction is a reaction in which ions are physically adsorbed and desorbed on the electrode surface, releasing electric charge, the pore spaces between the granules in the negative electrode active material layer change, which affects the magnitude of the non-Faradaic specific capacitance Cdl.

[0040] The coating weight of the negative electrode active material layer = (weight of the negative electrode sheet - weight of the negative electrode current collector) / area of ​​the negative electrode sheet. If the tested negative electrode sheet is coated on both sides, the area of ​​the negative electrode sheet is twice the area of ​​the sample.

[0041] The bulk density of the negative electrode active material is as follows.

[0042] In some embodiments, the bulk density of the negative electrode active material in the negative electrode active material layer is 1 g / cm 3 ~2.5g / cm 3 Specifically, the bulk density may be any one of 1, 1.5, 1.8, 2.0, 2.2, and 2.5, or a range consisting of any two of these numbers. The bulk density represents the average density of a stack of loose granules, including the pores inside and outside the granules and the voids between the granules, and is calculated by dividing the powder mass by the volume of the container occupied by the powder. The bulk density can be adjusted to a predetermined range depending on the particle size of the raw materials, the firing conditions, etc. The bulk density value indicates the uniformity of the negative electrode active material granules. The more uniform the negative electrode active material granules, the greater the porosity of the negative electrode sheet, which can improve the liquid phase diffusion ability of lithium ions and is beneficial for the progress of non-Faradaic reactions in the battery. Increasing the non-Faradaic specific capacity Cdl of the negative electrode sheet increases the number of electrochemically active sites, which is beneficial for the contact between the negative electrode active material and the electrolyte, accelerating the rate of ion-electron conduction, reducing the resistance to charge transfer, and effectively improving the charging ratio performance of the secondary battery.

[0043] For the bulk density test of the negative electrode active material, reference can be made to GB / T31057.1-2014 Granular Material Physical Property Test Part 1 Bulk Density Measurement.

[0044] The granular dispersity of the negative electrode active material is as follows.

[0045] In some embodiments, the granular dispersity of the negative electrode active material is 1.5 to 5, and may be any one of, or a range consisting of any two of, 1.5, 1.8, 2.0, 2.2, 2.5, 2.7, 3.0, 3.2, 3.5, 3.8, 4.0, 4.2, 4.5, 4.8, and 5. The granular dispersity may represent the degree of dispersion of various particle size components, and the dispersity affects the dispersion effect of the powder materials during the stirring process, resulting in a slurry with excellent uniformity and stability, resistance to settling, effective adjustment of the uniformity of the coating weight of the negative electrode sheet, enhanced stability of the negative electrode sheet, and adjustment of non-Faraday processes, improving the lithium ion transmission efficiency between the positive and negative electrodes, and improving the power supply performance of the secondary battery.

[0046] In some embodiments, the granular dispersity of the negative electrode active material is 1.5 to 3.5. When the granular dispersity of the negative electrode active material is in this range, the uniformity of the negative electrode slurry is improved, the apparent performance of the formed negative electrode sheet is better, and the overall performance of the secondary battery is better.

[0047] The granular dispersity of the negative electrode active material can be measured using a laser particle size analyzer, and is expressed as follows: granular dispersity of negative electrode active material=(Dv99−Dv10) / Dv50.

[0048] The test method for the non-Faraday specific capacitance value Cdl is as follows.

[0049] In some embodiments, referring to FIGS. 1 to 3, a test method for the non-Faraday specific capacitance value Cdl of a negative electrode sheet includes the following steps.

[0050] In step S1, the non-Faraday potential range confirmation step, the negative electrode sheet is assembled into a half cell (abbreviated as a button cell) and subjected to a cyclic voltammogram (CV) test, where the voltage range is 0.005 to 3.0 V and the scan rate is 0.1 to 1 mV / s. Figure 1 shows the cyclic voltammogram of the negative electrode sheet at a scan rate of 0.1 mV / s. Referring to Figure 1, the cyclic voltammogram contains two curves, each representing two scans at the same scan rate. Since the first cycle is irreversible, the peak positions of the two cycles are different. The non-Faraday potential range is the flat section of the curve, i.e., in the range of 1.5 V to 3 V.

[0051] In step S2, the cathodic scan step in the non-Faraday section, a potential range of 1.5 V to 3 V was selected from the potential range confirmed in step S1, and a linear scan voltammogram (LSV) test was performed. The scan direction was from high potential to low potential, and a voltage-current curve was collected. Here, the selected potential range was 2.6 to 2.7 V, and the scan rate was 0.05-5 mV / s. Figure 2 shows the linear scan voltammogram at a scan rate of 0.1 mV / s.

[0052] Furthermore, the median value U of the potential range of 2.6 to 2.7 V was selected at a scan rate of 0.1 mV / s, and the corresponding current value U = 2.65 was obtained. The current density value J1 was calculated according to the corresponding active material mass, in units of A / g. The current values ​​corresponding to the median value U at different scan rates within the scan rate range of 0.05 to 5 mV / s were selected, and different current density values ​​were calculated. A scatter diagram of scan rate vs. current density was obtained.

[0053] In step S3, the non-Faraday specific capacitance value calculation step, a linear function is obtained by fitting based on the scatter diagram of the scanning rate versus current density collected in step S2, and the slope K of the linear function is the non-Faraday specific capacitance value Cdl of the negative electrode sheet in the cathode scanning direction.

[0054] The button cell was assembled as follows. The resulting negative electrode sheet was dried, cut into small circular sheets, weighed, and then transferred to a vacuum oven and dried at 100°C for 8 hours. The cells were then transferred to a glove box filled with argon gas for assembly. The assembly method was standard in the art. The non-Faradaic potential range was confirmed using a cyclic voltammogram curve, and the current value was measured within the potential range using a linear scan voltammogram curve to calculate the non-Faradaic specific capacitance (Cdl).

[0055] The negative electrode current collector is as follows.

[0056] In some embodiments, the negative electrode current collector includes, but is not limited to, a metal foil, a metal cylinder, a metal tape roll, a metal sheet, a metal thin film, a metal sheet mesh, a metal stamping, a metal foam, etc. In some embodiments, the negative electrode current collector is a metal foil. In some embodiments, the negative electrode current collector is an aluminum foil or a copper foil. As used herein, the term "copper foil" includes copper alloy foil.

[0057] In some embodiments, the negative electrode current collector is a conductive resin, hi some embodiments, the conductive resin comprises a film obtained by depositing copper on a polypropylene film.

[0058] The negative electrode active material layer is as follows.

[0059] The negative electrode active material layer may be a single layer or multiple layers, and each of the multiple layers may contain the same or different negative electrode active materials. The negative electrode active material is any material that can reversibly absorb and release metal ions, such as lithium ions. In some embodiments, the chargeable capacity of the negative electrode active material is greater than the dischargeable capacity of the positive electrode active material to prevent lithium metal from being deposited on the negative electrode sheet during charging.

[0060] In some embodiments, the thickness of the negative electrode active material layer refers to the thickness of the negative electrode active material layer coated on one side of the negative electrode current collector. In some embodiments, the thickness of the negative electrode active material layer on one side is 15 μm or more. In some embodiments, the thickness of the negative electrode active material layer on one side is 20 μm or more. In some embodiments, the thickness of the negative electrode active material layer on one side is 30 μm or more. In some embodiments, the thickness of the negative electrode active material layer on one side is 150 μm or less. In some embodiments, the thickness of the negative electrode active material layer on one side is 120 μm or less. In some embodiments, the thickness of the negative electrode active material layer on one side is 100 μm or less. In some embodiments, the thickness of the negative electrode active material layer falls within a range consisting of any two of the above numbers. When the thickness of the negative electrode active material layer falls within the above range, the electrolyte can penetrate to the vicinity of the interface of the negative electrode current collector, improving the charge / discharge characteristics of the secondary battery at high current densities. At the same time, by setting the volume ratio of the negative electrode current collector to the negative electrode active material within an appropriate range, the capacity of the secondary battery can be ensured.

[0061] In some embodiments, the negative electrode active material layer includes a negative electrode active material, a conductive agent, an adhesive, and a dispersant.

[0062] The negative electrode active material is as follows.

[0063] In some embodiments, the negative electrode active material comprises one or more of artificial graphite, natural graphite, soft carbon, hard carbon, amorphous carbon, carbon nanotubes, and mesocarbon microspheres.

[0064] The conductive agent is as follows:

[0065] In some embodiments, the conductive agent comprises one or more of carbon black, graphite, carbon fiber, carbon nanotubes, or graphene, preferably carbon black.

[0066] The adhesives are as follows:

[0067] The adhesive improves adhesion between the negative electrode active materials. The type of adhesive is not particularly limited as long as it is a material that is stable against the electrolyte and the solvent used in manufacturing the electrode. In some embodiments, the adhesive includes sodium carboxymethyl cellulose and styrene butadiene rubber.

[0068] The dispersants are as follows:

[0069] In some embodiments, the dispersant comprises diethylhexanol, which is an environmentally friendly organic compound with low cost and wide availability. Its low surface tension makes it easy to adsorb and spread on the surface of a liquid. The material is subjected to mechanical shear and friction, and there is also internal friction between the granules. Under the action of various forces, the raw material granules tend to be highly dispersed, making the slurry more uniform and the dispersion effect good. The thickness of the produced dry sheet is uniform, and problems such as wrinkles that affect the electrical performance can be avoided. The stability of the sheet can be improved, the transmission efficiency of lithium ions between the positive and negative electrodes can be improved, electrochemical polarization can be reduced, and non-Faraday reaction processes can be accelerated, thereby meeting the requirements for power battery power rating and cycle life.

[0070] II, electrolyte

[0071] In some embodiments, the electrolyte comprises a sulfur-containing additive, and the sulfur-containing additive comprises at least one of Formulas (1)-(5). [ka]

[0072] The content of the sulfur-containing additive is A%, based on the mass of the electrolyte, and 0.05≦Cdl×A%≦12.5, preferably 0.01≦A≦5. Specifically, A may be any one of 0.1, 0.5, 0.7, 1, 1.5, 1.8, 2.2, 2.7, 3, and 4, or a range consisting of any two of these numbers. When the negative electrode sheet has a non-Faradaic specific capacity of 50 nF / g to 250 nF / g and the electrolyte contains a sulfur-containing additive, the sulfur-containing additive has high stability and ionic conductivity. The interfacial film formed by the sulfur-containing additive is primarily composed of organic sulfides, resulting in low impedance and improved lithium ion conduction, thereby extending the life of the secondary battery. It also reduces side reactions within the electrolyte and between the electrolyte and the negative electrode material, improving the lithium ion transfer rate, reducing the resistance of the SEI film, thereby reducing the resistance of the secondary battery, reducing polarization, improving charge / discharge efficiency, and preventing internal short circuits in the secondary battery caused by lithium deposition on the negative electrode sheet. The synergistic effect of the negative electrode sheet and the electrolyte is beneficial to improving the cycle performance of the battery. An appropriate content of the sulfur-containing additive improves lithium ion conduction efficiency, accelerates non-Faradaic reaction processes, and improves the ability to rapidly charge at high rates. In some embodiments, the sulfur-containing additive has a value of 0.1≦A≦4. In some embodiments, the sulfur-containing additive has a value of 0.5≦A≦3. When the mass percentage of the sulfur-containing additive is within the above range and the non-Faraday specific capacity of the negative electrode sheet is 50 nF / g to 250 nF / g, an electrochemical reaction occurs between the two, the formed protective film is complete, and the film has appropriate density, which reduces the polarization phenomenon and improves the cycle performance of the secondary battery.

[0073] The lithium salts are as follows:

[0074] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium organoborate, lithium perchlorate, and sulfonimide-type lithium salt. The amount of the lithium salt is not particularly limited as long as it does not impair the effects of the present application.

[0075] III. Positive electrode sheet

[0076] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector.

[0077] The positive electrode active material layer is as follows.

[0078] The positive electrode active material layer may be a single layer or multiple layers, and each of the multiple negative electrode active material layers may contain the same or different positive electrode active materials. The positive electrode active material is any material that can reversibly absorb and release metal ions, such as lithium ions.

[0079] In some embodiments, the positive electrode active material includes one or more of lithium manganate, lithium iron phosphate (LFP), and ternary materials.

[0080] In some embodiments, the active cathode material can include a ternary material, and the ternary material can include lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide.

[0081] In some embodiments, the cathode active material comprises lithium nickel cobalt manganese oxide, with a molar ratio of elemental nickel, elemental cobalt, and elemental manganese of 1:1:1, wherein the content of elemental nickel is 0.5 or more.

[0082] In some embodiments, the cathode active material comprises lithium nickel cobalt manganese oxide, with a molar ratio of elemental nickel, cobalt, and manganese of 1:1:1, wherein the content of elemental nickel is less than or equal to 0.85.

[0083] In some embodiments, the positive electrode active material may include doping elements and / or coating elements, and there are no special requirements for the doping elements and / or coating elements, as long as the positive electrode active material becomes more stable.

[0084] The positive electrode active material further includes a positive electrode conductive agent, a positive electrode adhesive, and a solvent.

[0085] The positive electrode conductive agent is as follows:

[0086] The type of positive electrode conductive agent is not particularly limited, and any known conductive agent can be used. Positive electrode conductive agents include, but are not limited to, graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, amorphous carbon materials such as acicular coke, carbon nanotubes, graphene, etc. The above positive electrode conductive agents may be used alone or in any combination.

[0087] The positive electrode adhesive is as follows.

[0088] The type of positive electrode adhesive used in manufacturing the positive electrode active material layer is not particularly limited, and in the case of a coating method, it may be a material that is soluble or dispersible in the liquid medium used in manufacturing the electrode. Examples of positive electrode adhesives may include, but are not limited to, one or more of the following: Resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubber-like polymers such as styrene-butadiene rubber (SBR), nitrile rubber (NBR), fluororubber, isoprene rubber, and ethylene-propylene rubber; thermoplastic elastomeric polymers such as styrene-butadiene-styrene block copolymers or their hydrogenated products, ethylene-propylene-diene terpolymer (EPDM), styrene-ethylene-butadiene-ethylene copolymers, and styrene-isoprene-styrene block copolymers or their hydrogenated products; soft resin-like polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluoropolymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; and polymer compositions having ionic conductivity for alkali metal ions (especially lithium ions). The positive electrode adhesives may be used alone or in any combination.

[0089] The solvents are as follows:

[0090] The type of solvent used to form the positive electrode slurry is not limited, and any solvent capable of dissolving or dispersing the positive electrode active material, positive electrode conductive agent, and positive electrode adhesive may be used. Examples of the solvent used to form the positive electrode slurry include, but are not limited to, aqueous and organic solvents. Examples of aqueous media include water and mixtures of alcohol and water. Examples of organic media include, but are not limited to, diethylenetriamine, N,N-dimethylaminopropylamine, diethyl ether, propylene oxide, tetrahydrofuran (THF), N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, hexamethylphosphoramide, and dimethyl sulfoxide.

[0091] The positive electrode current collector is as follows.

[0092] The type of positive electrode current collector is not particularly limited, and may be any known material suitable for use as a positive electrode current collector. Examples of positive electrode current collectors include, but are not limited to, metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; carbon materials such as carbon cloth and carbon paper; and composite materials comprising a polymer and a metal layer. In some embodiments, the positive electrode current collector is a metal material. In some embodiments, the positive electrode current collector is aluminum.

[0093] The shape of the positive electrode current collector is not particularly limited. When the positive electrode current collector is made of a metal material, the shape of the positive electrode current collector includes, but is not limited to, a metal foil, a metal cylinder, a metal tape roll, a metal plate, a metal thin film, a metal plate mesh, a stamped metal, a metal foam, etc. When the positive electrode current collector is made of a carbon material, the shape of the positive electrode current collector includes, but is not limited to, a carbon plate, a carbon thin film, and a carbon cylinder. In some embodiments, the positive electrode current collector is a metal foil. In some embodiments, the metal foil is in a mesh shape. The thickness of the metal foil is not particularly limited. In some embodiments, the thickness of the metal foil is 1 μm or more, 3 μm or more, or 5 μm or more. In some embodiments, the thickness of the metal foil is 1 mm or less, 50 μm or less, or 20 μm or less. In some embodiments, the thickness of the metal foil is within a range consisting of any two of the above numbers.

[0094] IV, separator

[0095] To prevent short circuits, a separator is usually placed between the positive electrode and the negative electrode, and in this case, the electrolyte of the present invention is usually used by permeating the separator.

[0096] V. Application

[0097] Furthermore, an embodiment of the present application further provides a battery pack, which includes a secondary battery. Typical applications of the battery pack include, but are not limited to, electric toys, electric tools, battery-powered vehicles, electric vehicles, energy storage devices, ships, spacecraft, etc.

[0098] Hereinafter, the method for manufacturing a secondary battery provided by the present invention will be described based on specific examples.

[0099] Example 1

[0100] The positive electrode sheet was produced as follows.

[0101] A positive electrode slurry was prepared by mixing a positive electrode active material, a positive electrode conductive agent, a positive electrode adhesive, and a solvent. The mass percentage ratio of the positive electrode active material NCM811, the positive electrode conductive agent carbon black, and the positive electrode adhesive polyvinylidene fluoride (PVDF) was 96:2:2, and the solvent was N-methylpyrrolidone (NMP). The resulting positive electrode slurry was uniformly coated on both sides of a positive electrode current collector (aluminum foil) and then dried at 120 °C to obtain a positive electrode sheet. The thickness of the positive electrode sheet was adjusted by roll pressing, and its compaction density was 3.5 g / cm. 3 Adjust to.

[0102] The negative electrode sheet was produced as follows.

[0103] First, a negative electrode slurry was prepared. The negative electrode active material in the negative electrode slurry included artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene rubber, and diethylhexanol. The mass ratio of the artificial graphite, conductive carbon black, sodium carboxymethyl cellulose, styrene-butadiene rubber, and diethylhexanol was 96.5:1.2:1.2:1.0:0.1, and the bulk density of the artificial graphite was 1.5 g / cm. 3 , the dispersity is 2.0.

[0104] The specific method for preparing the negative electrode slurry is as follows: 50% artificial graphite, conductive carbon black, 50% artificial graphite, and 70% sodium carboxymethylcellulose are sequentially added to a double planetary mixer. The stirring tank is rotated at a revolution speed of 20 r / min and a rotation speed of 800 r / min for 30 minutes to mix uniformly, and then a portion of the deionized water is added and stirred for 1 hour to form a first mixed powder material. After scraping and bottom rotation, the remaining 30% sodium carboxymethylcellulose and deionized water are added to the first mixed powder material. The revolution speed is set to 25 r / min and a rotation speed of 2500 r / min and the mixture is stirred at high speed for 90 minutes. A vacuum of -0.085 MPa is maintained during this process, and the slurry is dispersed to form a second mixed solution. After scraping and bottom rotation, the adhesive styrene butadiene rubber and 50% diethylhexanol were added to the second mixed solution, and the mixture was stirred at a revolution speed of 20 r / min, a rotation speed of 500 r / min, and a low speed of 30 min, with a vacuum of -0.085 MPa to form a third mixed solution. Finally, 50% diethylhexanol was added to the third mixed solution, and the mixture was stirred at a revolution speed of 10 r / min, a rotation speed of 100 r / min, and a low speed of 30 min, with a vacuum of -0.085 MPa to form a fourth mixed solution. Finally, deionized water is added to further adjust the viscosity of the slurry, and the revolution speed is set to 25 r / min and the rotation speed to 300 r / min. Stirring for 30 minutes is more beneficial for uniform dispersion of the slurry. During this process, the vacuum is adjusted to -0.085 MPa, and when the viscosity of the slurry is 2000 mPa·s to 3500 mPa·s, the slurry passes. The slurry is then defoamed at a rotation speed of 200 r / min, stored, and sieved through a 200-mesh sieve to produce anode slurry. The resulting anode slurry is then uniformly coated on one or both sides of the copper foil of the anode current collector, with the coating density at 9.5 mg / cm. 2 The mixture is then calcined and dried, and then roll-cut to obtain a negative electrode sheet. The calcination temperature is 90°C to 110°C, the drying time is 24 hours, and the porosity P of the negative electrode sheet after roll-pressing is 30%.

[0105] Here, the preparation of the negative electrode slurry mainly involves thoroughly mixing the active material and inactive components, fully demonstrating the electrochemical performance, including the uniformity of the slurry in the electrode sheet, avoiding aggregation and sedimentation, ensuring the adjustable coating weight of the sheet, and ensuring the consistency of the active material and inactive components, thereby ensuring the mobility between the positive and negative electrodes of the lithium ion battery, and improving the electrochemical performance of the entire battery.

[0106] The electrolyte solution was prepared as follows.

[0107] Ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (EDC) are mixed in a volume ratio of 1:1:1, and then 1 mol / L of LiPF6 is added and mixed uniformly to prepare an electrolyte.

[0108] The secondary battery is manufactured as follows.

[0109] The negative electrode sheet and positive electrode sheet produced using the above steps are dried and then wound together with a separator using a winding machine to produce an electric core. The positive electrode aluminum tab and the negative electrode copper-nickel plated tab are welded to the electric core. The welded electric core is then packaged in a pouch-shaped aluminum plastic film, and the separator is made of PP film. After injection and chemical formation to a constant volume, a secondary battery is produced.

[0110] The non-Faraday specific capacitance value Cdl test of the negative electrode sheet is as follows.

[0111] Step 1: Disassemble the secondary battery in a glove box, obtain the sheet in the negative electrode overhang area, soak it in dimethyl carbonate (DMC) solution, cut it, and then assemble it with a metallic lithium sheet to form a button half-cell. Alternatively, cut the negative electrode sheet that is not assembled into a battery, and then assemble it with a metallic lithium piece to form a button half-cell.

[0112] Step 2: Conduct a CV test on the button cell half-cell in the voltage range of 0.005 V to 3.0 V, with a scan rate of 0.1 mV / s, ensuring that the non-Faraday potential range is 2.6 V to 2.7 V.

[0113] Step 3: Next, LSV tests were performed from 2.7 V to 2.6 V, with the scan rates of 0.1 mV / s, 0.2 mV / s, 0.5 mV / s, 1 mV / s, and 2 mV / s, respectively. The midpoint of the potential range, 2.65 V, was selected to obtain the corresponding current values ​​of -4.32E-07 A, -5.50E-07 A, -1.15E-06 A, -2.08E-06 A, and -3.80E-06 A. Based on the corresponding mass of the active material, 0.02175 g, the current density values ​​of -1.25E-05 A / g, -2.08E-05 A / g, -4.75E-05 A / g, -8.87E-05 A / g, and -1.64E-04 A / g were calculated.

[0114] Step 4: Based on the scan rate and current density values ​​obtained in Step 3, a scatter plot of scan rate-current density is made and fitted to obtain a linear function, the slope of which is -8E-05, i.e., the non-Faraday specific capacitance Cdl of the negative electrode sheet in the cathode scan direction is 80 nF / g.

[0115] Here, the negative electrode sheet overhang region refers to the portion of the negative electrode sheet that protrudes from the positive electrode sheet in the length and width directions.

[0116] Example 2

[0117] In Example 2, a secondary battery is fabricated by the method of Example 1, but the other parts are the same as those of Example 1 except for the following differences.

[0118] Coating weight of negative electrode sheet (CW mg / cm) 2 7mg / cm 2 The porosity P of the negative electrode sheet is 25%, the resistance R mΩ of the negative electrode active material layer is 3 mΩ, and the non-Faraday specific capacitance Cdl nF / g of the negative electrode sheet is 140 nF / g.

[0119] Example 3

[0120] In Example 3, a secondary battery is fabricated by the method of Example 1, but the other parts are the same as those of Example 1 except for the following differences.

[0121] Coating weight of negative electrode sheet (CW mg / cm) 2 12 mg / cm 2 The porosity P of the negative electrode sheet is 25%, the resistance R mΩ of the negative electrode active material layer is 15 mΩ, and the non-Faraday specific capacitance Cdl nF / g of the negative electrode sheet is 200 nF / g.

[0122] Example 4

[0123] In Example 4, a secondary battery is fabricated by the method of Example 1, but the other parts are the same as those of Example 1 except for the following differences.

[0124] Coating weight of negative electrode sheet (CW mg / cm) 2 9 mg / cm 2 The porosity P of the negative electrode sheet is 20%, the resistance R mΩ of the negative electrode active material layer is 1 mΩ, and the non-Faraday specific capacitance Cdl nF / g of the negative electrode sheet is 250 nF / g.

[0125] Example 5

[0126] In Example 5, a secondary battery is fabricated by the method of Example 1, but the other parts are the same as those of Example 1 except for the following differences.

[0127] Coating weight of negative electrode sheet (CW mg / cm) 2 9 mg / cm 2 The porosity P of the negative electrode sheet is 40%, the resistance R mΩ of the negative electrode active material layer is 8 mΩ, and the non-Faraday specific capacitance Cdl nF / g of the negative electrode sheet is 50 nF / g.

[0128] Example 6

[0129] In Example 6, a secondary battery is fabricated by the method of Example 1, but the other parts are the same as those of Example 1 except for the following differences.

[0130] Coating weight of negative electrode sheet (CW mg / cm) 2 12 mg / cm 2 The porosity P of the negative electrode sheet is 25%, the resistance R mΩ of the negative electrode active material layer is 15 mΩ, and the non-Faraday specific capacitance Cdl nF / g of the negative electrode sheet is 200 nF / g.

[0131] Example 7

[0132] In Example 7, a secondary battery was fabricated by the method of Example 1, but the other parts were the same as those of Example 1 except for the following differences.

[0133] Coating weight of negative electrode sheet (CW mg / cm) 2 10.5mg / cm 2 The porosity P of the negative electrode sheet is 26%, the resistance R mΩ of the negative electrode active material layer is 12 mΩ, and the non-Faraday specific capacitance Cdl nF / g of the negative electrode sheet is 230 nF / g.

[0134] Example 8

[0135] In Example 8, a secondary battery was fabricated by the method of Example 1, but the other parts were the same as those of Example 1 except for the following differences.

[0136] Coating weight of negative electrode sheet (CW mg / cm) 2 9 mg / cm 2 The porosity P of the negative electrode sheet is 20%, the resistance R mΩ of the negative electrode active material layer is 2 mΩ, and the non-Faraday specific capacitance Cdl nF / g of the negative electrode sheet is 250 nF / g.

[0137] Example 9

[0138] In Example 9, a secondary battery was fabricated by the method of Example 1, but the other parts were the same as those of Example 1 except for the following differences.

[0139] Coating weight of negative electrode sheet (CW mg / cm) 2 10mg / cm 2 The porosity P of the negative electrode sheet is 40%, the resistance R mΩ of the negative electrode active material layer is 2 mΩ, and the non-Faraday specific capacitance Cdl nF / g of the negative electrode sheet is 50 nF / g.

[0140] Example 10

[0141] In Example 10, a secondary battery is fabricated by the method of Example 1, but the other parts are the same as those of Example 1 except for the following differences.

[0142] Coating weight of negative electrode sheet (CW mg / cm) 2 9.2 mg / cm 2 The porosity P of the negative electrode sheet is 30%, the resistance R mΩ of the negative electrode active material layer is 2.5 mΩ, and the non-Faraday specific capacitance Cdl nF / g of the negative electrode sheet is 65 nF / g.

[0143] Example 11

[0144] In Example 11, a secondary battery was fabricated by the method of Example 1, but the other parts were the same as those of Example 1 except for the following differences.

[0145] Coating weight of negative electrode sheet (CW mg / cm) 2 9.1 mg / cm 2 The porosity P of the negative electrode sheet is 25%, the resistance R mΩ of the negative electrode active material layer is 6.3 mΩ, and the non-Faraday specific capacitance Cdl nF / g of the negative electrode sheet is 150 nF / g.

[0146] Example 12

[0147] In Example 12, a secondary battery was fabricated by the method of Example 1, but the other parts were the same as those of Example 1 except for the following differences.

[0148] Coating weight of negative electrode sheet (CW mg / cm) 2 9.6 mg / cm 2 The porosity P of the negative electrode sheet is 30%, the resistance R mΩ of the negative electrode active material layer is 9.5 mΩ, and the non-Faraday specific capacitance Cdl nF / g of the negative electrode sheet is 150 nF / g.

[0149] Example 13

[0150] In Example 13, a secondary battery was fabricated by the method of Example 1, but the other parts were the same as those of Example 1 except for the following differences.

[0151] Coating weight of negative electrode sheet (CW mg / cm) 2 10mg / cm 2 The porosity P of the negative electrode sheet is 22%, the resistance R mΩ of the negative electrode active material layer is 11 mΩ, and the non-Faraday specific capacitance Cdl nF / g of the negative electrode sheet is 150 nF / g.

[0152] Comparative Example 1

[0153] In Comparative Example 1, a secondary battery was fabricated by the method of Example 1, but the other parts were the same as those of Example 1 except for the following differences.

[0154] Coating weight of negative electrode sheet (CW mg / cm) 2 5mg / cm 2 The porosity P of the negative electrode sheet is 42%, the resistance R mΩ of the negative electrode active material layer is 10 mΩ, and the non-Faraday specific capacitance Cdl nF / g of the negative electrode sheet is 260 nF / g.

[0155] Comparative Example 2

[0156] In Comparative Example 2, a secondary battery was fabricated by the method of Example 1, but the other parts were the same as those of Example 1 except for the following differences.

[0157] Coating weight of negative electrode sheet (CW mg / cm) 2 14 mg / cm2 The porosity P of the negative electrode sheet is 18%, the resistance R mΩ of the negative electrode active material layer is 12 mΩ, and the non-Faraday specific capacitance Cdl nF / g of the negative electrode sheet is 45 nF / g.

[0158] The performance test process and test results of the secondary battery according to the embodiment of the present application are as follows.

[0159] (1) Dynamic performance test

[0160] The secondary battery is left at 25°C for 30 minutes, fully charged at xC, and fully discharged at 1C 10 times, then fully charged at xC again. After that, the negative electrode sheet is disassembled and the state of lithium deposition on the surface of the negative electrode sheet is observed. If lithium is not deposited on the surface of the negative electrode, the charge rate xC is increased by 0.1C increments and the test is repeated until lithium is deposited on the surface of the negative electrode. The maximum charge rate of the battery is determined by subtracting 0.1C from the charge rate xC at this point.

[0161] (2) Energy density test

[0162] The secondary battery was left at 25°C for 30 minutes, fully charged at 1C, and fully discharged at 1C, and the actual discharge energy was recorded. The lithium-ion battery was weighed on an electronic balance, and the ratio of the actual 1C discharge energy to the weight was the actual energy density of the secondary battery. Here, if the actual energy density is 80% or less of the target energy density, the actual energy density of the secondary battery is considered to be very low. If the actual energy density is 80% or more but 95% or less of the target energy density, the actual energy density of the secondary battery is considered to be low. If the actual energy density is 95% or more but 105% or less of the target energy density, the actual energy density of the secondary battery is considered to be appropriate. If the actual energy density is 105% or more but 120% or less of the target energy density, the actual energy density of the secondary battery is considered to be high. If the actual energy density reaches 120% of the target energy density, the actual energy density of the secondary battery is considered to be very high.

[0163] (3) Cycle performance test

[0164] The secondary battery is subjected to a cycle test in which it is left at 25°C for 30 minutes, discharged at a constant current of 1C, left at rest for 10 minutes, charged at a constant current and constant voltage of 1C, and left at rest for 10 minutes, followed by full charge and full discharge. The capacity retention rate after 1000 cycles is recorded.

[0165] Table 1 shows the performance test results of the secondary batteries according to Examples 1 to 13 and the performance test results of the secondary batteries according to Comparative Examples 1 and 2.

[0166] [Table 1]

[0167] Referring to Table 1, the secondary batteries according to Examples 1 to 13 have excellent dynamic performance, high or very high energy density, and a capacity retention rate of 91% to 96% in cycle performance. Therefore, the secondary batteries according to the examples of the present application have high or very high energy density and excellent cycle performance (a capacity retention rate of 91% to 96% in cycle performance) while being fast charged at a large rate.

[0168] On the other hand, the coating amount of the negative electrode active material layer in Comparative Example 1 was 5 mg / cm 2 The porosity P of the negative electrode sheet was 42%, and the non-Faraday specific capacitance Cdl of the negative electrode sheet reached 260 nF / g. Therefore, the dynamic performance of the secondary battery according to Comparative Example 1 was deteriorated, the energy density was very low, and the capacity retention rate after the cycle performance test was only 85%. The coating amount of the negative electrode active material layer in Comparative Example 2 was 14 mg / cm. 2 The porosity P of the negative electrode sheet was 18%, and the non-Faraday specific capacity value Cdl of the negative electrode sheet was 260. The secondary battery according to Comparative Example 2 had a high energy density, but the capacity retention rate after the cycle performance test was only 86%, resulting in a decrease in dynamic performance.

[0169] Therefore, it is difficult for the secondary batteries according to Comparative Examples 1 and 2 to maintain high energy density and excellent cycle performance while being charged at a high rate.

[0170] Example 14

[0171] In Example 14, a secondary battery was fabricated by the method of Example 1, and the coating weight CW of the negative electrode active material layer was 2 9 mg / cm 2 and the porosity P is 35%, but other parts are the same as in Example 1 except for the following differences.

[0172] The bulk density of the negative electrode active material is 1.5 g / cm 3 The granular dispersity of the negative electrode active material is set to 2, and the non-Faraday specific capacity Cdl nF / g of the negative electrode sheet is set to 200 nF / g.

[0173] Example 15

[0174] In Example 15, a secondary battery was fabricated by the method of Example 1, and the coating weight CW of the negative electrode active material layer was 2 9 mg / cm 2 and the porosity P is 35%, but other parts are the same as in Example 1 except for the following differences.

[0175] The bulk density of the negative electrode active material is 1 g / cm 3 The granular dispersity of the negative electrode active material is set to 1.5, and the non-Faraday specific capacity Cdl nF / g of the negative electrode sheet is set to 240 nF / g.

[0176] Example 16

[0177] In Example 16, a secondary battery was fabricated by the method of Example 1, and the coating weight CW of the negative electrode active material layer was 2 9 mg / cm 2 and the porosity P is 35%, but other parts are the same as in Example 1 except for the following differences.

[0178] The bulk density of the negative electrode active material is 1.8 g / cm3 The granular dispersity of the negative electrode active material is set to 2.5, and the non-Faraday specific capacity Cdl nF / g of the negative electrode sheet is set to 180 nF / g.

[0179] Example 17

[0180] In Example 17, a secondary battery was fabricated by the method of Example 1, and the coating weight CW of the negative electrode active material layer was 2 9 mg / cm 2 and the porosity P is 35%, but other parts are the same as in Example 1 except for the following differences.

[0181] The bulk density of the negative electrode active material is 2 g / cm 3 The granular dispersity of the negative electrode active material is set to 3, and the non-Faraday specific capacity Cdl nF / g of the negative electrode sheet is set to 150 nF / g.

[0182] Example 18

[0183] In Example 18, a secondary battery was fabricated by the method of Example 1, and the coating weight CW of the negative electrode active material layer was 2 9 mg / cm 2 and the porosity P is 35%, but other parts are the same as in Example 1 except for the following differences.

[0184] The bulk density of the negative electrode active material is 2.2 g / cm 3 The granular dispersity of the negative electrode active material is set to 4, and the non-Faraday specific capacity Cdl nF / g of the negative electrode sheet is set to 100 nF / g.

[0185] Example 19

[0186] In Example 19, a secondary battery was fabricated by the method of Example 1, and the coating weight CW of the negative electrode active material layer was 2 9 mg / cm 2 and the porosity P is 35%, but other parts are the same as in Example 1 except for the following differences.

[0187] The bulk density of the negative electrode active material is 2.5 g / cm3 The granular dispersity of the negative electrode active material is set to 5, and the non-Faraday specific capacity Cdl nF / g of the negative electrode sheet is set to 60 nF / g.

[0188] Table 2 shows the performance test results of the secondary batteries according to Examples 14 to 19.

[0189] [Table 2]

[0190] Referring to Table 2, the secondary batteries according to Examples 14 to 19 have dynamic performances of 2C to 4C, and therefore, the secondary batteries according to Examples 14 to 19 have high or very high energy density and excellent cycle performance while undergoing high-rate charging.

[0191] Example 20

[0192] In Example 20, a secondary battery was fabricated by the method of Example 1, but the other parts were the same as those of Example 1 except for the following differences.

[0193] The sulfur-containing additive represented by formula (4) is selected as the sulfur-containing additive in the electrolyte, and the content of the sulfur-containing additive in the electrolyte is 0.05%.

[0194] Example 21

[0195] In Example 21, a secondary battery was fabricated by the method of Example 1, but the other parts were the same as those of Example 1 except for the following differences.

[0196] The sulfur-containing additive represented by formula (4) is selected as the sulfur-containing additive in the electrolyte, and the content of the sulfur-containing additive in the electrolyte is 0.1%.

[0197] Example 22

[0198] In Example 22, a secondary battery was fabricated by the method of Example 1, but the other parts were the same as those of Example 1 except for the following differences.

[0199] The sulfur-containing additive represented by formula (4) is selected as the sulfur-containing additive in the electrolyte, and the content of the sulfur-containing additive in the electrolyte is 0.5%.

[0200] Example 23

[0201] In Example 23, a secondary battery was fabricated by the method of Example 1, but the other parts were the same as those of Example 1 except for the following differences.

[0202] The sulfur-containing additive represented by formula (4) is selected as the sulfur-containing additive in the electrolyte, and the content of the sulfur-containing additive in the electrolyte is 1%.

[0203] Example 24

[0204] In Example 24, a secondary battery was fabricated by the method of Example 1, but the other parts were the same as those of Example 1 except for the following differences.

[0205] The sulfur-containing additive represented by formula (4) is selected as the sulfur-containing additive in the electrolyte, and the content of the sulfur-containing additive in the electrolyte is 2%.

[0206] Example 25

[0207] In Example 25, a secondary battery was fabricated by the method of Example 1, but the other parts were the same as those of Example 1 except for the following differences.

[0208] The sulfur-containing additive represented by formula (4) is selected as the sulfur-containing additive in the electrolyte, and the content of the sulfur-containing additive in the electrolyte is 5%.

[0209] Example 26

[0210] In Example 26, a secondary battery was fabricated by the method of Example 1, but the other parts were the same as those of Example 1 except for the following differences.

[0211] The sulfur-containing additive represented by formula (3) is selected as the sulfur-containing additive in the electrolyte, and the content of the sulfur-containing additive in the electrolyte is 0.1%.

[0212] Example 27

[0213] In Example 27, a secondary battery was fabricated by the method of Example 1, but the other parts were the same as those of Example 1 except for the following differences.

[0214] The sulfur-containing additive represented by formula (3) is selected as the sulfur-containing additive in the electrolyte, and the content of the sulfur-containing additive in the electrolyte is 1%.

[0215] Example 28

[0216] In Example 28, a secondary battery was fabricated by the method of Example 1, but the other parts were the same as those of Example 1 except for the following differences.

[0217] The combination of formula (3) and formula (4) is selected as the sulfur-containing additive in the electrolyte, and the content of the sulfur-containing additive represented by formula (3) in the electrolyte is 0.5%, and the content of the sulfur-containing additive represented by formula (4) is 0.5%.

[0218] Example 29

[0219] In Example 29, a secondary battery was fabricated by the method of Example 1, but the other parts were the same as those of Example 1 except for the following differences.

[0220] The combination of formula (1) and formula (3) is selected as the sulfur-containing additive in the electrolyte, and the content of the sulfur-containing additive represented by formula (1) in the electrolyte is 0.3%, and the content of the sulfur-containing additive represented by formula (3) is 0.5%.

[0221] Table 3 shows the performance test results of the secondary batteries according to Examples 14 to 19.

[0222] [Table 3]

[0223] Referring to Table 3, the secondary batteries according to Examples 20 to 29 have dynamic performances reaching 2.6C to 4C, and therefore, the secondary batteries according to Examples 20 to 29 have high or very high energy density while undergoing high-rate charging, and also have excellent cycle performance (the capacity retention rate of the cycle performance reaches 94 to 96%).

[0224] Although the present application has described in detail the secondary battery and battery pack according to the embodiments of the present application, and the present application has used specific examples to explain the principles and embodiments of the present application, the explanation of the above embodiments is intended to facilitate understanding of the technical solutions of the present application and their core ideas. Those skilled in the art should understand that some of the technical features described in the above embodiments may be modified or replaced with equivalents, and that such modifications and replacements do not deviate from the essence of the corresponding technical solutions and the scope of the technical solutions of each embodiment of the present application.

Claims

1. In a secondary battery including a positive electrode sheet, an electrolyte, and a separator, the negative electrode sheet further 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 including a negative electrode active material, the negative electrode active material including graphite; Here, the non-Faraday specific capacity of the negative electrode sheet is Cdl mF / g, and 50≦Cdl≦250. Secondary battery.

2. The resistance of the negative electrode active material layer is R mΩ, and 4≦0.1×Cdl−R≦24. The secondary battery according to claim 1 .

3. The numerical range of R is 1≦R≦15. The secondary battery according to claim 1 or 2.

4. The porosity P of the negative electrode sheet is 20% to 40%. The secondary battery according to claim 1 or 2.

5. The coating weight of the negative electrode active material layer on one surface of the negative electrode current collector is CW mg / cm ２ and 7≦CW≦12. The secondary battery according to claim 1 or 2.

6. The bulk density of the negative electrode active material is 1 g / cm ３ ~2.5g / cm ３ That is, The secondary battery according to claim 1 or 2.

7. The granular dispersity of the negative electrode active material is 1.5 to 5. The secondary battery according to claim 1 or 2.

8. The electrolyte contains a sulfur-containing additive, and the sulfur-containing additive contains at least one of formulas (1) to (5). 【Chemistry 1】 The secondary battery according to claim 1 or 2.

9. The content of the sulfur-containing additive is A% based on the mass of the electrolyte, and 0.05≦Cdl×A%≦12.5; The secondary battery according to claim 8.

10. The content of the sulfur-containing additive is A% based on the mass of the electrolyte, and 0.01≦A≦5. The secondary battery according to claim 8.

11. The secondary battery according to claim 1 or 2, Battery pack.

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