Secondary batteries and electrical equipment

Abstract

The present application provides a secondary battery and an electric device, the secondary battery including a positive electrode sheet and a negative electrode sheet, the positive electrode sheet including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the negative electrode sheet including a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The secondary battery satisfies 0.5≦(σ1 / σ2) / CB≦9.4. The present application limits the relationship between the areal density and the CB value to balance the lithium desorption speed of the positive / negative electrode sheets, prevent lithium deposition and a drop in battery capacity during operation of the secondary battery, and improve the life of the secondary battery.

Description

[Technical field]

[0001] This application claims priority to a Chinese patent application filed with the China Patent Office on October 27, 2022, bearing application number 202211327819.X and entitled "Secondary Battery and Electrical Device", the entire contents of which are incorporated herein by reference.

[0002] The present application relates to the field of battery technology, and in particular to secondary batteries and electrical devices. [Background technology]

[0003] Although lithium-ion batteries have great advantages in the field of energy storage, they still have some problems in practical use. Take lithium iron phosphate batteries as an example. The service life of a single lithium iron phosphate battery is 4,000-6,000 times, which is difficult to meet the 20-30 year service life (more than 10,000 cycles) required by energy storage projects with high life requirements. The loss of active lithium is the cause of the life attenuation of energy storage lithium-ion batteries. In the process of lithium desorption due to battery cycles, the SEI is destroyed and formed due to the expansion and contraction of graphite and the elution of positive electrode transition metals, which increases the film area and thickness of the SEI, consuming the limited active lithium in the battery system and ultimately shortening the service life of the battery. How to reduce and replenish the active lithium consumed during the battery attenuation process is an important issue for extending the life of lithium iron phosphate batteries.

[0004] To solve these problems, the general method is to "refill lithium" the negative electrode, and there are two types of refill lithium: physical refill lithium and electrochemical refill lithium. However, physical refill lithium is prone to lithium deposition in the battery after cycling, and even causes short circuit of the battery, which poses safety risks. Electrochemical refill lithium can make up for the shortcomings of physical refill lithium, but the current method has low effect, complicated process, and high cost, so it is not suitable for practical production and popularization. In addition, researchers have selected graphite negative electrodes with special performance indicators such as small specific surface area, narrow particle size distribution, and surface coating modification, and selected electrolytes with good infiltration performance at room temperature and high temperature, and used appropriate battery composition design to alleviate the volume expansion and contraction of graphite during cycling, reduce the specific surface area of ​​graphite, reduce the destruction of SEI and the consumption of active lithium during its formation, and extend the service life of lithium iron phosphate batteries as much as possible. Therefore, there is a need to develop secondary batteries that have an ultra-long cycle life, excellent electrochemical performance, are easy to process and manufacture, and have lower operating costs.

[0005] The present application provides a secondary battery for the purpose of preventing lithium deposition and a drop in battery capacity during operation of the secondary battery and improving the life of the secondary battery by defining the relationship between the areal density and the CB value and balancing the lithium desorption rate of the positive / negative electrode sheets. Summary of the Invention [Means for solving the problem]

[0006] In a first aspect, the present invention provides a secondary battery including a positive electrode sheet and a negative electrode sheet, the positive electrode sheet including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the negative electrode sheet including a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, and the secondary battery satisfies 0.5≦(σ1 / σ2) / CB≦9.4. Here, σ1 is the surface density of the positive electrode active material layer, and its unit is g / m 2 It is. σ2 is the surface density of the negative electrode active material layer, and its unit is g / m 2 It is. CB is the ratio of the capacity per unit area of ​​the negative electrode sheet to the capacity per unit area of ​​the positive electrode sheet.

[0007] In some embodiments, 140≦σ1 / CB≦750. In some embodiments, 75≦σ2 / CB≦360. In some embodiments, 0.8≦CB≦1.1. In some embodiments, the areal density σ of the positive electrode active material layer is 150 g / m 2 ≦σ1≦600 g / m 2 Meet the following. In some embodiments, the areal density σ of the negative electrode active material layer is 80 g / m 2 ≦σ2≦290 g / m 2 Meet the following. In some embodiments, the secondary battery satisfies 5≦σ1 / a≦20, where a is the porosity of the positive electrode active material layer, and is expressed in %.

[0008] In some embodiments, 28%≦a≦32%. In some embodiments, the secondary battery satisfies 2.5≦σ2 / b≦9.1, where b is the porosity of the negative electrode active material layer, and is expressed in %. In some embodiments, 30%≦b≦38%. In some embodiments, 1.0≦(σ1 / σ2) / CB≦6.0. In some embodiments, 2.0≦(σ1 / σ2) / CB≦3.0.

[0009] In some embodiments, the active positive material of the positive sheet includes one or more of lithium iron phosphate, lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide. In some embodiments, the negative electrode active material of the negative electrode sheet includes one or more of artificial graphite, natural graphite, amorphous carbon, carbon nanotubes, and mesocarbon microspheres.

[0010] In a second aspect, an embodiment of the present application provides an electrical device including the secondary battery, the secondary battery serving as a power supply for the electrical device.

[0011] Compared with the conventional technology, the secondary battery of the present application includes a positive electrode sheet and a negative electrode sheet, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The secondary battery satisfies 0.5≦(σ1 / σ2) / CB≦9.4. The present application ensures a surplus design of the positive electrode, balances the lithium desorption speed of the positive / negative electrode sheets, prevents lithium deposition and capacity drop during operation of the secondary battery, and improves the life of the secondary battery. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present application provides a secondary battery and an electric device, and in order to make the objectives, technical solutions and effects of the present application clearer and more explicit, the present application will be described in more detail below with reference to examples. It should be understood that the specific examples described herein are only used to interpret the present application, and do not limit the present application.

[0013] secondary battery The present application provides a secondary battery, the secondary battery including a positive electrode sheet and a negative electrode sheet, the positive electrode sheet including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the negative electrode sheet including a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The secondary battery satisfies 0.5≦(σ1 / σ2) / CB≦9.4, where σ1 is the areal density of the positive electrode active material layer and is expressed in g / m 2 σ2 is the surface density of the negative electrode active material layer, and its unit is g / m 2 CB is the ratio of the capacity per unit area of ​​the negative electrode sheet to the capacity per unit area of ​​the positive electrode sheet.

[0014] When the capacity per gram of the positive / negative electrode material is constant, the greater the surface density of the positive / negative active material, the higher the reversible capacity of the positive / negative electrode sheet, so σ1 / σ2 is correlated with the design CB value of the secondary battery. Meanwhile, the lithium desorption rate of the positive / negative electrode sheet is correlated with the surface density of the active material layer of the positive / negative electrode sheet. The higher the surface density of the electrode sheet coating, the greater the polarization of the system, the greater the resistance to lithium desorption, and the slower the rate.

[0015] The present application ensures a positive electrode redundancy design by limiting the value of the ratio of (σ1 / σ2) / CB so that sufficient lithium can replenish the loss of active lithium during the operation of the secondary battery. At the same time, it balances the lithium desorption rate of the positive / negative electrode sheets, prevents lithium deposition and capacity drop during the operation of the secondary battery, and improves the cycle life of the secondary battery. When (σ1 / σ2) / CB<0.5, the relative coating weight of the negative electrode sheet is too large, the lithium desorption rate is slow, the risk of lithium deposition in the secondary battery system increases, side reactions increase, and the decay of life is accelerated. When (σ1 / σ2) / CB>9.4, the relative coating weight of the positive electrode sheet is too large, the polarization of the positive electrode increases, the lithium desorption rate is slow, and the lithium ion desorption during the high-power charging process is insufficient, resulting in a drop in the capacity and energy density of the secondary battery.

[0016] In some embodiments, 1.0≦(σ1 / σ2) / CB≦6.0. In some embodiments, 2.0≦(σ1 / σ2) / CB≦3.0.

[0017] By further optimizing the combination of the positive / negative electrode areal density and CB, the present application has reliably improved the cycle life of the secondary battery while also improving the energy efficiency and energy density of the secondary battery.

[0018] In some embodiments, the value of (σ1 / σ2) / CB is any one of the following values, or a range consisting of any two of the following values: 0.5, 0.8, 1.0, 1.1, 1.3, 1.5, 1.7, 2.0, 1.3, 1.5, 1.7, 2.0, 2.2, 2.5, 2.8, 3.0, 3.3, 3.5, 3.8, 4.0, 4.3, 4.5, 4.8, 5.0, 5.3, 5.5, 5.8, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 8.7, 9.0, 9.4. In some embodiments, the unit areas of the positive and negative sheets are equal when calculating the CB value. In some embodiments, the capacity per unit area of ​​the negative electrode sheet is the charge capacity per unit area of ​​the negative electrode sheet. In some embodiments, the capacity per unit area of ​​the positive electrode sheet is the discharge capacity per gram per unit area of ​​the positive electrode sheet.

[0019] In some embodiments, the CB value is determined by the following method. The capacity per unit area of ​​the negative electrode sheet is obtained as follows: hold active material on one side of a unit area of ​​negative electrode sheet, assemble it with a lithium sheet, separator, and electrolyte to form a button battery, discharge it at 0.1C to 0.005V, discharge it at 0.05mA to 0.005V, discharge it at 0.02mA to 0.005V, and charge it at 0.1C to 2V, and the resulting charge capacity is the capacity per unit area of ​​the negative electrode sheet. The capacity per unit area of ​​the positive electrode sheet is obtained as follows: hold active material on one side of a unit area of ​​positive electrode sheet, assemble it with a lithium sheet, separator, and electrolyte to form a button battery, charge it to 3.7V at 0.1C, apply a constant voltage of 50μA, and discharge it to 2.0V at 0.1C. The obtained discharge capacity is the capacity per unit area of ​​the positive electrode sheet.

[0020] In some embodiments, 140≦σ1 / CB≦750. The range of σ1 / CB for secondary batteries has been further limited, ensuring processing performance while improving the energy density of the secondary batteries. In some embodiments, the value of σ1 / CB is any of the following values, or is in a range consisting of any two of: 140, 150, 180, 200, 230, 250, 270, 290, 300, 320, 330, 340, 350, 370, 380, 390, 400, 420, 430, 450, 470, 480, 500, 520, 530, 540, 550, 560, 580, 600, 630, 650, 680, 700, 750.

[0021] In some embodiments, 75≦σ2 / CB≦360. In some embodiments, the value of σ2 / CB is 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 205, 210, 215, 220, 225, 230, 235, 240, 245, 250, 255, 260, 265, 270, 275, 280, 285, 290, 295, 300, 305, 310, 315, 320, 325, 330, 335, 340, 345, 350, 355, 360, or in a range consisting of any two of these values. The range of σ2 / CB for secondary batteries has been further limited, ensuring processing performance while improving the energy density of the secondary batteries.

[0022] In some embodiments, the range of CB values ​​is 0.8≦CB≦1.1. The present application utilizes a surplus design of the positive electrode sheet to increase the reversible capacity of the positive electrode sheet of the battery, and uses a constant capacity method under charge measurement control to release only a portion of lithium ions into the positive electrode sheet during operation of the battery. The surplus lithium ions are used as a reserve to replenish the active lithium consumed during operation of the secondary battery, so that the active lithium is always kept within an appropriate range, improving the recovery rate of storage capacity and energy efficiency.

[0023] In some embodiments, the CB value is any value of 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, or in a range consisting of any two of these values. The method for measuring areal density is as follows: 2 Take a positive or negative electrode sheet, weigh it as m1g, scrape off the positive or negative active layer on both sides of the electrode sheet, and weigh the foil material as m2g. The areal density is (m1-m2) / S g / m 2 It becomes.

[0024] In some embodiments, the areal density σ of the positive electrode active material layer is 150 g / m 2 ≦σ1≦600 g / m 2 Meet the following. In some embodiments, σ ​​(units are g / m 2 ) may be any of the following values: 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, 700, or in a range consisting of any two of these values.

[0025] In some embodiments, the areal density σ of the negative electrode active material layer is 80 g / m 2 ≦σ2≦290 g / m 2 Meet the following. In some embodiments, σ ​​(units are g / m 2) is any one of 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, or in a range consisting of any two of these values.

[0026] The present application improves the energy density of a secondary battery by further limiting the surface densities of the positive electrode active material layer and the negative electrode active material layer while ensuring the processing performance of the positive electrode sheet, and at the same time, matches the lithium desorption rate of the positive / negative electrodes, thereby improving the cycle life. In some embodiments, the secondary battery satisfies 5≦σ1 / a≦20, where a is the porosity of the positive electrode active material layer, and is expressed in %.

[0027] The lithium desorption rate of the positive electrode sheet is negatively correlated with its surface density and positively correlated with the porosity of the electrode sheet. In the present application, by limiting σ1 / a and controlling the lithium desorption rate of the positive electrode sheet, a certain balance with the lithium desorption rate of the negative electrode sheet is achieved, preventing lithium deposition due to an imbalance in the lithium desorption rate during the operation of the secondary battery, and ensuring an improvement in cycle life.

[0028] In some embodiments, the values ​​of σ1 / a are 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9, 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9, 9.0, 9.1, 9.4, 9.5, 9.6, 9.8, 9.9, 9.0, 9.1, 9.5, 9.6, 9.8, 9.9, 9.0, 9.1, 9.5, 9.6, 9.8, 9.9, 9.0, 9.1, 9.2, 9.3, 9.4 ... 2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9, 10.0, 10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9, 11.0, 11.1, 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9, 12.0, 12.1, 12.2, 12.3, 12.4, 12.5, 12.6, 12.7, 12.8, 12.9, 13.0, 13.1 ,13.2,13.3,13.4,13.5,13.6,13.7,13.8,13.9,14.0,14.1,14.2,14.3,14.4,14.5,14.6,14.7,14.8,14.9,15.0,15.1,15.2,15.3,15.4,15.5,15.6,15.7,15.8,15.9,16.0,16.1,16.2,16.3,16.4,16.5,16.6,16.7,16.8,16. 9, 17.0, 17.1, 17.2, 17.3, 17.4, 17.5, 17.6, 17.7, 17.8, 17.9, 18.0, 18.1, 18.2, 18.3, 18.4, 18.5, 18.6, 18.7, 18.8, 18.9, 19.0, 19.1, 19.2, 19.3, 19.4, 19.5, 19.6, 19.7, 19.8, 19.9, 20.0, or in a range consisting of any two of these values. In some embodiments, 28%≦a≦32%.

[0029] The lithium desorption rate of the positive electrode sheet is positively correlated with the porosity of the electrode sheet. In the present application, the porosity a of the positive electrode sheet is further limited to control the lithium desorption rate of the positive electrode sheet, thereby achieving a certain degree of balance with the lithium desorption rate of the negative electrode sheet, preventing lithium deposition due to an imbalance in the lithium desorption rates during operation of the secondary battery, and improving the cycle life. In some embodiments, the value of a (in %) is any one of the following values ​​or a range consisting of any two of the following values: 28.0, 28.1, 28.2, 28.3, 28.4, 28.5, 28.6, 28.7, 28.8, 28.9, 29.0, 29.1, 29.2, 29.3, 29.4, 29.5, 29.6, 29.7, 29.8, 29.9, 30.0, 30.1, 30.2, 30.3, 30.4, 30.5, 30.6, 30.7, 30.8, 30.9, 31.0, 31.1, 31.2, 31.3, 31.4, 31.5, 31.6, 31.7, 31.8, 31.9, 32.0.

[0030] In some embodiments, 2.5≦σ2 / b≦9.1, where b is the porosity of the negative electrode active material layer, in %. The lithium desorption rate of the negative electrode sheet is negatively correlated with its surface density and positively correlated with the porosity of the electrode sheet. By limiting σ2 / b and controlling the lithium desorption rate of the negative electrode sheet, a certain degree of balance with the lithium desorption rate of the positive electrode sheet can be achieved, preventing lithium deposition due to an imbalance in the lithium desorption rate during operation of the secondary battery and improving the cycle life.

[0031] In some embodiments, the value of σ2 / b is 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, 9.0, 9.1, or in a range consisting of any two of these values. In some embodiments, 30%≦b≦38%.

[0032] The lithium desorption rate of the negative electrode sheet is positively correlated with the porosity of the electrode sheet. By limiting the porosity b of the negative electrode sheet and controlling the lithium desorption rate of the negative electrode sheet, a certain degree of balance with the lithium desorption rate of the positive electrode sheet can be achieved, preventing lithium deposition due to an imbalance in the lithium desorption rates during operation of the secondary battery and improving the cycle life. In some embodiments, the value of b (in %) is 30.0, 30.1, 30.2, 30.3, 30.4, 30.5, 30.6, 30.7, 30.8, 30.9, 31.0, 31.1, 31.2, 31.3, 31.4, 31.5, 31.6, 31.7, 31.8, 31.9, 32.0, 32.1, 32.2, 32.3, 32.4, 32.5, 32.6, 32.7, 32.8, 32.9, 33.0, 33.1, 33.2, 33.3, 33.4, 33.5, 33.6, 33.7, 33.8, 33.9, 34.0, 34.1, 34.2, 34.3, 34.4, 34.5, 34.6, 34.7, 34.8, 34.9, 35.0, 35.1, 35.2, 35.3, 35.4, 35.5, 35.6, 35.7, 35.8, 35.9, 36.0, 36.1, 36.2, 36.3, 36.4, 36.5, 36.6, 36.7, 36.8, 36.9, 37.0, 37.1, 37.2, 37.3, 37.4, 37.5, 37.6, 37.7, 37.8, 37.9, 38.0, 38.1, 38.1, .1, 34.2, 34.3, 34.4, 34.5, 34.6, 34.7, 34.8, 34.9, 35.0, 35.1, 35.2, 35.3, 35.4, 35.5, 35.6, 35.7, 35.8, 35.9, 36.0, 36.1, 36.2, 36.3, 36.4, 36.5, 36.6, 36.7, 36.8, 36.9, 37.0, 37.1, 37.2, 37.3, 37.4, 37.5, 37.6, 37.7, 37.8, 37.9, 38.0, or in a range consisting of any two of the values.

[0033] In this application, both the areal density and the porosity can be measured by existing measurement methods. In some embodiments, the areal density of the positive electrode active material layer is measured by the following method: 2 The weight (g) of the positive electrode sheet is measured, and the weight (g) of the positive electrode current collector is subtracted to obtain the coating weight (g) of the positive electrode active material layer. This is then divided by the area S1 of the positive electrode sheet to obtain the surface density σ1 (unit: g / m 2 ) to get the

[0034] In some embodiments, the areal density of the negative electrode active material layer is measured by the following method: 2) is measured, the weight (g) of the negative electrode sheet is subtracted from the weight (g) of the negative electrode current collector to obtain the coating weight (g) of the negative electrode active material layer, which is then divided by the area S2 of the negative electrode sheet to obtain the surface density σ2 (unit: g / m 2 ) to get the

[0035] In some embodiments, the porosity of the positive electrode active material layer and the porosity of the negative electrode active material layer are measured by mercury intrusion porosimetry. Positive electrode sheet In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material disposed on the positive electrode current collector. In some embodiments, the active cathode material includes one or more of lithium iron phosphate, lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide.

[0036] In some embodiments, the positive electrode active material is lithium iron phosphate, lithium cobalt oxide, lithium nickel oxide, or lithium manganese oxide, and the manufacturing method can be any of known techniques such as high temperature solid phase method, carbothermal reduction method, spray drying method, template method, or hydrothermal synthesis method. Specifically, lithium iron phosphate, which is a positive electrode active material, is produced by the following method: A lithium source (Li2CO3), an iron source (FePO4), and a carbon source are mixed and pretreated at 300 to 500°C, and then sintered at 600 to 850°C to produce lithium iron phosphate as a positive electrode active material.

[0037] In some embodiments, the positive electrode active material is lithium cobalt oxide. The manufacturing method can be any existing technique such as a high temperature solid phase method or a sol-gel method. In concrete terms, the positive electrode active material, lithium cobalt oxide, is produced by the following method: a lithium source (Li2CO3), a cobalt source (Co3O4), and ethanol are mixed and ground, pretreated at 300°C, sintered at 600°C, and a solid-state reaction is carried out at 800°C to produce lithium cobalt oxide.

[0038] In some embodiments, the positive electrode sheet further includes a conductive agent and an adhesive, and the type and content of the conductive agent and the adhesive are not particularly limited and may be selected according to actual needs. In some embodiments, the conductive agent may include conductive carbon black, carbon nanotubes, graphene, etc., and the adhesive may include polyvinylidene fluoride. In some embodiments, the positive electrode sheet is manufactured by dispersing the positive electrode active material or the positive electrode active material obtained by the above method, the conductive agent, and the adhesive in a solvent, N-methylpyrrolidone (NMP), in a specific ratio, stirring uniformly, applying the resulting slurry to an aluminum foil, and then forming a positive electrode sheet by processes such as rolling, stripping, and cutting. By changing the rolling parameters, the corresponding properties and parameters of the positive electrode sheet can also be controlled. It is sufficient that the positive electrode active material layer of the present application is controlled to satisfy the above characteristics.

[0039] Negative electrode sheet In some embodiments, the negative electrode sheet includes a negative electrode current collector, a negative electrode active material coated on the negative electrode current collector, an adhesive, and a conductive agent. The types and contents of the negative electrode active material, the adhesive, and the conductive agent are not particularly limited and may be selected according to actual needs. In some embodiments, the negative electrode active material includes one or more of artificial graphite, natural graphite, amorphous carbon, carbon nanotubes, and mesocarbon microspheres.

[0040] electrolyte In some embodiments, the main components of the electrolyte solution include a lithium salt, an organic solvent, and an additive. Here, the types and compositions of the lithium salt and the organic solvent are not particularly limited and may be selected according to actual needs. Here, the lithium salt may include lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, etc., the solvent may include ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, propyl propanoate, etc., and the additive may include lithium difluorophosphate, lithium bis(oxalato)borate, succinonitrile, etc.

[0041] Separator In some embodiments, the type of the separator is not particularly limited and may be selected according to actual needs. The separator may be a polypropylene film, a polyethylene film, a polyvinylidene fluoride, a spandex film, an aramid film, or a multi-layer composite film modified by coating. In some embodiments, a secondary battery is manufactured as follows: a positive electrode sheet, a separator, and a negative electrode sheet are stacked in this order, a separator is placed between the positive electrode sheet and the negative electrode sheet to serve as an insulator, the stack is then wound to form a rectangular core, the stack is inserted into a battery case, and the battery is dried at 65 to 95°C to remove moisture, and then an electrolyte is injected and the battery is sealed. The secondary battery is obtained through processes such as leaving, hot / cold, chemical formation, fixing, capacity selection, etc.

[0042] In some embodiments, the fabrication of a secondary battery includes the following steps. (1) Lithium iron phosphate, a positive electrode conductive agent, a positive electrode adhesive, and a positive electrode solvent are mixed to prepare a positive electrode slurry, and the positive electrode slurry is applied to the surface of a positive electrode current collector to obtain a positive electrode sheet. (2) Graphite, anode dispersant, anode conductive agent, anode adhesive, and anode solvent are mixed to prepare anode slurry, and the anode slurry is applied to the surface of anode current collector to obtain anode sheet. (3) In the manufacturing process of a lithium-ion battery, the positive electrode sheet, negative electrode sheet, and separator manufactured in the present application are assembled with other battery components, and then undergo processes such as molding, drying, packaging, liquid injection, chemical formation, and capacity selection to obtain a long-life lithium iron phosphate lithium-ion battery, and the battery types include softbank, cylindrical, aluminum case, etc., where the design CB value of the battery satisfies 0.8≦CB≦1.1, that is, the reversible capacity of the negative electrode sheet of the battery / the reversible capacity of the positive electrode sheet of the battery is 0.8-1.10, and satisfies 0.5≦(σ1 / σ2) / CB≦9.4. In some embodiments, the types of secondary batteries include softbank batteries, cylindrical batteries, aluminum case batteries, and the like.

[0043] Electrical Equipment The electrical device of the present application includes the above-mentioned secondary battery. In some embodiments, the electric device of the present application may be, but is not limited to, a backup power source, a motor, an electric car, an electric motorcycle, an electric assist bicycle, a bicycle, an electric tool, a large household battery, and the like.

[0044] Example 1 The manufacturing method of the positive electrode sheet is as follows: Lithium iron phosphate, conductive carbon black (SP), and PVDF are mixed in a mass ratio of 97:0.7:2.3, then added to NMP and mixed well to make a homogeneous mixture, and then coated on both sides of (12+1+1)μm carbon-coated aluminum foil, and then the electrode sheet is dried, rolled, stripped, and cut to obtain the positive electrode sheet. The manufacturing method of the negative electrode sheet is as follows: Graphite, conductive carbon black (SP), CMC, and SBR are mixed in a mass ratio of 96.3:0.7:1.1:1.9, then added to water and mixed thoroughly. After uniform mixing, the mixture is applied to both sides of 6 μm copper foil, and then the electrode sheet is dried, rolled, stripped, and cut to obtain the negative electrode sheet.

[0045] The separator is a polyethylene film. The electrolyte is prepared as follows: Ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate, which are organic solvents, are mixed in a volume ratio of 1:1:1. In a glove box with an argon atmosphere and a moisture content of <10 ppm, thoroughly dried lithium hexafluorophosphate is dissolved in the above organic solvent to a content of 1 mol / L, and the mixture is mixed uniformly to obtain the electrolyte.

[0046] In the manufacturing process of the lithium-ion battery, the positive electrode sheet, negative electrode sheet, and separator manufactured in the present application are assembled with other battery components, and then undergo processes such as molding, drying, packaging, electrolyte injection, chemical formation, and capacity selection to obtain a long-life lithium iron phosphate lithium-ion battery, and the battery type includes a prismatic case battery. Examples 2-14 and Comparative Example 1-2 are all manufactured according to the method of Example 1, except that the amount of active material applied and the thickness of the active material layer of the electrode sheet are adjusted to obtain the desired design CB value and areal density. The parameters of the manufactured batteries are shown in Table 1.

[0047] Battery performance measurement The cycle capacity retention rate is as follows: The nominal capacity of a secondary battery is C1, and a 1C / 1C cycle is performed a corresponding number of times at a specified temperature (25°C) to determine the discharge capacity C2, and the capacity retention rate = C2 / C1 x 100%. Energy efficiency is the percentage of energy output when discharging a lithium-ion battery compared to the energy input during the last charge.

[0048] The method for measuring energy efficiency is as follows: (1) Charge a secondary battery at a constant current of 1C up to the battery's nominal capacity, and let the charging energy be E1. (2) Leave it for 30 minutes. (3) Discharge the battery at a constant current of 1C down to the lower voltage limit (2.5V) and let the discharge energy be E2. (4) The secondary battery energy efficiency value is E2 / E1.

[0049] The method for measuring the recovery rate of storage capacity is as follows. (1) At room temperature, charge the secondary battery at a constant current of 1C up to the battery's nominal capacity of X1Ah. (2) The secondary battery is placed in a 60°C oven and stored there for 400 days. (3) Discharge the secondary battery at room temperature at 1C to 2.5V. (4) Leave it for 30 minutes. (5) At room temperature, the secondary battery is charged to 3.65 V at a constant current and voltage of 1 C, and the cut-off current is 0.05 C. (6) Leave it for 30 minutes. (7) At room temperature, discharge the secondary battery to 2.5 V at a constant current of 1 C, and the discharge capacity is X2 Ah. (8) The capacity recovery rate of a secondary battery is X2 / X1.

[0050] Table 1 shows the performance parameters of the secondary batteries prepared in Examples 1-14 and Comparative Examples 1-2. [Table 1]

[0051] Table 2 shows the measurement results of Examples 1-14 and Comparative Examples 1-2. [Table 2]

[0052] As can be seen from Tables 1 and 2, the present application limits the relationship between the positive / negative electrode areal density and the design CB value, and limits the porosity and respective areal density of the positive / negative electrode sheets to ensure a redundancy design of the positive electrode, so that sufficient lithium can replenish the loss of active lithium during the operation of the secondary battery. At the same time, it balances the lithium desorption speed of the positive / negative electrode sheets, and prevents lithium deposition and capacity drop during the operation of the secondary battery, thereby greatly improving the cycle, storage life and energy efficiency of the secondary battery.

[0053] In Examples 1-7, the porosity a% and b% of the positive / negative electrode sheets are constant at 30% and 32%, respectively, but with the increase of (σ1 / σ2) / CB and σ1 / a and the decrease of σ2 / b, the capacity retention rate of the secondary battery at 6000 cycles at 1C / 1C at 25°C, the storage capacity recovery rate at 60°C, and the energy efficiency at 1C / 1C at 25°C all tend to increase first and then decrease. The main reason is that with the increase of (σ1 / σ2) / CB, the design CB value decreases, and the more sufficient the excess design amount of the positive electrode is, the more active lithium is available to supplement the operation of the secondary battery. This is advantageous for improving cycle and storage life. However, with the increase of (σ1 / σ2) / CB, the area density σ1 of the positive electrode increases, or the area density σ2 of the negative electrode decreases, which leads to the deterioration of the kinetics of the positive electrode or the improvement of the kinetics of the negative electrode, resulting in inconsistency in the lithium desorption rate of the positive / negative electrode sheets. Therefore, when (σ1 / σ2) / CB increases to a certain extent, the cycle, storage life and energy efficiency of the secondary battery begin to decline.

[0054] In Examples 8 to 14, when the design CB values, σ1, σ2, (σ1 / σ2) / CB of the core are not changed, with the increase of a and b and the decrease of σ1 / a and σ2 / b, the capacity retention rate of the secondary battery at 6000 cycles at 25°C, the storage capacity recovery rate at 60°C, and the energy efficiency at 1C / 1C at 25°C all tend to increase first and then decrease. The main reason is that as a and b increase, the porosity of the positive / negative electrode sheets increases, improving the kinetics of the positive / negative electrode sheets of the secondary battery, which is favorable for improving the cycle, storage life, and energy efficiency. However, the larger the porosity of the positive / negative electrode sheets, the more inconsistent the lithium desorption rate of the positive / negative electrode sheets becomes, and the more likely it is that lithium deposition will occur during the operation of the secondary battery. Therefore, when a and b increase to a certain extent, the cycle, storage life, and energy efficiency of the secondary battery begin to decline.

[0055] In the above embodiments, the description of each embodiment has its own focus, and the parts of the embodiments that are not described in detail can refer to the relevant descriptions of other embodiments. The above is a detailed description of the secondary battery and electric device according to the embodiment of the present application. The specific embodiment is for explaining the principle and embodiment of the present invention, that is, it is only used to help understand the method of the present invention and its core idea. At the same time, those skilled in the art may change the specific embodiment and application scope based on the idea of ​​the present application, and in summary, it should be understood that the above description is not a limitation on the present application.

Claims

1. a positive electrode sheet including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector; a negative electrode sheet including a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector; Including, 0.5≦(σ １ / σ ２ ) / CB≦9.4 is satisfied, Here, σ １ is the surface density of the positive electrode active material layer, and is expressed in g / m ２ and σ ２ is the surface density of the negative electrode active material layer, and is expressed in g / m ２ and CB is the ratio of the capacity per unit area of ​​the negative electrode sheet to the capacity per unit area of ​​the positive electrode sheet, A secondary battery comprising:

2. 1.0≦(σ １ / σ ２ ) / CB≦6.0; 2. The secondary battery according to claim 1 .

3. 2.0≦(σ １ / σ ２ ) / CB≦3.0; 2. The secondary battery according to claim 1 .

4. 140≦σ １ / CB≦750; 4. The secondary battery according to claim 1, wherein the second electrode is a conductive material.

5. 75≦σ ２ / CB≦360; 4. The secondary battery according to claim 1, wherein the second electrode is a conductive material.

6. 0.8≦CB≦1.1; 6. The secondary battery according to claim 1, wherein the second electrode is a conductive material.

7. 5≦σ １ / a ≦ 20 is satisfied, Here, a is the porosity of the positive electrode active material layer, and the unit is %.

7. The secondary battery according to claim 1, wherein the second electrode is a conductive material.

8. 2≦σ ２ / b ≦ 9 is satisfied, Here, b is the porosity of the negative electrode active material layer, and the unit is %.

8. The secondary battery according to claim 1, wherein the second electrode is a conductive material.

9. The areal density σ of the positive electrode active material layer １ is 150≦σ １ Satisfying ≦600, 9. The secondary battery according to claim 1, wherein the second electrode is a conductive material.

10. The surface density σ of the negative electrode active material layer ２ is 80≦σ ２ ≦290, 10. The secondary battery according to claim 1, wherein the second electrode is a conductive material.

11. 28%≦a≦32%; The secondary battery according to any one of claims 7 to 10.

12. 30%≦b≦38%; The secondary battery according to any one of claims 8 to 11.

13. The positive electrode active material of the positive electrode sheet includes one or more of lithium iron phosphate, lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide; The secondary battery according to any one of claims 1 to 12.

14. The negative electrode active material of the negative electrode sheet includes one or more of artificial graphite, natural graphite, amorphous carbon, carbon nanotubes, and mesocarbon microspheres; The secondary battery according to any one of claims 1 to 13.

15. The secondary battery according to any one of claims 1 to 14, 1. An electrical device comprising:

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