Positive electrode composite materials, positive electrode sheets, secondary batteries and electrical equipment

Abstract

This application provides a positive electrode composite material, a positive electrode sheet, a secondary battery, and an electrical device. The positive electrode composite material includes at least two different positive electrode active materials, and the particle size and ion diffusion coefficient of the different active materials satisfy a certain mathematical relationship, so that the positive electrode composite material can have both high energy density and high power.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to positive electrode composite materials, positive electrode sheets, secondary batteries, and electrical devices. Background Technology

[0002] With the rapid development of battery technology, the market demands increasingly higher volumetric energy density for batteries. The industry typically improves volumetric energy density by increasing the compaction density of electrode sheets or by enhancing the operating voltage of active electrode materials. However, these two factors are always interdependent. For example, doping and modifying materials to increase their operating voltage can reduce the diffusion coefficient of active ions, affecting battery performance. Conversely, reducing the particle size of the material can decrease the compaction density of the electrode sheets.

[0003] Currently, the industry often tries to alleviate the above problems by mixing active material particles of different sizes or mixing different materials. Obviously, this will lead to a large difference in the ionic conductivity of different materials in the composite material, so the improvement on the energy density of the final battery is limited, and it still cannot take into account both the energy density and power performance of the battery. Summary of the Invention

[0004] In view of this, this application provides a positive electrode composite material, which includes at least two different positive electrode active materials, and the particle size and active ion diffusion coefficient of the different active materials satisfy a certain mathematical relationship, so that the positive electrode composite material can have both high energy density and good power performance.

[0005] A first aspect of this application provides a positive electrode composite material, comprising a first active material and a second active material, wherein the first active material and the second active material satisfy the following relationship:

[0006]

[0007] Wherein, r1 is the average primary particle size of the first active material, and r2 is the average primary particle size of the second active material, and r1 and r2 are in the same unit; D1 is the active ion diffusion coefficient of the first active material, and D2 is the active ion diffusion coefficient of the second active material, and D1 and D2 are in the same unit; and r1 and r2 are not equal, and / or D1 and D2 are not equal.

[0008] In the aforementioned positive electrode composite material, the diffusion time of active ions inside the first active material is (0.5-2) times that inside the second active material. The diffusion time of active ions inside the entire positive electrode composite material particles is limited to a controllable time range, which facilitates the adjustment of the overall high ionic conductivity of the positive electrode composite material. It also ensures that the charge and discharge performance of each region of the final positive electrode sheet is consistent, which is also conducive to the normal utilization of the material capacity. Each active material exerts its inherent energy density properties, so the positive electrode composite material can have both high energy density and good power performance.

[0009] The second aspect of this application provides a positive electrode sheet, including the positive electrode composite material provided in the first aspect of this application. Due to the use of the aforementioned positive electrode composite material, the diffusion time of active ions in each region within the active material layer of the positive electrode sheet is uniformly high, resulting in high consistency in the charge / discharge capacity of each region of the positive electrode sheet. Furthermore, this positive electrode sheet can be used to provide a battery that combines high energy density and high power.

[0010] A third aspect of this application provides a secondary battery, including the positive electrode provided in the second aspect of this application. Due to the use of the aforementioned positive electrode, this secondary battery can possess both high energy density and high power performance.

[0011] A fourth aspect of this application provides an electrical device that includes the secondary battery provided in the third aspect of this application. Due to the use of the aforementioned secondary battery, the electrical device has a longer battery life. Detailed Implementation

[0012] This application provides a cathode composite material comprising at least two different cathode active materials. The particle size and / or ion diffusion coefficient of the various active materials are different, and the particle size and active ion diffusion coefficient of the different active materials satisfy a certain mathematical relationship, so that the cathode composite material can have both high energy density and high power.

[0013] A first aspect of this application provides a positive electrode composite material, comprising a first active material and a second active material, wherein the first active material and the second active material satisfy the following relationship:

[0014]

[0015] Wherein, r1 is the average primary particle size of the first active material, and r2 is the average primary particle size of the second active material, and r1 and r2 are in the same unit; D1 is the active ion diffusion coefficient of the first active material, and D2 is the active ion diffusion coefficient of the second active material, and D1 and D2 are in the same unit; and r1 and r2 are not equal, and / or D1 and D2 are not equal.

[0016] In the above mathematical formula, r1 and r2 represent the primary particle size of the active material, which are length values, and D1 and D2 represent the active ion diffusion coefficients of the active material (e.g., lithium ions), which can be in cm. 2 / s, then r1 2 / D1 and r2 2 / D2 is measured in units of time, which can be used to measure the diffusion time of active ions within the active material particles. It can be understood that in the above-mentioned cathode composite material, r1 of the first cathode active material... 2 / D1 and r2 of the second positive electrode active material 2 / D2 satisfies the above quantitative relationship, which means that the diffusion time of active ions inside the first active material is (0.5-2) times that of active ions inside the second active material. The diffusion time of active ions inside the entire positive electrode composite particle is limited to a controllable time range, which makes it easier to adjust the overall ionic conductivity of the positive electrode composite material to be high, and also makes the charge and discharge performance of each region of the final positive electrode sheet more consistent. It is also conducive to the normal performance of the material capacity. On this basis, each active material exerts its inherent energy density attribute, so the positive electrode composite material can have both high energy density and good power performance.

[0017] For example, the above The values ​​can be 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 1.95, 1.98, etc. If... If the value is too large or too small, it will cause the diffusion time of active ions inside the active particles in the cathode composite material to vary too much. This will result in uneven diffusion time of active ions in the overall cathode composite material, making it impossible to achieve precise control. Therefore, it is impossible to obtain a battery that has both high energy density and high power performance.

[0018] Understandably, if at least one set of parameters, such as the average particle size of the primary particles and the diffusion coefficient of the active ions, are different between the first positive electrode active material and the second positive electrode active material, they are considered as two different active materials.

[0019] In this application, the average particle size of the primary particles of each active material is distinguished. Of course, in practical applications, there may be a phenomenon where multiple primary particles of active materials agglomerate into secondary particles. This application does not limit the particle size of the secondary particles of each active material, as long as the particle size of its primary particles meets the technical solution of this application.

[0020] In this application, the average primary particle size of each active material is determined by scanning electron microscopy (SEM). Specifically, SEM images of the active materials can be taken, and the average primary particle size of the sample can be determined using image analysis software such as ImageJ or particle size analysis software. Specifically, the particle size of the active material particles is observed under SEM (the number of active material particles in the sample is generally above 500, preferably above 1000), and the particle size corresponding to the cumulative percentage of active material particles reaching 50% is the aforementioned average primary particle size.

[0021] In this application, the active ion diffusion coefficient of each active material can be determined by electrochemical impedance spectroscopy (EIS). For example, taking a lithium-ion battery as an example, EIS testing of the active ion diffusion coefficient may include the following steps:

[0022] Different active materials to be tested are used as positive electrode materials and placed on both sides of the current collector suitable for the positive electrode to obtain active material electrodes.

[0023] The active material electrodes, negative electrode (e.g., lithium foil), and separator are assembled into a coin cell. A charge-discharge cycle test is performed at 25°C and a current rate of 0.1C. After 3 cycles, the state of charge (SOC) of the battery is adjusted, and the EIS (Electrostatic Indices) is measured to obtain the Warburg impedance factor σ. The active ion diffusion coefficient of each active material is then calculated using the following formula:

[0024]

[0025] Where D represents the active ion diffusion coefficient of the active material, R is the gas constant, R = 8.314 J / (mol·K); T is the absolute temperature, specifically, when the above coin cell was subjected to the above EIS test at 25°C, T = 298.15 K; n is the number of electrons per mole participating in the electrochemical reaction (for Li...). + For example, this value is 1), A is the active area of ​​the electrode; F is the Faraday constant, specifically 96485 C / mol, and C is the active ion Li in the cathode material. + The concentration. Corresponding to the positive electrode composite material of this application, the active ion diffusion coefficient of the first active material is denoted as D1, and the active ion diffusion coefficient of the second active material is denoted as D2. For other types of ion batteries, the material of the negative electrode needs to be changed for adaptation.

[0026] In this application, the second active material may include only one active material, or it may include two or more active materials simultaneously. For example, it may be a positive electrode composite material including a first active material, a second active material A, and a second active material B, where r1 is the average primary particle size of the first active material, and r... 2-1 The average particle size of the primary particles of the second active material A mentioned above, r 2-2 The average primary particle size of the second active material B is defined as r1, r2, r3, r4, r5, r6, r7, r8, r9, r1, r1, r2, r1, r2, r3, r4 ...3, r4, r3, r4, r3, r4, r3, r4, r3, r4 2-1 r 2-2 In the same units; D1 is the active ion diffusion coefficient of the first active material mentioned above, D 2-1 The active ion diffusion coefficient of the second active material A mentioned above, D 2-2 The active ion diffusion coefficient of the second active material B mentioned above, wherein D1, D 2-1 With D 2-2 Counted in the same unit; and the r1, r 2-1 The r 2-2 None of the three are equal, and / or the aforementioned D1, D 2-1 With D 2-2 Since all three are unequal, for ease of expression, the mathematical relationship between the first active material and the two second active materials can be analyzed into the following form:

[0027]

[0028] At this point, λ1 and λ2 can be the same or different.

[0029] The above description is merely a further analysis and explanation of the aforementioned technical solution. The fundamental principles and achieved technical effects are the same, and will not be repeated here. Those skilled in the art can determine the types and quantities of the second active material according to actual needs, and analyze, adapt, and expand the quantitative relationships between the primary active material, the average particle size of the primary particles, and the diffusion coefficient of the active ions among the first active material and various second active materials based on the principles described above.

[0030] In some embodiments of this application, control When the value is within the above range, the uniformity of ion diffusion time within each active material particle in the cathode composite material can be further improved, thereby facilitating better control of the ionic conductivity of the cathode composite material and ultimately leading to a battery with superior power performance and energy density. In some specific embodiments, At this time, the ionic conductivity uniformity of the positive electrode composite material is better, and it is easier to obtain a battery with both high power and high energy density. It can be understood that when the positive electrode composite material contains multiple second active materials, the above formula can be analyzed. Exemplarily, when the positive electrode composite material contains second active material A and second active material B, after analysis, the aforementioned λ1 and λ2 are both within the range of 0.8 - 1.25. In some specific embodiments, λ1 = λ2 = 1, that is,

[0031] In the present application, the above active ions may be at least one of lithium ions, sodium ions, potassium ions, magnesium ions, aluminum ions, etc.

[0032] In some embodiments of the present application, r1 and r2 are not equal. That is, the average primary particle size of the first active material is not equal to the average primary particle size of the second active material. In some specific embodiments, when the positive electrode composite material contains two or more second active materials, the average primary particle sizes of the active material particles are not equal to each other. At this time, the active ion diffusion coefficients D1 and D2 of the active material particles may be equal or not equal. In some specific embodiments, when multiple second active materials are contained simultaneously, the average primary particle sizes of different second active materials and each second active material and the first active material are not equal to each other. For example, r1 ≠ r 2-1 ≠r 2-2 。At this time, D1, D 2-1 and D 2-2 Among the three may be all different from each other, or may be all equal, or any two values between D1, D 2-1 and D 2-2 are equal. Under this condition, the active ion diffusion time inside the active material particles in each part of the positive electrode composite material system is basically the same. However, when materials with different particle sizes are combined, the positive electrode composite material can reach a higher tap density, so the energy density of the final battery can be further improved.

[0033] In some specific embodiments, when r1 and r2 are not equal, D1 and D2 are also different. Further, in some specific embodiments, r1 > r2 and D1 < D2, or it satisfies: r2 > r1 and D2 < D1. At this time, it is more beneficial to regulate and The ratio is close to 1, which makes the diffusion time of active ions among the active material particles in the cathode composite material more similar, thus making it more advantageous to obtain a battery with both high energy density and high power performance. It is understood that when the cathode composite material contains multiple secondary active materials, the above embodiments are also applicable. Those skilled in the art can adapt them according to the actual situation and the quantitative relationship between the average particle size of the primary particles and the diffusion coefficient of active ions provided in this application, which will not be elaborated here.

[0034] In some embodiments of this application, when the active ion is lithium ion, the first active material and the second active material independently include at least one of a phosphate-based cathode material and an oxide cathode material; wherein, the phosphate-based cathode material includes Li 1-a A a Mn x M y Fe 1-x-y (P 1-b E b O4, 0≤a<1, 0≤x+y<1, 0≤b<1; A includes K + Ca + Na + and NH4 + At least one of the following, M includes one or more of Ti, V, Co, Ni, Cu, Zn, Mg, Ca, Al, Nb, and Mo, and E includes one or more of N, Si, and B; the oxide cathode material includes, but is not limited to, at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based materials, lithium cobalt oxide, and lithium manganese oxide. Lithium manganese oxide can be spinel lithium manganese oxide (LiMn₂O₄) or layered lithium manganese oxide (LiMnO₂). Understandably, elemental doping of lithium iron phosphate materials is beneficial to improving the overall electrochemical performance of the material. In particular, lithium manganese iron phosphate materials obtained by manganese doping of lithium iron phosphate have a high average operating voltage, which is beneficial to improving the energy density of the cathode composite material. When lithium, iron, and / or phosphorus sites are substituted again on the basis of lithium manganese iron phosphate, the ionic and electronic conductivity, structural stability, operating voltage, and other properties of the material can be further improved. Understandably, when the cathode composite material contains multiple secondary active materials, the above embodiments are also applicable, and those skilled in the art can adapt them according to actual conditions, which will not be elaborated here.

[0035] In some specific embodiments, the first and second active materials are independently selected from phosphate-based cathode materials; or the first and second active materials are independently selected from oxide-based cathode materials. That is, the cathode composite material can be a mixed system of different phosphate-based cathode materials or a mixed system of different oxide-based cathode materials. At this time, it is easier to obtain a cathode composite material with uniform ionic conductivity. When the cathode composite material is all phosphate-based cathode materials, the safety performance of the final battery can be ensured to be higher. It can be understood that when the cathode composite material contains multiple second active materials, the above implementation manner is also equally applicable, and those skilled in the art can adapt according to the actual situation, which will not be elaborated here.

[0036] In some embodiments of the present application, the first active material is Li 1-a1 A a1 Mn x1 M y1 Fe 1-x1-y1 (P 1-b1 E b1 )O4, 0 ≤ a1 < 1, 0 ≤ x1 + y1 < 1, 0 ≤ b1 < 1; the second active material is Li 1-a2 A a2 Mn x2 M y2 Fe 1-x2-y2 (P 1-b2 E b2 )O4, 0 ≤ a2 < 1, 0 ≤ x2 + y2 < 1, 0 ≤ b2 < 1; x1 > x2 and r1 < r2, or x1 < x2 and r1 > r2. The higher the content of Mn element in the active material, the higher the average working voltage of the material, which is beneficial to improving the energy density of the material. However, as the content of Mn element increases, its ionic conductivity will decrease accordingly. Therefore, controlling the average primary particle size of the active material with a high Mn content to be smaller can make its ionic conductivity higher, so it is easier to successfully obtain a battery with both high energy density and high power performance. It can be understood that when the cathode composite material contains multiple second active materials, the above implementation manner is also equally applicable, and those skilled in the art can adapt according to the actual situation, which will not be elaborated here.

[0037] In some embodiments of the present application, the first active material is Li 1-a1 A a1 Mn x1 M y1 Fe 1-x1-y1 (P 1-b1 E b1 )O4, 0 ≤ a1 < 1, 0 ≤ x1 + y1 < 1, 0 ≤ b1 < 1; the second active material is Li 1-a2 A a2 Mn x2 M y2Fe 1-x2-y2 (P 1-b2 E b2 O4, 0≤a2<1, 0≤x2+y2<1, 0≤b2<1; x1=x2, and D1≠D2 and / or r1≠r2. When the above conditions are met, two different phosphoric acid-based positive electrode active materials with relatively high average operating voltages can be obtained. It is understood that the above embodiments are also applicable when the positive electrode composite material contains multiple secondary active materials. Those skilled in the art can adapt them according to actual conditions, and further details are omitted here.

[0038] In some embodiments of this application, r1 and r2 are respectively in the range of 20nm-5μm. That is, the average particle size of the primary particles of the first and second active materials are respectively in the range of 20nm-5μm. Exemplarily, the average particle size of the primary particles of the first and second active materials can be 20nm, 30nm, 50nm, 60nm, 80nm, 100nm, 200nm, 500nm, 800nm, 1μm, 2μm, 3μm, 4μm, 5μm, etc. In some specific embodiments, r1 and r2 are respectively in the range of 50nm-1μm. In this case, it is more advantageous to control the diffusion path of active ions inside the active material particles to be shorter, thereby improving the ionic conductivity of the cathode composite material and achieving a higher compaction density. It is understood that when the cathode composite material contains multiple secondary active materials, the above embodiments are also applicable, and those skilled in the art can adapt them according to the actual situation, which will not be elaborated here.

[0039] In some embodiments of this application, the first active material and the second active material can be directly mixed. Specifically, the mixing methods include, but are not limited to, ball milling, powder mixing, and liquid phase mixing.

[0040] Accordingly, embodiments of this application provide a positive electrode sheet, including the positive electrode composite material provided in embodiments of this application. Due to the use of the aforementioned positive electrode composite material, the diffusion time of active ions in each region within the active material layer of the positive electrode sheet is relatively high, resulting in high consistency of charge and discharge capabilities in each region of the positive electrode sheet. Furthermore, this positive electrode sheet can be used to provide a battery that combines high energy density and high power performance.

[0041] In some embodiments of this application, the positive electrode sheet includes a positive current collector and an active material layer disposed on at least one side surface of the positive current collector. The active material layer includes a positive electrode composite material, a binder, and optionally a conductive agent and a dispersant. The binder, conductive agent, and dispersant are conventional choices in the battery field. The aforementioned positive current collector can be various materials suitable for use as a current collector in the positive electrode sheet, including but not limited to elemental metal foils, alloy foils, metal-plated polymer films, or the aforementioned materials with carbon coatings on their surfaces.

[0042] In some embodiments of this application, the aforementioned positive electrode composite material, binder, conductive agent, and optional dispersant are added to a solvent (which may be N-methylpyrrolidone), mixed evenly to obtain a positive electrode slurry, and then the positive electrode slurry is coated on the surface of the positive electrode current collector. After drying, rolling, slitting and other processes, the above-mentioned positive electrode sheet is obtained.

[0043] Understandably, in other embodiments, the aforementioned first active material, second active material, binder, conductive agent, and optional binder may also be directly added to a solvent and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry is then coated onto the surface of the positive electrode current collector, and then subjected to processes such as drying, rolling, and slitting to obtain the aforementioned positive electrode sheet.

[0044] This application also provides a secondary battery, including the positive electrode provided in this application embodiment. Due to the use of the aforementioned positive electrode, the secondary battery can possess both high energy density and high power performance. The secondary battery can be a battery using a liquid electrolyte, or a semi-solid or solid battery using a semi-solid electrolyte or a solid electrolyte. In some embodiments, the secondary battery may include the aforementioned positive electrode, negative electrode, and a separator and electrolyte disposed between the positive and negative electrodes. In other embodiments, the secondary battery may include a positive electrode, a negative electrode, and a semi-solid or solid electrolyte disposed between the positive and negative electrodes. Furthermore, when using a semi-solid or solid electrolyte, the positive and negative electrodes may also contain semi-solid electrolyte materials or solid electrolyte materials.

[0045] In some embodiments of this application, the secondary battery may be a lithium-ion battery, a sodium-ion battery, a potassium-ion battery, a dual-ion battery, etc.

[0046] This application also provides an electrical device, including the secondary battery provided in this application embodiment. Due to the use of the aforementioned secondary battery, this electrical device has a longer battery life.

[0047] In some embodiments of this application, the electrical equipment includes, but is not limited to, 3C electronic products (such as mobile phones, tablets, wearable electronic devices, etc.) and vehicles (such as new energy vehicles, ships, etc.).

[0048] The technical solution of this application will be described in detail below with reference to several embodiments.

[0049] Example 1

[0050] A positive electrode composite material comprising a first active material LiMn in a mass ratio of 1:1. 0.6 Fe 0.4 PO4 and the second active material LiMn 0.8Fe 0.2 PO4. The average particle size r1 of the primary active material is 200 nm, and the diffusion coefficient D1 of the active ions (specifically lithium ions) is 8 × 10⁻⁶. -14 cm 2 / s; the average particle size r2 of the primary particles of the second active material is 100 nm, and the diffusion coefficient D2 of the active ions (specifically lithium ions) is 2 × 10⁻⁶. -14 cm 2 / s.

[0051] Example 2

[0052] The only difference from Example 1 is that the average particle size r2 of the primary particles of the second active material is 141 nm.

[0053]

[0054] Example 3

[0055] The only difference from Example 1 is that the average particle size r2 of the primary particles of the second active material is 70.7 nm.

[0056]

[0057] Example 4

[0058] The only difference from Example 1 is that the second active material is LiMn. 0.9 Fe 0.1 PO4 has an average primary particle size r2 of 100 nm and an active ion (specifically lithium ion) diffusion coefficient D2 of 1 × 10⁻⁶. -14 cm 2 / s.

[0059]

[0060] Example 5

[0061] The only difference from Example 1 is that the second active material is LiMn. 08 Fe 019 V 001 PO4 has an active ion (specifically lithium ion) diffusion coefficient D2 of 4 × 10⁻⁶. -14 cm 2 / s.

[0062] Example 6

[0063] The only difference from Example 1 is that both the first and second active materials are LiMn. 0.6 Fe 0.4Both PO4 and PO4 have active ion (specifically lithium ion) diffusion coefficients D1 and D2 of 8 × 10⁻⁶. -14 cm 2 / s; the average primary particle size r1 of the first active material is 200nm, and the average primary particle size r2 of the second active material is 163nm.

[0064] Example 7

[0065] A positive electrode composite material comprising a first active material LiMn in a mass ratio of 1:1. 0.6 Fe 0.4 PO4 and the second active material LiMn 0.8 Fe 0.19 V 0.01 PO4. The average particle size r1 of the primary active material is 200 nm, and the diffusion coefficient D1 of the active ions (specifically lithium ions) is 8 × 10⁻⁶. -14 cm 2 / s; the average particle size r2 of the primary particles of the second active material is 200 nm, and the diffusion coefficient D2 of the active ions (specifically lithium ions) is 4 × 10⁻⁶. -14 cm 2 / s.

[0066] Example 8

[0067] A positive electrode composite material comprising a first active material LiMn in a mass ratio of 1:1. 0.8 Fe 0.2 PO4 and the second active material LiMn 0.8 Fe 0.19 V 0.01 PO4. The average particle size r1 of the primary active material is 800 nm, and the diffusion coefficient D1 of the active ions (specifically lithium ions) is 2 × 10⁻⁶. -14 cm 2 / s; the average particle size r2 of the primary particles of the second active material is 1600 nm, and the diffusion coefficient D2 of the active ions (specifically lithium ions) is 4 × 10⁻⁶. -14 cm 2 / s.

[0068] Example 9

[0069] A positive electrode composite material includes a first active material LiMn2O4 and a second active material LiNi in a mass ratio of 1:1. 0.5 Mn 1.5 O4, wherein the average particle size r1 of the primary active material is 4 μm, and the diffusion coefficient D1 of the active ion (specifically lithium ion) is 4 × 10⁻⁶.-9 cm 2 / s; the average particle size r2 of the primary particles of the second active material is 2 μm, and the diffusion coefficient D2 of the active ions (specifically lithium ions) is 1 × 10⁻⁶. -9 cm 2 / s.

[0070]

[0071] To highlight the beneficial effects of the embodiments, the following comparative examples are provided.

[0072] Comparative Example 1

[0073] The only difference from Example 1 is that the average particle size r2 of the primary particles of the second active material is 50 nm.

[0074]

[0075] Comparative Example 2

[0076] The only difference from Comparative Example 1 is that the average particle size r2 of the primary particles of the second active material is 158 nm.

[0077]

[0078] Comparative Example 3

[0079] The only difference from Example 1 is that the second active material is LiMn. 0.7 Fe 0.29 V 0.01 PO4 has an active ion (specifically lithium ion) diffusion coefficient D2 of 8 × 10⁻⁶. -14 cm 2 / s.

[0080] Comparative Example 4

[0081] The only difference from Example 1 is that the second active material is LiMn. 0.92 Fe 0.08 PO4 has a diffusion coefficient D2 of 0.8 × 10⁻⁶ for its active ions (specifically lithium ions). -14 cm 2 / s.

[0082] Comparative Example 5

[0083] The only difference from Example 9 is that the average particle size r2 of the primary particles of the second active material is 1 μm.

[0084] The parameters of the first and second active materials of each embodiment and comparative example are summarized in Table 1.

[0085] Table 1

[0086]

[0087]

[0088] It should be noted that the lithium-ion diffusion coefficients of the active materials in the above embodiments and comparative examples were all determined using the EIS method. Specifically, the following steps are included:

[0089] The active materials, binder (specifically polyvinylidene fluoride), and conductive agent (specifically Super P) are mixed evenly in a solvent at a mass ratio of 90:5:5 to obtain a positive electrode slurry. The positive electrode slurry is then coated onto the surface of a positive electrode current collector (specifically aluminum foil), and after drying, rolling, and slitting, the active material electrodes are obtained.

[0090] The active material electrode, negative electrode (lithium foil), and separator were assembled into a coin cell. A charge-discharge cycle test was conducted at 25°C with a current rate of 0.1C. After three cycles, the state of charge (SOC) of the battery was adjusted, and the EIS (Electrostatic Indices) was measured to obtain the Warburg impedance factor σ. The active ion diffusion coefficient of each active material was calculated using the following formula:

[0091]

[0092] Where D represents the active ion diffusion coefficient of the active material, R is the gas constant, R = 8.314 J / (mol·K); T is the absolute temperature, T = 298.15 K; and n is the number of electrons per mole participating in the electrode reaction (for Li...). + For example, this value is 1), A is the surface area of ​​the active material electrode, F is the Faraday constant, specifically 96485 C / mol, and C is the active ion Li in the cathode material. + The concentration.

[0093] The positive electrode sheet was prepared using the positive electrode composite material provided in the above embodiments and comparative examples, and the battery was assembled and tested. The specific operation is as follows:

[0094] (1) The positive electrode composite material, binder (specifically polyvinylidene fluoride), and conductive agent (specifically carbon nanotubes) provided in each embodiment and comparative example are added to the solvent (specifically N-methylpyrrolidone) in a mass ratio of 90:5:5. After mixing evenly, a positive electrode slurry is obtained. The positive electrode slurry is coated on the surface of the positive electrode current collector (specifically aluminum foil), and after drying, rolling and cutting, each positive electrode sheet is obtained.

[0095] (2) The above positive electrode plates, negative electrode plates, and separators are stacked alternately to form a full cell, and electrolyte is injected.

[0096] (3) Performance Testing

[0097] The electrochemical performance of the batteries prepared in the above embodiments and comparative examples was tested as follows:

[0098] The 0.1C charge specific capacity of the battery was determined by charging it to 4.3V at a constant current and constant voltage of 0.1C at 25±3℃, with a cutoff current of 0.02C. The 0.1C charge specific capacity was then calculated.

[0099] Determine the 1C charging constant current ratio of the battery: Charge the battery to 4.3V at a constant current and constant voltage of 1C at 25±3℃, with a cutoff current of 0.02C. Calculate the specific capacity and total specific capacity of the constant current section, and calculate the 1C charging constant current ratio.

[0100] The total charging time of the battery under constant current and constant voltage at 0.33C and cutoff current at 0.02C was determined: the battery was charged to 4.3V at constant current and constant voltage at 0.33C at 25±3℃, and the cutoff current was 0.02C. The total charging time of the entire process was calculated.

[0101] Table 2 summarizes the electrochemical parameters of the batteries in each example and comparative example.

[0102]

[0103]

[0104] As can be seen from the data in Table 2, when the first and second positive electrode active materials of the embodiments and comparative batteries are both selected from phosphate-based positive electrode materials or both selected from oxide positive electrode materials, the electrochemical parameters of the batteries in the embodiments of this application are all superior to those of the comparative batteries. Specifically, a shorter total charging time indicates that Li₂ is extracted from the battery's positive electrode. + The faster the charging rate, the higher the battery's power performance. All the batteries were first charged at 1C constant current and constant voltage to 4.3V, then charged at 4.3V constant voltage with the current gradually reduced to 0.02C before stopping. The greater the proportion of batteries charged at 1C constant voltage and constant current, the faster the battery charges and the better its power performance.

[0105] Furthermore, when the cathode materials are both phosphoric acid-based cathode materials, specifically when the first active material is both LiMn... 0.6 Fe 0.4 Both PO4 and the second active material are LiMn 0.8 Fe 0.2 At PO4, it can be seen from the data in Examples 1-3 that when When the value is in the range of 0.8-1.25 (Example 1), the battery exhibits higher specific capacity, higher charging constant current ratio, shorter total charging time, and better overall battery performance.

[0106] In the description of this specification, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0107] The above description is an exemplary embodiment of this application. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principles of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

Claims

1. A positive electrode composite material, characterized in that, The positive electrode composite material includes a first active material and a second active material, and the first active material and the second active material satisfy the following relationship: Wherein, r1 is the average primary particle size of the first active material, and r2 is the average primary particle size of the second active material, and r1 and r2 are in the same unit; D1 is the active ion diffusion coefficient of the first active material, and D2 is the active ion diffusion coefficient of the second active material, and D1 and D2 are in the same unit; and r1 and r2 are not equal, and / or D1 and D2 are not equal.

2. The positive electrode composite material according to claim 1, characterized in that, The r1 and the r2 are not equal.

3. The positive electrode composite material according to claim 1, characterized in that, The first active material and the second active material independently comprise at least one of a phosphoric acid-based cathode material and an oxide cathode material; wherein, the phosphoric acid-based cathode material includes Li 1-a A a Mn x M y Fe 1-x-y (P 1-b E b O4, 0≤a<1, 0≤x+y<1, 0≤b<1; A includes K + Ca 2+ Na + and NH4 + At least one of the following, M includes one or more of Ti, V, Co, Ni, Cu, Zn, Mg, Ca, Al, Nb and Mo, and E includes one or more of N, Si and B; the oxide cathode material includes one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based materials, lithium cobalt oxide and lithium manganese oxide.

4. The positive electrode composite material according to claim 3, characterized in that, The first active material is Li 1- a1 A a1 Mn x1 M y1 Fe 1-x1-y1 (P 1-b1 E b1 )O4, 0 ≤ a1 < 1, 0 ≤ x1 + y1 < 1, 0 ≤ b1 < 1; the second active material is Li 1- a2 A a2 Mn x2 M y2 Fe 1-x2-y2 (P 1-b2 E b2 )O4, 0 ≤ a2 < 1, 0 ≤ x2 + y2 < 1, 0 ≤ b2 < 1; x1 > x2 and r1 < r2, or, x1 < x2 and r1 > r2.

5. The positive electrode composite material according to claim 3, characterized in that, The first active material is Li 1- a1 A a1 Mn x1 M y1 Fe 1-x1-y1 (P 1-b1 E b1 O4, 0≤a1<1, 0≤x1+y1<1, 0≤b1<1; the second active material is Li 1- a2 A a2 Mn x2 M y2 Fe 1-x2-y2 (P 1-b2 E b2 )O4, 0≤a2<1, 0≤x2+y2<1, 0≤b2<1; x1=x2.

6. The positive electrode composite material according to claim 1, characterized in that, The r1 and r2 are respectively in the range of 20nm-5μm.

7. The positive electrode composite material according to any one of claims 1-6, characterized in that, 8. A positive electrode sheet, characterized in that, The positive electrode sheet includes the positive electrode composite material as described in any one of claims 1-7.

9. A secondary battery, characterized in that, The secondary battery includes the positive electrode as described in claim 8.

10. An electrical appliance, characterized in that, The electrical equipment includes the secondary battery as described in claim 9.

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