Positive plate, battery and electronic equipment

Abstract

The invention provides a positive plate, a battery and electronic equipment. The positive plate comprises a positive current collector and a positive active layer positioned on at least one surface of the positive current collector; the positive electrode active layer comprises a first positive electrode active layer and a second positive electrode active layer which are sequentially stacked in a direction far away from the positive electrode current collector; the first positive electrode active layer comprises a first positive electrode active material, and the first positive electrode active material comprises lithium manganese iron phosphate and a lithium oxide compound; the second positive electrode active layer comprises a second positive electrode active material, and the second positive electrode active material comprises a lithium oxide compound and nickel cobalt lithium manganate. When the positive plate is applied to the battery, the battery is not easy to generate gas during high-temperature storage, so that the safety performance of the battery is improved.

Description

Technical Field

[0001] This invention relates to a positive electrode, a battery, and an electronic device, belonging to the field of new energy technology. Background Technology

[0002] Currently, in order to reduce battery production costs and improve battery cycle life and energy density, lithium manganese iron phosphate and lithium nickel cobalt manganese oxide are often mixed as positive electrode active materials to prepare positive electrode sheets, thereby manufacturing batteries. However, under high temperature conditions, the side reactions between lithium manganese iron phosphate and lithium nickel cobalt manganese oxide are intense, resulting in serious gas production in the battery, which seriously affects the safety performance of the battery. Summary of the Invention

[0003] This invention provides a positive electrode sheet that, when applied to a battery, can prevent the battery from generating gas during high-temperature storage, thereby improving the battery's safety performance.

[0004] The present invention provides a battery including the above-mentioned positive electrode, which is not prone to gas generation when stored at high temperature and has excellent safety performance.

[0005] The present invention provides an electronic device whose driving source or energy storage source is the aforementioned battery. Therefore, the battery device has excellent battery life and longevity, and has broad market application prospects.

[0006] The present invention provides a positive electrode sheet, wherein the positive electrode sheet includes a positive current collector and a positive active layer located on at least one surface of the positive current collector;

[0007] The positive electrode active layer includes a first positive electrode active layer and a second positive electrode active layer stacked sequentially in the direction away from the positive electrode current collector;

[0008] The first positive electrode active layer includes a first positive electrode active material, which includes lithium manganese iron phosphate and lithium oxide compounds;

[0009] The second positive electrode active layer includes a second positive electrode active material, which includes lithium oxide compound and lithium nickel cobalt manganese oxide.

[0010] In the positive electrode as described above, the molecular formula of the lithium manganese iron phosphate is LiFe. x Mn (1-x) PO4, where 0.1 ≤ x ≤ 0.5.

[0011] The positive electrode as described above, wherein at least a portion of the surface of the lithium manganese iron phosphate has a carbon coating layer.

[0012] The positive electrode as described above, wherein the lithium nickel cobalt manganese oxide has the molecular formula LiNi. z Coy M1 (1-z-y) O2, where M1 is Mn and / or Al, 0.33≤z≤0.95, 0≤y≤0.3.

[0013] In the positive electrode as described above, the molecular formula of the lithium oxide compound is Li. c M2 a O b M2 is at least one of Mn, Ni and Co, 1≤a≤2, 2≤b≤3, and 0.9≤c≤2.

[0014] In the positive electrode sheet as described above, the mass ratio of the lithium oxide compound, the lithium manganese iron phosphate and the lithium nickel cobalt manganese oxide in the positive electrode active layer is (0.4-9.5):(0.25-9.2):(0.25-4.75).

[0015] In the positive electrode sheet as described above, the mass ratio of the lithium oxide compound to the lithium manganese iron phosphate in the first positive electrode active material is (0.5-9.5):(9.5-0.5); and / or,

[0016] In the second positive electrode active material, the mass ratio of the lithium oxide compound to the lithium nickel cobalt manganese oxide is (0.5-9.5):(9.5-0.5).

[0017] In the positive electrode sheet described above, the ratio of the areal density of the first positive electrode active layer to the areal density of the second positive electrode active layer is (5-9):(1-5).

[0018] In the positive electrode sheet described above, the areal density of the first positive electrode active layer is 125-225 g / m². 2 ; and / or,

[0019] The areal density of the second positive electrode active layer is 25-125 g / m². 2 .

[0020] In the positive electrode sheet described above, the ratio of the thickness of the first positive electrode active layer to the thickness of the second positive electrode active layer is (5-10):(1-5).

[0021] The positive electrode sheet as described above, wherein the thickness of the first positive electrode active layer is 40-90 μm; and / or,

[0022] The thickness of the second positive electrode active layer is 8-50 μm.

[0023] The positive electrode sheet as described above, wherein the lithium manganese iron phosphate particle size is 20-200 nm; and / or,

[0024] The lithium oxide compound has a particle size of 4-30 μm; and / or,

[0025] The lithium nickel cobalt manganese oxide has a particle size of 0.3-35 μm.

[0026] The present invention provides a battery, wherein the battery includes a positive electrode as described above.

[0027] The present invention provides an electronic device, wherein the driving source or energy storage source of the electronic device is a battery as described above.

[0028] The positive electrode sheet of the present invention has a special composition. When applied to a battery, the positive electrode sheet can improve the high-temperature storage performance of the battery, thereby improving the safety performance of the battery.

[0029] The battery of the present invention, having included the above-mentioned positive electrode, has excellent high-temperature storage performance and is suitable for widespread application.

[0030] The present invention provides an electronic device whose driving source or energy storage source is the aforementioned battery. Therefore, the battery device has excellent battery life and longevity, and has broad market application prospects. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments of the present invention or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the positive electrode sheet in some embodiments of the present invention.

[0033] Explanation of reference numerals in the attached figures:

[0034] 1: Positive current collector;

[0035] 2: First positive electrode active layer;

[0036] 3: Second positive electrode active layer. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0038] Figure 1This is a schematic diagram of the positive electrode structure in some embodiments of the present invention. For example... Figure 1 As shown, a first aspect of the present invention provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector 1 and a positive active layer located on at least one surface of the positive current collector 1;

[0039] The positive electrode active layer includes a first positive electrode active layer 2 and a second positive electrode active layer 3 stacked sequentially in the direction away from the positive electrode current collector 1;

[0040] The first positive electrode active layer 2 includes a first positive electrode active material, which includes lithium iron manganese phosphate and lithium oxide compounds.

[0041] The second positive electrode active layer 3 includes a second positive electrode active material, which includes lithium manganese oxide and lithium nickel cobalt manganese oxide.

[0042] In this invention, the surfaces of the positive current collector 1 refer to the two surfaces with the largest area that are arranged opposite each other in the positive current collector 1. This invention can form a positive electrode sheet by depositing a positive active layer on one surface of the positive current collector 1, or by depositing positive active layers on both surfaces of the positive current collector 1 respectively.

[0043] When one surface of the positive current collector 1 has a positive active layer, the positive electrode sheet sequentially includes the positive current collector 1, the first positive active layer 2, and the second positive active layer 3 in the stacking direction; when both surfaces of the positive current collector 1 have positive active layers, the positive electrode sheet sequentially includes the second positive active layer 3, the first positive active layer 2, the positive current collector 1, the first positive active layer 2, and the second positive active layer 3 in the stacking direction.

[0044] The present invention does not specifically limit the positive current collector 1, and it can be any positive current collector 1 commonly used in the art, such as aluminum foil.

[0045] It is understood that the first positive electrode active layer 2 and the second positive electrode active layer 3 of the present invention further include a conductive agent and a binder. The conductive agent can be a commonly used conductive agent in the art. For example, the conductive agent in the first positive electrode active layer 2 and the second positive electrode active layer 3 can each be independently selected from at least one of conductive carbon black, conductive graphite, coarse conductive carbon nanotubes, fine conductive carbon nanotubes, arrayed tubes, single-walled conductive carbon nanotubes, and modified derivatives of the above substances. The binder can be a commonly used binder in the art. For example, the binder in the first positive electrode active layer 2 and the second positive electrode active layer 3 can each independently include polyvinylidene fluoride (PVDF). Further, the molecular weight of PVDF can be 500,000 to 1,000,000 Da.

[0046] The first positive electrode active layer 2 of the present invention is disposed close to the positive electrode current collector 1. The first positive electrode active material of the first positive electrode active layer 2 includes lithium manganese iron phosphate and lithium oxide compound. In the first positive electrode active material, the potential difference between lithium manganese iron phosphate and lithium oxide compound is small, which can mitigate the occurrence of interfacial side reactions between lithium manganese iron phosphate and lithium oxide compound, reduce the risk of gas generation in the battery under high-temperature storage, and improve the safety performance of the battery. Furthermore, since the particle size difference between lithium manganese iron phosphate and lithium oxide compound is usually large, the stacking of particles of different sizes also helps to increase the compaction density of the positive electrode sheet, thereby ensuring the energy density of the battery; the second positive electrode active layer 2... The second positive electrode active layer 3 is located on the outer layer of the positive electrode sheet. The second positive electrode active layer 3 includes a second positive electrode active material, which includes lithium oxide compound and lithium nickel cobalt manganese oxide. The potential difference between the lithium oxide compound and lithium nickel cobalt manganese oxide is small, which can slow down the occurrence of interfacial side reactions between lithium nickel cobalt manganese oxide and lithium oxide compound, reduce the risk of gas generation in the battery under high temperature storage, and improve the safety performance of the battery. In addition, the lithium nickel cobalt manganese oxide on the outer layer of the positive electrode sheet is conducive to adsorbing and intercepting metal Mn and Fe ions dissolved from the inner layer of the positive electrode sheet, reducing the risk of metal ions in the positive electrode sheet detaching and attacking the SEI film of the negative electrode, which is beneficial to improving the battery life.

[0047] It is worth mentioning that, due to the advantages of high-rate charge and discharge of lithium oxide compounds, the positive electrode sheet of the present invention, which includes lithium oxide compounds, also has excellent charge and discharge capabilities in the high-voltage range.

[0048] Therefore, by using lithium oxide compounds and lithium manganese iron phosphate as the first positive electrode active material of the first positive electrode active layer 2, and lithium oxide compounds and lithium nickel cobalt manganese oxide as the second positive electrode active material of the second positive electrode active layer 3, this invention can reduce the gas generation problem caused by potential mismatch between positive electrode active materials and improve the high-temperature storage performance of the battery. Furthermore, using a mixture of large-particle lithium oxide compounds and small-particle lithium manganese iron phosphate can increase the compaction density of the positive electrode sheet, ensuring the energy density of the battery. The introduction of lithium oxide compounds further improves the charge and discharge capabilities of the battery. In summary, when the positive electrode sheet of this invention is applied to a battery, it enables the battery to possess excellent high-temperature storage performance, rate performance, and energy density.

[0049] This invention does not specifically limit the use of lithium manganese iron phosphate, and can be any commonly used lithium manganese iron phosphate-containing material in the art. In some embodiments of this invention, the molecular formula of lithium manganese iron phosphate is LiFe. x Mn (1-x) PO4, where 0.1 ≤ x ≤ 0.5.

[0050] Furthermore, at least a portion of the surface of lithium manganese iron phosphate has a carbon coating layer.

[0051] The lithium manganese iron phosphate of the present invention has an olivine structure. A portion of the surface of the lithium manganese iron phosphate may have a carbon coating layer; the entire surface of the lithium manganese iron phosphate may also have a carbon coating layer. In the present invention, lithium manganese iron phosphate with a carbon coating layer can be prepared by methods commonly used in the art, or it can be obtained commercially.

[0052] In some implementations, EDS can be used to perform a surface scan of the cross-section of the positive electrode to identify the characteristic elements of each positive electrode active material. Then, a spot scan of the EDS can be used to perform further elemental analysis on the corresponding positive electrode active material to obtain its specific composition. For example, the molar percentage of Fe and the molar percentage of Manganese in lithium manganese iron phosphate can be obtained.

[0053] In this invention, when lithium manganese iron phosphate includes a carbon coating layer, the carbon coating layer can protect the core and improve the stability of lithium manganese iron phosphate, and also improve its conductivity. Therefore, this lithium manganese iron phosphate can improve the high-temperature storage performance and rate performance of the battery.

[0054] This invention does not specifically limit the use of lithium nickel cobalt manganese oxide, and it can be any metal oxide containing Ni, Co, Mn, or Li commonly used in the art. In some embodiments of this invention, the molecular formula of lithium nickel cobalt manganese oxide is LiNi. z Co y M1 (1-z-y) O2, where M1 is Mn and / or Al, 0.33≤z≤1, 0≤y≤0.33.

[0055] For example, lithium nickel cobalt manganese oxide can be at least one of NCM111, NCM523, NCM712, NCM811 or other high-nickel ternary materials. Furthermore, lithium nickel cobalt manganese oxide can be at least one of monocrystalline or polycrystalline materials.

[0056] In some embodiments of the present invention, the molecular formula of the lithium oxide compound is Li. c M2 a O b M2 is at least one of Mn, Ni and Co, 1≤a≤2, 2≤b≤3, and 0.9≤c≤2.

[0057] For example, the lithium oxide compound of the present invention may be at least one of the following: spinel-structured lithium manganese oxide (LiMn2O4), layered Li2MnO3, orthogonal layered LiMnO2, layered LiNiO2, and layered LiCoO2.

[0058] Furthermore, the lithium oxide compound is lithium manganese oxide. When the lithium oxide compound is lithium manganese oxide, the fully charged static potential of lithium iron manganese phosphate is approximately 4.0V, and the fully charged static potential of lithium manganese oxide is approximately 4.1V. In the first positive electrode active material, the potential difference between lithium iron manganese phosphate and lithium manganese oxide is approximately 0.1V. This smaller potential difference can further mitigate the occurrence of interfacial side reactions between lithium iron manganese phosphate and lithium manganese oxide, reduce the risk of gas generation during high-temperature storage, and improve battery safety. Furthermore, since the particle size difference between lithium iron manganese phosphate and lithium manganese oxide is usually large, the accumulation of particles of different sizes also helps to increase the compaction density of the positive electrode sheet, thereby ensuring the energy density of the battery. The second positive electrode active layer 3 is located on the outer layer of the positive electrode sheet. Layer 3 includes a second positive electrode active material, comprising lithium manganese oxide and lithium nickel cobalt manganese oxide. The fully charged static potential of lithium manganese oxide is approximately 4.1V, and that of lithium nickel cobalt manganese oxide is approximately 4.25V. The potential difference between lithium manganese oxide and lithium nickel cobalt manganese oxide is approximately 0.15V. This small potential difference helps mitigate interfacial side reactions between lithium nickel cobalt manganese oxide and lithium manganese oxide, reducing the risk of gas generation during high-temperature storage and improving battery safety. Furthermore, the lithium nickel cobalt manganese oxide on the outer layer of the positive electrode helps adsorb and intercept dissolved Mn and Fe ions from the inner layer of the positive electrode, reducing the risk of metal ions escaping from the positive electrode and attacking the SEI film of the negative electrode, thus improving battery life. Simultaneously, lithium manganese oxide has the advantage of high-rate charge and discharge; the positive electrode in this invention, including lithium manganese oxide, exhibits superior charge and discharge capabilities in the high-voltage range.

[0059] In some embodiments of the present invention, the positive electrode active layer includes a positive electrode active material. When the mass ratio of lithium oxide compound, lithium manganese iron phosphate and lithium nickel cobalt manganese oxide in the positive electrode active material is (0.4-9.5):(0.25-9.2):(0.25-4.75), the lithium oxide compound, lithium manganese iron phosphate and lithium nickel cobalt manganese oxide in the positive electrode active layer can be better matched, giving full play to the role of lithium oxide compound, lithium manganese iron phosphate and lithium nickel cobalt manganese oxide, thereby enabling the battery to have excellent high-temperature storage performance, rate performance and energy density.

[0060] In some embodiments of the present invention, the mass ratio of lithium oxide compound to lithium manganese iron phosphate in the first positive electrode active material is (0.5-9.5):(0.5-9.5); and / or,

[0061] In the second positive electrode active material, the mass ratio of lithium oxide compound to lithium nickel cobalt manganese oxide is (0.5-9.5):(0.5-9.5).

[0062] In some implementations, SEM and EDS can be used together to obtain the interface between the first positive electrode active layer 2 and the second positive electrode active layer 3. Then, EDS regional surface scanning can be used to determine the elemental proportions of layers with different thicknesses, obtain the elemental distribution of the positive electrode active material in the first positive electrode active layer 2 and the elemental distribution of the positive electrode active material in the second positive electrode active layer 3, and thus obtain the mass ratio of lithium oxide to lithium manganese iron phosphate in the first positive electrode active material and the mass ratio of lithium oxide to lithium nickel cobalt manganese oxide in the second positive electrode active material.

[0063] When the mass ratio of lithium manganese oxide to lithium manganese iron phosphate in the first positive electrode active material meets the above range, the lithium oxide compound can be better matched with the lithium manganese iron phosphate, giving full play to the role of the lithium oxide compound and the lithium manganese iron phosphate, so that the positive electrode has excellent rate performance, high temperature storage performance and energy density.

[0064] When the mass ratio of lithium oxide to lithium nickel cobalt manganese oxide in the second positive electrode active material meets the above range, the lithium oxide and lithium nickel cobalt manganese oxide can be better matched, giving full play to the role of the lithium oxide and lithium nickel cobalt manganese oxide, so that the positive electrode has both excellent energy density and high temperature storage performance.

[0065] Furthermore, in the first positive electrode active material, the mass ratio of lithium oxide compound to lithium manganese iron phosphate is (1-9):(9-1); and / or,

[0066] In the second positive electrode active material, the mass ratio of lithium oxide compound to lithium nickel cobalt manganese oxide is (1-9):(9-1).

[0067] In some embodiments of the present invention, when the ratio of the areal density of the first positive electrode active layer 2 to the areal density of the second positive electrode active layer 3 is (5-9):(1-5), the first positive electrode active layer 2 and the second positive electrode active layer 3 can be better matched, thereby enabling the battery to have superior high-temperature storage performance, rate performance, and energy density. Here, areal density refers to the mass of positive electrode active material per unit area in the positive electrode active layer.

[0068] Furthermore, when the areal density of the first positive electrode active layer 2 is 125-225 g / m² 2 ; and / or,

[0069] The areal density of the second positive electrode active layer 3 is 25-125 g / m³. 2 During storage, the amount of gas produced is significantly reduced, increasing the safety of the battery throughout its lifespan.

[0070] The inventors also discovered in their research that when the ratio of the thickness of the first positive electrode active layer 2 to the thickness of the second positive electrode active layer 3 is (5-10):(1-5), the amount of gas generated during storage is significantly reduced, which increases the safety of the battery during its life cycle.

[0071] Furthermore, the thickness of the first positive electrode active layer 2 is 40-90 μm; and / or,

[0072] When the thickness of the second positive electrode active layer 3 is 8-50μm, the positive electrode sheet can further reduce the amount of gas generated during battery storage and improve the safety of the battery during its life cycle when it is applied to a battery.

[0073] In some implementations, SEM and EDS can be used together to test the cross-section of the positive electrode sheet. The thickness of the first positive electrode active layer 2 and the second positive electrode active layer 3 can be obtained by using the SEM scale tool in conjunction with the EDS surface scan.

[0074] In some embodiments of the present invention, when the particle size of lithium manganese iron phosphate is 20-200 nm; and / or,

[0075] The particle size of lithium manganese oxide is 4-30 μm; and / or,

[0076] When the particle size of lithium nickel cobalt manganese oxide is 0.3-35 μm, in the first positive electrode active layer 2, the small particles of lithium manganese iron phosphate can stack better with the large particles of lithium manganese oxide, thereby increasing the compaction density of the first positive electrode active layer 2 and ensuring that the battery has excellent energy density. In the second positive electrode active layer 3, lithium manganese oxide and lithium nickel cobalt manganese oxide can stack better, thereby increasing the compaction density of the second positive electrode active layer 3 and ensuring that the battery has excellent energy density. Here, the particle size refers to the particle size distribution range of each material.

[0077] In some implementations, SEM can be used to test the cross-section of the positive electrode, and the particle size of lithium oxide, lithium manganese iron phosphate, and lithium nickel cobalt manganese oxide can be obtained using the SEM scale.

[0078] A second aspect of the present invention provides a battery comprising the positive electrode of the first aspect.

[0079] It is understood that a battery also includes a separator, a negative electrode, an electrolyte, and an outer packaging. In this invention, the positive electrode, separator, and negative electrode can be stacked to form a stacked electrode assembly, which is then placed in an outer packaging, and an electrolyte is injected into the outer packaging. After sealing and formation, a battery is obtained. Alternatively, the positive electrode, separator, and negative electrode can be stacked and then wound to form a wound electrode assembly. The electrode assembly is then placed in an outer packaging, and an electrolyte is injected into the outer packaging. After sealing and formation, a battery is obtained.

[0080] The battery of the present invention, because it includes the positive electrode sheet of the first aspect, has excellent rate performance, high-temperature storage performance and energy density, and has broad application prospects.

[0081] A third aspect of the present invention provides an electronic device, wherein the driving source or energy storage source of the electronic device is a battery of the second aspect.

[0082] In some implementations, the electronic device can be any device that uses a secondary battery as a power source or energy storage source, such as a mobile phone, a navigator, a drone, or an electric vehicle.

[0083] Since the driving source or energy storage source of the electronic device of the present invention is the battery of the second aspect, the electronic device has excellent safety performance and battery life, and has a wide market application prospect.

[0084] The present invention will now be described in detail through specific embodiments.

[0085] Example 1

[0086] The battery in this embodiment is prepared by a method including the following steps:

[0087] 1) Preparation of positive electrode sheet

[0088] A positive electrode sheet is prepared by a double-layer coating method. The positive electrode sheet includes an aluminum foil and positive electrode active layers located on the two surfaces of the aluminum foil.

[0089] The positive electrode active layer includes a first positive electrode active layer and a second positive electrode active layer in sequence in the direction away from the current collector;

[0090] The first positive electrode active layer comprises a first positive electrode active material, a conductive agent (conductive carbon black), and a binder (polyvinylidene fluoride), with a mass ratio of 95:2:3 for the first positive electrode active material, the conductive agent, and the binder; the first positive electrode active material comprises LiFeO2 sourced from Defang Nano. 0.4 Mn 0.6 The PO4 component is designated dy16 (with a carbon coating content of 1.6 wt%), and lithium manganese oxide is also present. The mass ratio of lithium manganese iron phosphate to lithium manganese oxide is 9.5:0.5. The lithium manganese iron phosphate has a carbon coating on its surface, and its molecular formula is LiFe. 0.4 Mn 0.6 PO4;

[0091] The second positive electrode active layer comprises a second positive electrode active material, a conductive agent (conductive carbon black), and a binder (polyvinylidene fluoride), with a mass ratio of 95:2:3 for the second positive electrode active material, the conductive agent, and the binder. The second positive electrode active material comprises lithium nickel cobalt manganese oxide and lithium manganese oxide, with a mass ratio of 0.5:9.5 for lithium manganese oxide and lithium nickel cobalt manganese oxide. The lithium nickel cobalt manganese oxide is LiNi. 0.7 Co 0.1 Mn 0.2 O2;

[0092] The positive electrode active layer includes positive electrode active material, in which the mass ratio of lithium manganese iron phosphate, lithium manganese oxide, and lithium nickel cobalt manganese oxide is 4.75:0.5:4.75.

[0093] The areal density ratio of the first positive electrode active layer to the second positive electrode active layer is 5:5, and the areal density of the first positive electrode active layer on one side is 125 g / m². 2 The single-sided areal density of the second positive electrode active layer is 125 g / m². 2 ;

[0094] The thickness ratio of the first positive electrode active layer to the second positive electrode active layer is 5.3:4.7, the thickness of the first positive electrode active layer is 41.5 μm, and the thickness of the second positive electrode active layer is 36.2 μm.

[0095] The D50 of lithium manganese oxide is 23 μm, that of lithium iron manganese phosphate is 110 nm, and that of lithium nickel manganese cobalt oxide is 25 μm.

[0096] 2) Preparation of negative electrode sheet

[0097] The negative electrode sheet includes a copper foil and negative electrode active layers located on two surfaces of the copper foil;

[0098] The negative electrode active layer includes artificial graphite, conductive agent carbon black, and binder sodium carboxymethyl cellulose, and the mass ratio of artificial graphite, conductive agent, and binder is 94:1:5.

[0099] The capacity excess (N / P) of the negative electrode is 10%.

[0100] 3) Battery manufacturing

[0101] In the glove box, the positive electrode sheet, polypropylene PE separator, and negative electrode obtained after cutting and pressing are stacked to obtain the electrode assembly. The electrode assembly is placed in the aluminum-plastic film, the electrolyte is injected into the aluminum-plastic film, and the battery is obtained after sealing and formation.

[0102] The electrolyte includes solvent, LiPF6, VC, DTD and PS. The concentration of LiPF6 in the electrolyte is 1 mol / L. The solvent includes EC and EMC with a volume ratio of 3:7. The mass percentage of VC is 1.5%, the mass percentage of DTD is 1%, and the mass percentage of PS is 1%.

[0103] Example 2

[0104] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0105] 1) Preparation of positive electrode sheet

[0106] In the first positive electrode active material, the mass ratio of lithium manganese iron phosphate to lithium manganese oxide is 0.5:9.5;

[0107] In the second positive electrode active material, the mass ratio of lithium manganese oxide to lithium nickel cobalt manganese oxide is 9.5:0.5;

[0108] In the positive electrode active material, the mass ratio of lithium manganese iron phosphate, lithium manganese oxide, and lithium nickel cobalt manganese oxide is 0.25:9.5:0.25.

[0109] Example 3

[0110] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0111] 1) Preparation of positive electrode sheet

[0112] In the first positive electrode active material, the mass ratio of lithium iron manganese phosphate to lithium manganese oxide is 9:1.

[0113] In the second positive electrode active material, the mass ratio of lithium manganese oxide to lithium nickel cobalt manganese oxide is 1:9.

[0114] In the positive electrode active material, the mass ratio of lithium manganese iron phosphate, lithium manganese oxide, and lithium nickel cobalt manganese oxide is 4.5:1:4.5.

[0115] Example 4

[0116] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0117] 1) Preparation of positive electrode sheet

[0118] In the first positive electrode active material, the mass ratio of lithium iron manganese phosphate to lithium manganese oxide is 1:9;

[0119] In the second positive electrode active material, the mass ratio of lithium manganese oxide to lithium nickel cobalt manganese oxide is 9:1.

[0120] In the positive electrode active material, the mass ratio of lithium manganese iron phosphate, lithium manganese oxide, and lithium nickel cobalt manganese oxide is 0.5:9:0.5.

[0121] Example 5

[0122] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0123] 1) Preparation of positive electrode sheet

[0124] In the first positive electrode active material, the mass ratio of lithium iron manganese phosphate to lithium manganese oxide is 5:5.

[0125] In the second positive electrode active material, the mass ratio of lithium manganese oxide to lithium nickel cobalt manganese oxide is 5:5.

[0126] In the positive electrode active material, the mass ratio of lithium manganese iron phosphate, lithium manganese oxide, and lithium nickel cobalt manganese oxide is 2.5:5:2.5.

[0127] Example 6

[0128] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0129] 1) Preparation of positive electrode sheet

[0130] The ratio of the areal density of the first positive electrode active layer to that of the second positive electrode active layer is 6:4; the areal density of the first positive electrode active layer on one side is 150 g / m². 2 The single-sided areal density of the second positive electrode active layer is 100 g / m². 2 ;

[0131] In the positive electrode active material, the mass ratio of lithium manganese iron phosphate, lithium manganese oxide, and lithium nickel cobalt manganese oxide is 5.7:0.5:3.8.

[0132] Example 7

[0133] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0134] 1) Preparation of positive electrode sheet

[0135] The ratio of the areal density of the first positive electrode active layer to the areal density of the second positive electrode active layer is 7:3; the areal density of the first positive electrode active layer is 175 g / m². 2 The single-sided areal density of the second positive electrode active layer is 75 g / m². 2 ;

[0136] In the positive electrode active material, the mass ratio of lithium manganese iron phosphate, lithium manganese oxide, and lithium nickel cobalt manganese oxide is 6.65:0.5:2.85.

[0137] Example 8

[0138] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0139] 1) Preparation of positive electrode sheet

[0140] The ratio of the areal density of the first positive electrode active layer to the areal density of the second positive electrode active layer is 8:2; the areal density of the first positive electrode active layer is 200 g / m². 2 The single-sided surface density of the second positive electrode active layer is 50 g / m;

[0141] In the positive electrode active material, the mass ratio of lithium manganese iron phosphate, lithium manganese oxide, and lithium nickel cobalt manganese oxide is 7.6:0.5:1.9.

[0142] Example 9

[0143] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0144] 1) Preparation of positive electrode sheet

[0145] The ratio of the areal density of the first positive electrode active layer to that of the second positive electrode active layer is 9:1; the areal density of the first positive electrode active layer is 225 g / m². 2 The single-sided areal density of the second positive electrode active layer is 25 g / m². 2 ;

[0146] In the positive electrode active material, the mass ratio of lithium manganese iron phosphate, lithium manganese oxide, and lithium nickel cobalt manganese oxide is 8.55:0.5:0.95.

[0147] Example 10

[0148] The battery preparation method in this embodiment is basically the same as that in Example 1, except that lithium cobalt oxide is used instead of lithium manganese oxide.

[0149] Example 11

[0150] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0151] 1) Preparation of positive electrode sheet

[0152] In the positive electrode active material, the mass ratio of lithium manganese iron phosphate, lithium manganese oxide, and lithium nickel cobalt manganese oxide is 4.8:0.4:4.8.

[0153] In the first positive electrode active material, the mass ratio of lithium manganese iron phosphate to lithium manganese oxide is 9.6:0.4;

[0154] In the second positive electrode active material, the mass ratio of lithium manganese oxide to lithium nickel cobalt manganese oxide is 0.4:9.6.

[0155] Example 12

[0156] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0157] 1) Preparation of positive electrode sheet

[0158] The areal density ratio of the first active layer to the second active layer is 9.5:0.5, wherein the areal density of the first active layer is 237.5 g / m³. 2 The density of the second active layer is 12.5 g / m³.2 .

[0159] Example 13

[0160] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0161] 1) Preparation of positive electrode sheet

[0162] The D50 of lithium manganese iron phosphate, a positive electrode active material, is 180 nm.

[0163] Example 14

[0164] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0165] 1) Preparation of positive electrode sheet

[0166] The D50 of lithium manganese oxide in the positive electrode active material is 35 μm.

[0167] Example 15

[0168] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0169] 1) Preparation of positive electrode sheet

[0170] The D50 of lithium nickel cobalt manganese oxide, the positive electrode active material, is 42 μm.

[0171] Example 16

[0172] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0173] 1) Preparation of positive electrode sheet

[0174] Using LiCo 0.9 Mn 0.1 O2 replaces lithium manganese oxide.

[0175] Example 17

[0176] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0177] 1) Preparation of positive electrode sheet

[0178] Using LiFe 0.3 Mn 0.7 PO4 (1.65% by mass of carbon coating) replaced lithium manganese iron phosphate in Example 1.

[0179] Example 18

[0180] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0181] 1) Preparation of positive electrode sheet

[0182] LiMnO2 was used to replace lithium manganese oxide in Example 1.

[0183] Example 19

[0184] The battery preparation method in this embodiment is basically the same as that in Embodiment 1, except that:

[0185] 1) Preparation of positive electrode sheet

[0186] Using LiNi 0.8 Co 0.1 Mn 0.1 O2 replaces lithium nickel cobalt manganese oxide in Example 1.

[0187] Comparative Example 1

[0188] The preparation method of the battery in this comparative example is basically the same as that in Example 1, except that:

[0189] 1) Preparation of positive electrode sheet

[0190] A positive electrode sheet is prepared by a single-layer coating method. The positive electrode sheet includes an aluminum foil and positive electrode active layers located on two surfaces of the aluminum foil.

[0191] The positive electrode active layer comprises positive electrode active material, conductive agent (conductive carbon black), and binder (polyvinylidene fluoride), with a mass ratio of 95:2:3 for the first positive electrode active material, conductive agent, and binder. The positive electrode active material comprises lithium nickel cobalt manganese oxide and lithium manganese iron phosphate (purchased from Defang Nano, model dy16, with a carbon content of 1.6% wt), with a mass ratio of 5:5 between lithium nickel cobalt manganese oxide and lithium manganese iron phosphate. The surface of the lithium manganese iron phosphate has a carbon coating layer, and the molecular formula of lithium manganese iron phosphate is LiFe. 0.4 Mn 0.6 PO4, lithium nickel cobalt manganese oxide is LiNi 0.7 Co 0.1 Mn 0.2 O2;

[0192] The areal density of the positive electrode active layer is 250 g / Ah, and the thickness of the positive electrode active layer is 100 μm.

[0193] Comparative Example 2

[0194] The preparation method of the battery in this comparative example is basically the same as that in Comparative Example 1, except that:

[0195] 1) Preparation of positive electrode sheet

[0196] Among the positive electrode active materials, lithium manganese iron phosphate has the molecular formula LiFe. 0.5 Mn 0.5 PO4 (the carbon coating has a mass percentage of 1.65%).

[0197] Comparative Example 3

[0198] The preparation method of the battery in this comparative example is basically the same as that in Comparative Example 1, except that:

[0199] 1) Preparation of positive electrode sheet

[0200] Among the positive electrode active materials, lithium manganese iron phosphate has the molecular formula LiFe. 0.1 Mn 0.9 PO4 (the carbon coating has a mass percentage of 1.65%).

[0201] Comparative Example 4

[0202] The preparation method of the battery in this comparative example is basically the same as that in Comparative Example 1, except that:

[0203] 1) Preparation of positive electrode sheet

[0204] A positive electrode sheet is prepared by a single-layer coating method. The positive electrode sheet includes an aluminum foil and positive electrode active layers located on two surfaces of the aluminum foil.

[0205] The positive electrode active layer comprises positive electrode active material, conductive agent (conductive carbon black), and binder (polyvinylidene fluoride), with a mass ratio of 95:2:3. The positive electrode active material comprises lithium nickel cobalt manganese oxide, lithium manganese iron phosphate (purchased from Defang Nano, model dy16, with a carbon coating content of 1.65%), and lithium manganese oxide, with a mass ratio of 4.75:4.75:0.5. The lithium manganese iron phosphate has a carbon coating layer on its surface, and its molecular formula is LiFe. 0.4 Mn 0.6 PO4, lithium nickel cobalt manganese oxide is LiNi 0.7 Co 0.1 Mn 0.2 O2;

[0206] The areal density of the positive electrode active layer is 250 g / m². 2 The thickness of the positive electrode active layer is 100 μm.

[0207] Comparative Example 5

[0208] The preparation method of the battery in this comparative example is basically the same as that in Example 1, except that:

[0209] 1) Preparation of positive electrode sheet

[0210] The first active material does not include lithium manganese oxide.

[0211] Comparative Example 6

[0212] The preparation method of the battery in this comparative example is basically the same as that in Example 1, except that:

[0213] 1) Preparation of positive electrode sheet

[0214] The second active material does not include lithium manganese oxide.

[0215] Performance testing

[0216] The following performance tests were performed on the cathode materials and batteries in the examples and comparative examples, and the test results are shown in Table 1.

[0217] 1. Storage performance test

[0218] The gas production characteristics of a fully charged battery stored at 60℃ for 28 days were tested. The gas production was measured using the water displacement method, which is based on the formula: F 浮力 =ρgV 排 ρ is the density of pure water, g is the acceleration due to gravity, and V is the velocity of water. 排 Let V be the volume of the battery. Since ρ and g are both constants, the volume V of the battery before and after gas production is... 排 Changes directly affect F 浮力 Size;

[0219] Before and after storage, the actual buoyancy of the battery needs to be measured. Based on the change in buoyancy (F1-F2) before and after storage, the actual volume change after gas production, i.e., the amount of gas produced, can be calculated. The formula is: The gas production is normalized by dividing the actual capacity of the battery by its capacity.

[0220] 2. Energy density

[0221] Energy density = (C0 × V) ÷ m;

[0222] Among them, C O The battery discharge capacity is measured in Ah, which is the battery discharge capacity obtained by charging it to the rated upper limit voltage of 4.3V with the rated current and then discharging it to the rated lower limit voltage of 2.5V with the rated current. V refers to the average voltage of a 100% SOC battery when discharged to the rated lower limit voltage with the rated current, and is measured in V. m refers to the total mass of the battery, and is measured in kg.

[0223] 3. Ratio performance

[0224] A lithium-ion battery is charged to its rated upper limit voltage of 4.3V using the rated current, and then discharged at a constant current of 1.5 times the rated current to its lower limit cutoff voltage of 2.5V. The discharge capacity C obtained at this 1.5 times discharge current is recorded. 1.5The formula for calculating rate performance (discharge ratio) is as follows:

[0225] Discharge ratio = C 1.5 ÷C0×100%.

[0226] Table 1

[0227]

[0228]

[0229] A1 is the areal density of the first positive electrode active layer; A2 is the areal density of the second positive electrode active layer; A1:A2 is the ratio of the areal density of the first positive electrode active layer to the areal density of the second positive electrode active layer; h1 is the thickness of the first positive electrode active layer; h2 is the thickness of the second positive electrode active layer; h1:h2 is the ratio of the thickness of the first positive electrode active layer to the thickness of the second positive electrode active layer.

[0230] As can be seen from Table 1, the battery in the embodiment of the present invention has excellent high-temperature storage performance, energy density and rate performance, indicating that the present invention can improve the overall performance of the battery to a certain extent by making the positive electrode active layer include a first positive electrode active layer of lithium oxide compound and LFMP and a second positive electrode active layer of lithium oxide compound and NCM.

[0231] In particular, it can be seen from Examples 1 and 10 and 17 that when the lithium oxide compound is lithium manganese oxide, the obtained battery has better high-temperature storage performance, energy density and rate performance.

[0232] As can be seen from Examples 1 and 11, by selecting the content of lithium iron manganese phosphate and lithium oxide in the first positive electrode active layer, and by selecting the content of lithium oxide and lithium nickel cobalt manganese oxide in the second positive electrode active layer, the rate performance of the battery can be improved.

[0233] As can be seen from Examples 1 and 12, by selecting the ratio of the surface thickness of the first positive electrode active layer to the second positive electrode active layer, the ratio of the surface density of the first positive electrode active layer to the second positive electrode active layer can be affected, thereby improving the high-temperature storage performance, energy density and rate performance of the battery.

[0234] As can be seen from Examples 1 and 13-15, by selecting the particle size of lithium manganese iron phosphate, the particle size of lithium oxide, and the particle size of lithium nickel cobalt manganese oxide, the high-temperature storage performance, energy density, and rate performance of the battery can be further improved.

[0235] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode sheet, characterized by, The positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer on at least one surface of the positive electrode current collector; The positive electrode active layer comprises a first positive electrode active layer and a second positive electrode active layer stacked in sequence in a direction away from the positive electrode current collector; The first positive electrode active layer comprises a first positive electrode active material, and the first positive electrode active material comprises lithium manganese iron phosphate and a lithium oxide compound; The second positive electrode active layer comprises a second positive electrode active material, and the second positive electrode active material comprises a lithium oxide compound and lithium nickel cobalt manganese oxide.

2. The positive electrode sheet according to claim 1, characterized by The molecular formula of the lithium iron manganese phosphate is LiFe x Mn (1-x) PO4, wherein 0.1≤x≤0.

5.

3. The positive electrode sheet according to claim 2, characterized by At least part of the surface of the lithium manganese iron phosphate has a carbon coating layer.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized by, The molecular formula of the lithium nickel cobalt manganese oxide is LiNi z Co y M1 (1-z-y) O2, wherein M1 is Mn and / or Al, 0.33≤z≤0.95, 0≤y≤0.

3.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized by, The lithium oxygen compound has a molecular formula of Li c M2 a O b wherein M2 is at least one of Mn, Ni, and Co, 1≤a≤2, 2≤b≤3, and 0.9≤c≤2.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized by, In the positive electrode active layer, the mass ratio of the lithium oxide compound, the lithium manganese iron phosphate and the lithium nickel cobalt manganese oxide is (0.4-9.5):(0.25-9.2):(0.25-4.75).

7. The positive electrode sheet according to claim 6, characterized by In the first positive electrode active material, the mass ratio of the lithium oxide compound and the lithium manganese iron phosphate is (0.5-9.5):(9.5-0.5); and / or, In the second positive electrode active material, the mass ratio of the lithium oxide compound and the lithium nickel cobalt manganese oxide is (0.5-9.5):(9.5-0.5).

8. The positive electrode sheet according to any one of claims 1 to 7, characterized by, The ratio of the area density of the first positive electrode active layer to the area density of the second positive electrode active layer is (5-9):(1-5).

9. The positive electrode sheet according to claim 8, characterized by The first positive electrode active layer has an area density of 125 to 225 g / m 2 ; and / or, The second positive electrode active layer has an area density of 25 to 125 g / m 2 .

10. The positive electrode sheet according to any one of claims 1 to 9, characterized by, The ratio of the thickness of the first positive electrode active layer to the thickness of the second positive electrode active layer is (5-10):(1-5).

11. The positive electrode sheet according to claim 10, characterized by The thickness of the first positive electrode active layer is 40-90μm; and / or, The thickness of the second positive electrode active layer is 8-50μm.

12. The positive electrode sheet according to any one of claims 1 to 11, characterized by, The particle size of the lithium manganese iron phosphate is 20-200nm; and / or, The particle size of the lithium oxide compound is 4-30μm; and / or, The particle size of the lithium nickel cobalt manganese oxide is 0.3-35μm.

13. A battery, characterized by The battery comprises the positive electrode sheet according to any one of claims 1-12.

14. An electronic device, comprising: The driving source or energy storage source of the electronic device is the battery according to claim 13.

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