Secondary battery and manufacturing method therefor, positive electrode sheet, negative electrode sheet, and electric device

Abstract

The present disclosure relates to the technical field of lithium batteries. Disclosed are a secondary battery and a manufacturing method therefor, a positive electrode sheet, a negative electrode sheet, and an electric device. A lithium iron phosphate positive electrode material, Li2NiO2 and Li5FeO4 are used as a positive electrode active material, and by adjusting a blending proportion and defining parameters such as the blending proportion, the capacity per gram of the active material, and an electrolyte injection coefficient to satisfy specific relationships, the capacity per gram and cycle performance of lithium iron phosphate batteries can be remarkably improved, enabling lithium ion batteries to have the advantages such as high energy density, good cycle performance, and high safety.

Description

Secondary battery, preparation method thereof, positive electrode sheet, negative electrode sheet and electric device

[0001] Cross-reference to Related Applications

[0002] The present disclosure claims priority to the application No. 2024104587174, filed on April 17, 2024, with the Chinese Patent Office, and entitled "Secondary battery, preparation method thereof, positive electrode sheet, negative electrode sheet and electric device", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of lithium battery, in particular, to a secondary battery, a preparation method thereof, a positive electrode sheet, a negative electrode sheet and an electric device. BACKGROUND

[0004] The endurance problem of new energy vehicles has become an important factor restricting its development. Currently, the mainstream power batteries are mainly ternary batteries and lithium iron phosphate batteries. The ternary battery has high energy density, but relatively low economy and safety. The lithium iron phosphate battery has lower energy density, but lower manufacturing cost, higher safety, and better cycle life. Therefore, to solve the endurance problem of new energy vehicles, improving the energy density and cycle life of lithium iron phosphate batteries is a relatively direct and feasible method.

[0005] With the progress of battery design and process manufacturing technology, the utilization of internal space of the battery shell has reached the extreme, and it is very difficult to improve the energy density through the internal space. Currently, the energy density and cycle performance of the material are mainly improved by optimizing the positive active material. The consumption of active lithium by the solid electrolyte interface (SEI) of the lithium ion battery negative electrode leads to the reduction of the initial capacity and the reduction of the service life. The lithium source can be added before the battery charging and discharging cycle to improve the first charge and discharge efficiency and supplement the lithium loss during the cycle. Currently, there are mainly two ways of lithium supplement: negative electrode lithium supplement and positive electrode lithium supplement.

[0006] The negative electrode lithium supplement technology develops earlier, mainly including lithium foil lithium supplement, lithium powder lithium supplement, chemical lithium supplement, etc. The lithium foil lithium supplement utilizes the self-discharge mechanism. In the presence of potential difference, in the presence of electrolyte, when the negative electrode material contacts with the lithium metal foil, the electrons spontaneously move to the negative electrode, accompanied by Li + insertion in the negative electrode. The lithium powder lithium supplement can be directly added to the surface of the negative electrode sheet or added during the negative electrode slurry process. The negative electrode lithium supplement has high pre-lithiation capacity, but it has high requirements for equipment and environment, and the active lithium has high chemical reactivity, which has serious safety hazards.

[0007] The positive electrode lithium supplement technology usually adopts an electrochemical method, and the positive electrode lithium supplement additive is added in the lithium ion battery. During the charging process of the battery, the positive electrode lithium supplement additive releases active lithium to make up for the consumption of the negative electrode SEI, and at the same time, the cycle life of the battery can be improved. The positive electrode lithium supplement additive is safe, but a single positive electrode lithium supplement additive still has many deficiencies. For example, Li5FeO4 has high capacity, and the theoretical specific capacity can be as high as 867 mAh / g, but the stability in the air environment is poor, and oxygen is generated during delithiation; Li2NiO2 has excellent processing performance, and no gas is generated during delithiation, but the impedance is large, which affects the rate performance and cycle performance of the battery.

[0008] Therefore, the existing positive electrode lithium supplement technology cannot simultaneously improve the energy density and cycle life of the lithium iron phosphate battery.

[0009] In view of this, the present disclosure is proposed.

[0010] SUMMARY

[0011] The purpose of the present disclosure is to provide a secondary battery and a preparation method thereof, a positive electrode sheet, a negative electrode sheet and an electric device, aiming to simultaneously improve the energy density and cycle life of the lithium iron phosphate battery.

[0012] The present disclosure is achieved in this way:

[0013] In a first aspect, the present disclosure provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet and a separator, the positive electrode sheet comprising a positive electrode active material and a positive electrode current collector, and the negative electrode sheet comprising a negative electrode active material and a negative electrode current collector; the positive electrode active material comprises a lithium iron phosphate positive electrode material, a first lithium supplement additive and a second lithium supplement additive, the first lithium supplement additive is Li2NiO2, and the second lithium supplement additive is Li5FeO4;

[0014] The secondary battery has a first performance parameter a and a second performance parameter β, and satisfies the following relationship:

[0015] Wherein, the first performance parameter a satisfies: 1.0≤a≤1.13; the second performance parameter β satisfies: 6<β<10;

[0016] In the formula, A1 represents the mass proportion of the lithium iron phosphate positive electrode material in the positive electrode active material;

[0017] A2 represents the mass proportion of the first lithium supplement additive in the positive electrode active material;

[0018] A3 represents the mass proportion of the second lithium supplement additive in the positive electrode active material;

[0019] M1 represents the first charge specific capacity of the lithium iron phosphate positive electrode material, in mAh / g;

[0020] M2 represents the specific capacity of the first lithium supplement additive in the first charge, in mAh / g;

[0021] M3 represents the specific capacity of the second lithium supplement additive in the first charge, in mAh / g;

[0022] M4 represents the specific capacity of the negative active material in the first charge, in mAh / g;

[0023] X represents the coating amount of the positive active material on the positive current collector, in mg / cm 2 ;

[0024] Y represents the coating amount of the negative active material on the negative current collector, in mg / cm 2 ;

[0025] C represents the injection coefficient, in g / Ah;

[0026] The secondary battery satisfies at least one of the following conditions:

[0027] A1+A2+A3=1, 80%≤A1≤99%, 0<A2≤15%, 0<A3≤15%;

[0028] X is 17mg / cm 2 -32mg / cm 2 ;

[0029] In the condition that the voltage range of the secondary battery in discharge is 2.0-4.4V, the value range of M1 is 150mAh / g-170mAh / g; the value range of M2 is 400mAh / g-500mAh / g; the value range of M3 is 650mAh / g-750mAh / g;

[0030] The value range of M4 is 350mAh / g-400mAh / g;

[0031] The negative active material is graphite; the value range of Y is 5mg / cm 2 -20mg / cm 2 ;

[0032] The value of C satisfies: C≤3.6g / Ah;

[0033] In the optional embodiment, when the positive electrode sheet is prepared, the total material coated on the positive current collector is referred to as the positive total material, and the mass percentage of the positive active material in the positive total material is 92%-99%. In the optional embodiment, when the negative electrode sheet is prepared, the total material coated on the negative current collector is referred to as the negative total material, and the mass percentage of the negative active material in the negative total material is 85%-99%.

[0034] In an optional embodiment, the negative current collector is selected from at least one of a copper foil and a composite copper foil, and the thickness of the negative current collector is 1-20 μm.

[0035] In an optional embodiment, the separator comprises a substrate and a coating layer attached to the substrate, the thickness of the substrate is 5-20 μm, and the thickness of the coating layer is 1-6 μm.

[0036] In an optional embodiment, the substrate is selected from at least one of polypropylene and polyethylene; and the coating layer is a ceramic material.

[0037] In an optional embodiment, the doping element in the lithium iron phosphate positive electrode material is selected from at least one of Ti, Al, Mg, V, Ni and Mn; and the content of the doping element is less than 5000 ppm.

[0038] In an optional embodiment, the doping element in the first lithium supplement additive Li2NiO2 is selected from at least one of Ti, Al, Co and Mn.

[0039] In an optional embodiment, the content of the doping element in the first lithium supplement additive Li2NiO2 is less than 5000 ppm.

[0040] In an optional embodiment, the doping element in the second lithium supplement additive Li5FeO4 is selected from at least one of Mn, Cu, Mo, Al, Ti, Mg, Zr and Zn; and in an optional embodiment, the content of the doping element in the second lithium supplement additive Li5FeO4 is less than 5000 ppm.

[0041] In an optional embodiment, the second lithium supplement additive is coated with a carbon layer, and the mass fraction of carbon in the second lithium supplement additive is 0.2-5.0%.

[0042] In a second aspect, the disclosure further provides a preparation method of the secondary battery in any one of the above embodiments, wherein the first performance parameter α and the second performance parameter β are defined in the process of preparing the secondary battery, and the first performance parameter α and the second performance parameter β meet the requirements.

[0043] In a third aspect, the disclosure further provides a positive electrode tab, which comprises a positive electrode active material and a positive current collector, the positive electrode active material comprises a lithium iron phosphate positive electrode material, a first lithium supplement additive and a second lithium supplement additive, the first lithium supplement additive is Li2NiO2, and the second lithium supplement additive is Li5FeO4; the positive electrode tab is used to make a secondary battery, the secondary battery comprises the positive electrode tab, a negative electrode tab and a separator, the negative electrode tab comprises a negative electrode active material and a negative current collector.

[0044] The secondary battery has the first performance parameter α and the second performance parameter β, and meets the following relationship:

[0045] wherein the first performance parameter a satisfies: 1.0≤a≤1.13; the second performance parameter β satisfies: 6<β<10;

[0046] In the formula, A1 represents the mass proportion of the lithium iron phosphate positive electrode material in the positive electrode active material;

[0047] A2 represents the mass proportion of the first lithium supplement additive in the positive electrode active material;

[0048] A3 represents the mass proportion of the second lithium supplement additive in the positive electrode active material;

[0049] M1 represents the initial charge specific capacity of the lithium iron phosphate positive electrode material, in mAh / g;

[0050] M2 represents the initial charge specific capacity of the first lithium supplement additive, in mAh / g;

[0051] M3 represents the initial charge specific capacity of the second lithium supplement additive, in mAh / g;

[0052] M4 represents the initial charge specific capacity of the negative electrode active material, in mAh / g;

[0053] X represents the coating amount of the positive electrode active material on the positive electrode current collector, in mg / cm 2 ;

[0054] Y represents the coating amount of the negative electrode active material on the negative electrode current collector, in mg / cm 2 ;

[0055] C represents the injection coefficient, in g / Ah;

[0056] The secondary battery satisfies at least one of the following conditions:

[0057] A1+A2+A3=1, 80%≤A1≤99%, 0<A2≤15%, 0<A3≤15%;

[0058] X is 17mg / cm 2 -32mg / cm 2 ;

[0059] In the voltage range of 2.0-4.4V during discharging of the secondary battery, the value range of M1 is 150mAh / g-170mAh / g; the value range of M2 is 400mAh / g-500mAh / g; the value range of M3 is 650mAh / g-750mAh / g;

[0060] M4 is in the range of 350 mAh / g-400 mAh / g;

[0061] The negative active material is graphite; Y is in the range of 5 mg / cm 2 -20 mg / cm 2 ;

[0062] C is in the range satisfying C≤3.6 g / Ah;

[0063] In a fourth aspect, the disclosure also provides a negative electrode sheet, the negative electrode sheet comprising a negative active material and a negative current collector, the negative electrode sheet being used for manufacturing a secondary battery, the secondary battery comprising a positive electrode sheet, the negative electrode sheet and a separator, the positive electrode sheet comprising a positive active material and a positive current collector, the positive active material comprising a lithium iron phosphate positive material, a first lithium supplement additive and a second lithium supplement additive, the first lithium supplement additive being Li2NiO2, and the second lithium supplement additive being Li5FeO4.

[0064] The secondary battery has a first performance parameter α and a second performance parameter β, and satisfies the following relationship:

[0065] The first performance parameter α satisfies 1.0≤α≤1.13, and the second performance parameter β satisfies 6<β<10.

[0066] In the formula, A1 represents the mass proportion of the lithium iron phosphate positive material in the positive active material;

[0067] A2 represents the mass proportion of the first lithium supplement additive in the positive active material;

[0068] A3 represents the mass proportion of the second lithium supplement additive in the positive active material;

[0069] M1 represents the first charge specific capacity of the lithium iron phosphate positive material, in mAh / g;

[0070] M2 represents the first charge specific capacity of the first lithium supplement additive, in mAh / g;

[0071] M3 represents the first charge specific capacity of the second lithium supplement additive, in mAh / g;

[0072] M4 represents the first charge specific capacity of the negative active material, in mAh / g;

[0073] X represents the coating amount of the positive active material on the positive current collector, in mg / cm 2 ;

[0074] Y represents the coating amount of the negative active material on the negative current collector, in mg / cm 2 ;

[0075] C represents a liquid injection coefficient, with a unit of g / Ah;

[0076] The secondary battery satisfies at least one of the following conditions:

[0077] A1+A2+A3=1, 80%≤A1≤99%, 0<A2≤15%, 0<A3≤15%;

[0078] X is 17mg / cm 2 -32mg / cm 2 ;

[0079] In the voltage range of 2.0-4.4V during discharging of the secondary battery, the value range of M1 is 150mAh / g-170mAh / g; the value range of M2 is 400mAh / g-500mAh / g; the value range of M3 is 650mAh / g-750mAh / g;

[0080] The value range of M4 is 350mAh / g-400mAh / g;

[0081] The negative active material is graphite; the value range of Y is 5mg / cm 2 -20mg / cm 2 ;

[0082] The value of C satisfies: C≤3.6g / Ah;

[0083] In a fifth aspect, the disclosure also provides a power utilization device comprising the secondary battery in any of the above embodiments or the secondary battery prepared by the preparation method in any of the above embodiments.

[0084] The disclosure has the following beneficial effects: by using lithium iron phosphate positive electrode material, Li2NiO2 and Li5FeO4 as positive active material, by adjusting the blending ratio, limiting the mixing ratio, the gram capacity of the active material and the liquid injection coefficient and other parameters to satisfy a specific relationship, the gram capacity and cycle performance of the lithium iron phosphate battery can be significantly improved, so that the lithium ion battery can have the advantages of high energy density, good cycle performance, high safety and the like. DETAILED DESCRIPTION

[0085] In order to make the purpose, technical scheme and advantages of the embodiments of the disclosure clearer, the technical scheme in the embodiments of the disclosure will be described clearly and completely below. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0086] The embodiment of the present disclosure provides a secondary battery, which comprises a positive electrode sheet, a negative electrode sheet and a separator, a first performance parameter alpha and a second performance parameter beta are defined according to parameters of the positive electrode sheet, the negative electrode sheet and the separator, and the first performance parameter alpha and the second performance parameter beta meet a specific value range through an expression of the first performance parameter alpha and the second performance parameter beta, so that the secondary battery has the advantages of high energy density and good cycle performance.

[0087] Specifically, the positive electrode sheet comprises a positive electrode active material and a positive electrode current collector, and the positive electrode active material is a main component of a positive electrode active coating formed on the positive electrode current collector; the negative electrode sheet comprises a negative electrode active material and a negative electrode current collector, and the negative electrode active material is a main component of a negative electrode active coating formed on the negative electrode current collector. The method for regulating the values of the first performance parameter alpha and the second performance parameter beta provided by the embodiment of the present disclosure is for a lithium iron phosphate battery, and specifically, the positive electrode active material comprises a lithium iron phosphate positive electrode material, a first lithium supplement additive and a second lithium supplement additive, the first lithium supplement additive is Li2NiO2, and the second lithium supplement additive is Li5FeO4. By adding the double lithium supplement materials Li2NiO2 and Li5FeO4, the disadvantages of a single lithium supplement material can be compensated, and a battery with high energy density and good cycle performance can be prepared.

[0088] The expression of the first performance parameter alpha and the second performance parameter beta is as follows:

[0089] The first performance parameter alpha meets 1.0<=alpha<=1.13, and the second performance parameter beta meets 6<beta<10. By regulating the values of alpha and beta, the inventors find that the battery can balance the energy density and the cycle performance in this range.

[0090] Specifically, the value of the first performance parameter alpha can be 1.00, 1.02, 1.05, 1.08, 1.10, 1.13, etc., and the value of the second performance parameter beta can be 6.0, 7.0, 8.0, 9.0, 10.0, etc.

[0091] In the expression of the first performance parameter alpha and the second performance parameter beta, the meanings of the parameters are as follows:

[0092] A1 represents the mass percentage of the lithium iron phosphate positive electrode material in the positive electrode active material, and when it is brought into the expression, a percentage is brought in, for example, 90% is brought in, that is, 0.9.

[0093] A2 represents the mass percentage of the first lithium supplement additive in the positive electrode active material, and when it is brought into the expression, a percentage is also brought in, for example, 5% is brought in, that is, 0.05.

[0094] A3 represents the mass percentage of the second lithium supplement additive in the positive electrode active material, and when the expression is brought in, the percentage is also brought in, such as 5%, that is, 0.05.

[0095] In some embodiments, A1+A2+A3=1, under the premise of satisfying the sum of the three equal to 1, 80%≤A1≤99%, 0

[0096] M1 represents the first charge specific capacity of lithium iron phosphate positive electrode material, unit: mAh / g, under the condition of voltage interval 2.0-4.4V of secondary battery discharge, its value is relatively fixed, generally 150mAh / g-170mAh / g, preferably 158mAh / g-165mAh / g, such as 150mAh / g, 160mAh / g, 170mAh / g, etc.

[0097] M2 represents the first lithium supplement additive Li2NiO2 first charge specific capacity, unit: mAh / g, because the material is fixed, under the condition of voltage interval 2.0-4.4V of secondary battery discharge, its value is also relatively fixed, generally 400mAh / g-500mAh / g, preferably 400mAh / g-440mAh / g, such as 400mAh / g, 420mAh / g, 430mAh / g, 440mAh / g, 450mAh / g, 480mAh / g, 500mAh / g, etc.

[0098] M3 represents the second lithium supplement additive Li5FeO4 first charge specific capacity, unit: mAh / g, because the material is fixed, under the condition of voltage interval 2.0-4.4V of secondary battery discharge, its value is also relatively fixed, generally 650mAh / g-750mAh / g, preferably 690mAh / g-710mAh / g, such as 650mAh / g, 680mAh / g, 700mAh / g, 750mAh / g.

[0099] M4 represents the specific capacity of the negative active material in the first charge, in units of mAh / g, and the values of different materials are slightly different, the value of M4 is 350 mAh / g-400 mAh / g; preferably 370 mAh / g-380 mAh / g. For example, the negative active material can be a graphite material, specifically artificial graphite or natural graphite, or a mixture of artificial graphite and natural graphite, and the specific capacity of the graphite in the first charge M4 is 375 mAh / g.

[0100] C represents the injection coefficient, which is a fixed constant determined when designing the battery, and is the ratio of the injection amount of the electrolyte to the design discharge capacity of the battery, the calculation formula of the electrolyte injection coefficient = injection amount / capacity, in units of g / Ah.

[0101] In some embodiments, the value of C satisfies: C≤3.6 g / Ah, preferably 2.9 g / Ah-3.5 g / Ah, such as 2.9 g / Ah, 3.0 g / Ah, 3.1 g / Ah, 3.2 g / Ah, 3.3 g / Ah, 3.4 g / Ah, 3.5 g / Ah, etc.

[0102] X represents the amount of positive active material coated on the positive current collector, in units of mg / cm 2 . That is, X represents the amount of positive active material (including lithium iron phosphate positive material, first lithium supplement additive and second lithium supplement additive) per square centimeter of positive current collector, the value of X is 17 mg / cm 2 -32 mg / cm 2 , such as 17 mg / cm 2 , 20 mg / cm 2 , 25 mg / cm 2 , 30 mg / cm 2 , 32 mg / cm 2 , etc.

[0103] Specifically, when preparing the positive electrode sheet, the total material coated on the positive current collector is referred to as the total positive material, and the mass fraction of the positive active material in the total positive material is 92%-99%, and the remaining components are conductive agents (such as conductive carbon black), binders (such as polyvinylidene fluoride), and dispersants (such as N-methyl pyrrolidone). That is, the single-sided coating area density of the positive active material X = a*X 正极总材料 , and the value of a is 92%-99%.

[0104] Specifically, the lithium iron phosphate positive material contains LiFePO4 as the main component, and also contains a small amount of doping elements, the doping elements are selected from at least one of Ti, Al, Mg, V, Ni and Mn, and can be any one or several of the above, and the content of each doping element is less than 5000 ppm.

[0105] Specifically, the first lithium supplement additive Li2NiO2may also contain a small amount of doping elements, the doping elements are selected from at least one of Ti, Al, Co and Mn, can be any one or several of the above, and the doping amount is not limited and can be less than 5000ppm.

[0106] Specifically, the second lithium supplement additive Li5FeO4may also contain a small amount of doping elements, the doping elements are selected from at least one of Mn, Cu, Mo, Al, Ti, Mg, Zr and Zn, can be any one or several of the above. The surface of the second lithium supplement additive can also be coated with a carbon layer, and the mass fraction of carbon in the second lithium supplement additive is 0.2-5.0%, preferably 0.5%-3.0%, such as 0.2%, 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, etc.

[0107] Y represents the amount of negative electrode active material coated on the negative electrode current collector, in mg / cm2. 2 ; that is, Y represents the amount of negative electrode active material (such as graphite) per square centimeter of negative electrode current collector. The value range of Y is 5mg / cm2 2 -20mg / cm2 2 , preferably 8mg / cm2 2 -15mg / cm2 2 , such as 5mg / cm2 2 , 8mg / cm2 2 , 10mg / cm2 2 , 12mg / cm2 2 , 15mg / cm2 2 , 18mg / cm2 2 , 20mg / cm2 2 , etc.

[0108] Specifically, the total material attached to the negative electrode current collector is referred to as the total negative material, and the mass fraction of the negative electrode active material in the total negative material is 85%-99%, preferably 92%-99%, and the remaining components are conductive agents (such as conductive carbon black), binders (such as polyvinylidene fluoride), and dispersants (such as N-methyl pyrrolidone). That is, the single-sided coating area density of the negative electrode active material Y = b*Y 负极总材料 , b is the proportion of the negative electrode active material in the total negative material, and the value is 92%-99%.

[0109] In some embodiments, the negative electrode current collector is selected from at least one of copper foil and composite copper foil, and the thickness of the negative electrode current collector is 1μm-20μm, preferably 4μm-10μm, such as 1μm, 2μm, 4μm, 6μm, 8μm, 10μm, 15μm, 20μm, etc.

[0110] In some embodiments, the diaphragm comprises a substrate and a coating attached to the substrate, the thickness of the substrate is 5-20 μm (such as 5 μm, 10 μm, 15 μm, 20 μm, etc.), and the thickness of the coating is 1-6 μm (such as 1 μm, 2 μm, 4 μm, 6 μm, etc.). The substrate is selected from at least one of polypropylene (PP) and polyethylene (PE), which can be PP, PE, or a composite material of PP / PE. The coating is a ceramic material, and the specific material is not limited, which is mainly aluminum oxide or a binder, or a composite material of aluminum oxide and a binder.

[0111] It should be noted that the first performance parameter α represents the excess ratio of the charging capacity of the negative electrode sheet to the charging capacity of the positive electrode sheet. If the α value is too low, there is a risk of lithium precipitation on the negative electrode sheet during charging; if the α value is too high, the coating amount of the negative electrode sheet is too large, and the negative electrode sheet needs to consume more active lithium when forming the SEI film (solid electrolyte interface film), which is not conducive to the capacity of the positive electrode material, and will reduce the energy density of the battery.

[0112] It should be noted that the number of battery cells of the secondary battery provided by the embodiments of the present disclosure is not limited, which can be in the form of a battery pack.

[0113] The embodiments of the present disclosure provide a preparation method of a secondary battery, in which a first performance parameter α and a second performance parameter β are defined during the preparation of the secondary battery, and the first performance parameter α and the second performance parameter β meet the requirements.

[0114] Specifically, during the preparation process, the values of A1, A2, A3, M2, and M3, the surface density of the active material coating during the preparation of the positive electrode sheet and the negative electrode sheet, the liquid injection coefficient, and other parameters are adjusted, the value ranges of the above parameters are adjusted, and the expressions of the first performance parameter α and the second performance parameter β are constructed, so that the values of α and β meet a specific range. The inventors have found that by using the method, the relationship between the energy density and the cycle life can be better balanced, the energy density of the battery cell can be effectively improved, and the cycle life can be maintained at a good level.

[0115] The embodiments of the present disclosure also provide a positive electrode sheet, which comprises a positive electrode active material and a positive electrode current collector, the positive electrode active material comprises a lithium iron phosphate positive electrode material, a first lithium supplement additive, and a second lithium supplement additive, the first lithium supplement additive is Li2NiO2, and the second lithium supplement additive is Li5FeO4; the positive electrode sheet is used to make a secondary battery, the secondary battery comprises the positive electrode sheet, a negative electrode sheet, and a diaphragm, the negative electrode sheet comprises a negative electrode active material and a negative electrode current collector.

[0116] The secondary battery has a first performance parameter α and a second performance parameter β, and satisfies the following relationship:

[0117] wherein the first performance parameter a satisfies: 1.0≤a≤1.13, and the second performance parameter β satisfies: 6<β<10;

[0118] In the formula, A1 represents the mass proportion of the lithium iron phosphate positive electrode material in the positive electrode active material;

[0119] A2 represents the mass proportion of the first lithium supplement additive in the positive electrode active material;

[0120] A3 represents the mass proportion of the second lithium supplement additive in the positive electrode active material;

[0121] M1 represents the initial charge specific capacity of the lithium iron phosphate positive electrode material, in mAh / g;

[0122] M2 represents the initial charge specific capacity of the first lithium supplement additive, in mAh / g;

[0123] M3 represents the initial charge specific capacity of the second lithium supplement additive, in mAh / g;

[0124] M4 represents the initial charge specific capacity of the negative electrode active material, in mAh / g;

[0125] X represents the coating amount of the positive electrode active material on the positive electrode current collector, in mg / cm 2 ;

[0126] Y represents the coating amount of the negative electrode active material on the negative electrode current collector, in mg / cm 2 ;

[0127] C represents the injection coefficient, in g / Ah.

[0128] The value range of each parameter can be found in the foregoing description of the parameters, which is not repeated here.

[0129] The embodiments of the present disclosure also provide a negative electrode sheet, which comprises a negative electrode active material and a negative electrode current collector, and is used to make a secondary battery. The secondary battery comprises a positive electrode sheet, a negative electrode sheet and a separator. The positive electrode sheet comprises a positive electrode active material and a positive electrode current collector. The positive electrode active material comprises a lithium iron phosphate positive electrode material, a first lithium supplement additive and a second lithium supplement additive. The first lithium supplement additive is Li2NiO2, and the second lithium supplement additive is Li5FeO4.

[0130] The secondary battery has a first performance parameter a and a second performance parameter β, and satisfies the following relationship:

[0131] wherein the first performance parameter a satisfies: 1.0≤a≤1.13, and the second performance parameter β satisfies: 6<β<10;

[0132] A1 represents the mass proportion of the lithium iron phosphate positive electrode material in the positive electrode active material;

[0133] A2 represents the mass proportion of the first lithium supplement additive in the positive electrode active material;

[0134] A3 represents the mass proportion of the second lithium supplement additive in the positive electrode active material;

[0135] M1 represents the first charge specific capacity of the lithium iron phosphate positive electrode material, in mAh / g;

[0136] M2 represents the first charge specific capacity of the first lithium supplement additive, in mAh / g;

[0137] M3 represents the first charge specific capacity of the second lithium supplement additive, in mAh / g;

[0138] M4 represents the first charge specific capacity of the negative electrode active material, in mAh / g;

[0139] X represents the coating amount of the positive electrode active material on the positive electrode current collector, in mg / cm 2 ;

[0140] Y represents the coating amount of the negative electrode active material on the negative electrode current collector, in mg / cm 2 ;

[0141] C represents the injection coefficient, in g / Ah.

[0142] The value range of each parameter can be found in the foregoing parameter specification, and is not repeated here.

[0143] The present disclosure also provides a power utilization device, which comprises the secondary battery and can further comprise a power utilization device, and the secondary battery is used to supply power to the power utilization device.

[0144] The features and performance of the present disclosure are further described in detail below in combination with embodiments.

[0145] Embodiment 1

[0146] The present embodiment provides a preparation method of a secondary battery, and the expression of the first performance parameter α and the second performance parameter β is constructed during the preparation process, so that the parameter value meets the requirements, and the specific steps are as follows:

[0147] (1) Preparation of the positive electrode sheet

[0148] Take the positive active material lithium iron phosphate LiFePO4, take the lithium supplement additive Li2NiO2, the doping element is Al, and the doping element content is 500ppm. Take the lithium supplement additive Li5FeO4, the doping element is Al and Ti, and the total doping element content is 8000ppm. M1 takes the value of 160mAh / g, M2 takes the value of 420mAh / g, and M3 takes the value of 700mAh / g.

[0149] Take lithium iron phosphate, Li2NiO2 and Li5FeO4 as the positive active material, and control the mass ratio of lithium iron phosphate, Li2NiO2 and Li5FeO4 in the positive active material to be 95.5%, 0.5% and 4% respectively.

[0150] Mix the positive active material, the conductive agent conductive carbon black and the binder polyvinylidene fluoride according to the mass ratio of 97:1:2, add the dispersant polyvinylpyrrolidone to form a positive electrode slurry with a solid content of 57%-61%, uniformly coat the positive electrode slurry on the positive and negative surfaces of the positive current collector, control the coating amount of the positive active material on the positive current collector to be 24.6mg / cm 2 , and after drying, form a coating, compact the electrode sheet by rolling to obtain a positive electrode sheet, and control the compacted density P.D. to be 2.55g / cm 3 . The positive current collector is an aluminum foil with a thickness of 13μm.

[0151] (2) Preparation of negative electrode sheet

[0152] Mix the negative active material artificial graphite, the conductive agent conductive carbon black, the binder styrene-butadiene rubber SBR and the dispersant sodium carboxymethyl cellulose CMC according to the mass ratio of 95:1:2:2, add the dispersant deionized water to form a negative electrode slurry with a solid content of 48%-53%, uniformly coat the negative electrode slurry on the positive and negative surfaces of the negative current collector, control the coating amount Y of the negative active material on the negative current collector to be 13.2mg / cm 2 , obtain the coated electrode sheet by heating and drying, and compact the electrode sheet by rolling to obtain a negative electrode sheet. The initial charge specific capacity M4 of the negative active material is 375mAh / g, and the negative current collector is a copper foil with a thickness of 6μm.

[0153] (3) Preparation of separator

[0154] Coat a nano-aluminum oxide coating on the positive and negative surfaces of the separator, dry the coating in a vacuum oven, remove the solvent, the thickness of the PE-based film is 7μm, and the thickness of the coating is 3μm.

[0155] (4) Assembly

[0156] The positive and negative electrode sheets and the separator film obtained above are Z-shaped stacked in the order of "separator-negative electrode sheet-separator-positive electrode sheet", ensuring that the positive electrode sheet is completely in the middle position of the negative electrode sheet, and after stacking, heat pressing-tab welding-packaging-baking are performed, the total water content of the positive and negative electrode sheets and the separator film after baking is controlled to be 250 ppm, electrolyte is injected, and the injection coefficient C is controlled to be 3.5 g / Ah.

[0157] The embodiment also provides a secondary battery prepared by the preparation method.

[0158] Example 2-5

[0159] Example 2-5 differs from Example 1 only in that the values of the parameters are different, and the different values of the parameters are listed in Table 1.

[0160] Comparative Example 1-2

[0161] Comparative Example 1-2 differs from Example 1 only in that the values of the parameters are different, and the different values of the parameters are listed in Table 1.

[0162] Table 1: Parameter control in the preparation process of examples and comparative examples and performance of the secondary batteries obtained

[0163] As can be seen from Table 1, by controlling 1.0≤α≤1.13, 6<β<10, the energy density and the cycle performance can be considered, and out of the above range will result in an undesirable energy density or poor life.

[0164] The above only describes preferred embodiments of the present disclosure and is not intended to limit the present disclosure. For those skilled in the art, the present disclosure can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present disclosure shall be included in the protection scope of the present disclosure. Industrial applicability

[0165] The present disclosure uses lithium iron phosphate positive electrode material, Li2NiO2 and Li5FeO4 as positive electrode active material, by adjusting the blending ratio, limiting the mixing ratio, the gram capacity of the active material and the injection coefficient and other parameters to meet a specific relationship, the gram capacity and cycle performance of the lithium iron phosphate battery can be significantly improved, the theoretical guidance can be provided in the preparation process, and it is easy to implement, and has very good industrial applicability.

Claims

1. A secondary battery, comprising:a positive electrode plate;a negative electrode plate; anda separator;wherein the positive electrode plate comprises a positive electrode active material and a positive electrode current collector; the negative electrode plate comprises a negative electrode active material and a negative electrode current collector; the positive electrode active material comprises a lithium iron phosphate (LFP) positive electrode material, a first lithium supplementing additive and a second lithium supplementing additive; the first lithium supplementing additive comprises Li2NiO2; and the second lithium supplementing additive comprises Li5FeO4;the secondary battery has a first performance parameter a and a second performance parameter p respectively satisfying the following formulas:i !*#(!"*$"%!#*$#%!$*$$) *@■; and($#%$$)*)**+***!#%!$+ 26;wherein the first performance parameter a satisfies 1.0<a<1.13; and the second performance parameter p satisfies 6<p<10;A1 represents a weight percentage of the LFP positive electrode material in the positive electrode active material;A2 represents a weight percentage of the first lithium supplementing additive in the positive electrode active material;A3 represents a weight percentage of the second lithium supplementing additive in the positive electrode active material;M1 represents an initial charge specific capacity of the LFP positive electrode material, expressed in a unit of mAh / g;M2 represents an initial charge specific capacity of the first lithium supplementing additive, expressed in a unit of mAh / g;M3 represents an initial charge specific capacity of the second lithium supplementing additive, expressed in a unit of mAh / g;M4 represents an initial charge specific capacity of the negative electrode active material, expressed in a unit of mAh / g;X represents a coating amount of the positive electrode active material on the positive electrode current collector, expressed in a unit of mg / cm2;Y represents a coating amount of the negative electrode active material on the negative electrode current collector, expressed in a unit of mg / cm2;C represents an electrolyte filling coefficient, expressed in a unit of g / Ah;the secondary battery satisfies at least one of the following conditions:A1+A2+A3=1, 80%<Ai<99%, 0<A2<15%, and 0<A3<15%;X is 17-32 mg / cm2;in response to a case that a discharge voltage range of the secondary battery is 2.04.4 V, M1 is 150-170 mAh / g, M2 is 400-500 mAh / g, and M3 is 650-750 mAh / g;M4 is 350-400 mAh / g;the negative electrode active material is graphite, and Y is 5-20 mg / cm2; andC satisfies C<3.6 g / Ah.

2. The secondary battery according to claim 1, wherein a material coated on the positive electrode current collector in the preparation of the positive electrode plate is a total positive electrode composite, and a weight percentage of the positive electrode active material in the total positive electrode composite is 92-99%.

3. The secondary battery according to claim 1 or 2, wherein a material coated on the negative electrode current collector in the preparation of the negative electrode plate is a total negative electrode composite, and a weight percentage of the negative electrode active material in the total negative electrode composite is 85-99%.

4. The secondary battery according to claim 3, wherein the negative electrode current collector is selected from the group consisting of copper foil, composite copper 24foil and a combination thereof; and a thickness of the negative electrode current collector is 1-20 gm.

5. The secondary battery according to any one of claims 1-4, wherein the separator comprises a substrate and a coating attached to the substrate; a thickness of the substrate is 5-20 gm; and a thickness of the coating is 1-6 gm.

6. The secondary battery according to claim 5, wherein the substrate is made of polypropylene (PP), polyethylene (PE) or a combination thereof; and the coating is made of a ceramic material.

7. The secondary battery according to any one of claims 1-6, wherein the LFP positive electrode material is doped with an element selected from the group consisting of Ti, Al, Mg, V, Ni, Mn and a combination thereof; and a content of the element doped in the LFP positive electrode material is less than 5,000 ppm.

8. The secondary battery according to any one of claims 1-7, wherein the first lithium supplementing additive is doped with an element selected from the group consisting of Ti, Al, Co, Mn and a combination thereof.

9. The secondary battery according to claim 8, wherein a content of the element doped in the first lithium supplementing additive is less than 5,000 ppm.

10. The secondary battery according to any one of claims 1-9, wherein the second lithium supplementing additive is doped with an element selected from the group consisting of Mn, Cu, Mo, Al, Ti, Mg, Zr, Zn and a combination thereof.

11. The secondary battery according to claim 10, wherein a content of the element doped in the second lithium supplementing additive is less than 5,000 ppm.

12. The secondary battery according to claim 10 or 11, wherein a surface of the second lithium supplementing additive is coated with a carbon layer; and a weightpercentage of carbon in the second lithium supplementing additive is 0.2-5.0%.

13. A method of preparing the secondary battery according to any one of claims 112, comprising:in the preparation of the secondary battery, defining the first performance parameter a and the second performance parameter P, and setting the first performance parameter a and the second performance parameter P to meet corresponding requirements.

14. A positive electrode plate, comprising:a positive electrode active material; anda positive electrode current collector;wherein the positive electrode active material comprises a lithium iron phosphate (LFP) positive electrode material, a first lithium supplementing additive and a second lithium supplementing additive; the first lithium supplementing additive is Li2NiO2, and the second lithium supplementing additive is Li5FeO4; the positive electrode plate is configured to prepare a secondary battery comprising the positive electrode plate, a negative electrode plate and a separator; and the negative electrode plate comprises a negative electrode active material and a negative electrode current collector;the secondary battery has a first performance parameter a and a second performance parameter P respectively satisfying the following formulas:i !*#(!"*$"%!#*$#%!$*$$) *&; and($#%$$)*)**+***!#%!$+ 2C;wherein the first performance parameter a satisfies 1.0<a<1.13; and the second performance parameter P satisfies 6<P<10;A1 represents a weight percentage of the LFP positive electrode material in the positive electrode active material;A2 represents a weight percentage of the first lithium supplementing additive in the positive electrode active material;A3 represents a weight percentage of the second lithium supplementing additive in the positive electrode active material;M1 represents an initial charge specific capacity of the LFP positive electrode material, expressed in a unit of mAh / g;M2 represents an initial charge specific capacity of the first lithium supplementing additive, expressed in a unit of mAh / g;M3 represents an initial charge specific capacity of the second lithium supplementing additive, expressed in a unit of mAh / g;M4 represents an initial charge specific capacity of the negative electrode active material, expressed in a unit of mAh / g;X represents a coating amount of the positive electrode active material on the positive electrode current collector, expressed in a unit of mg / cm2;Y represents a coating amount of the negative electrode active material on the negative electrode current collector, expressed in a unit of mg / cm2;C represents an electrolyte filling coefficient, expressed in a unit of g / Ah;the secondary battery satisfies at least one of the following conditions:A1+A2+A3=1, 80%<Ai<99%, 0<A2<15%, and 0<A3<15%;X is 17-32 mg / cm2;in response to a case that a discharge voltage range of the secondary battery is 2.04.4 V, M1 is 150-170 mAh / g, M2 is 400-500 mAh / g, and M3 is 650-750 mAh / g;M4 is 350-400 mAh / g;the negative electrode active material is graphite, and Y is 5-20 mg / cm2; andC satisfies C<3.6 g / Ah.

15. A negative electrode plate, comprising:a negative electrode active material; anda negative electrode current collector;wherein the negative electrode plate is configured to prepare a secondary batterycomprising a positive electrode plate, the negative electrode plate and a separator; the positive electrode plate comprises a positive electrode active material and a positive electrode current collector; the positive electrode active material comprises a lithium iron phosphate (LFP) positive electrode material, a first lithium supplementing additive and a second lithium supplementing additive, wherein the first lithium supplementing additive is Li2NiO2, and the second lithium supplementing additive is Li5FeO4;the secondary battery has a first performance parameter a and a second performance parameter P respectively satisfying the following formulas:i !*#(!"*$"%!#*$#%!$*$$) *&; and($#%$$)*)**+***!#%!$+ 2C;wherein the first performance parameter a satisfies 1.0<a<1.13; and the second performance parameter P satisfies 6<P<10;A1 represents a weight percentage of the LFP positive electrode material in the positive electrode active material;A2 represents a weight percentage of the first lithium supplementing additive in the positive electrode active material;A3 represents a weight percentage of the second lithium supplementing additive in the positive electrode active material;M1 represents an initial charge specific capacity of the LFP positive electrode material, expressed in a unit of mAh / g;M2 represents an initial charge specific capacity of the first lithium supplementing additive, expressed in a unit of mAh / g;M3 represents an initial charge specific capacity of the second lithium supplementing additive, expressed in a unit of mAh / g;M4 represents an initial charge specific capacity of the negative electrode active material, expressed in a unit of mAh / g;X represents a coating amount of the positive electrode active material on the positive electrode current collector, expressed in a unit of mg / cm2;Y represents a coating amount of the negative electrode active material on thenegative electrode current collector, expressed in a unit of mg / cm2;C represents an electrolyte filling coefficient, expressed in a unit of g / Ah;the secondary battery satisfies at least one of the following conditions:A1+A2+A3=1, 80%<Ai<99%, 0<A2<15%, and 0<A3<15%;5 X is 17-32 mg / cm2;in response to a case that a discharge voltage range of the secondary battery is 2.04.4 V, M1 is 150-170 mAh / g, M2 is 400-500 mAh / g, and M3 is 650-750 mAh / g;M4 is 350-400 mAh / g;the negative electrode active material is graphite, and Y is 5-20 mg / cm2; and10 C satisfies C<3.6 g / Ah.

16. An electrically-powered device, comprising:the secondary battery according to any one of claims 1-12; ora secondary battery prepared according to the method of claim 13.