Lithium ion battery, lithium supplementing method thereof and electronic equipment

Abstract

The invention provides a lithium ion battery, a lithium supplementing method thereof and electronic equipment, and particularly relates to the technical field of lithium ion batteries. The lithium ion battery comprises a negative pole piece and a positive pole piece, and the positive pole piece comprises a positive current collector and a positive active material layer arranged on at least one side of the positive current collector; the positive electrode active material layer comprises a positive electrode active material and a positive electrode lithium supplement agent, the positive electrode active material comprises lithium-containing phosphate, the positive electrode lithium supplement agent at least comprises a first lithium supplement agent lithium ferrite and a second lithium supplement agent, and the mass percentage of the lithium ferrite to the total mass of the positive electrode active material and the positive electrode lithium supplement agent is a, 0 < a < = 3%. According to the invention, at least two lithium supplementing agents are introduced into the positive pole piece, and the addition proportion of the lithium supplementing agents is controlled, so that a synergistic effect is achieved, the advantages of various lithium supplementing agents are exerted, and the cycle life of the battery is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a lithium ion battery and a lithium replenishing method and electronic equipment thereof. Background Art

[0002] When lithium-ion batteries are charged for the first time, the active lithium in the positive electrode is usually consumed to form a SEI film on the surface of the negative electrode, resulting in a lower first-cycle coulombic efficiency and a higher initial irreversible capacity loss, thereby reducing the capacity and energy density of lithium-ion batteries. At present, the solution to this problem is to replenish lithium to increase the capacity and energy density of lithium-ion batteries. Lithium replenishment methods include positive electrode replenishment and negative electrode replenishment. However, since the process of negative electrode replenishment is complicated and difficult to apply in actual production, the existing technology mostly adopts the method of positive electrode replenishment. Adding a lithium replenisher to the positive electrode can not only increase the energy density of the battery cell, but also extend the service life of the battery cell.

[0003] Therefore, it is necessary to provide a new lithium replenishment method to improve the electrical performance of the battery cell. Summary of the invention

[0004] In view of the above shortcomings of the prior art, the present invention provides a lithium ion battery and a lithium replenishment method and an electronic device thereof to improve the energy density and cycle stability of the lithium ion battery.

[0005] To achieve the above-mentioned purpose and other related purposes, the present invention provides a lithium-ion battery and a lithium replenishment method and an electronic device thereof, wherein the lithium-ion battery comprises: a negative electrode plate and a positive electrode plate, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one side of the positive electrode current collector; the positive electrode active material layer comprises a positive electrode active material and a positive electrode lithium replenisher, the positive electrode active material comprises a lithium-containing phosphate, the positive electrode lithium replenisher comprises at least a first lithium replenisher lithium ferrite and a second lithium replenisher, the mass of the lithium ferrite accounts for a percentage of the total mass of the positive electrode active material and the positive electrode lithium replenisher is a, then 0<a≤3%.

[0006] In an example of the present invention, the lithium-containing phosphate includes lithium iron phosphate; and the second lithium supplement includes lithium nickelate.

[0007] In an example of the present invention, the value of a is 3%.

[0008] In an example of the present invention, the percentage of the mass of the lithium nickelate to the total mass of the positive electrode active material and the positive electrode lithium supplement is x, then 0<x≤20%.

[0009] In an example of the present invention, the lithium-ion battery further includes a diaphragm and an electrolyte, wherein the diaphragm is disposed between the positive electrode plate and the negative electrode plate, and the electrolyte is used to transfer lithium ions between the positive electrode plate and the negative electrode plate.

[0010] In one example of the present invention, the addition ratio of the lithium ferrite is fixed, and the discharge capacity in grams of the lithium-ion battery is negatively linearly correlated with the addition ratio of the lithium nickelate; and / or, the addition ratio of the lithium ferrite is fixed, and the number of cycles of the lithium-ion battery is positively linearly correlated with the addition ratio of the lithium nickelate.

[0011] In an example of the present invention, the discharge capacity in grams of the lithium-ion battery is Cap, and the addition ratio of Cap to the lithium nickelate satisfies the relationship Cap=151.5*(1-3%-x)+123.5*x.

[0012] In an example of the present invention, the number of cycles of the lithium-ion battery at 70% SOH is Cls, and the addition ratio of Cls to the lithium nickelate satisfies the relationship Cls=10000*(1+x*10).

[0013] Another aspect of the present invention provides a lithium replenishment method for a lithium ion battery, the lithium replenishment method comprising at least the following steps:

[0014] Prepare multiple groups of batteries, determine the amount of lithium ferrite added to the positive electrode plate, and adjust the amount of the second lithium supplement agent added to the positive electrode plate to prepare multiple groups of batteries with different addition ratios of the second lithium supplement agent;

[0015] Testing battery performance, testing the discharge capacity and cycle number of multiple groups of batteries;

[0016] Data quantification processing, based on the test results of multiple groups of the batteries, quantified relationships between the battery discharge capacity in grams and the addition ratio of lithium nickelate and between the number of cycles and the addition ratio of the second lithium supplement are obtained;

[0017] Determine the lithium replenishment system, and determine the lithium replenishment system of the lithium-ion battery based on the quantitative relationship.

[0018] The present invention further provides an electronic device, which comprises the lithium-ion battery described above.

[0019] The present invention introduces at least two lithium supplement agents into the positive electrode plate of the lithium-ion battery, and controls the addition ratio of each lithium supplement agent to achieve a synergistic effect, give full play to the advantages of various lithium supplement agents, and improve the cycle life of the battery. The lithium supplement agent is selected from lithium ferrite and lithium nickelate, and the high lithium supplement efficiency of lithium ferrite is combined with the controllable gas production of lithium nickelate, which can continuously improve the cycle life of the battery cell under the premise of ensuring controllable gas production.

[0020] The present invention fixes the amount of lithium ferrite added, and obtains a quantitative relationship between the addition ratio of lithium nickelate and the performance of the lithium ion battery by changing the addition ratio of lithium nickelate, and the energy density and cycle stability of the battery can be quantified based on this quantitative relationship. And because lithium nickelate particles are secondary particles, the addition of lithium nickelate can increase the contact between the positive electrode active materials and between the positive electrode active materials and the conductive agent, thereby reducing the direct current internal resistance (DCR value) of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 FIG. 1 is a flow chart of a lithium replenishment method for a lithium-ion battery according to an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0025] Unless otherwise specified or incompatible herewith, the terms and phrases used herein shall have the following meanings:

[0026] As used herein, "plurality", "multiple", "multiple times", etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0027] Herein, "preferred", "better" and "more preferred" are only used to describe implementation methods or examples with better effects, and it should be understood that they do not constitute a limitation on the scope of protection of the present invention. If multiple "preferred" items appear in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "preferred" item is independent.

[0028] Herein, “further”, “furthermore”, “particularly”, etc. are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of the present invention.

[0029] In this article, when it comes to numerical ranges, unless otherwise specified, the distribution of optional values ​​within the numerical range is considered continuous and includes the two numerical endpoints (i.e., the minimum value and the maximum value) of the numerical range, as well as every value between the two numerical endpoints. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be combined.

[0030] Lithium iron phosphate (LiFePO 4 , LFP)-based lithium-ion batteries have been widely developed and applied in large-scale energy storage, commercial vehicles and other fields due to their advantages such as low cost, good cycle stability and high safety. However, during the first charging process, lithium-ion batteries usually consume 5-10% of the active lithium from the positive electrode to form a solid electrolyte interface film (SEI) on the surface of the negative electrode, resulting in lower first-cycle coulomb efficiency and higher initial irreversible capacity loss. In addition, the capacity decay of LFP batteries during cycling is also attributed to the continuous consumption of active lithium. Therefore, adding a lithium supplement to the positive electrode to supplement the active lithium can not only increase the energy density of the battery cell, but also extend the service life of the battery cell.

[0031] At present, the commonly used positive electrode lithium supplements in the industry are mainly lithium nickel oxide (LiNiO 2 , LNO) and lithium ferrite (Li 5 FeO 4, LFO). Among them, LNO has high material maturity and does not produce gas; however, its first cycle 4.2V charging gram capacity is low, only 420mAh / g, and because the highest working voltage after the first cycle is 3.65V, some active lithium is in the positive electrode LNO after the first cycle discharge and no longer participates in the subsequent charging and discharging process, so the efficiency of LNO to supplement active lithium is low; in addition, LNO has poor conductivity, and adding LNO will increase the polarization of the battery cell, which is not conducive to the rate performance and low temperature performance of the battery cell. The first cycle 4.2V charging gram capacity of LFO is as high as 650mAh / g, and the reversible gram capacity is extremely low, only 20mAh / g, so it has a higher lithium replenishment efficiency; and the conductivity of carbon-coated LFO is equivalent to that of LFP, which basically does not lead to the increase of polarization; however, the material maturity of LFO is low, and it produces more gas during the formation and aging process, and storage gas production will also affect the performance of the battery cell.

[0032] In the prior art, a single lithium supplement is often used to supplement the positive electrode with lithium. However, although a single lithium supplement can supplement the loss of active lithium to a certain extent, it also brings other problems. For example, excessive addition of LFO will cause serious gas production in the battery cell, affecting the life of the battery cell. Although LNO does not have the problem of gas production, its lithium supplement efficiency is low and its conductivity is poor. When the addition ratio is too high, it also leads to increased polarization of the battery cell, which is not conducive to the rate performance and low temperature performance of the battery cell. Based on this, the present invention provides a lithium ion battery, a lithium supplement method for a lithium ion battery, and an electronic device comprising a lithium ion battery.

[0033] The first aspect of the present invention provides a lithium-ion battery, which includes a negative electrode plate and a positive electrode plate. The positive electrode plate includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive current collector can be made of a conventional material with good conductivity and mechanical strength in the art, such as aluminum foil, carbon-coated aluminum foil, etc. The positive current collector has two surfaces opposite to each other in its own thickness direction, and the positive active material layer is disposed on any one or both of the two opposite surfaces of the positive current collector.

[0034] The positive electrode active material layer includes a positive electrode active material and a positive electrode lithium supplement. In the present application, the positive electrode active material includes a lithium-containing phosphate, for example, lithium iron phosphate (LiFePO 4 , LFP), lithium manganese iron phosphate (LiMn x Fe (1-x) PO 4 , 0<x<1, LFMP) etc. Further, the positive electrode active material is lithium iron phosphate, which has good cycle stability, high safety and low cost. The positive electrode lithium supplement includes at least a first lithium supplement lithium ferrite (Li 5 FeO 4, LFO) and the second lithium replenisher, the first lithium replenisher, lithium ferrite, has an extremely high first-cycle charging gram capacity and an extremely low first-cycle coulomb efficiency. Adding lithium ferrite can provide a high lithium replenishment efficiency, that is, lithium ferrite is the first choice for positive electrode lithium replenisher, but lithium ferrite produces more gas during the formation and aging process, and excessive lithium ferrite will also bring greater challenges to the gas production of the battery cell. In this application, the amount of lithium ferrite added accounts for a percentage of the total mass of the positive electrode active material and the positive electrode lithium replenisher, then 0<a≤3%. That is, the addition ratio of lithium ferrite is limited to 3% or less, which can not only improve the lithium replenishment efficiency of the positive electrode lithium replenisher, but also control the gas production. Of course, since the amount of lithium ferrite added is 3% or less, the amount of active lithium that can be replenished will be limited. By adding a second lithium replenisher to further replenish the active lithium, the cycle life of the battery cell can be continuously improved.

[0035] In one embodiment, the second lithium supplement includes lithium nickelate (LiNiO 2 , LNO), lithium nickel oxide materials are highly mature and do not produce gas. The matching use of lithium ferrite and lithium nickel oxide with an addition amount of less than 3% can exert a synergistic effect and continuously improve the cycle life of the battery while ensuring that the gas production is controllable.

[0036] In one embodiment, the percentage of the added amount of lithium ferrite to the total mass of the positive electrode active material and the positive electrode lithium supplement is 3%, and the percentage of the added amount of lithium nickelate to the total mass of the positive electrode active material and the positive electrode lithium supplement is x, then 0<x≤20%. Further preferably, 3%≤x≤15%, for example, x can be 5%, 8% or 12%, and so on.

[0037] The inventors have found through extensive research that when the addition ratio of lithium ferrite is fixed, the discharge capacity in grams of lithium-ion batteries is negatively linearly correlated with the addition ratio of lithium nickelate, and the cycle stability of lithium-ion batteries is positively linearly correlated with the addition ratio of lithium nickelate. That is, the discharge capacity in grams of lithium-ion batteries gradually decreases with the increase of the addition ratio of lithium nickelate, and the cycle life gradually increases with the increase of the addition ratio of lithium nickelate.

[0038] In one embodiment, the amount of lithium ferrite added is fixed at 3%, the discharge capacity in grams of the lithium-ion battery is Cap, and the number of cycles of the lithium-ion battery at 70% SOH is Cls. Based on a large amount of data, it is found that the addition ratio of Cap to lithium nickelate satisfies the relationship Cap=151.5*(1-3%-x)+123.5*x(1);

[0039] The addition ratio of Cls to the lithium nickelate satisfies the relationship Cls=10000*(1+x*10)(2);

[0040] In formula (1) and formula (2), x is the percentage of the amount of lithium nickelate added to the total mass of the positive electrode active material layer and the positive electrode lithium supplement. According to formula (1) and formula (2), the gram capacity and cycle number of lithium-ion batteries can be quantified. Those skilled in the art can derive a suitable lithium supplement system according to formula (1) and formula (2) based on the actual requirements of the gram capacity and cycle performance of the battery.

[0041] In some embodiments, the positive electrode active material layer further includes a positive electrode conductor, a positive electrode binder and a positive electrode dispersant, and the positive electrode conductor, the positive electrode binder and the positive electrode dispersant can be selected from conventional material types in the art. As an example, the positive electrode conductor is selected from one of conductive carbon black (SP), acetylene black, nano metal powder, graphene, carbon nanotubes (CNT), carbon nanofibers, or a combination of two or more mixed in any proportion. The positive electrode binder is selected from one or more mixtures of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, sodium carboxymethyl cellulose, and styrene-butadiene rubber. The positive electrode dispersant is selected from one or more of polyvinyl pyrrolidone (PVP), polyethylene glycol, polyacrylic acid, and polyacrylate.

[0042] In some embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode current collector can be made of a material with good electrical conductivity and mechanical strength, such as copper foil. The negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active material layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, a negative electrode conductive agent, a negative electrode binder and a thickener. The negative electrode active material, the negative electrode conductive agent, the negative electrode binder and the thickener can be selected from conventional material types in the art, and no specific restrictions are made here.

[0043] As an example, the negative electrode material is selected from carbon and / or silicon negative electrode materials, such as elemental silicon, silicon oxide compounds, silicon carbon compounds, graphite, etc., and the graphite can be natural graphite, artificial graphite, soft carbon, hard carbon, etc. The negative electrode conductive agent is selected from one of conductive carbon black, nano silver powder, acetylene black, graphene, carbon nanotubes, carbon nanofibers, etc., or a combination of two or more mixed in any proportion. The negative electrode binder is selected from any one of polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), or a combination of several mixed in any proportion; the thickener can be sodium carboxymethyl cellulose (CMC-Na).

[0044] In one embodiment, the lithium-ion battery also includes a diaphragm and an electrolyte. The diaphragm is arranged between the positive electrode plate and the negative electrode plate to play an isolation role. During the battery charging and discharging process, lithium ions are embedded and released back and forth between the positive electrode plate and the negative electrode plate, and the electrolyte plays a role in conducting lithium ions between the positive electrode plate and the negative electrode plate.

[0045] The diaphragm may be selected from conventional types in the art, for example, a polypropylene (PP) or polyethylene (PE) porous membrane, or a composite membrane of PE and ceramics.

[0046] The electrolyte may be a combination of conventional types in the art, including an organic solvent and a lithium salt (selected according to the type of battery), wherein the solvent may be selected from one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), etc., or a plurality of them mixed in any proportion. The lithium salt is selected from LiPF 6 (Lithium hexafluorophosphate), LiBF 4 (Lithium Tetrafluoroborate)LiClO 4 (Lithium Perchlorate), LiAsF 6 (lithium hexafluoroarsenate), LiFSI (lithium bis(fluorosulfonyl imide), LiTFSI (lithium bis(trifluoromethanesulfonyl imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalatoborate), LiBOB (lithium dioxalatoborate), LiPO 2 F 2 (lithium difluorophosphate), LiDFOP (lithium difluorobis(oxalate phosphate), LiTFOP (lithium tetrafluorooxalate phosphate) or a combination thereof in any proportion. The mass content of lithium salt in the electrolyte is 5% to 20%. Additives may also be added to the electrolyte, the additives including film-forming additives and functional additives that can improve battery performance, for example, vinylene carbonate (VC), 1,3-propane sultone (PS), diethylene sulfate (DTD), etc., and those skilled in the art may select according to actual needs. The conventional amount of additives in the electrolyte is 1% to 4% of the mass of the electrolyte, for example, 2%.

[0047] The preparation process of lithium-ion batteries is described below:

[0048] (1) Preparation of positive electrode sheet

[0049] The above-mentioned positive electrode active material, positive electrode lithium supplement agent, positive electrode conductive agent, positive electrode dispersant and positive electrode binder are mixed in a certain mass ratio, and then the solvent N-methylpyrrolidone (NMP) is added to the mixer and stirred evenly, and then the solvent is added according to the solid content of 45% to 70% and stirred and mixed evenly to obtain the positive electrode slurry; and then the positive electrode slurry is evenly coated on the positive electrode collector, and the positive electrode sheet is obtained after drying, rolling and cutting.

[0050] (2) Preparation of negative electrode sheet

[0051] The above-mentioned negative electrode active material, negative electrode binder, negative electrode conductive agent and thickener are added into a mixer in a certain proportion and stirred evenly, and then deionized water is added according to a solid content of 45% to 70% and stirred and mixed evenly to obtain a negative electrode slurry; the negative electrode slurry is then evenly coated on the negative electrode collector, and the negative electrode sheet is obtained after drying, rolling and cutting.

[0052] (3) Preparation of electrolyte

[0053] In an argon atmosphere glove box with a water content of <10 ppm, a fully dried lithium salt (LiPF 6 ) is dissolved in an organic solvent and mixed evenly to obtain an electrolyte, wherein LiPF 6 The concentration is 1 mol / L.

[0054] (4) Preparation of diaphragm

[0055] A 12 μm thick polypropylene (PP) or polyethylene (PE) porous polymer film is selected.

[0056] (5) Battery assembly:

[0057] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked or wound in sequence to obtain an electrode assembly, with the separator being placed between the positive and negative electrode sheets to play a role of isolation. Then, the electrode assembly is hot pressed, shelled, transferred to a vacuum oven for drying at 120°C, and the electrolyte prepared above is injected for formation, aging, and sealing welding, and finally a square shell battery (i.e., a lithium-ion battery) is prepared.

[0058] Those skilled in the art will understand that the above-described method for preparing a lithium-ion battery is only an example, and other commonly used methods in the art may be used without departing from the contents disclosed in the present application.

[0059] See also Figure 1 The second aspect of the present invention provides a lithium replenishment method for a lithium ion battery, the lithium replenishment method at least comprising steps S1 to S4:

[0060] S1. Determine the amount of lithium ferrite added to the positive electrode plate, and adjust the amount of the second lithium supplement agent added to the positive electrode plate to prepare multiple groups of batteries with different addition ratios of the second lithium supplement agent;

[0061] S2. Test the discharge capacity and cycle number of multiple battery groups;

[0062] S3. According to the test results of multiple groups of batteries, the quantitative relationship between the battery discharge capacity in grams and the addition ratio of the second lithium supplement agent and the number of cycles and the addition ratio of the second lithium supplement agent are obtained;

[0063] S4. Determine the lithium replenishment system for lithium-ion batteries based on the quantitative relationship.

[0064] Although lithium ferrite has a high lithium replenishment efficiency as a positive electrode lithium replenisher, it produces more gas during the formation and aging process. The inventors of this application have found through a lot of research that when the addition amount of lithium ferrite (the mass of lithium ferrite compared to the total mass of the positive electrode active material and the positive electrode lithium replenisher) is less than or equal to 3%, the gas production of the battery cell is controllable. Therefore, the addition amount of lithium ferrite in step S1 is less than or equal to 3%, for example, it can be 1%, 2% or 3%. Further preferably, the addition amount of lithium ferrite is 3%, which can maximize its own advantages.

[0065] After the amount of lithium ferrite to be added is determined, a second lithium supplement is selected for use with the lithium ferrite. Preferably, the second lithium supplement is lithium nickelate, which can further supplement active lithium without introducing gas production problems. Furthermore, the amount of lithium nickelate added (the mass of lithium nickelate compared to the total mass of the positive electrode active material and the positive electrode lithium supplement) x is 0<x≤20%, and further, 3<x≤15%.

[0066] In order to further study the quantitative relationship between the addition ratio of lithium nickelate and battery performance, step S1 fixes the addition amount of lithium ferrite, and by adjusting the addition ratio of lithium nickelate, multiple groups of lithium nickelate batteries with different addition ratios are prepared. In this embodiment, the addition amount of lithium ferrite is fixed to 3%, and the addition amount x of lithium nickelate is selected in the range of 0 to 20%. The addition amount of lithium nickelate in the positive electrode plates of multiple groups of batteries can be 1%, 2%, 3%...20%, etc. The negative electrode plates, diaphragms and electrolytes of the batteries can be prepared according to conventional methods in the field, please refer to the above for details. In other embodiments, the addition amount of lithium ferrite can also be fixed to 1%, 2%, etc.

[0067] Step S2 is to test the performance of the battery, and the discharge capacity and cycle performance of the multiple groups of batteries prepared in step S1 are tested respectively. The specific test is carried out according to the conventional method in the field. The example is as follows:

[0068] (1) Discharge capacity in grams: ① Adjust the temperature of the temperature box to 25℃ and leave it for 2 hours; ② Discharge at 0.33C constant current to 2.5V and leave it for 30 minutes; ③ Charge at 0.33C constant current and constant voltage to 3.65V, constant voltage to 0.05C, and leave it for 30 minutes; ④ Discharge at 0.33C constant current to 2.5V and leave it for 30 minutes; ⑤ Cycle steps ③④ twice, for a total of three charge and discharges, and leave it for 30 minutes; ⑥ Charge at 0.33C constant current and constant voltage to 3.65V, constant voltage to 0.05C, and leave it for 30 minutes; ⑦ Discharge at 0.33C constant current to 2.5V; ⑧ Discharge at 0.33C constant current to 2V and leave it for 30 minutes; Take the discharge capacity of step ⑦ to calculate the capacity in grams of the battery cell.

[0069] (2) The cycle test process is as follows: ① Adjust the temperature of the temperature box to 25°C and leave it for 2 hours; ② Charge to 3.65V at 0.5P constant power and leave it for 5 minutes; ③ Discharge to 2.5V at 0.5P constant power and leave it for 5 minutes; ④ Cycle steps ②③ 2 times, a total of 3 charge and discharges, and leave it for 5 minutes; ④ Discharge to 2.5V at 0.5P constant power and leave it for 5 minutes; ⑤ Charge to 3.65V at 0.5P constant power and leave it for 5 minutes; ⑥ Charge to 3.65V at 0.1P constant power and leave it for 5 minutes; ⑦ Discharge to 2.5V at 0.5P constant power and leave it for 5 minutes; ⑧ Cycle steps ⑤⑥⑦ and perform long cycle test until the capacity retention rate is 70% SOH; the number of cycles when the capacity retention rate decays to 70% SOH is taken as the cycle life of the battery cell.

[0070] Step S3 is data quantification processing, in which the data of the multiple battery groups obtained in step S2 are processed to obtain the quantitative relationship between the addition ratio of lithium nickel oxide and the battery discharge capacity in grams and the quantitative relationship between the addition ratio of lithium nickel oxide and the number of cycles of the battery cell. The method of data quantification processing is data fitting, and formulas (1) and (2) are obtained.

[0071] Step S4 determines the lithium replenishment system, that is, the lithium replenishment system that meets the performance requirements of the lithium-ion battery can be determined based on the quantitative relationship in step S3.

[0072] The present invention also provides an electronic device, which comprises the secondary battery described above in the present invention. The secondary battery can be used in the electronic device in the form of a single cell, a battery module or a battery pack.

[0073] The electronic devices of the present invention include, but are not limited to, mobile phones, tablets, laptop computers, electric toys, battery cars, new energy vehicles, ships, spacecraft, etc. Among them, electric toys can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles and spacecraft, etc. New energy vehicles can be pure electric vehicles, hybrid vehicles or extended-range vehicles, etc.

[0074] The technical scheme of the present invention is described in detail below through several specific examples and comparative examples. Unless otherwise specified, the raw materials and reagents used in the following examples are all commercially available products, or can be prepared by conventional methods in the art, and the instruments used in the examples are all commercially available.

[0075] Example 1

[0076] This embodiment provides a lithium-ion battery, which includes a positive electrode plate, a separator, a negative electrode plate and an electrolyte. The preparation process is as follows:

[0077] (1) Preparation of positive electrode: LiFePO 4 As the positive electrode active material, LFO and LNO are positive electrode lithium supplements, and the three are mixed to prepare a composite positive electrode active material, among which LiFePO 4 The weight ratio of LFO and LNO is 96%:3%:1%. The composite positive electrode active material is mixed with a binder PVDF, a positive electrode dispersant PVP, a conductive agent SP and CNT in a weight ratio of 97:1.8:0.1:0.6:0.5, N-methylpyrrolidone (NMP) is added, and the system is stirred in a vacuum mixer until the system is uniform to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on a carbon-coated aluminum foil current collector, dried in a vacuum drying oven, and then cold pressed and cut to obtain a positive electrode sheet.

[0078] (2) Preparation of negative electrode sheets: The negative electrode active material artificial graphite, binder polyacrylic acid (PAA) and styrene-butadiene rubber (SBR), thickener sodium carboxymethyl cellulose (CMC-Na) and conductive agent Super P are mixed in a mass ratio of 97.3:1.3:0.5:0.5:0.4, deionized water is added, and negative electrode slurry is obtained under the action of a vacuum mixer; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil; it is dried in a vacuum drying oven, and then cold pressed and cut to obtain negative electrode sheets.

[0079] (3) Preparation of electrolyte: In an argon atmosphere glove box with a water content of <10 ppm, battery-grade ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and ethyl acetate (EA) were mixed in a mass ratio of 1:1:2:6 to form an organic solvent, and lithium salt LiPF was added in a certain proportion. 6 , mix evenly to obtain an electrolyte. LiPF 6 The concentration is 1 mol / L.

[0080] (4) Battery assembly: Using a 12 μm thick polypropylene film (PP) as a separator, the positive electrode sheet, separator, and negative electrode sheet prepared above are wound, so that the separator is located between the positive and negative electrodes to play a role of isolation. Then, hot pressing and shelling are carried out, and the battery is transferred to a vacuum oven at 120°C for drying. After the above-prepared electrolyte is injected, formation, aging, and sealing pin welding are carried out, and finally a square shell battery (i.e., lithium-ion battery) with a capacity of 100Ah is prepared.

[0081] Example 2

[0082] The difference between this embodiment and embodiment 1 is that the composition of the positive electrode sheet is LFP:LFO:LNO (weight ratio) = 95%:3%:2%, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0083] Example 3

[0084] The difference between this embodiment and embodiment 1 is that the composition of the positive electrode sheet is LFP:LFO:LNO (weight ratio) = 94%:3%:3%, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0085] Example 4

[0086] The difference between this embodiment and embodiment 1 is that the composition of the positive electrode sheet is LFP:LFO:LNO (weight ratio) = 93%:3%:4%, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0087] Example 5

[0088] The difference between this embodiment and embodiment 1 is that the composition of the positive electrode sheet is LFP:LFO:LNO (weight ratio) = 92%:3%:5%, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0089] Example 6

[0090] The difference between this embodiment and embodiment 1 is that the composition of the positive electrode sheet is LFP:LFO:LNO (weight ratio) = 87%:3%:10%, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0091] Example 7

[0092] The difference between this embodiment and embodiment 1 is that the composition of the positive electrode sheet is LFP:LFO:LNO (weight ratio) = 82%:3%:15%, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0093] Example 8

[0094] The difference between this embodiment and embodiment 1 is that the composition of the positive electrode sheet is LFP:LFO:LNO (weight ratio) = 77%:3%:20%, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0095] Comparative Example 1:

[0096] The difference between this comparative example and Example 1 is that the composition of the positive electrode sheet is LFP:LFO:LNO (weight ratio) = 100%:0%:0%, and the other conditions and parameters are exactly the same as those in Example 1.

[0097] Comparative Example 2:

[0098] The difference between this comparative example and Example 1 is that the composition of the positive electrode sheet is LFP:LFO:LNO (weight ratio) = 97%:3%:0%, and the other conditions and parameters are exactly the same as those in Example 1.

[0099] The electrochemical performance of the batteries obtained in Examples 1 to 8 and Comparative Examples 1 to 2 was tested. The test results are shown in Table 1. The test method is as follows:

[0100] The capacity test process is as follows: ① Adjust the temperature of the temperature box to 25℃ and leave it for 2 hours; ② Discharge at 0.33C constant current to 2.5V and leave it for 30 minutes; ③ Charge at 0.33C constant current and constant voltage to 3.65V, constant voltage to 0.05C, and leave it for 30 minutes; ④ Discharge at 0.33C constant current to 2.5V and leave it for 30 minutes; ⑤ Cycle steps ③④ 2 times, for a total of 3 charge and discharges, and leave it for 30 minutes; ⑥ Charge at 0.33C constant current and constant voltage to 3.65V, constant voltage to 0.05C, and leave it for 30 minutes; ⑦ Discharge at 0.33C constant current to 2.5V; ⑧ Discharge at 0.33C constant current to 2V and leave it for 30 minutes; Take the discharge capacity of step ⑦ to calculate the gram capacity of the battery cell;

[0101] The cycle test process is as follows: ① Adjust the temperature of the temperature box to 25℃ and leave it for 2 hours; ② Charge to 3.65V at 0.5P constant power and leave it for 5 minutes; ③ Discharge to 2.5V at 0.5P constant power and leave it for 5 minutes; ④ Cycle steps ②③ 2 times, a total of 3 charge and discharges, and leave it for 5 minutes; ④ Discharge to 2.5V at 0.5P constant power and leave it for 5 minutes; ⑤ Charge to 3.65V at 0.5P constant power and leave it for 5 minutes; ⑥ Charge to 3.65V at 0.1P constant power and leave it for 5 minutes; ⑦ Discharge to 2.5V at 0.5P constant power and leave it for 5 minutes; ⑧ Cycle steps ⑤⑥⑦ for long cycle test until the capacity retention rate is 70% SOH (70% State of Health); the number of cycles when the capacity retention rate decays to 70% SOH is taken as the cycle life of the battery cell;

[0102] DC resistance (DCR) test:

[0103] (1) Constant capacity: ① 0.5P constant power charging to 3.65V, set aside for 5 minutes; ② 0.5P constant power discharge to 2.5V, set aside for 5 minutes; ③ Cycle steps ①② twice, the second cycle 0.5P discharge capacity is C0;

[0104] (2) DCR measurement: ① 0.5P constant power charge to 3.65V, leave for 5 minutes; ② 0.33C0 constant current discharge to 50% SOC, leave for 2 hours, record the terminal voltage V0; ③ 2C constant current discharge for 30 seconds (0.1 second sampling), record the voltage V of the discharge for 30 seconds; ④ DCR can be calculated based on V0, V and current.

[0105] Table 1: Test results of Examples 1 to 8 and Comparative Examples 1 to 2

[0106]

[0107] The results in Table 1 show that in Comparative Example 1, no lithium supplement was added, and the discharge capacity in grams, number of cycles and DCR of the battery were relatively poor. In Comparative Example 2, 3% LFO was added, and the discharge capacity in grams, cycle performance and DCR of the battery were significantly improved compared with Comparative Example 1. In Examples 1 to 8, when the amount of LFO added was fixed, as the addition ratio of LNO increased, the discharge capacity in grams Cap of the battery gradually decreased, and the number of cycles Cls gradually increased, that is, the discharge capacity in grams was negatively linearly correlated with the addition ratio of LNO, and the number of cycles was positively linearly correlated with the addition ratio of LNO.

[0108] According to the test results, it can be deduced that the relationship between the discharge capacity Cap and the number of cycles Cls of the battery with 3% LFO and different proportions of LNO added lithium supplement and the LNO addition ratio x satisfies the formula (1) and formula (2) respectively:

[0109] Cap=151.5*(1-3%-x)+123.5*x (1);

[0110] Cls=10000*(1+x*10) (2).

[0111] The addition ratio of LNO in each embodiment is respectively substituted into the above formula (1) and (2) to verify the accuracy of the formula, and the predicted value is obtained, see Table 1. By comparing the actual measured value and the predicted value, it can be seen that the difference between the two is small, indicating that formula (1) and formula (2) have a certain reference value. According to the quantitative relationship of formula (1) and formula (2), an accurate calculation method can be provided for designing the energy density and cycle number of the battery cell.

[0112] In addition, it can be seen from the test results in Table 1 that when LFO is fixed, as the proportion of LNO added increases, the DCR value of the battery continues to decrease. Therefore, LFO combined with a certain proportion of LNO as a composite lithium supplement can improve the DCR of the battery.

[0113] The present invention introduces at least two lithium supplements into the positive electrode plate of the lithium-ion battery, and controls the addition ratio of each lithium supplement to achieve a synergistic effect, give play to the advantages of various lithium supplements, and improve the cycle life of the battery. The lithium supplements are selected from lithium ferrite and lithium nickelate, and the high lithium supplement efficiency of lithium ferrite is combined with the controllable gas production of lithium nickelate, which can continuously improve the cycle life of the battery cell under the premise of ensuring controllable gas production. In addition, the present invention designs experiments with different lithium nickelate addition ratios by fixing the addition ratio of lithium ferrite, and obtains a quantitative relationship formula between the battery's gram capacity, the number of cycles, and the lithium nickelate addition ratio. According to the quantitative relationship, the energy density and cycle stability can be quantified, providing a reference for the application of the lithium supplement system. Therefore, the present invention effectively overcomes some practical problems in the prior art and has a high utilization value and use significance.

[0114] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A lithium-ion battery, It is characterized in that include: Negative electrode; A positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector; The positive electrode active material layer includes a positive electrode active material and a positive electrode lithium replenisher, the positive electrode active material includes a lithium-containing phosphate, the positive electrode lithium replenisher includes at least a first lithium replenisher, lithium ferrite, and a second lithium replenisher, the mass of the lithium ferrite accounts for a percentage of the total mass of the positive electrode active material and the positive electrode lithium replenisher, then 0<a≤3%.

2. The lithium ion battery according to claim 1, It is characterized in that The lithium-containing phosphate includes lithium iron phosphate; and the second lithium supplement includes lithium nickelate.

3. The lithium ion battery according to claim 2, It is characterized in that The value of a is 3%.

4. The lithium ion battery according to claim 3, It is characterized in that The percentage of the mass of the lithium nickelate to the total mass of the positive electrode active material and the positive electrode lithium supplement is x, and 0<x≤20%.

5. The lithium ion battery according to claim 1, It is characterized in that The lithium-ion battery further comprises a diaphragm and an electrolyte, wherein the diaphragm is arranged between the positive electrode sheet and the negative electrode sheet.

6. The lithium ion battery according to claim 2, It is characterized in that The addition ratio of the lithium ferrite is fixed, and the discharge capacity in grams of the lithium-ion battery is negatively linearly correlated with the addition ratio of the lithium nickelate; and / or, the addition ratio of the lithium ferrite is fixed, and the cycle performance of the lithium-ion battery is positively linearly correlated with the addition ratio of the lithium nickelate.

7. The lithium ion battery according to claim 4, It is characterized in that The discharge capacity in grams of the lithium-ion battery is Cap, and the addition ratio of Cap to the lithium nickelate satisfies the relationship Cap=151.5*(1-3%-x)+123.5*x.

8. The lithium ion battery according to claim 4, It is characterized in that The number of cycles of the lithium-ion battery at 70% SOH is Cls, and the addition ratio of Cls to the lithium nickelate satisfies the relationship Cls=10000*(1+x*10).

9. A lithium replenishing method for a lithium ion battery according to any one of claims 1 to 8, It is characterized in that The following steps are involved: Prepare multiple groups of batteries, determine the amount of lithium ferrite added to the positive electrode plate, and adjust the amount of the second lithium supplement agent added to the positive electrode plate to prepare multiple groups of batteries with different addition ratios of the second lithium supplement agent; Testing battery performance, testing the discharge capacity and cycle number of multiple groups of batteries; Data quantification processing, according to the test results of multiple groups of the batteries, quantified relationships between the battery discharge capacity in grams and the addition ratio of the second lithium supplement agent and between the number of cycles and the addition ratio of the second lithium supplement agent are obtained; Determine the lithium replenishment system, and determine the lithium replenishment system of the lithium-ion battery based on the quantitative relationship.

10. An electronic device, It is characterized in that A lithium ion battery comprising any one of claims 1 to 8.

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