A positive electrode sheet and a battery

Abstract

The application discloses a positive pole piece and a battery, the positive pole piece comprises a positive pole current collector and a positive material layer arranged on at least one surface of the positive pole current collector; the positive material layer comprises a positive active material; the positive active material comprises a lithium transition metal oxide and a lithium supplementing additive; the lithium transition metal oxide comprises one or more of LiCoO2, LiNiO2, LiFePO4 and LixNiyM1-yO2, wherein 0.9<=x<=1.2, 0.5<=y<1, and M comprises one or more of Co, Mn, Al, Mg, Ti, Fe, Cr, Mo and Ca; and the lithium supplementing additive comprises at least one of a lithium-containing compound and a modified material of the lithium-containing compound. In the positive pole piece, the specific lithium supplementing additive is added, so that the battery made of the positive pole piece can maximize the effect of supplementing lithium without lithium precipitation reaction, and the energy density and the cycle performance of the battery are improved.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to a positive electrode and a battery. Background Technology

[0002] The rapid development of technologies such as electric vehicles and electronic devices has led to a continuous increase in demand for high-energy-density lithium-ion batteries. As a crucial measure to improve battery energy density, the application of high-specific-capacity anode materials has also attracted increasing attention. However, compared to traditional graphite-based materials, high-specific-capacity anode materials exhibit larger initial irreversible capacity and lower cycle stability, severely impacting battery energy density and lifespan. Therefore, for the practical application of high-capacity anodes, there is an urgent need to develop commercially available pre-lithiation technologies to compensate for irreversible capacity losses during initial operation and cycling.

[0003] Currently, the mainstream pre-lithiation methods are mainly divided into two types: negative electrode pre-lithiation and positive electrode pre-lithiation. Negative electrode pre-lithiation primarily achieves lithium replenishment by directly contacting the electrode material with metallic lithium. However, due to the extremely reactive nature of lithium, the processing is difficult, costly, and risky, hindering large-scale commercialization. Therefore, using lithium replenishment additives for positive electrode pre-lithiation has become the preferred choice for most manufacturers. However, how to rationally utilize lithium replenishment additives in battery systems is a problem that needs to be solved in silicon-carbon negative electrode battery systems. Summary of the Invention

[0004] Therefore, the purpose of this invention is to provide a positive electrode and a battery. This invention, by controlling the lithium-replenishing additive and its dosage, enables the secondary battery incorporating the lithium-replenishing additive to maximize its lithium-replenishing effect while ensuring that the battery does not undergo lithium plating, thereby improving the battery's energy density and cycle performance.

[0005] First aspect:

[0006] The present invention provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector;

[0007] The positive electrode material layer comprises a positive electrode active material; the positive electrode active material includes lithium transition metal oxide and lithium supplementation additives;

[0008] The lithium transition metal oxide includes one or more of LiCoO2, LiNiO2, LiFePO4, and LixNiyM1-yO2, wherein 0.9≤x≤1.2, 0.5≤y<1, and M includes one or more of Co, Mn, Al, Mg, Ti, Fe, Cr, Mo, and Ca;

[0009] The lithium supplementation additive includes at least one of lithium-containing compounds and lithium-containing modified materials;

[0010] The modified materials containing lithium compounds include materials obtained by coating and / or doping lithium compounds.

[0011] The lithium-containing compounds include one or more of Li6CoO4, Li2NiO2, Li5FeO4, Li2O, Li2O2, Li2S, Li3N, and LiF.

[0012] The lithium supplementing additive is selected from one or more of Li6CoO4, Li2NiO2, Li5FeO4, Li2O, Li2O2, Li2S, Li3N, LiF, and their respective modified materials. The modified material can be a coating modification and / or doping modification of the material.

[0013] The positive current collector has two surfaces opposite each other in its thickness direction. The positive electrode material layer can be disposed on either of the two surfaces, or it can be disposed on both surfaces separately.

[0014] The positive electrode material layer comprises a positive electrode active material, a binder, and a conductive agent; the positive electrode active material includes lithium transition metal oxide and lithium supplementation additives.

[0015] The positive electrode material layer is formed by coating a positive electrode slurry and then drying and cold pressing it. The positive electrode slurry is formed by dispersing positive electrode active materials, conductive agents, and binders in a solvent and stirring them evenly; the solvent can be N-methylpyrrolidone (NMP).

[0016] The binder for the positive electrode material layer includes one or more of polyvinylidene fluoride (PVDF), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0017] The conductive agents in the positive electrode material layer include one or more of superconducting carbon, carbon black (such as Super P (activated carbon), acetylene black, Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0018] The lithium supplementation additive accounts for 0.5-20 wt.% of the mass of the cathode material layer. Preferably, it accounts for 1-5 wt.%.

[0019] The volume average particle size Dv of the lithium supplement additive 50 Satisfying 2μm≤Dv 50 ≤10μm; optional 3μm≤Dv 50 ≤9μm.

[0020] The particle size range (Dv) of the lithium supplementation additive 90 -Dv 10 ) / Dv 50 Satisfies: 1.0 ≤ (Dv) 90 -Dv 10 ) / Dv 50 ≤2.0; optional, 1.01≤(Dv) 90 -Dv 10 ) / Dv 50 ≤1.9.

[0021] The lithium supplemental additive has a volume average particle size DV 50 Volume average particle size (DV) of lithium transition metal oxides 50 The following condition must be met: 0.5 * Lithium transition metal oxide DV 50 ≤Lithium Supplement Additive DV 50 ≤2*Lithium transition metal oxide DV50.

[0022] The specific surface area of ​​the lithium supplement additive is 0.5 m². 2 / g~3.0m 2 / g; preferably 0.55m 2 / g~1.9m 2 / g, the specific surface area of ​​the lithium supplement additive is within this range, which can further improve the cycle life.

[0023] The initial charge capacity of the lithium replenishment additive is 310mAh / g-3000mAh / g; preferably, the initial charge capacity of the lithium replenishment additive is 480mAh / g-3000mAh / g. When the initial charge capacity of the lithium replenishment additive is greater than 310mAh / g, the cycle life can be further improved.

[0024] The irreversible capacity of the lithium replenishing additive is 300mAh / g-3000mAh / g; preferably, the irreversible capacity of the lithium replenishing additive is 400mAh / g-3000mAh / g. The irreversible capacity of the lithium replenishing additive is greater than 300mAh / g, which can further improve the cycle life.

[0025] The pH of the lithium supplement additive is 8-13; optionally 11.5-12.5.

[0026] The second aspect:

[0027] The present invention provides a secondary battery, comprising a negative electrode, an electrolyte, and a positive electrode as described above.

[0028] The negative electrode sheet includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector; the negative electrode material layer includes a negative electrode active material, a binder, a conductive agent, and an additive; the negative electrode active material includes graphite and silicon material.

[0029] The negative electrode material layer is formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is formed by dispersing negative electrode active materials, binders, conductive agents, and additives in a solvent and stirring them evenly; the solvent can be N-methylpyrrolidone (NMP) or deionized water.

[0030] The conductive agents in the negative electrode material layer include one or more of superconducting carbon, carbon black (such as Super P, acetylene black, Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0031] The binder in the negative electrode material layer includes one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, polyacrylic acid (PAA), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0032] Additives in the negative electrode material layer include thickeners (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, etc.

[0033] In the secondary battery of the present invention, the negative electrode current collector is made of a material with good electrical conductivity and mechanical strength.

[0034] The secondary battery satisfies: 1.2 ≥ initial lithium insertion NP ratio ≥ 1.01; and / or; 1.2 ≥ initial lithium desorption NP ratio > 1.02;

[0035] Wherein, the initial lithium insertion NP ratio = (coating surface density of the negative electrode active material * initial lithium insertion capacity of the negative electrode active material) / (coating surface density of the positive electrode lithium transition metal oxide * initial delithiation capacity of the positive electrode lithium transition metal oxide + coating surface density of the positive electrode lithium replenishment additive * initial delithiation capacity of the positive electrode lithium replenishment additive)

[0036] quantity);

[0037] Initial lithium removal NP ratio = (coating areal density of negative electrode active material * initial lithium removal capacity of negative electrode active material)

[0038] / (coating areal density of lithium transition metal oxide in the cathode * initial lithium intercalation capacity of lithium transition metal oxide in the cathode + coating areal density of lithium supplementation additive in the cathode * initial lithium intercalation capacity of lithium supplementation additive in the cathode).

[0039] It should be noted that, among them, "coating surface density of negative electrode active material" refers to the amount of negative electrode active material coated on a unit area of ​​negative electrode current collector in the negative electrode material layer; "coating surface density of lithium transition metal oxide of positive electrode" refers to the amount of lithium transition metal oxide coated on a unit area of ​​positive electrode current collector in the positive electrode material layer; and "coating surface density of lithium supplementation additive of positive electrode" refers to the amount of lithium supplementation additive coated on a unit area of ​​positive electrode current collector in the positive electrode material layer.

[0040] When the above conditions are met, the higher the amount of lithium additive added, the more obvious the lithium replenishment effect.

[0041] 1.2≥Initial Lithium Intercalation NP Ratio≥1.01 ensures that, under the existing battery coating process, during the first charge of the full cell, all lithium ions extracted from the positive electrode are intercalated into the negative electrode without lithium plating.

[0042] The first lithium removal NP ratio of 1.2 ≥ 1.02 ensures that during the first discharge of the full cell, all lithium ion vacancies that can be inserted into the positive electrode are filled by lithium ions extracted from the negative electrode, preventing the positive electrode from being empty and avoiding lithium plating caused by excessively rapid decay of the negative electrode during cycling.

[0043] The negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, and silicon materials.

[0044] The silicon material includes one or more of elemental silicon, silicon oxides, silicon-carbon composites, and silicon alloys.

[0045] In the aforementioned secondary battery, there are no specific restrictions on the type of electrolyte, which can be selected according to requirements. The electrolyte includes at least one of solid electrolyte and liquid electrolyte (i.e., electrolyte solution). In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte lithium salt and an electrolyte solvent. Optionally, the lithium salt includes one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiCIO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium dioxalate borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorodioxalate phosphate), and LiTFOP (lithium tetrafluorooxalate phosphate).

[0046] Optionally, the electrolyte solvent includes one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 14-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0047] In some embodiments, the electrolyte may optionally include additives. These additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives capable of improving certain battery performance characteristics, such as additives that improve battery overcharge performance, high-temperature performance, and low-temperature performance.

[0048] In some embodiments, the secondary battery also includes a separator. The separator is disposed between the positive and negative electrodes, serving as a barrier. The secondary battery of the present invention does not have particular limitations on the type of separator; any known porous separator used in secondary batteries can be selected. For example, the separator can be selected from one or more of the following: glass fiber film, non-woven fabric film, polyethylene film, polypropylene film, polyvinylidene fluoride film, and multilayer composite films comprising one or more of these materials.

[0049] In some embodiments, the secondary battery may include an outer packaging. The outer packaging is used to encapsulate the positive electrode, the negative electrode, and the electrolyte.

[0050] In some implementations, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0051] Secondary batteries can be prepared using methods known in the art. For example, a positive electrode, a separator, and a negative electrode are formed into an electrode assembly by a winding or stacking process, wherein the separator is positioned between the positive and negative electrode to provide isolation; the electrode assembly is placed in an outer package, an electrolyte is injected, and the package is sealed to obtain a secondary battery.

[0052] The present invention does not impose any particular restrictions on the shape of the secondary battery, which can be cylindrical, square, pouch, or any other arbitrary shape.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] By adjusting the lithium replenishment additive and its usage, as well as the initial lithium insertion ratio and initial lithium removal ratio of the battery, the secondary battery with the lithium replenishment additive can maximize the lithium replenishment effect while ensuring that the battery does not undergo lithium plating reaction, thereby improving the battery's energy density and cycle performance. Attached Figure Description

[0055] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0056] Figure 1 Comparative Example 2: Photos of the electrode plates disassembled after the first full charge;

[0057] Figure 2 Comparative Example 2: Photos of the electrode plates disassembled after the first full charge;

[0058] Figure 3 Photo of the electrode plates after being fully charged and disassembled following 300 cycles of comparative example 3;

[0059] Figure 4 This is a photograph of the electrode sheet after being fully charged and disassembled following 300 cycles in Example 5. Detailed Implementation

[0060] The present invention will be described in detail below with reference to embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several adjustments and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0061] Example 1

[0062] This embodiment provides a secondary battery.

[0063] Positive electrode sheet:

[0064] Based on the total mass of the cathode material layer, the cathode material layer formulation is as follows: 1.1 wt.% Super P + 0.6 wt.% CNT (carbon nanotubes) + 1.1 wt.% PVDF + 1.8 wt.% Li₂NiO₂ + 95.4 wt.% NCM811 (LiNiO₂). 0.8 Co 0.1 Mn 0.1 O2). In the positive electrode sheet: the coating areal density of NCM811 is 381.6 g / m². 2 The coating density of the lithium supplement additive Li2NiO2 on the positive electrode is 7.2 g / m².2 The initial delithiation capacity of NCM811 is 225 mAh / g, and the initial lithiation capacity of NCM811 is 198 mAh / g; the initial delithiation capacity of Li2NiO2 is 448 mAh / g, and the initial lithiation capacity of Li2NiO2 is 90 mAh / g.

[0065] Negative electrode plate:

[0066] Based on the total mass of the negative electrode material layer, the formulation of the negative electrode material layer is: 85.7 wt.% graphite.

[0067] +9.5wt.% SiO + 1.1wt.% Super P + 3wt.% PAA + 0.6wt.% SBR + 0.1wt.% SWCNT (single-walled carbon nanotubes). In the negative electrode sheet, the coating areal density of the negative electrode active material (graphite + SiO) is 186.6 g / m². 2 The initial lithium insertion capacity of the negative electrode active material (graphite + SiO) is 491 mAh / g, and the initial lithium de-lithiation capacity is 455 mAh / g.

[0068] Other parameters of the positive / negative electrode plates are shown in Table 1.

[0069] The obtained positive electrode, negative electrode and PE separator are combined and a secondary battery is obtained by conventional battery preparation method.

[0070] Example 2

[0071] This embodiment provides a secondary battery.

[0072] Positive electrode sheet:

[0073] Based on the total mass of the cathode material layer, the cathode material layer formulation is as follows: 1.1 wt.% Super P + 0.6 wt.% CNT (carbon nanotubes) + 1.1 wt.% PVDF + 2 wt.% Li₂NiO₂ + 95.2 wt.% NCM₅₂₃ (LiNiO₂) 0.5 Co 0.2 Mn 0.3 O2). In the positive electrode sheet: the coating areal density of NCM523 is 380.8 g / m². 2 The coating areal density of the lithium supplementation additive Li2NiO2 in the positive electrode is 8 g / m². 2 The initial delithiation capacity of NCM523 is 205 mAh / g, and the initial lithiation capacity of NCM523 is 180 mAh / g; the initial delithiation capacity of Li2NiO2 is 448 mAh / g, and the initial lithiation capacity of Li2NiO2 is 90 mAh / g.

[0074] Negative electrode plate:

[0075] Based on the total mass of the negative electrode material layer, the formulation of the negative electrode material layer is: 85.7 wt.% graphite.

[0076] +9.5wt.% SiO + 1.1wt.% Super P + 3wt.% PAA + 0.6wt.% SBR + 0.1wt.% SWCNT (single-walled carbon nanotubes). In the negative electrode sheet, the coating areal density of the negative electrode active material (graphite + SiO) is 173.2 g / m². 2 The initial lithium insertion capacity of the negative electrode active material (graphite + SiO) is 491 mAh / g, and the initial lithium de-lithiation capacity is 455 mAh / g.

[0077] Other parameters of the positive / negative electrode plates are shown in Table 1.

[0078] The obtained positive electrode, negative electrode and PE separator are combined and a secondary battery is obtained by conventional battery preparation method.

[0079] Example 3

[0080] This embodiment provides a secondary battery.

[0081] Positive electrode sheet:

[0082] Based on the total mass of the cathode material layer, the cathode material layer formulation is: 1.1% Super P + 0.6% CNT (carbon nanotubes) + 1.1% PVDF + 1.2% Li5FeO4 + 96% NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O2). In the positive electrode sheet: the coating areal density of NCM811 is 384 g / m². 2 The coating density of the lithium supplement additive Li5FeO4 in the positive electrode is 4.8 g / m². 2 The initial delithiation capacity of NCM811 is 225 mAh / g, and the initial lithiation capacity is 198 mAh / g. The initial delithiation capacity of Li5FeO4 is 652 mAh / g, and the initial lithiation capacity is 10 mAh / g.

[0083] Negative electrode plate:

[0084] Based on the total mass of the negative electrode material layer, the formulation of the negative electrode material layer is: 85.7% graphite + 9.5% SiO + 1.1% Super P + 3% PAA + 0.6% SBR + 0.1% SWCNT (single-walled carbon nanotubes). In the negative electrode sheet, the coating areal density of the negative electrode active material (graphite + SiO) is 186.6 g / m². 2The initial lithium insertion capacity of the negative electrode active material (graphite + SiO) is 491 mAh / g, and the initial lithium de-lithiation capacity is 455 mAh / g.

[0085] Other parameters of the positive / negative electrode plates are shown in Table 1.

[0086] The obtained positive electrode, negative electrode and PE separator are combined and a secondary battery is obtained by conventional battery preparation method.

[0087] Example 4

[0088] This embodiment provides a secondary battery.

[0089] Positive electrode sheet:

[0090] Based on the total mass of the cathode material layer, the cathode material layer formulation is: 1.1% Super P + 0.6% CNT (carbon nanotubes) + 1.1% PVDF + 1.8% Li5FeO4 + 95.4% NCM811 (LiNi) 0.8 Co 0.1 Mn 0.1 O2). In the positive electrode sheet: the coating areal density of NCM811 is 381.6 g / m². 2 The coating density of the lithium supplement additive Li5FeO4 in the positive electrode is 7.2 g / m². 2 The initial delithiation capacity of NCM811 is 225 mAh / g, and the initial lithiation capacity is 198 mAh / g. The initial delithiation capacity of Li5FeO4 is 652 mAh / g, and the initial lithiation capacity is 10 mAh / g.

[0091] Negative electrode plate:

[0092] Based on the total mass of the negative electrode material layer, the formulation of the negative electrode material layer is: 75.1% graphite.

[0093] +18.8% SiC + 1.1% Super P + 4% PAA + 0.8% SBR + 0.2% SWCNT (single-walled carbon nanotubes). In the negative electrode sheet, the coating areal density of the negative electrode active material (graphite + SiC) is 152.1 g / m². 2 The initial lithium insertion capacity of the negative electrode active material (graphite + SiC) is 612 mAh / g, and the initial lithium de-lithiation capacity is 560 mAh / g.

[0094] Other parameters of the positive / negative electrode plates are shown in Table 1.

[0095] The obtained positive electrode, negative electrode and PE separator are combined and a secondary battery is obtained by conventional battery preparation method.

[0096] Example 5

[0097] This embodiment provides a secondary battery.

[0098] Positive electrode sheet:

[0099] Based on the total mass of the cathode material layer, the cathode material layer formulation is: 1.1% Super P + 0.6% CNT (carbon nanotubes) + 1.1% PVDF + 4.7% Li5FeO4 + 92.5% NCM811 (LiNi) 0.8 Co 0.1 Mn 0.1 O2). In the positive electrode sheet: the coating areal density of NCM811 is 370 g / m². 2 The coating areal density of the lithium supplementation additive Li5FeO4 in the positive electrode is 18.8 g / m². 2 The initial delithiation capacity of NCM811 is 225 mAh / g, and the initial lithiation capacity is 198 mAh / g. The initial delithiation capacity of Li5FeO4 is 652 mAh / g, and the initial lithiation capacity is 10 mAh / g.

[0100] Negative electrode plate:

[0101] Based on the total mass of the negative electrode material layer, the formulation of the negative electrode material layer is: 64.6% graphite.

[0102] The coating areal density of the negative electrode active material (graphite + SiC) is 129.2 g / m², consisting of 27.7% SiC, 1.2% Super P, 5% PAA, 1.1% SBR, and 0.4% SWCNT (single-walled carbon nanotubes). 2 The initial lithium insertion capacity of the negative electrode active material (graphite + SiC) is 793 mAh / g, and the initial lithium de-lithiation capacity is 659 mAh / g.

[0103] Other parameters of the positive / negative electrode plates are shown in Table 1.

[0104] The obtained positive electrode, negative electrode and PE separator are combined and a secondary battery is obtained by conventional battery preparation method.

[0105] Comparative Example 1

[0106] The difference between this comparative example and Example 5 is that Li5FeO4 is not added.

[0107] Positive electrode sheet:

[0108] Based on the total mass of the cathode material layer, the cathode material layer formulation is: 1.1% Super P + 0.6% CNT (carbon nanotubes) + 1.1% PVDF + 97.2% NCM811 (LiNi) 0.8 Co 0.1 Mn 0.1 O2). In the positive electrode sheet: the coating areal density of NCM811 is 370 g / m². 2 The initial delithiation capacity of NCM811 is 225 mAh / g, and the initial lithium insertion capacity of NCM811 is 198 mAh / g.

[0109] Negative electrode plate:

[0110] Based on the total mass of the negative electrode material layer, the formulation of the negative electrode material layer is: 64.6% graphite.

[0111] The coating areal density of the negative electrode active material (graphite + SiC) is 129.2 g / m², consisting of 27.7% SiC, 1.2% Super P, 5% PAA, 1.1% SBR, and 0.4% SWCNT (single-walled carbon nanotubes). 2 The initial lithium insertion capacity of the negative electrode active material (graphite + SiC) is 793 mAh / g, and the lithium removal capacity of the negative electrode active material (graphite + SiC) is 659 mAh / g.

[0112] Other parameters of the positive / negative electrode plates are shown in Table 1.

[0113] The obtained positive electrode, negative electrode and PE separator are combined, and the battery preparation method is the same as in Example 5.

[0114] Comparative Example 2

[0115] Positive electrode sheet:

[0116] Based on the total mass of the cathode material layer, the cathode material layer formulation is: 1.1% Super P + 0.6% CNT (carbon nanotubes) + 1.1% PVDF + 10% Li5FeO4 + 87.2% NCM811 (LiNi) 0.8 Co 0.1 Mn 0.1 O2). In the positive electrode sheet: the coating areal density of NCM811 is 348.8 g / m². 2 The coating areal density of the lithium supplementation additive Li5FeO4 in the positive electrode is 40 g / m². 2 The initial delithiation capacity of NCM811 is 225 mAh / g, and the initial lithiation capacity is 198 mAh / g. The initial delithiation capacity of Li5FeO4 is 652 mAh / g, and the initial lithiation capacity is 10 mAh / g.

[0117] Negative electrode plate:

[0118] Based on the total mass of the negative electrode material layer, the formulation of the negative electrode material layer is: 64.6% graphite.

[0119] The coating areal density of the negative electrode active material (graphite + SiC) is 129.2 g / m², consisting of 27.7% SiC, 1.2% Super P, 5% PAA, 1.1% SBR, and 0.4% SWCNT (single-walled carbon nanotubes). 2 The initial lithium insertion capacity of the negative electrode active material (graphite + SiC) is 793 mAh / g, and the initial lithium de-lithiation capacity is 659 mAh / g.

[0120] Other parameters of the positive / negative electrode plates are shown in Table 1.

[0121] The obtained positive electrode, negative electrode and PE separator are combined, and the battery preparation method is the same as in Example 5.

[0122] Comparative Example 3

[0123] Positive electrode sheet:

[0124] Based on the total mass of the cathode material layer, the cathode material layer formulation is: 1.1% Super P + 0.6% CNT (carbon nanotubes) + 1.1% PVDF + 2% Li5FeO4 + 95.2% NCM811 (LiNi) 0.8 Co 0.1 Mn 0.1 O2). In the positive electrode sheet: the coating areal density of NCM811 is 380.8 g / m². 2 The coating areal density of the lithium supplementation additive Li5FeO4 in the positive electrode is 8 g / m². 2 The initial delithiation capacity of NCM811 is 225 mAh / g, and the initial lithiation capacity is 198 mAh / g. The initial delithiation capacity of Li5FeO4 is 652 mAh / g, and the initial lithiation capacity is 10 mAh / g.

[0125] Negative electrode plate:

[0126] Based on the total mass of the negative electrode material layer, the formulation of the negative electrode material layer is: 64.6% graphite.

[0127] The coating of the anode active material (graphite + SiC) is composed of 27.7% SiC, 1.2% Super P, 5% PAA, 1.1% SBR, and 0.4% SWCNT (single-walled carbon nanotubes), with a coating areal density of 116 g / m³. 2The initial lithium insertion capacity of the negative electrode active material (graphite + SiC) is 793 mAh / g, and the initial lithium de-lithiation capacity is 659 mAh / g.

[0128] Other parameters of the positive / negative electrode plates are shown in Table 1.

[0129] The obtained positive electrode, negative electrode and PE separator are combined, and the battery preparation method is the same as in Example 5.

[0130] test

[0131] First full charge test: The stacked batteries prepared in each embodiment and each comparative example were tested at room temperature of 2522℃: 1CC to 4.2V, CV to 0.05C, and left to stand for 5 minutes. The fully charged batteries were then disassembled to observe whether lithium was deposited on the surface of the negative electrode.

[0132] Cyclic test: The stacked batteries prepared in the examples and comparative examples were tested at room temperature of 25-22°C: Step 1: 1CC to 4.2V, CV to 0.05C, Step 2: stand for 5 minutes, Step 3: 1DC to 2.8V, Step 4: stand for 5 minutes, Step 5: cycle Step 1 to Step 4 until the discharge capacity decays to 80% of the initial discharge capacity.

[0133] Table 1

[0134]

[0135]

[0136] Comparing Example 5 with Comparative Example 1, it can be seen that the addition of LFO lithium supplementation additive significantly improves cycle performance.

[0137] Comparing Example 5 with Comparative Example 2, it can be seen that when the initial lithium intercalation NP ratio is <1.01, the lithium ions extracted from the positive electrode for the first time cannot be completely intercalated by the negative electrode, resulting in lithium plating. Figure 1 For comparison example 2, photos of the electrode plates being disassembled after the first full charge are shown. Figure 2 This is a photograph of the electrode sheet being disassembled during the first full charge in Example 5.

[0138] Comparing Example 5 with Comparative Example 3, it can be seen that when the initial lithium removal NP ratio is <1.02, as the negative electrode decays during the cycling process, the lithium ions removed from the positive electrode cannot be completely filled by the effective vacancies of the negative electrode, resulting in lithium deposition after cycling, which in turn leads to accelerated cycle decay. Figure 3 The photos show the electrode plates after being fully charged and disassembled following a 300-cycle cycle as a comparative example. Figure 4 This is a photograph of the electrode sheet after being fully charged and disassembled following 300 cycles in Example 5.

[0139] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A secondary battery, characterized in that, Includes negative electrode, electrolyte, and positive electrode; The positive electrode includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector; The positive electrode material layer comprises a positive electrode active material; the positive electrode active material includes lithium transition metal oxide and lithium supplementation additives; The lithium transition metal oxide includes one or more of LiCoO2, LiNiO2, LiFePO4, and LixNiyM1-yO2, wherein 0.9≤x≤1.2 and 0.5≤y<1; M includes one or more of Co, Mn, Al, Mg, Ti, Fe, Cr, Mo, and Ca; The lithium supplementary additive includes at least one of lithium-containing compounds and lithium-containing modified materials; The modified materials containing lithium compounds include materials obtained by coating and / or doping lithium compounds. The lithium-containing compounds include one or more of Li6CoO4, Li2NiO2, Li5FeO4, Li2O, Li2O2, Li2S, Li3N, and LiF; The pH of the lithium supplement additive is 8-13; The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector; The negative electrode material layer includes negative electrode active materials such as graphite and silicon. The secondary battery satisfies: 1.2 ≥ initial lithium insertion NP ratio ≥ 1.01; and 1.2 ≥ initial delithiation NP ratio > 1.02; Wherein, the initial lithium insertion NP ratio = (coating surface density of the negative electrode active material × initial lithium insertion capacity of the negative electrode active material) / (coating surface density of the positive electrode lithium transition metal oxide × initial delithiation capacity of the positive electrode lithium transition metal oxide + coating surface density of the positive electrode lithium replenishment additive × initial delithiation capacity of the positive electrode lithium replenishment additive). The initial delithiation NP ratio = (coating density of the negative electrode active material × initial delithiation capacity of the negative electrode active material) / (coating density of the positive electrode lithium transition metal oxide × initial lithium insertion capacity of the positive electrode lithium transition metal oxide + coating density of the positive electrode lithium supplementation additive × initial lithium insertion capacity of the positive electrode lithium supplementation additive).

2. The secondary battery according to claim 1, characterized in that, The lithium supplementation additive accounts for 0.5-20 wt.% of the positive electrode material layer by mass.

3. The secondary battery according to claim 1, characterized in that, The volume average particle size Dv of the lithium supplement additive 50 Satisfying 2μm≤Dv 50 ≤10μm.

4. The secondary battery according to claim 1, characterized in that, The particle size range (Dv) of the lithium supplementation additive 90 -Dv 10 ) / Dv 50 Satisfies: 1.0 ≤ (Dv) 90 -Dv 10 ) / Dv 50 ≤2.

0.

5. The secondary battery according to claim 1, characterized in that, The lithium supplemental additive has a volume average particle size DV 50 Volume average particle size (DV) of lithium transition metal oxides 50 The following conditions must be met: 0.5× Lithium transition metal oxide DV 50 ≤Lithium Supplement Additive DV 50 ≤2×Lithium transition metal oxide DV 50 .

6. The secondary battery according to claim 1, characterized in that, The specific surface area of ​​the lithium supplement additive is 0.5 m². 2 / g~3.0m 2 / g; and / or; the initial charge capacity of the lithium replenishment additive is 310mAh / g-3000mAh / g; and / or; the irreversible capacity of the lithium replenishment additive is 300mAh / g-3000mAh / g.

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