CN109449446B

CN109449446B - Secondary battery

Info

Publication number: CN109449446B
Application number: CN201811209263.8A
Authority: CN
Inventors: 王家政; 申玉良; 康蒙; 何立兵
Original assignee: Contemporary Amperex Technology Co Ltd
Current assignee: Contemporary Amperex Technology Co Ltd
Priority date: 2018-10-17
Filing date: 2018-10-17
Publication date: 2020-09-11
Anticipated expiration: 2038-10-17
Also published as: WO2020078357A1; CN109449446A

Abstract

The invention provides a secondary battery, which comprises a positive pole piece, a negative pole piece, electrolyte and an isolating film, wherein the positive pole piece comprises a positive current collector and a positive diaphragm which is arranged on at least one surface of the positive current collector and comprises a positive active substance, and the negative pole piece comprises a negative current collector and a negative diaphragm which is arranged on at least one surface of the negative current collector and comprises a negative active substance. The secondary battery further satisfies: 1.0. ltoreq. CB/[ (D99)_{Negative pole}‑D90_{Negative pole})/D50_{Negative pole}]Less than or equal to 4.0. The invention obtains the secondary battery with long cycle life, high energy density and quick charging capability by matching the relationship between the battery capacity excess coefficient and the particle size distribution of the cathode active material.

Description

Secondary battery

Technical Field

The invention relates to the field of batteries, in particular to a secondary battery.

Background

The rechargeable battery has the outstanding characteristics of light weight, high energy density, no pollution, no memory effect, long service life and the like, so the rechargeable battery is widely applied to the fields of mobile phones, computers, household appliances, electric tools and the like. Among them, the charging time and the service life are more and more paid attention by the terminal consumers, and are also important factors limiting the popularization of the rechargeable battery.

How to obtain a battery with long cycle life and quick charging performance is a common problem in the industry at present.

Disclosure of Invention

In view of the problems of the background art, it is an object of the present invention to provide a secondary battery that combines a long cycle life, a high energy density, and a rapid charging capability.

In order to achieve the above object, the present invention provides a secondary battery, a pack thereofDraw together positive pole piece, negative pole piece, electrolyte and barrier film, positive pole piece includes the anodal mass flow body and sets up on the anodal mass flow body at least one surface and including the anodal active material's positive diaphragm, negative pole piece includes the negative mass flow body and sets up on the negative mass flow body at least one surface and including the negative active material's negative diaphragm. The secondary battery further satisfies: 1.0. ltoreq. CB/[ (D99)_{Negative pole}-D90_{Negative pole})/D50_{Negative pole}]Less than or equal to 4.0. Wherein CB is a battery capacity excess coefficient; d50_{Negative pole}The corresponding particle diameter when the cumulative volume percentage of the negative active material reaches 50 percent is expressed in the unit of mu m; d90_{Negative pole}The corresponding particle diameter when the cumulative volume percentage of the negative active material reaches 90 percent, and the unit is mum; d99_{Negative pole}The particle diameter is expressed in μm corresponding to 99% of the cumulative volume percentage of the negative electrode active material.

Compared with the prior art, the invention at least comprises the following beneficial effects: the invention obtains the secondary battery with long cycle life, high energy density and quick charging capability by matching the relationship between the battery capacity excess coefficient and the particle size distribution of the cathode active material.

Detailed Description

The secondary battery according to the present invention is explained in detail below.

The secondary battery comprises a positive pole piece, a negative pole piece, electrolyte and an isolating film, wherein the positive pole piece comprises a positive current collector and a positive diaphragm which is arranged on at least one surface of the positive current collector and comprises a positive active material, and the negative pole piece comprises a negative current collector and a negative diaphragm which is arranged on at least one surface of the negative current collector and comprises a negative active material.

The secondary battery of the present invention also satisfies: 1.0. ltoreq. CB/[ (D99)_{Negative pole}-D90_{Negative pole})/D50_{Negative pole}]Less than or equal to 4.0. Wherein CB is a battery capacity excess coefficient; d50_{Negative pole}The corresponding particle diameter when the cumulative volume percentage of the negative active material reaches 50 percent is expressed in the unit of mu m; d90_{Negative pole}The corresponding particle diameter when the cumulative volume percentage of the negative active material reaches 90 percent, and the unit is mum; d99_{Negative pole}The particle diameter is expressed in μm corresponding to 99% of the cumulative volume percentage of the negative electrode active material.

In some embodiments of the invention, CB/[ (D99)_{Negative pole}-D90_{Negative pole})/D50_{Negative pole}]The lower limit of (B) may be 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, CB/[ (D99)_{Negative pole}-D90_{Negative pole})/D50_{Negative pole}]The upper limit value of (b) may be 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0. Preferably, 1.2 ≦ CB/[ (D99)_{Negative pole}-D90_{Negative pole})/D50_{Negative pole}]Less than or equal to 3.0; more preferably, 1.5 ≦ CB/[ (D99)_{Negative pole}-D90_{Negative pole})/D50_{Negative pole}]≤2.5。

The inventor researches to find that the key of improving the quick charge capacity of the battery is the negative electrode, and when the battery is quickly charged, if the minimum potential of the negative electrode is above the reduction potential of active ions (for example, the minimum potential of the negative electrode needs to be more than 0V vs Li/Li for a lithium ion battery)⁺) And the dynamic performance of the negative pole piece is considered to meet the requirement of quick charging of the battery. Similarly, when the battery is charged quickly, if the lowest potential of the negative electrode is below the reduction potential of the active ions, the active ions are preferentially reduced and precipitated on the surface of the negative electrode instead of being embedded into the negative electrode active material, and at this time, the dynamic performance of the negative electrode plate is considered to be unable to meet the requirement of the battery for quick charging. Therefore, the negative charging potential needs to be designed appropriately.

The inventors have made extensive studies to find that the magnitude of the negative electrode charge potential is related to the battery capacity excess coefficient CB and the particle size distribution of the negative electrode active material.

The capacitance of the negative pole piece capable of receiving active ions under a certain area is defined as M_{Negative pole}The capacitance M is the capacitance that can provide active ions when the positive electrode plate and the negative electrode plate have the same area_{Is just}If the battery capacity excess coefficient CB is equal to M_{Negative pole}/M_{Is just}. Technically speaking, the battery capacity excess coefficient CB can influence the magnitude of the negative electrode charging potential by influencing the actual state of charge (i.e., SOC) of the negative electrode. Battery containerThe larger the excess coefficient CB is, the higher the charging potential of the negative electrode is at high SOC in the quick charging process of the battery, the less the negative electrode is easy to reduce and separate out active ions, and the volume expansion of the negative electrode piece and the side reaction of the negative electrode piece and electrolyte are less, which is beneficial to improving the quick charging capacity and the cycle life of the battery; on the contrary, the smaller the capacity excess coefficient CB of the battery is under the same condition, the lower the charge potential of the negative electrode at a high SOC during the rapid charging of the battery is, the more easily the negative electrode is reduced and precipitated by active ions, and the poorer the rapid charging capability of the battery is.

Among the negative electrode active materials, the large particles of the negative electrode active material have a narrow particle size distribution and are closely related to the lowest potential of the negative electrode. The large-particle negative electrode active material is less prone to embedding active ions and is more prone to reduction and precipitation of the active ions in the negative electrode, and the wider the particle size distribution of the large-particle negative electrode active material is, the larger the occupation ratio of the large-particle negative electrode active material in all the negative electrode active materials is, the more the negative electrode is prone to reduction and precipitation of the active ions; however, under otherwise identical conditions, the wider the particle size distribution of the large-particle negative active material, the more easily the negative active material is compacted, and the higher the volumetric energy density of the battery can be obtained.

The inventor has found that (D99)_{Negative pole}-D90_{Negative pole})/D50_{Negative pole}Characterizing the width of the particle size distribution of the large-particle negative active material, and satisfying 1.0. ltoreq. CB/[ (D99)_{Negative pole}-D90_{Negative pole})/D50_{Negative pole}]When not more than 4.0, in the charging process of the battery, the charging potential of the negative electrode can be kept in a more reasonable state, the negative electrode plate can have good dynamic performance, and meanwhile, the secondary battery can have long cycle life, high energy density and quick charging capacity.

If CB/[ (D99)_{Negative pole}-D90_{Negative pole})/D50_{Negative pole}]>4.0, the possible reason is that CB is relatively large, (D99)_{Negative pole}-D90_{Negative pole})/D50_{Negative pole}Relatively small (i.e., narrow particle size distribution of large-particle negative active material, small proportion of large-particle negative active material in the total negative active material), although both of them are favorable for improving the rapid charging capability of the battery, they are unfavorable for improving the rapid charging capability of the batteryThe compaction density of the negative pole piece and the energy density loss of the battery are more.

If CB/[ (D99)_{Negative pole}-D90_{Negative pole})/D50_{Negative pole}]<1.0, probably because the particle size distribution of the large-particle negative active material is relatively wide, active ions are difficult to embed into the negative active material, the lowest potential of the negative electrode is small during charging, and the negative electrode is easy to reduce and separate out the active ions, so that the improvement of the quick charging capability of the battery is not facilitated; the reason that the battery capacity excess coefficient CB is designed to be relatively small is also probably that the charging potential of the negative electrode is low when the SOC of the negative electrode is high in the process of quick charging of the battery, the negative electrode is easy to reduce and separate out active ions, and the improvement of the quick charging capacity of the battery is not facilitated.

The particle size distribution of the positive active material also affects the rapid charging ability of the battery during the charging process of the battery. This is because the liquid-phase diffusion of active ions inside the porous electrode involves two parts, namely, the liquid-phase diffusion inside the positive electrode porous electrode and the liquid-phase diffusion inside the negative electrode porous electrode. And the whole liquid phase diffusion power of active ions in the battery is determined by the most difficult part of liquid phase diffusion, namely, the short plate effect exists. The liquid phase diffusion in the porous electrode is related to the width of the particle size distribution of the entire active material (i.e., (D90-D10)/D50), and under the same conditions, the wider the particle size distribution of the entire active material, the more difficult the liquid phase diffusion of the active ions in the porous electrode, because the wider the particle size distribution of the entire active material, the stronger the ability of the active material particles to occupy the pores in the porous electrode after the active material particles are associated with each other, and the greater the liquid phase diffusion resistance of the active ions in the porous electrode.

If the particle size distribution width of the entire positive electrode active material is too different from that of the entire negative electrode active material, the liquid phase diffusion kinetics of active ions inside the battery is limited by one electrode, and the battery cannot achieve the best performance. The inventors have found through extensive studies that when the secondary battery satisfies 0.5. ltoreq. [ (D90)_{Is just}-D10_{Is just})/D50_{Is just}]/[(D90_{Negative pole}-D10_{Negative pole})/D50_{Negative pole}]When the ratio is less than or equal to 3.0, the positive electrode and the negative electrode are activatedThe particle size distribution of the whole substance is matched to reach balance, and the battery can obtain the highest rapid charging capability on the basis of not sacrificing energy density.

Wherein, D90_{Is just}And D90_{Negative pole}Respectively corresponding grain diameters when the cumulative volume percentage of the active substances of the anode and the cathode reaches 90 percent, and the unit is mum; d50_{Is just}And D50_{Negative pole}Respectively corresponding grain diameters with the unit of mum when the cumulative volume percentage of the active substances of the anode and the cathode reaches 50 percent; d10_{Is just}And D10_{Negative pole}The particle diameters are respectively corresponding to the cumulative volume percentage of the positive electrode active material and the negative electrode active material which reach 10 percent, and the unit is mum.

In some embodiments of the invention, [ (D90)_{Is just}-D10_{Is just})/D50_{Is just}]/[(D90_{Negative pole}-D10_{Negative pole})/D50_{Negative pole}]The lower limit of (B) may be 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, [ (D90)_{Is just}-D10_{Is just})/D50_{Is just}]/[(D90_{Negative pole}-D10_{Negative pole})/D50_{Negative pole}]The upper limit value of (b) may be 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0. Preferably, 1.0 ≦ [ (D90)_{Is just}-D10_{Is just})/D50_{Is just}]/[(D90_{Negative pole}-D10_{Negative pole})/D50_{Negative pole}]≤2.5。

When [ (D90)_{Is just}-D10_{Is just})/D50_{Is just}]/[(D90_{Negative pole}-D10_{Negative pole})/D50_{Negative pole}]>3.0, the particle size distribution of the whole positive electrode active material is relatively too wide, which is not favorable for liquid phase diffusion of active ions in the positive electrode porous electrode; when [ (D90)_{Is just}-D10_{Is just})/D50_{Is just}]/[(D90_{Negative pole}-D10_{Negative pole})/D50_{Negative pole}]<0.5 may be because the particle size distribution of the negative electrode active material as a whole is relatively excessively broad, which is disadvantageous in liquid phase diffusion of active ions inside the negative electrode porous electrode.

Preferably, the particle size distribution width of the whole positive electrode active material satisfies 0.8 ≦ (D90)_{Is just}-D10_{Is just})/D50_{Is just}Less than or equal to 4.0. Wherein the content of the first and second substances,(D90_{is just}-D10_{Is just})/D50_{Is just}The lower limit of (D) may be 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, (D90)_{Is just}-D10_{Is just})/D50_{Is just}The upper limit value of (b) may be 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0. More preferably, the particle size distribution width of the entire positive electrode active material satisfies 1.2. ltoreq. D90_{Is just}-D10_{Is just})/D50_{Is just}≤3.5。

Preferably, the width of the particle size distribution of the negative electrode active material as a whole satisfies 0.9. ltoreq. D90_{Negative pole}-D10_{Negative pole})/D50_{Negative pole}Less than or equal to 6.5. Wherein (D90)_{Negative pole}-D10_{Negative pole})/D50_{Negative pole}The lower limit of (D) may be 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, (D90)_{Negative pole}-D10_{Negative pole})/D50_{Negative pole}The upper limit value of (b) may be 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, 4.0, 4.2, 4.5, 4.8, 5.0, 5.2, 5.5, 5.8, 6.0, 6.2, 6.5. More preferably, the width of the particle size distribution of the negative electrode active material as a whole satisfies 1.2. ltoreq. D90_{Negative pole}-D10_{Negative pole})/D50_{Negative pole}≤4.5。

In the secondary battery of the present invention, preferably, the particle diameter D50 of the negative electrode active material_{Negative pole}2-18 μm; more preferably, the particle diameter D50 of the negative electrode active material_{Negative pole}5-15 μm. Preferably, the particle diameter D90 of the negative electrode active material_{Negative pole}5-40 μm; more preferably, the particle diameter D90 of the negative electrode active material_{Negative pole}Is 10-30 μm. Preferably, the particle diameter D99 of the negative electrode active material_{Negative pole}10-50 μm; more preferably, the particle diameter D99 of the negative electrode active material_{Negative pole}15-50 μm. Preferably, the particle diameter D10 of the negative electrode active material_{Negative pole}1-12 μm; more preferably, the particle diameter D10 of the negative electrode active material_{Negative pole}Is 4-10 μm.

When the particle size of the negative active material falls into the preferable range, the uniformity of the negative pole piece is higher, the influence on the improvement effect of the battery performance caused by more side reactions generated by too small particle size and electrolyte can be avoided, and the influence on the improvement effect of the battery performance caused by the solid phase conduction of active ions in the negative active material particles blocked by too large particle size can be avoided.

In the secondary battery of the present invention, preferably, the particle diameter D10 of the positive electrode active material_{Is just}0.2-6 μm; more preferably, the particle diameter D10 of the positive electrode active material_{Is just}0.4 to 4.5 μm. Preferably, the particle diameter D50 of the positive electrode active material_{Is just}0.8-32 μm; more preferably, the particle diameter D50 of the positive electrode active material_{Is just}Is 1-28 μm. Preferably, the particle diameter D90 of the positive electrode active material_{Is just}1-100 μm; more preferably, the particle diameter D90 of the positive electrode active material_{Is just}Is 3-92 μm.

When the particle size of the positive active material falls within the preferable range, the uniformity of the positive pole piece is higher, the improvement effect on the battery performance caused by the influence of more side reactions generated between too small particle size and electrolyte can be avoided, and the improvement effect on the battery performance caused by the influence of too large particle size on the solid phase conduction of active ions in the positive active material particles can be avoided.

In the secondary battery of the present invention, preferably, the battery capacity excess coefficient CB is 0.8 to 2.0; more preferably, the battery capacity excess coefficient CB is 1.0-1.5. When the battery capacity excess factor falls within the above-described preferred range, the battery can maintain the high energy density advantage while the rapid charging capability is improved better.

In the secondary battery of the present invention, the negative electrode membrane may be disposed on one of the surfaces of the negative electrode current collector or may be disposed on both surfaces of the negative electrode current collector. The negative electrode diaphragm can also comprise a conductive agent and a binder, wherein the types and the contents of the conductive agent and the binder are not particularly limited and can be selected according to actual requirements. The type of the negative current collector is not particularly limited, and can be selected according to actual requirements.

In the secondary battery of the present invention, the positive electrode membrane may be disposed on one of the surfaces of the positive electrode current collector and may also be disposed on both surfaces of the positive electrode current collector. The positive electrode membrane also can comprise a conductive agent and a binder, wherein the types and the contents of the conductive agent and the binder are not particularly limited and can be selected according to actual requirements. The type of the positive current collector is not particularly limited, and can be selected according to actual requirements.

It should be noted that, when the positive electrode diaphragm and the negative electrode diaphragm are respectively disposed on two surfaces of the positive electrode current collector and the negative electrode current collector, as long as the positive electrode diaphragm on any one surface of the positive electrode current collector and the negative electrode diaphragm on any one surface of the negative electrode current collector satisfy the present invention, the battery is considered to fall within the protection scope of the present invention. Meanwhile, the parameters of the positive and negative electrode diaphragms provided by the invention also refer to the parameters of the single-sided positive and negative electrode diaphragms.

The secondary battery of the present invention may be a lithium ion battery or a sodium ion battery.

When the secondary battery is a lithium ion battery: the positive active material may be selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt aluminum oxide, olivine-structured lithium-containing phosphate, and the like, but the present invention is not limited to these materials, and other conventionally known materials that may be used as a positive active material for a lithium ion battery may also be used. These positive electrode active materials may be used alone or in combination of two or more. Preferably, the positive active material may be selected from LiCoO₂、LiNiO₂、LiMnO₂、LiMn₂O₄、LiNi_1/3Co_1/3Mn_1/3O₂(NCM333)、LiNi_0.5Co_0.2Mn_0.3O₂(NCM523)、LiNi_0.6Co_0.2Mn_0.2O₂(NCM622)、LiNi_0.8Co_0.1Mn_0.1O₂(NCM811)、LiNi_0.85Co_0.15Al_0.05O₂、LiFePO₄(LFP)、LiMnPO₄One or more of them.

When the secondary battery is a sodium ion battery: the front partThe polar active material can be selected from transition metal oxide Na_xMO₂(M is a transition metal, preferably one or more selected from Mn, Fe, Ni, Co, V, Cu and Cr, 0<x is less than or equal to 1), polyanionic materials (phosphate, fluorophosphate, pyrophosphate, sulfate), prussian blue materials and the like, but the application is not limited to the materials, and other conventionally known materials which can be used as the positive electrode active material of the sodium ion battery can be used. These positive electrode active materials may be used alone or in combination of two or more. Preferably, the positive electrode active material may be selected from NaFeO₂、NaCoO₂、NaCrO₂、NaMnO₂、NaNiO₂、NaNi_1/2Ti_1/2O₂、NaNi_1/2Mn_1/2O₂、Na_2/3Fe_1/3Mn_2/3O₂、NaNi_1/3Co_1/3Mn_1/3O₂、NaFePO₄、NaMnPO₄、NaCoPO₄Prussian blue material with the general formula A_aM_b(PO₄)_cO_xY_3-xWherein A is selected from H⁺、Li⁺、Na⁺、K⁺、NH⁴⁺M is transition metal cation, preferably one or more selected from V, Ti, Mn, Fe, Co, Ni, Cu and Zn, Y is halogen anion, preferably one or more selected from F, Cl and Br, 0<a≤4，0<b is less than or equal to 2, c is less than or equal to 1 and less than or equal to 3, and x is more than or equal to 0 and less than or equal to 2).

In the secondary battery of the present invention, the specific kind of the negative electrode active material is not particularly limited and may be selected according to actual needs. Preferably, the negative electrode active material can be selected from one or more of carbon materials, silicon-based materials, tin-based materials and lithium titanate. Wherein, the carbon material can be selected from one or more of graphite, soft carbon, hard carbon, carbon fiber and mesocarbon microbeads; the graphite can be one or more selected from artificial graphite and natural graphite; the silicon-based material can be one or more selected from simple substance silicon, silicon-oxygen compound, silicon-carbon compound and silicon alloy; the tin-based material can be one or more selected from simple substance tin, tin oxide compound and tin alloy. More preferably, the negative electrode active material is selected from one or more of a carbon material and a silicon-based material.

In the secondary battery, the isolating film is arranged between the positive pole piece and the negative pole piece and plays an isolating role. The kind of the separator is not particularly limited, and may be any separator material used in the existing battery, such as polyethylene, polypropylene, polyvinylidene fluoride, and multi-layer composite films thereof, but is not limited thereto.

In the secondary battery of the present invention, the type of the electrolyte is not particularly limited, and may be a liquid electrolyte (also referred to as an electrolyte solution) or a solid electrolyte. Preferably, the electrolyte uses a liquid electrolyte. Wherein, the liquid electrolyte comprises an electrolyte salt and an organic solvent, and the specific types of the electrolyte salt and the organic solvent are not particularly limited and can be selected according to actual requirements. The electrolyte may further include an additive, and the type of the additive is not particularly limited, and the additive may be a negative electrode film-forming additive, a positive electrode film-forming additive, or an additive capable of improving certain properties of the battery, such as an additive for improving overcharge properties of the battery, an additive for improving high-temperature properties of the battery, an additive for improving low-temperature properties of the battery, and the like.

The present application is further illustrated below by taking a lithium ion battery as an example and combining specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present application.

Example 1

(1) Preparation of positive pole piece

Mixing a positive electrode active substance, a conductive agent acetylene black and a binder polyvinylidene fluoride (PVDF) according to a mass ratio of 96:2:2, adding a solvent N-methyl pyrrolidone (NMP), and stirring under the action of a vacuum stirrer until the system is uniform to obtain positive electrode slurry; and uniformly coating the positive electrode slurry on a positive electrode current collector aluminum foil, airing at room temperature, transferring to an oven for continuous drying, and then performing cold pressing and slitting to obtain the positive electrode piece. Wherein, the parameters of the anode active material are detailed in table 1.

(2) Preparation of negative pole piece

Mixing a negative electrode active substance, a conductive agent acetylene black, a thickening agent sodium carboxymethyl cellulose (CMC) and a binder Styrene Butadiene Rubber (SBR) according to a mass ratio of 96.4:1:1.2:1.4, adding solvent deionized water, and stirring under the action of a vacuum stirrer until the system is uniform to obtain negative electrode slurry; and uniformly coating the negative electrode slurry on a copper foil of a negative current collector, airing at room temperature, transferring to an oven for continuous drying, and then performing cold pressing and slitting to obtain a negative electrode plate. The parameters of the negative electrode active material are shown in table 1.

(3) Preparation of the electrolyte

Mixing Ethylene Carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) according to a volume ratio of 1:1:1 to obtain an organic solvent, and then fully drying lithium salt LiPF₆Dissolving the mixture in the mixed organic solvent to prepare electrolyte with the concentration of 1 mol/L.

(4) Preparation of the separator

Polyethylene film was selected as the barrier film.

(5) Preparation of lithium ion battery

Stacking the positive pole piece, the isolating film and the negative pole piece in sequence to enable the isolating film to be positioned between the positive pole piece and the negative pole piece to play an isolating role, and then winding to obtain a bare cell; and placing the bare cell in an outer packaging shell, drying, injecting electrolyte, and performing vacuum packaging, standing, formation, shaping and other processes to obtain the lithium ion battery.

Lithium ion batteries of examples 2 to 24 and comparative examples 1 to 6 were prepared in a similar manner to example 1, with the specific differences shown in table 1.

Table 1: parameters for examples 1-24 and comparative examples 1-6

The performance test of the battery is explained next.

1. Pole piece testing

(1) Particle size measurement of positive and negative electrode active materials

The particle diameters of the positive and negative electrode active materials can be measured by using a laser diffraction particle size distribution measuring instrument (Mastersizer 3000).

(2) Battery capacity excess factor CB test

Capacitance test of unit area positive pole piece

Step 1): fully discharging the battery containing the positive pole piece of each example and each comparative example, standing for 5 minutes, and charging to a cut-off voltage, wherein the charging process is specifically that 1/3C is used for constant-current charging to the cut-off voltage, then the constant-voltage charging is carried out to 0.03C by the cut-off voltage, and the charging capacity C obtained at the moment₀Namely the discharge capacity of the anode plate.

Step 2): the total area of the positive electrode diaphragm (the total area is the coating area; if the coating is double-sided, the coating areas on the two sides are added) is measured and calculated.

Step 3): the capacity of the positive electrode sheet per unit area is defined as the discharge capacity (mAh) of the positive electrode sheet/the total area (cm) of the positive electrode sheet²) And calculating the capacitance M of the positive pole piece in unit area_{Is just}。

Capacitance test of negative pole piece in unit area

Step 1): taking the negative pole pieces of the above embodiments and comparative examples, and obtaining a negative minimum wafer with a certain area and coated on one side by using a punching die. Using a metal lithium sheet as a counter electrode, a Celgard membrane as a separation membrane and dissolved with LiPF₆A (concentration of 1mol/L) solution of EC + DMC + DEC (volume ratio of 1:1:1) is used as an electrolyte, and 6 CR2430 button cells are assembled in an argon-protected glove box. Standing for 12h after the button cell is assembled, performing constant current discharge at a discharge current of 0.05 ℃ until the voltage is 5mV, then performing constant current discharge at a discharge current of 50 muA until the voltage is 5mV, then performing constant current discharge at a discharge current of 10 muA until the voltage is 5mV, standing for 5 minutes, finally performing constant current charge at a charge current of 0.05 ℃ until the final voltage is 2V, and recording the charge capacity. The average value of the charging capacity of the 6 button cells is the average electric capacity of the negative pole piece.

Step 2): the diameter d of the negative mini-disc was measured using a caliper and the area of the negative mini-disc was calculated.

Step 3): the average capacitance (mAh) of the negative electrode sheet per unit area/the area (cm) of the negative electrode sheet²) And calculating the capacitance M of the negative pole piece in unit area_{Negative pole}。

③ excess coefficient of battery capacity CB ═ M_{Negative pole}/M_{Is just}。

2. Battery testing

(1) Dynamic performance test

At 25 ℃, the batteries prepared in the examples and the comparative examples are fully charged with x C and fully discharged with 1C for 10 times, then the batteries are fully charged with x C, then the negative pole piece is disassembled, and the lithium precipitation condition on the surface of the negative pole piece is observed. And if the lithium is not separated from the surface of the negative electrode, the charging multiplying power x C is gradually increased by taking 0.1C as a gradient, the test is carried out again until the lithium is separated from the surface of the negative electrode, and the test is stopped, wherein the maximum charging multiplying power of the battery is obtained by subtracting 0.1C from the charging multiplying power x C.

(2) Cycle performance test

The cells prepared in examples and comparative examples were charged at 3C rate, discharged at 1C rate, and subjected to full charge discharge cycle test at 25C until the capacity of the cell was less than 80% of the initial capacity and the number of cycles recorded.

(3) Actual energy density test

Fully charging the batteries prepared in the examples and the comparative examples at a rate of 1C and fully discharging the batteries at a rate of 1C at 25 ℃, and recording the actual discharge energy at the moment; the cell was weighed using an electronic balance at 25 ℃; the ratio of the actual discharge energy of the battery 1C to the weight of the battery is the actual energy density of the battery.

Wherein, when the actual energy density is less than 80% of the target energy density, the actual energy density of the battery is considered to be very low; when the actual energy density is greater than or equal to 80% of the target energy density and less than 95% of the target energy density, the actual energy density of the battery is considered to be low; when the actual energy density is greater than or equal to 95% of the target energy density and less than 105% of the target energy density, the actual energy density of the battery is considered to be moderate; when the actual energy density is not less than 105% of the target energy density and less than 120% of the target energy density, the actual energy density of the battery is considered to be high; when the actual energy density is 120% or more of the target energy density, the actual energy density of the battery is considered to be very high.

Table 2: results of Performance test of examples 1 to 24 and comparative examples 1 to 6

As can be seen from the test results of table 2: the batteries of examples 1 to 24 all satisfied 1.0. ltoreq. CB/[ (D99)_{Negative pole}-D90_{Negative pole})/D50_{Negative pole}]Not more than 4.0, a battery capacity excess coefficient CB and a large-particle negative electrode active material particle size distribution width (D99)_{Negative pole}-D90_{Negative pole})/D50_{Negative pole}The matching relation is good, the negative charging potential can be kept in a reasonable state when the battery is charged quickly, the negative pole piece can have good dynamic performance, and the obtained battery can have long cycle life, high energy density and quick charging capability.

Comparative examples 1 to 6 were compared with examples 1 to 24 in terms of the cell capacity excess coefficient CB and the width of the particle diameter distribution of the large-particle negative active material (D99)_{Negative pole}-D90_{Negative pole})/D50_{Negative pole}Failure to achieve a reasonable match, CB/[ (D99)_{Negative pole}-D90_{Negative pole})/D50_{Negative pole}]All fall outside the given range, the battery cannot simultaneously have long cycle life, high energy density and fast charging capability.

Further, the particle diameter D50 of the negative electrode active material_{Negative pole}Preferably 2 to 18 μm, D90_{Negative pole}Preferably 5 to 40 μm, D99_{Negative pole}Preferably 10 to 50 μm, and the uniformity of the negative electrode sheet when the particle diameter of the negative electrode active material falls within the above preferred rangeThe method has the advantages that the battery performance improving effect can be prevented from being influenced by more side reactions generated by too small particle size and electrolyte, and the battery performance improving effect can be prevented from being influenced by the solid phase conduction of lithium ions in the negative active material particles due to too large particle size. The battery capacity excess coefficient CB is preferably 0.8-2.0, and when the battery capacity excess coefficient is in the preferred range, the battery can better improve the quick charging capacity and keep the advantage of high energy density.

But when the particle diameter of the negative electrode active material D50_{Negative pole}、D90_{Negative pole}、D99_{Negative pole}And the cell capacity excess factor CB fails to satisfy the above-mentioned preferable range, as long as 1.0. ltoreq. CB/[ (D99)_{Negative pole}-D90_{Negative pole})/D50_{Negative pole}]4.0 or less, and referring to examples 17 to 20, the battery can still combine a long cycle life, a high energy density and a rapid charging capability.

Furthermore, on the premise that the negative pole piece has excellent dynamic performance, the ratio of the particle size distribution width of the whole positive and negative active materials is reasonably adjusted, so that the battery also meets the requirement that the particle size distribution width of the whole positive and negative active materials is not less than 0.5 [ (D90)_{Is just}-D10_{Is just})/D50_{Is just}]/[(D90_{Negative pole}-D10_{Negative pole})/D50_{Negative pole}]When the energy density is less than or equal to 3.0, the battery can obtain higher rapid charging capability without sacrificing the energy density.

In connection with example 19, [ (D90)_{Is just}-D10_{Is just})/D50_{Is just}]/[(D90_{Negative pole}-D10_{Negative pole})/D50_{Negative pole}]<0.5, the particle size distribution of the negative electrode active material as a whole is relatively too wide, which is disadvantageous in liquid phase diffusion of lithium ions in the negative electrode porous electrode, i.e., in rapid migration and intercalation of lithium ions into the negative electrode, and therefore, example 19 is relatively weak in improvement of the battery rapid charging capability as compared with other examples.

Example 11, example 20, [ (D90)_{Is just}-D10_{Is just})/D50_{Is just}]/[(D90_{Negative pole}-D10_{Negative pole})/D50_{Negative pole}]>3.0, the overall particle size distribution of the positive electrode active material is relatively too wide, which is not conducive to liquid phase diffusion of lithium ions within the porous positive electrode, and also means that rapid lithium ion diffusion is not facilitatedThe migration is embedded in the negative electrode, and thus examples 11 and 20 are relatively weak in improving the quick charging capability of the battery compared with other examples.

As can be seen from examples 21 to 24 and comparative examples 3 to 6, when different positive and negative electrode active materials were used for the batteries, as long as the batteries satisfied 1.0. ltoreq. CB/[ (D99)_{Negative pole}-D90_{Negative pole})/D50_{Negative pole}]Less than or equal to 4.0, and can also have long cycle life, high energy density and quick charging capability.

Variations and modifications to the above-described embodiments may occur to those skilled in the art based upon the disclosure and teachings of the above specification. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and variations of the present invention should fall within the scope of the claims of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. A secondary battery comprises a positive pole piece, a negative pole piece, electrolyte and an isolating film, wherein the positive pole piece comprises a positive current collector and a positive diaphragm which is arranged on at least one surface of the positive current collector and comprises a positive active material;

it is characterized in that the preparation method is characterized in that,

the positive electrode active material includes a lithium-containing phosphate of an olivine structure;

the negative active material includes graphite;

the secondary battery satisfies: 1.2. ltoreq. CB/[ (D99)_{Negative pole}-D90_{Negative pole})/D50_{Negative pole}]≤3.0；

Wherein the content of the first and second substances,

CB is the ratio of the capacitance of the positive pole piece and the capacitance of the negative pole piece with the same area;

D50_{negative pole}The corresponding particle diameter when the cumulative volume percentage of the negative active material reaches 50 percent is expressed in the unit of mu m;

D90_{negative pole}The corresponding particle diameter when the cumulative volume percentage of the negative active material reaches 90 percent, and the unit is mum;

D99_{negative pole}The particle diameter is expressed in μm corresponding to 99% of the cumulative volume percentage of the negative electrode active material.

2. The secondary battery according to claim 1,

the secondary battery satisfies: 1.5 ≦ CB/[ (D99)_{Negative pole}-D90_{Negative pole})/D50_{Negative pole}]≤2.5。

3. The secondary battery according to claim 2,

the secondary battery satisfies: 1.5 ≦ CB/[ (D99)_{Negative pole}-D90_{Negative pole})/D50_{Negative pole}]≤1.8。

4. The secondary battery according to claim 1, wherein the secondary battery further satisfies: 1.0 ≤ [ (D90)_{Is just}-D10_{Is just})/D50_{Is just}]/[(D90_{Negative pole}-D10_{Negative pole})/D50_{Negative pole}]≤2.5；

Wherein the content of the first and second substances,

D90_{is just}And D90_{Negative pole}Respectively corresponding grain diameters when the cumulative volume percentage of the active substances of the anode and the cathode reaches 90 percent, and the unit is mum;

D50_{is just}And D50_{Negative pole}Respectively corresponding grain diameters with the unit of mum when the cumulative volume percentage of the active substances of the anode and the cathode reaches 50 percent;

D10_{is just}And D10_{Negative pole}The particle diameters are respectively corresponding to the cumulative volume percentage of the positive electrode active material and the negative electrode active material which reach 10 percent, and the unit is mum.

5. The secondary battery according to claim 4, wherein the secondary battery further satisfies: 1.0 ≤ [ (D90)_{Is just}-D10_{Is just})/D50_{Is just}]/[(D90_{Negative pole}-D10_{Negative pole})/D50_{Negative pole}]≤1.6。

6. The secondary battery according to claim 4 or 5, wherein the negative electrode active material satisfies 1.2 ≦ (D90)_{Negative pole}-D10_{Negative pole})/D50_{Negative pole}≤4.5。

7. The secondary battery according to claim 6, wherein the negative electrode active material satisfies 1.6 ≦ (D90)_{Negative pole}-D10_{Negative pole})/D50_{Negative pole}≤2.8。

8. The secondary battery according to claim 4 or 5, wherein the positive electrode active material satisfies 1.2 ≦ (D90)_{Is just}-D10_{Is just})/D50_{Is just}≤3.5。

9. The secondary battery according to claim 8, wherein the positive electrode active material satisfies 2.0 ≦ (D90)_{Is just}-D10_{Is just})/D50_{Is just}≤3.0。

10. The secondary battery according to any one of claims 1 to 3, wherein the battery capacity excess coefficient CB is 1.10 to 1.30.

11. The secondary battery according to claim 10, wherein the battery capacity excess coefficient CB is 1.15 to 1.25.

12. The secondary battery according to any one of claims 1 to 5,

the particle diameter D50 of the negative electrode active material_{Negative pole}5-15 μm;

and/or the particle diameter D90 of the negative electrode active material_{Negative pole}5-20 μm;

and/or the particle diameter D99 of the negative electrode active material_{Negative pole}10 to 29.2 μm.

13. The secondary battery according to claim 12, wherein the negative electrode active materialParticle size D50_{Negative pole}5 to 12 mu m.

14. The secondary battery according to claim 12, wherein the particle diameter D90 of the negative electrode active material_{Negative pole}Is 10-16 μm.

15. The secondary battery according to claim 12, wherein the particle diameter D99 of the negative electrode active material_{Negative pole}15 to 18.8 mu m.

16. The secondary battery according to claim 4 or 5,

the particle diameter D10 of the positive electrode active material_{Is just}0.2-1.0 μm;

and/or the particle size D50 of the positive electrode active material_{Is just}0.8-3.0 μm;

and/or the particle size D90 of the positive electrode active material_{Is just}Is 1-10.6 μm.

17. The secondary battery according to claim 16, wherein the particle diameter D10 of the positive electrode active material_{Is just}0.4-0.8 μm.

18. The secondary battery according to claim 16, wherein the particle diameter D50 of the positive electrode active material_{Is just}Is 1-2.0 μm.

19. The secondary battery according to claim 16, wherein the particle diameter D90 of the positive electrode active material_{Is just}Is 3-6.8 μm.

20. The secondary battery according to claim 1, wherein the olivine-structured lithium-containing phosphate is selected from LiFePO₄、LiMnPO₄One or two of them.

21. The secondary battery according to claim 1, wherein the graphite is selected from one or more of artificial graphite and natural graphite.