CN113437250B

CN113437250B - Electrochemical device and electronic device

Info

Publication number: CN113437250B
Application number: CN202110685942.8A
Authority: CN
Inventors: 郑子桂; 易政; 杜鹏; 谢远森
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2021-06-21
Filing date: 2021-06-21
Publication date: 2022-06-10
Anticipated expiration: 2041-06-21
Also published as: CN113437250A

Abstract

The present application relates to an electrochemical device and an electronic device. The electrochemical device comprises a positive electrode, a diaphragm, an electrolyte and a negative electrode, wherein the negative electrode comprises a current collector and a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material, the negative electrode active material has a diffraction peak Q1 and a diffraction peak Q2 in an X-ray diffraction spectrum of 18-30 degrees, the half-peak width of the diffraction peak Q1 is 4-12 degrees, and the electrochemical device satisfies the following conditions: 1.0. ltoreq. CB/[ (Dv99-Dv90)/Dv50 ]. ltoreq.3.5, wherein Dv99, Dv90 and Dv50 denote Dv99, Dv90 and Dv50 of the negative electrode active material particles, respectively, in units of μm, and CB is a ratio of negative electrode capacity to positive electrode capacity in the same area. The electrochemical device has excellent quick charging performance, high energy density, good cycle performance and higher application value.

Description

Electrochemical device and electronic device

Technical Field

The present application relates to the field of energy storage technologies, and in particular, to an electrochemical device and an electronic device.

Background

Due to the characteristics that the lithium battery has high energy density and different formulas and can adapt to different use environments, the lithium battery realizes commercialization and is widely used in the market. Nowadays, by virtue of the advantages of high energy density and high safety, the lithium ion battery has completely occupied the consumer electronics market in a short time and is expanded to the field of electric automobiles, and the field not only requires the lithium ion battery to have larger capacity, but also continuously puts higher requirements on the energy density, the charge and discharge rate and the cycle stability of the lithium ion battery.

Disclosure of Invention

In view of the technical shortcomings in the prior art, the present invention provides an electrochemical device and an electronic device. The electrochemical device provided by the application has excellent quick charging performance, high energy density and excellent cycle performance.

In a first aspect, the present application provides an electrochemical device comprising a positive electrode, a separator, an electrolyte, and a negative electrode, the negative electrode comprising a current collector and a negative active material layer, the negative active material layer comprising a negative active material having a diffraction peak Q1 and a diffraction peak Q2 between 18 ° and 30 ° in an X-ray diffraction pattern, the diffraction peak Q1 having a half-peak width of 4 ° to 12 °, the electrochemical device satisfying: 1.0. ltoreq. CB/[ (Dv99-Dv90)/Dv50 ]. ltoreq.3.5, wherein Dv99, Dv90 and Dv50 respectively denote Dv99, Dv90 and Dv50 of the negative electrode active material particles in units of μm, and CB is a ratio of the negative electrode capacity to the positive electrode capacity in the same area.

In the embodiment of the application, the diffraction peak Q1 represents the diffraction peak of the hard carbon material, and the hard carbon material has considerable capacity, excellent quick charge performance and extremely low expansibility, so that the expansion of the pole piece can be effectively inhibited by using the hard carbon material, higher capacity can be obtained, and the energy density of the negative electrode is improved. Meanwhile, research shows that when the particle diameters of the CB and the anode active material particles of the lithium ion battery meet the following requirements: when the ratio of CB/[ (Dv99-Dv90)/Dv50] < 3.5 is more than or equal to 1.0, the uniformity of the negative electrode is higher, the influence on the improvement effect of the battery performance caused by the side reaction 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 influence of too large particle size on the solid phase conduction of active ions in the negative electrode active material particles can be avoided. Therefore, the negative electrode can have good dynamic performance, and meanwhile, the lithium ion battery can have long cycle life, high energy density and quick charging capability. According to some preferred embodiments of the present application, 1.5. ltoreq. CB/[ (Dv99-Dv90)/Dv50 ]. ltoreq.3.5.

According to some embodiments of the present application, the CB value ranges from 0.80 to 1.50, preferably the CB value ranges from 1.00 to 1.35. When the CB value is too large, irreversible capacity loss of the lithium battery is caused, so that the battery capacity is low, and the energy density is reduced.

According to some embodiments of the present application, the peak position (expressed in 2 θ) of the diffraction peak Q1 is less than the peak position (expressed in 2 θ) of the diffraction peak Q2. According to some embodiments of the present application, the half-width of the diffraction peak Q2 is less than 4 °. According to some embodiments of the present application, the half-width of the diffraction peak Q2 is 0.1 ° to 3.5 °. In the embodiment according to the present application, the diffraction peak Q2 represents a diffraction peak of a graphite material. Mixing the hard carbon active material with the graphite active material not only increases the contact between the hard carbon material particles and the hard carbon material particles or the graphite material particles, but also the whole pole piece material can obtain better electronic conductivity and lower internal resistance.

According to some embodiments of the present application, the negative active material layer has a cross-sectional porosity of P_{Negative pole}，P_{Negative pole}The value of (b) ranges from 15% to 35%. Due to the characteristic of hard carbon material particles, the negative electrode has higher porosity, so that the pole piece can be ensured to have higher liquid retention capacity in a higher compacted state, and better ionic conductivity can be obtained. However, this also causes more film formation consumption and a capacity loss. Thus, considering the kinetics and energy density of a lithium ion battery, preferably, P_{Negative pole}The value range of (a) is 15% to 30%; more preferably, P_{Negative pole}The value of (a) is in the range of 15% to 25%.

According to some embodiments of the present application, the negative electrode active material layer includes a first negative electrode active material layer including a first negative electrode active material including graphite; the second negative active material layer includes a second negative active material including hard carbon and graphite. Mix hard carbon active material and graphite active material and set up the second negative pole active material layer of contact more easily at electrolyte, can full play hard carbon material's the fast characteristic of filling, simultaneously, use hard carbon material not only can effectually restrain the inflation of pole piece, can also obtain higher capacity, promoted the energy density of negative pole.

According to some embodiments of the present application, the bonding strength between the negative active material layer and the current collector is N_{Negative pole}，N_{Negative pole}The value range of (1) is 3N/m to 30N/m; according to some embodiments of the present application, the mass of the hard carbon is 20% to 100% based on the mass of the second anode active material; according to some embodiments of the present application, the hard carbon is 40% to 60% by mass; according to some embodiments of the present application, the particle size of the graphite satisfies 3 μm ≦ D¹v50 is less than or equal to 12 mu m; the particle size of the hard carbon satisfies that D is more than or equal to 3 mu m²v50 is less than or equal to 10 mu m; according to some embodiments of the present application, the negative electrode has a sheet resistance of M_{Negative pole}，M_{Negative pole}The value range of (a) is from 2m Ω to 50m Ω; according to some embodiments of the present application, the first negative active material layer is located between the current collector and the second negative active material layer; according to some embodiments of the present application, the first negative electrode active material layer has a thickness of a μm and the second negative electrode active material layer has a thickness of b μm, wherein 20. ltoreq. a.ltoreq.50 and 30. ltoreq. b.ltoreq.100.

According to some embodiments of the present application, the mass of the hard carbon is 20% to 100% based on the mass of the second anode active material. The higher the content of the hard carbon negative electrode active material is, the lower the expansion is, and meanwhile, the dynamics of the lithium ion battery is also improved. However, since the first charge and discharge efficiency of the hard carbon negative active material is low, the advantage of the high content of the hard carbon negative active material in terms of energy efficiency is low, and thus, it is preferable that the mass of the hard carbon is 40 to 60%.

According to some embodiments of the present application, the first negative electrode active material layer has a thickness of a μm and the second negative electrode active material layer has a thickness of b μm, wherein 20. ltoreq. a.ltoreq.50 and 30. ltoreq. b.ltoreq.100. The thickness of the negative active material layer is preferably thick, since the adhesion between the negative active material and the current collector is reduced during long cycles, thereby causing a large expansion and capacity reduction of the lithium ion battery, and the thickness of the negative active material layer is preferably in the range of 20 μm to 50 μm for the thickness a of the first negative active material layer and 30 μm to 100 μm for the thickness b of the second negative active material layer.

According to some embodiments of the present application, the particle size of the graphite satisfies 3 μm ≦ D¹v50 is less than or equal to 12 mu m; the particle size of the hard carbon satisfies that D is more than or equal to 3 mu m²v50 is less than or equal to 10 mu m. According to some embodiments of the present application, the particle size of the graphite satisfies 4 μm ≦ D¹v50 is less than or equal to 8 mu m. According to some embodiments of the present application, the hard carbon has a particle size satisfying 3.5 μm ≦ D²v50 is less than or equal to 6.5 mu m. The lower the particle size of the active material particles, the better the kinetics of the lithium battery, the lower the particle size of the active material particles, which increases the specific surface area, forms more SEI film at the time of first charge, consumes more powerLithium ion, and therefore it is necessary to design the particle diameter Dv50 of graphite and hard carbon to be in an appropriate range.

According to some embodiments of the present application, the first anode active material layer has a cross-sectional porosity of P1, and P1 has a value ranging from 15% to 30%. According to some embodiments of the present application, the second anode active material layer has a cross-sectional porosity of P2, and P2 has a value ranging from 15% to 40%. The electrolyte can fully infiltrate active material particles due to larger section porosity, and the dynamic performance is improved; the porosity of the cross section is too large, the contact points among the active material particles are reduced, the internal resistance of the battery core is increased, and the energy density of the matrix is also lost.

According to some embodiments of the present application, the first negative electrode active material layer has a thickness of a μm, the second negative electrode active material layer has a thickness of b μm, and 0.5. ltoreq. a/b.ltoreq.1.67. Under the condition of certain hard carbon content, the thicknesses of the first negative active material layer and the second negative active material layer need to be matched, if the thickness ratio a/b of the first negative active material layer and the second negative active material layer is less than 0.5, the thickness of the first negative active material layer is relatively small, the material buffering effect of the first negative active material layer on the second negative active material layer with high hard carbon content in the pole piece cold pressing process is reduced, the bonding strength of the negative active material layer and a current collector is reduced, and the negative active material layer and the current collector are peeled off in the battery circulation process, so that the battery capacity is attenuated. If the thickness ratio a/b of the first negative active material layer to the second negative active material layer is larger than 1.67, the thickness expansion inhibiting effect of the second negative active material layer containing the hard carbon active material on the pole piece in the charging and discharging process of the battery is reduced, and the long-cycle performance of the battery is poor. Therefore, it is preferable that the thickness ratio a/b of the first anode active material layer to the second anode active material layer is in the range of 0.5 to 1.67.

According to some embodiments of the present application, the electrolyte includes at least one of fluoroether, fluoroether carbonate, or ether nitrile.

According to some embodiments of the present application, the electrolyte comprises a lithium salt comprising lithium bis (fluorosulfonyl) imide and lithium hexafluorophosphate, the lithium salt having a concentration of 1 to 2 mol/L. Lithium bis (fluorosulfonyl) imide (LiFSI), which can act synergistically with the negative electrodes of the present application to further improve cycle performance and expansion performance.

According to some embodiments of the present application, the mass ratio of the lithium bis (fluorosulfonyl) imide to the lithium hexafluorophosphate is 0.06 to 5.

In a second aspect, the present application provides an electronic device comprising an electrochemical device as described in the first aspect of the present application.

Drawings

Fig. 1 shows a cross-sectional sem image of a negative electrode in an electrochemical device according to an embodiment of the present disclosure, in which a first negative active material layer and a second negative active material layer in which a portion of hard carbon active material particles may be observed are clearly distinguished.

Fig. 2 shows XRD test results of the negative active material in the electrochemical device according to the embodiment of the present application, having a peak at a diffraction angle 2 θ of 26.4 °, which is a characteristic peak of graphite; a broad peak appears near diffraction angle 2 θ of 24 °, and the peak is a characteristic peak of hard carbon.

Detailed Description

To make the purpose, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below with reference to the embodiments, and it is obvious that the described embodiments are a part of the embodiments of the present application, and not all of the embodiments. The embodiments described herein are illustrative and are provided to provide a basic understanding of the present application. The embodiments of the present application should not be construed as limiting the present application. All other embodiments obtained by those skilled in the art without any creative effort based on the technical solutions and the given embodiments provided in the present application belong to the protection scope of the present application.

For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form ranges not explicitly recited; and any lower limit may be combined with any other lower limit to form a range not explicitly recited, and similarly any upper limit may be combined with any other upper limit to form a range not explicitly recited. Furthermore, each separately disclosed point or individual value may itself, as a lower or upper limit, be combined with any other point or individual value or with other lower or upper limits to form ranges not explicitly recited.

In the description herein, "above" and "below" include the present numbers unless otherwise specified.

Unless otherwise indicated, terms used in the present application have well-known meanings that are commonly understood by those skilled in the art. Unless otherwise indicated, the numerical values of the parameters mentioned in the present application can be measured by various measurement methods commonly used in the art (for example, the test can be performed according to the methods given in the examples of the present application).

A list of items to which the term "at least one of," "at least one of," or other similar term is connected may imply any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a and B" means a only; only B; or A and B. In another example, if items A, B and C are listed, the phrase "at least one of A, B and C" means a only; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and C. Item a may comprise a single component or multiple components. Item B may comprise a single component or multiple components. Item C may comprise a single component or multiple components.

The first aspect of the present application provides an electrochemical device, the electrochemical device includes positive pole, diaphragm, electrolyte and negative pole, the negative pole includes the mass flow body and negative active material layer, negative active material layer includes negative active material, in the X-ray diffraction map of negative active material, have diffraction peak Q1 and diffraction peak Q2 between 18 to 30, the half-peak width of diffraction peak Q1 is 4 to 12, the electrochemical device satisfies: 1.0. ltoreq. CB/[ (Dv99-Dv90)/Dv50 ]. ltoreq.3.5, wherein Dv99, Dv90 and Dv50 respectively denote Dv99, Dv90 and Dv50 of the negative electrode active material particles in units of μm, and CB is a ratio of the negative electrode capacity to the positive electrode capacity in the same area.

In the present application, Dv99 indicates that 99% of the particles in the volume-based particle size distribution are smaller than this value, Dv90 indicates that 90% of the particles in the volume-based particle size distribution are smaller than this value, and Dv50 indicates that 50% of the particles in the volume-based particle size distribution are smaller than this value. In the present application, CB is a ratio of the negative electrode capacity to the positive electrode capacity in the same area, that is, a capacity excess coefficient of the battery. In a lithium ion battery, the size and the particle size distribution range of the negative electrode active material particle size are closely related to the negative electrode active material capacity. The solid phase transfer rate of active ions in the large-particle negative active particles is far lower than the surface of the particles, the polarization is too large in the charging and discharging process, the particles are more difficult to embed and separate the active ions, the capacity of the negative active material is low, the rapid charging and discharging performance of the battery is reduced, and lithium is separated from the surface of the active material to cause safety problems.

Due to the fluctuation of the capacity of the negative active material, in order to prevent the negative electrode from lithium precipitation and ensure the safe use of the lithium ion battery, a large capacity excess coefficient, namely CB, needs to be selected during the design of the lithium ion battery, but when the CB value is too large, the irreversible capacity of the lithium battery is lost, so that the battery capacity is low and the energy density is reduced. According to some embodiments of the present application, the CB value ranges from 0.80 to 1.50, preferably the CB value ranges from 1.00 to 1.35.

Through research, the particle size distribution width of the large-particle negative active material can be characterized by (Dv99-Dv90)/Dv50, and when the particle sizes of the CB and the negative active material of the lithium ion battery meet the following conditions: when the ratio of CB/[ (Dv99-Dv90)/Dv50] < 3.5 is more than or equal to 1.0, the uniformity of the negative electrode is higher, the influence on the improvement effect of the battery performance caused by the side reaction 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 influence of too large particle size on the solid phase conduction of active ions in the negative electrode active material particles can be avoided. The negative electrode can have good dynamic performance, and meanwhile, the lithium ion battery can have long cycle life, high energy density and quick charging capability.

According to some preferred embodiments of the present application, 1.5. ltoreq. CB/[ (Dv99-Dv90)/Dv50 ]. ltoreq.3.5. According to some preferred embodiments of the present application, 2.0. ltoreq. CB/[ (Dv99-Dv90)/Dv50 ]. ltoreq.3.5. In some implementations, the value of CB/[ (Dv99-Dv90)/Dv50] is 1.5, 1.8, 2.0, 2.2, 2.5, 2.8, 3.0, 3.2, 3.5, etc.

According to some embodiments of the present application, the half-width of the diffraction peak Q2 is less than 4 °.

According to some embodiments of the present application, the half-width of the diffraction peak Q2 is 0.1 ° to 3.5 °.

According to some embodiments of the present application, the peak position of the diffraction peak Q1 is less than the peak position of the diffraction peak Q2.

According to some embodiments of the present application, the 2 θ value of the diffraction peak Q1 is in the range of 22 ° to 26 ° and can be assigned as a hard carbon active material, and the 2 θ value of the diffraction peak Q2 is in the range of 26.0 ° to 26.5 ° and can be assigned as a graphite active material.

According to some embodiments of the present application, the negative active material layer has a cross-sectional porosity of P_{Negative pole}，P_{Negative pole}The value of (a) is in the range of 15% to 35%. Preferably, P_{Negative pole}The value range of (a) is 15% to 30%; more preferably, P_{Negative pole}The value of (a) is in the range of 15% to 25%.

According to some embodiments of the present application, the negative electrode active material layer includes a first negative electrode active material layer including a first negative electrode active material including graphite; the second anode active material layer includes a second anode active material including hard carbon and graphite.

According to some embodiments of the present application, the first negative active material layer is located between the current collector and the second negative active material layer.

The hard carbon active material has considerable capacity, excellent quick charge performance and extremely low expansion, and the second negative active material layer compounded by the hard carbon active material and the graphite active material can effectively improve the energy efficiency and the quick charge capacity of the lithium battery. The slippage of the graphite particles during the cold pressing process can promote the compaction among the hard carbon material particles, so that the negative electrode can obtain higher compaction density, meanwhile, due to the characteristics of the hard carbon material particles, the negative electrode has higher porosity, the pole piece can be ensured to have higher liquid retention amount under a higher compaction state, and better ionic conductivity can be obtained; the hard carbon active material and the graphite active material are mixed, so that the contact between hard carbon material particles and hard carbon material particles or graphite material particles is increased, and the whole pole piece material can obtain better electronic conductivity and lower internal resistance; mix hard carbon active material and graphite active material and set up the second negative pole active material layer of contact more easily at electrolyte, can full play hard carbon material's the fast characteristic of filling, simultaneously, use hard carbon material not only can effectually restrain the inflation of pole piece, can also obtain higher capacity, promoted the energy density of negative pole.

According to some embodiments of the present application, the mass of the hard carbon is 20% to 100% based on the mass of the second anode active material. In some embodiments, the mass of the hard carbon is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 100% based on the mass of the second anode active material. The first charge and discharge efficiency of the hard carbon active material is low, resulting in a decrease in cell energy efficiency, and preferably, the mass of the hard carbon is 40 to 60% based on the mass of the second negative electrode active material. According to some embodiments of the present application, the first negative electrode active material layer has a thickness of a μm and the second negative electrode active material layer has a thickness of b μm, wherein 20. ltoreq. a.ltoreq.50 and 30. ltoreq. b.ltoreq.100. In some embodiments, a is 20, 25, 30, 33, 35, 40, 45, or 48, etc. In some embodiments, b is 30, 35, 38, 43, 45, 50, 55, 60, 68, 72, or 85, etc. The thickness of the negative electrode active material layer is set in consideration of the pole piece bounce, electrolyte wettability, and compatibility with the positive electrode active material layer, and the overall thickness is set in a reasonable range, and preferably, the thickness of the negative electrode active material layer is in a range of 50 μm to 150 μm, for example, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, or 140 μm. The first negative active material layer is a graphite negative active material, so that the resistance between the negative active material layer and a current collector can be effectively reduced, the damage of hard carbon material particles in the second negative active material layer to the current collector under the pole piece cold pressing process can be buffered, the pole piece bonding strength can be improved, and the thickness of the first negative active material layer is preferably within the range of 20-50 micrometers in consideration of the processing capacity of the coating process.

According to some embodiments of the present application, 0.5 ≦ a/b ≦ 1.67. In some embodiments, a/b is 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.85, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, or 1.67. Under the certain condition of hard carbon negative active material content, the thickness of first negative active material layer, two negative active material layers needs the phase-match, if both thickness ratio a/b < 0.5, under the negative active material layer thickness control is in certain circumstances, then first negative active material layer thickness is less relatively, then first negative active material layer reduces at pole piece cold pressing process material cushioning effect to the second negative active material layer of high hard carbon active material content, negative active material layer and mass flow body bonding strength reduce, peel off the mass flow body at battery circulation process negative active material layer, cause the battery capacity decay, simultaneously, first negative active material layer thickness is less relatively can promote the requirement to coating equipment ability by a wide margin. If the thickness ratio a/b of the two is more than 1.67, under the condition that the thickness of the negative active material layer is controlled to be constant, the thickness of the first negative active material layer is relatively large, the thickness expansion inhibition effect of the second negative active material layer containing the hard carbon active material on the pole piece in the battery charging and discharging process is reduced, and the long-cycle performance of the battery is poor. The thickness ratio a/b of the first and second anode active material layers is preferably in the range of 0.5 to 1.67.

According to some embodiments of the present application, the particle size of the graphite satisfies 3 μm ≦ D¹v50 is less than or equal to 12 mu m; the particle size of the hard carbon satisfies that D is more than or equal to 3 mu m²v50 is less than or equal to 10 mu m. According to some embodiments of the present application, the particle size of the graphite satisfies 4 μm ≦ D¹v50 is less than or equal to 8 mu m. According to some embodiments of the present application, the hard carbon has a particle size satisfying 3.5 μm ≦ D²v50 is less than or equal to 6.5 mu m. The lower the particle size of the active material particles, the better the kinetics of the lithium battery, and the lower the particle size of the active material particles, the greater the specific surface area, the more SEI films are formed upon first charge, and more lithium ions are consumed.

According to some embodiments of the present application, the first anode active material layer has a cross-sectional porosity P1 of 15% to 30%. According to some embodiments of the present application, the second anode active material layer has a cross-sectional porosity P2 of 15% to 40%, preferably, P2 of 15% to 30%. The electrolyte can fully infiltrate active material particles due to larger section porosity, and the dynamic performance is improved; the porosity of the cross section is too large, the contact points among the active material particles are reduced, the internal resistance of the battery core is increased, and the energy density of the matrix is also lost.

According to some embodiments of the present application, the negative electrode has a sheet resistance of M_{Negative pole}，M_{Negative pole}The value of (d) ranges from 2m Ω to 50m Ω.

According to some embodiments of the present application, the adhesive strength between the negative electrode active material layer and the current collector is N negative, and the value of N negative ranges from 3N/m to 30N/m. When the adhesive strength is less than 10N/m, the adhesive strength between the active material and the current collector is extremely weak, and stripping and burrs are easily generated in the rolling or slitting process, so that potential safety hazards of the battery cell are caused; when the ratio of the active material to the current collector is more than 20N/m, the bonding strength of the active material and the current collector is too high, the ratio of the binder to the active material is too high, namely, the binder is excessive, so that the internal resistance of the battery cell is too high, the dynamic loss is serious, and the attenuation of the long-cycle performance is accelerated.

According to the present application, the first and second anode active material layers may further include a thickener and a binder. The thickening agent can be one or a mixture of sodium carboxymethyl cellulose (CMC) and/or polyether modified organic matters; the binder can be water-soluble binder, and can be one or a mixture of more of styrene butadiene rubber, nitrile butadiene rubber, modified styrene butadiene rubber, water-soluble polyacrylonitrile copolymer and polyacrylate.

According to some embodiments of the present application, the negative electrode may be prepared according to a method comprising:

mixing a first active material, a thickening agent, a binder and a solvent to obtain first negative electrode active material layer slurry;

mixing a second active material, a thickening agent, a binder and a solvent to obtain second negative electrode active material layer slurry;

coating a conductive carbon coating on a current collector in advance, wherein the conductive carbon coating comprises one or a mixture of several of carbon nano tubes, graphene, KS-6, acetylene black and SP;

a double-die coating head extrusion type coating machine is adopted, a feeding channel communicated with two discharge ports is arranged in a coating head, first negative electrode active material layer slurry and second negative electrode active material layer slurry are extruded simultaneously under the control of a screw pump, the two slurries are coated on a negative current collector with a conductive coating at the same time, and a double-layer coating pole piece with a hard carbon-containing second negative electrode active material layer on the top layer and a hard carbon-free first negative electrode active material layer on the bottom layer is prepared. After one side of the current collector is coated, the other side is coated repeatedly in the above manner. The thickness of the first negative electrode active material layer is controlled to be in a desired thickness range, for example, in a range of 20 μm to 50 μm, and the thickness of the second negative electrode active material layer is controlled to be in a desired thickness range, for example, in a range of 30 μm to 100 μm, by adjusting extrusion parameters of a dual die head die coater.

After the negative electrode is used for the lithium ion battery, lithium can be prevented from being separated from the surface of the negative electrode under the condition of high-rate quick charge, and the safety application performance is better.

Materials, compositions, and methods of making positive electrodes useful in embodiments of the present application include any of the techniques disclosed in the prior art.

In some embodiments, the positive electrode includes a current collector and a positive active material layer on the current collector. In some embodiments, the current collector may include, but is not limited to: aluminum. In some embodiments, the positive active materials include, but are not limited to: lithium cobaltate (LiCoO)₂) Lithium Nickel Cobalt Manganese (NCM) ternary material, lithium iron phosphate (LiFePO)₄) Or lithium manganate (LiMn)₂O₄). In some embodiments, the positive active material layer further includes a binder, and optionally a conductive material. The binder improves the binding of the positive electrode active material particles to each other, and also improves the binding of the positive electrode active material to the current collector. In some embodiments, the adhesive includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, polyethylene, polypropylene, styrene butadiene rubber, acrylatedStyrene-butadiene rubber, epoxy resin or nylon, etc. In some embodiments, the conductive material includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

The positive electrode may be prepared by a preparation method well known in the art. For example, the positive electrode can be obtained by: the active material, the conductive material, and the binder are mixed in a solvent to prepare an active material composition, and the active material composition is coated on a current collector. In some embodiments, the solvent may include, but is not limited to: n-methyl pyrrolidone.

The electrolyte that may be used in the embodiments of the present application may be an electrolyte known in the art.

According to some embodiments of the present application, the electrolyte comprises a lithium salt comprising lithium bis (fluorosulfonyl) imide and lithium hexafluorophosphate, the lithium salt having a concentration of 1 to 2 mol/L. In some embodiments, the lithium salt concentration is 1mol/L, 1.15mol/L, 1.5mol/L, 1.7mol/L, 2mol/L, or the like. According to some embodiments of the present application, the mass ratio of the lithium bis (fluorosulfonyl) imide to the lithium hexafluorophosphate is 0.06 to 5. In some embodiments, the mass ratio of lithium bis (fluorosulfonyl) imide to lithium hexafluorophosphate is 0.06, 0.1, 0.15, 0.2, 0.25, 0.5, 0.75, 1.0, 1.2, 1.5, 2.0, 2.5, 3.0, or 4, and the like.

The material and shape of the separation film that can be used for the embodiment of the present application are not particularly limited, and may be any of the techniques disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance or the like formed of a material stable to the electrolyte of the present application.

For example, the release film may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer comprises at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be selected.

At least one surface of the substrate layer is provided with a surface treatment layer, and the surface treatment layer can be a polymer layer or an inorganic layer, and can also be a layer formed by mixing a polymer and an inorganic substance.

The inorganic layer includes inorganic particles including at least one of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate, and a binder. The binder comprises at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene.

The polymer layer comprises a polymer, and the material of the polymer comprises at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

In some embodiments, the electrochemical devices of the present application include, but are not limited to: all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors. In some embodiments, the electrochemical device is a lithium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

The electrochemical device has higher energy density, cycle performance and quick charge performance, and can meet the application requirements.

Electronic device

The present application further provides an electronic device comprising an electrochemical device according to the first aspect of the present application.

The electronic device or apparatus of the present application is not particularly limited. In some embodiments, the electronic device of the present application includes, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a cellular phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notebook, a calculator, a memory card, a portable recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a large household battery, a lithium ion capacitor, and the like.

Examples

1) Preparation of the positive electrode: the positive electrode active material lithium cobaltate (molecular formula is LiCoO)₂) Fully stirring and mixing acetylene black serving as a conductive agent and polyvinylidene fluoride (PVDF) serving as a binder in a proper amount of N-methylpyrrolidone (NMP) solvent according to a weight ratio of 96:2:2 to form uniform positive electrode slurry; and coating the slurry on an Al foil of a positive current collector, drying and cold pressing to obtain the positive electrode.

2) Preparation of a negative electrode: the first active substance, the thickening agent and the binding agent are sequentially 96.7 percent in solid content ratio: 1.0%: mixing the mixture with a solvent in a ratio of 2.3% to obtain a first negative electrode active material layer slurry; and sequentially adding 96.7% of a second active substance, a thickening agent and a binder according to the solid content ratio: 1.0%: mixing the mixture with a solvent in a ratio of 2.3% to obtain second negative electrode active material layer slurry; coating a graphene conductive carbon coating on a current collector in advance; a double-die coating head extrusion type coating machine is adopted, a feeding channel communicated with two discharge ports is arranged in a coating head, first negative electrode active material layer slurry and second negative electrode active material layer slurry are extruded simultaneously under the control of a screw pump, the two slurries are coated on a negative current collector with a conductive coating at the same time, and a double-layer coating pole piece with a hard carbon-containing second negative electrode active material layer on the top layer and a hard carbon-free first negative electrode active material layer on the bottom layer is prepared. After one side of the current collector is coated, the other side is coated repeatedly in the above manner. The thickness of the first negative electrode active material layer and the thickness of the second negative electrode active material layer are controlled by adjusting extrusion parameters of a double-die coating head extrusion coater.

3) And (3) isolation film: a PE porous polymer film is used as a separation film.

4) Electrolyte solution: mixing Ethylene Carbonate (EC) with diethyl carbonate (DEC) in a volume ratio of 3: 7, followed by mixing of the well-dried lithium salt LiPF₆The electrolyte was prepared by dissolving the above-mentioned components in a mixed organic solvent at a ratio of 1mol/L, and finally adding 2 wt% of fluoroethylene carbonate (FEC) based on the above-mentioned base electrolyte.

5) Preparing a lithium ion battery: stacking the anode, the isolating film and the cathode in sequence to enable the isolating film to be positioned between the anode and the cathode to play an isolating role, and then winding to obtain a bare cell; and (3) placing the bare cell in an outer packaging foil, injecting the prepared electrolyte into the dried cell, and performing vacuum packaging, standing, formation, shaping and other processes to complete the preparation of the lithium ion battery.

The test method comprises the following steps:

1 lithium ion Battery CB test

And taking the lithium ion batteries which are completely discharged, respectively disassembling an anode and a cathode, cleaning, drying, respectively punching 5 complete pole pieces on flat single-surface areas of the anode and the cathode by using a die head with the diameter of 14mm, respectively using a lithium piece as a counter electrode, and respectively assembling the pole pieces into button batteries for testing. Testing by referring to a gram capacity testing method, measuring the capacity of the positive electrode, recording the capacity as C1, C2, C3, C4 and C5, and calculating the capacity average value C of the punched pole piece of the positive electrode; similarly, the measured capacities of the negative electrode are denoted as a1, a2, A3, a4 and a5, and the average value a of the capacities of the punched negative electrode pieces is calculated, and the formula of the lithium ion battery CB is CB ═ a/C.

2. X-ray diffraction (XRD) testing

And taking the lithium ion battery with complete discharge, respectively disassembling the positive electrode and the negative electrode, cleaning, drying, scraping the powder of the negative electrode active material layer by using a scraper, and carrying out heat treatment on the scraped powder in a tubular furnace at 400 ℃ for 4 hours under the protection of argon gas so as to remove the binder adhered to the surface of the negative electrode active material.

Method for testing (002) crystal face diffraction peak (hereinafter referred to as "002 peak, 004 peak, 110 peak") of negative electrode material: testing the cathode active material by an X-ray powder diffractometer (XRD, instrument model: Bruker D8 ADVANCE), wherein the target material is Cu Ka; the voltage current was 40KV/40mA, the scan angle ranged from 5 ° to 80 °, the scan step was 0.00836 °, and the time per step was 0.3 s. Obtaining the X-ray diffraction pattern.

3. Method for testing particle size of negative electrode active material particles

And taking the lithium ion batteries which are completely discharged, respectively disassembling a negative electrode plate from each lithium ion battery, cleaning, drying, scraping the powder of the negative active material layer by using a scraper, and carrying out heat treatment on the scraped powder in a tubular furnace at 400 ℃ for 4 hours under the protection of argon gas so as to remove the adhesive adhered to the surface of the negative active material. Then, the particle size distribution was measured by a laser diffraction particle size distribution measuring instrument (Malverm Mastersizer 3000) according to the particle size distribution laser diffraction method GB/T19077-2016, and Dv50, Dv90 and Dv99 were obtained.

4. Lithium ion battery lithium separation test:

6 lithium ion batteries in each of examples and comparative examples were used. The lithium ion batteries of each example and comparative example were further divided into 3 subgroups according to charge rate. First, the cell was left to stand at 25 ℃ for 1 hour. Then, constant-current charging is carried out on the battery according to the charging multiplying power of 1C and 3C respectively, constant-voltage charging is carried out after the battery is charged to 4.5V, charging is stopped when the charging current is lower than 0.05C, and the battery is placed for 5 minutes; the cell was then discharged to 3V with a current density of 1C at constant current and left for 5 minutes. After 10 cycles of charge and discharge, the battery was disassembled, and the state of lithium deposition on the surface of the negative electrode and the state of the separator in contact with the negative electrode were observed. The charging rates of 1C and 3C correspond to the 1C lithium deposition case and the 3C lithium deposition case, respectively.

Judging the lithium separation degree at 1C and the lithium separation degree at 3C: judging according to the state that the separator in contact with the fully disassembled negative electrode is polluted, and judging that lithium is not separated when the whole separator in contact with the negative electrode is white and the area displayed as gray is less than 2%; when most of the isolating membrane contacted with the negative electrode is white, but gray can be observed at partial positions, and if the gray area is more than or equal to 2% and less than 20%, slight lithium precipitation is judged; when the part of the isolating membrane contacted with the negative electrode is white, but partial gray can still be obviously observed, and if the gray area is more than or equal to 20% and less than 60%, the lithium is judged to be separated; and when most of the isolating membrane contacted with the negative electrode is gray and the gray area is more than or equal to 60 percent, judging that the lithium is seriously separated.

5. And (3) testing the charging rate performance of the lithium ion battery:

and (3) taking 5 soft package batteries in each group, repeatedly charging and discharging the batteries through the following steps, counting the capacity (average value) of each charging stage, and calculating the capacity ratio of the CC stage. The method comprises the following specific steps: first, the cell was left to stand at 25 ℃ for 1 hour. Carrying out constant Current Charging (CC) on the battery at a charging rate of 1C, converting to constant voltage Charging (CV) after charging to 4.48V, stopping charging when the charging current is lower than 0.05C, and standing for 5 minutes; discharging the battery current to 3V by 0.2C, and standing for 5 minutes to ensure the integrity of the subsequent charging and discharging process. And then, the battery is fully charged by different multiplying powers of 0.2C, 0.5C, 1C, 2C, 3C and the like according to the previous CC + CV charging mode, the battery capacity is discharged at the multiplying power of 0.2C after the battery is placed aside for 5 minutes, and each multiplying power is circulated once. And calculating the ratio of the CC section capacity under different charging multiplying factors. As in table 1, the test is that the battery is fully charged at 1C rate according to the previous CC + CV charge mode, the formula is calculated: the CC block capacity ratio (1C) ([ CC block charge capacity/(CC + CV) total charge capacity ] × 100%

6. Lithium ion battery energy density testing

5 lithium ion batteries prepared by active materials of all comparative examples and examples are charged to 4.48V at a current of 1.5C and then charged to 0.05C at a constant voltage of 4.48V under the condition of normal temperature; standing for 5min, discharging to 3.0V at constant current of 0.025C, standing for 5min, recording the capacity at this time as D, the unit is mAh, charging the battery cell to 4.0V at 1.0C, measuring the length, width and thickness of the battery cell at this time, and calculating to obtain the volume V of the battery cell, the unit is unitIs mm³And calculating the volume energy density: VED ═ D (D × 3.89 × 1000)/V, in Wh/L. The energy density as a percentage of comparative example 1 is the percentage of the energy density of the example or comparative example compared to the energy density of comparative example 1 (artificial graphite) under the same test conditions.

7. Negative active material layer cross-sectional porosity test

And taking the fully placed lithium ion battery, disassembling, taking out the negative electrode, soaking the negative electrode for 20min by using DMC (ethylene carbonate), cleaning the negative electrode by using DMC and acetone in sequence, placing the negative electrode in an oven, and drying the negative electrode for 12h at the temperature of 80 ℃. Grinding the negative electrode ions to prepare a sample, observing the sample under an SEM, respectively cutting ten SEM pictures containing the section of the first active material layer and the section of the second active material layer with the area of A being 20 mu m multiplied by 20 mu m, and the section of the whole negative electrode, and calculating the area B of the pore at the darker part in the section by using image processing software (multiple), wherein the section porosity of the electrode piece is B/A multiplied by 100%. Thereby obtaining a first anode active material layer having a cross-sectional porosity of P1 and a second anode active material layer having cross-sectional porosities of P2 and P_{Negative pole}。

Negative ion milling (Cross-section) sample preparation procedure:

cutting the processed pole piece into a size of 0.5cm multiplied by 1cm, adhering the cut cathode on a silicon wafer carrier with a size of 1cm multiplied by 1.5cm by using a conductive adhesive, and then processing one end of the cathode by using argon ion polishing (the parameter is 8KV accelerating voltage, each sample is 4h), wherein the argon ion polishing is to ionize argon by using a high-voltage electric field to generate an ionic state, the generated argon ions bombard the surface of the cathode at a high speed under the action of the accelerating voltage, and the cathode is denuded layer by layer to achieve the polishing effect.

And (4) SEM test:

scanning Electron Microscopy (SEM) is the process of obtaining the morphology of a sample by the interaction of an electron beam with the sample and imaging with secondary electron signals. The scanning electron microscope used in the application is a JSM-6360LV model of JEOL company for analyzing the morphology and structure of a sample.

8. Cathode gram capacity testing method

And taking the lithium ion battery which is completely discharged, disassembling a negative electrode, cleaning, drying, then, using a lithium sheet as a positive electrode, and assembling the lithium ion battery into a button cell for testing. The button cells were discharged to 5.0mV at 0.05C, 5.0mV at 50 μ A, 5.0mV at 10 μ A, and 2.0V at 0.1C, and the capacity of the button cells at this time was recorded as gram capacity. 0.05C means a current value at 0.05 times the design gram capacity, and 0.1C means a current value at 0.1 times the design gram capacity.

9. Testing the cycle performance of the lithium ion battery:

the average value of 5 lithium ion batteries prepared in all comparative examples and examples was obtained. The lithium ion battery was repeatedly charged and discharged through the following steps, and the discharge capacity retention rate and the thickness expansion of the lithium ion battery were calculated.

Firstly, carrying out first charging and discharging in an environment of 25 ℃, carrying out constant current charging under a charging current of 0.7 ℃ until the upper limit voltage reaches 4.48V, then converting into constant voltage charging, then carrying out constant current discharging under a discharging current of 1.0 ℃ until the final voltage is 3V, and recording the first-cycle discharging capacity and the thickness of a full-charge core; then, 400 cycles of charge and discharge were performed, and the discharge capacity and the fully charged core thickness were recorded for the 400 th cycle.

Capacity retention ratio at 400 cycles (discharge capacity at 400 cycles/discharge capacity at the first cycle) × 100%;

cycle 400-cycle thickness change-full charge core thickness of the 400 th cycle-full charge core thickness of the first cycle)/full charge core thickness of the first cycle x 100%.

10. Negative diaphragm resistance test

And taking the lithium ion battery which is completely discharged, disassembling the cathode, cleaning and drying. The membrane resistance test adopts a single-probe method, and the specific test process is as follows: taking area is 154mm²The double-layer coated electrode slice small wafer is set with the test temperature of 25 ℃, the pressure of 0.4T and the pressure of 26MPa, 10 points at different positions are randomly selected for testing, and the final result is an average value, namely M_{Negative pole}。

11. Adhesion strength of active material layer to current collector (N)_{Negative pole})

Take out of full dischargeAnd disassembling the cathode of the lithium ion battery, and cleaning and drying the cathode. The instrument brand for testing the bonding strength between the active material layer and the current collector is Instron, the model is 33652, a pole piece (with the width of 30mm multiplied by the length of 100mm to 160mm) is taken, double-sided adhesive paper (with the model of 3M9448A, the width of 20mm multiplied by the length of 90mm to 150mm) is fixed on a steel plate, a paper tape with the same width as the pole piece and one side of the pole piece are fixed by the adhesive paper, a limiting block of a tensile machine is adjusted to a proper position, the paper tape is turned upwards and slides for 40mm, the sliding speed is 50mm/min, and the bonding strength N between the active material layer and the current collector under 180 degrees (namely, the reverse direction stretching) is tested_{Negative pole}。

12. Method for testing compaction density of negative electrode active material layer

And taking the lithium ion battery which is completely discharged, disassembling the cathode, cleaning and drying. The negative electrode (both sides of the negative electrode current collector are coated with the negative electrode active material layer) of a certain area S was weighed using an electronic balance, the weight was recorded as W1, and the thickness of the negative electrode D1 was measured using a ten-thousandth ruler. The negative active material layer was washed off using a dimethyl carbonate (DMC) solvent, dried, and the weight of the negative current collector was measured as W2, and the thickness of the negative current collector was measured using a ten-thousandth micrometer D2. The weight W0 and the thickness D0 of the negative electrode active material layer provided on the negative electrode current collector side and the compacted density of the negative electrode active material layer were calculated by the following formulas:

W0＝(W1-W2)/2

D0＝(D1-D2)/2

the compacted density is W0/(D0 × S).

Test results

Setting examples 1 to 10, comparative examples 1 to 3 were examined for the influence of the CB value, T value setting and particle diameter of the negative electrode active material particles of the lithium ion battery. The anodes of examples 1 to 10 and comparative examples 2 to 3 were prepared with reference to the above-described double-coated anode, Y being 20%, the thickness of the first anode active material layer was 50 μm, the thickness of the second anode active material layer was 30 μm, and comparative example 1 was a graphite anode active material single-layer coating, the thickness of the anode active material layer was 80 μm. The lithium ion batteries of the embodiments 1 to 5 have the same CB value and different T values; the lithium ion batteries of examples 6 to 10 are set to have similar T values and different CB values; comparative example 1 is a graphite negative active material, comparative example 2 is set to a large T value, and comparative example 3 is set to a small T value. The particle diameters Dv50 of the graphite anode active material particles and the hard carbon anode active material particles were each selected to be in the range of 5 μm to 10 μm.

Table 1 lithium ion battery information wherein: t ═ CB/[ (Dv99-Dv90)/Dv50]

Analysis of the test results according to examples 1 to 5 and comparative examples 1 to 3 shows that, at a fixed CB value of the lithium ion battery, the larger the T value, i.e., the more concentrated the particle size distribution of the negative electrode active material particles, the more excellent the dynamic performance of the lithium ion battery, and the more favorable the capacity exertion. Preferably, the value of T is in the range of 2 to 3.5. Analysis of the test results of examples 6 to 10 shows that the CB value setting of the lithium ion battery is directly related to the safety and energy density of the battery, a smaller CB value, i.e., the capacity of the negative active layer is lower than that of the positive active material layer, lithium precipitation is liable to occur at the negative electrode during charging, a larger CB value, irreversible capacity loss of the lithium battery, resulting in a lower battery capacity and a reduced energy density, and the CB value is preferably in the range of 1.00 to 1.35. Comparing example 2 with comparative example 1, it can be found that after the hard carbon material is introduced, the fast charging performance of the lithium battery is effectively improved, and the hard carbon material can be set to a relatively low CB value to obtain a higher energy density.

Example 3, example 11 to example 16 examine the influence of the porosity of the lithium ion battery on the battery performance, the first negative electrode active material layer thickness was 30 μm, and the second negative electrode active material layer thickness was 60 μm. Observing the negative active material layer by adopting SEM, and respectively calculating the section porosity P of the negative active material layer by image processing software_{Negative pole}The first negative electrode active material layer has a cross-sectional porosity P1, and the second negative electrode active material layer has a cross-sectional porosity P2.

TABLE 2 Effect of porosity of the section of the Anode active Material layer

Analysis of the test results from examples 3 to 11 to 16 shows a higher cross-sectional porosity P_{Negative pole}The method helps to improve the contact between the electrolyte and the anode active material layer particles, thereby improving the kinetics, but also brings more film formation consumption and capacity loss. The results show that the porosity P varies with the section_{Negative pole}The gram-volume of the negative active material layer shows a descending trend, and the capacity of the CC section of the lithium ion battery is improved to a certain extent compared with (1C). Comprehensively considering the dynamics and the energy density of the lithium ion battery, the preferred section porosity P_{Negative pole}In the range of 15% to 35%, more preferably the cross-sectional porosity P_{Negative pole}The range is 25% to 35%.

Based on example 3, on the basis of which the influence of the hard carbon active material content Y, the first active material layer thickness a and the second active material layer thickness b in the second anode material layer on the performance of the lithium ion battery was further examined, the design of the relevant parameters is shown in table 3. In which the negative active material of comparative example 1 was graphite and the second negative active material of example 27 was hard carbon.

Table 3 negative active material layer information and lithium ion battery performance information

Comparing the test results of examples 3, 17 to 26 and comparative example 1, it is found that under the condition that the mass content of the hard carbon is increased, the condition that the thickness of the lithium ion battery is changed in 400 cycles is obviously improved compared with the comparative example 1 that the negative electrode active material is graphite, the higher the content of the hard carbon negative electrode active material is, the lower the expansion is, and the dynamics of the lithium ion battery is also improved. However, the first charge-discharge efficiency of the hard carbon negative active material is low, so that the hard carbon negative active material has a large irreversible capacity in the first charge-discharge process, and the consumed capacity needs to be supplemented by designing a thicker positive electrode. Further, the lithium intercalation potential of the hard carbon negative electrode active material is lower than that of the graphite negative electrode material, and the capacity of the hard carbon negative electrode active material cannot be fully exhibited in the 4.48V system to which the graphite negative electrode active material is applied. The higher content of the hard carbon negative active material is less advantageous in terms of energy efficiency, and therefore, the hard carbon content is preferably 20% to 100%, more preferably 40% to 60%.

Meanwhile, the negative electrode sheet resistances of example 3, example 19, example 22 and comparative example 1, which were tested to have similar negative electrode thicknesses, were 16m Ω, 19m Ω, 23m Ω and 10m Ω, respectively, indicating that the hard carbon content was increased and the resistance of the negative electrode was increased, so it is preferable that the content of the hard carbon negative electrode active material was in the range of, preferably, 20% to 80%, and the thickness ratio a/b of the thickness of the first negative electrode active material layer to the thickness of the second negative electrode active material layer was in the range of 0.5 to 1.67. Meanwhile, it was found that the thickness b of the second negative electrode active material layer of example 26, which is 150 μm, was thick, and the adhesion between the negative electrode active material layer and the negative electrode current collector was decreased during a long cycle due to the thick thickness, thereby causing a large expansion and a capacity decrease of the lithium ion battery.

In addition, examples 28 to 30 examined the effect of lithium salt on the battery performance compared to example 3, and examples 28 to 30 differed from example 3 only in adjusting the composition of lithium salt, see table 4 specifically.

TABLE 4 electrolyte composition and test results

Note: LiFSI molar mass of 187.07g/mol, LiPF₆The molar mass is 151.91g/mol

From the test results of example 3 and examples 28 to 30, it can be obtained by adding LiFSI and LiPF in an appropriate mass ratio to the electrolyte₆Can be combined with the cathode hard carbon material of the application so as to improve the cycle performance and the expansion performance, particularly LiFSI and LiPF₆When the mass ratio of (2) is 0.062 to 1.23, both the cycle performance and the thickness variation are improved well.

Although illustrative embodiments have been illustrated and described, it will be appreciated by those skilled in the art that the above embodiments are not to be construed as limiting the application and that changes, substitutions and alterations can be made to the embodiments without departing from the spirit, principles and scope of the application.

Claims

1. An electrochemical device comprising a positive electrode, a separator, an electrolyte, and a negative electrode, the negative electrode comprising a current collector and a negative electrode active material layer, the negative electrode active material layer comprising a negative electrode active material having a diffraction peak Q1 and a diffraction peak Q2 between 18 ° and 30 ° in an X-ray diffraction pattern, the diffraction peak Q1 having a half-peak width of 4 ° to 12 °, the electrochemical device satisfying: 1.0 or less CB/[ (Dv99-Dv90)/Dv50] or less 3.5;

wherein Dv99, Dv90 and Dv50 represent Dv99, Dv90 and Dv50 of the anode active material particles, respectively, in μm;

CB is the ratio of the negative electrode capacity to the positive electrode capacity for the same area.

2. The electrochemical device according to claim 1, wherein at least one of the following conditions (a) to (d) is satisfied:

(a) the negative active material layer has a cross-sectional porosity of P_{Negative pole}Said P is_{Negative pole}The value range of (a) is 15% to 35%;

(b) the bonding strength between the negative active material layer and the current collector is N_{Negative pole}Said N is_{Negative pole}The value range of (1) is 3N/m to 30N/m;

(c) the membrane resistance of the negative electrode is M_{Negative pole}Said M is_{Negative pole}The value range of (a) is from 2m Ω to 50m Ω;

(d) the half-width of the diffraction peak Q2 was 0.1 ° to 3.5 °.

3. The electrochemical device according to claim 1, wherein the negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer,

the first negative electrode active material layer includes a first negative electrode active material including graphite;

the second anode active material layer includes a second anode active material including hard carbon and graphite.

4. The electrochemical device according to claim 3, wherein at least one of the following conditions (e) to (i) is satisfied:

(e) the mass of the hard carbon is 20% to 100% based on the mass of the second anode active material;

(f) the particle size of the graphite satisfies that D is more than or equal to 3 mu m¹v50 is less than or equal to 12 mu m; the particle size of the hard carbon satisfies that D is more than or equal to 3 mu m²v50≤10μm；

(g) The first negative active material layer is located between the current collector and the second negative active material layer;

(h) the thickness of the first negative electrode active material layer is a mu m, wherein a is more than or equal to 20 and less than or equal to 50;

(i) the thickness of the second negative electrode active material layer is b mu m, and b is more than or equal to 30 and less than or equal to 100.

5. The electrochemical device according to claim 3, wherein the first negative active material layer has a cross-sectional porosity of P1, the P1 is in a range of 15% to 30%, the second negative active material layer has a cross-sectional porosity of P2, and the P2 is in a range of 15% to 40%.

6. The electrochemical device according to claim 3, wherein the thickness of the first negative electrode active material layer is a μm, the thickness of the second negative electrode active material layer is b μm, and 0.5. ltoreq. a/b. ltoreq.1.67.

7. The electrochemical device of claim 1, the electrolyte comprising at least one of fluoroether, fluoroethylene carbonate, or ether nitrile.

8. The electrochemical device of claim 1, the electrolyte comprising a lithium salt comprising lithium bis (fluorosulfonyl) imide and lithium hexafluorophosphate, the lithium salt having a concentration of 1 to 2 mol/L.

9. The electrochemical device of claim 8, wherein a mass ratio of the lithium bis (fluorosulfonyl) imide to the lithium hexafluorophosphate is 0.06 to 5.

10. An electronic device comprising the electrochemical device of any one of claims 1 to 9.