Negative active material and electrochemical device and electronic device using the same

Abstract

The present application relates to a negative electrode active material, and an electrochemical device and an electronic device using the same. Specifically, the present application provides a negative electrode active material, wherein the negative electrode active material has a median particle diameter D 1 v50, the negative electrode active material has a median particle diameter D 2 v50 under a pressure of 1 t, and D 2 v50 / D 1 v50 is not less than 0.8. The negative electrode active material of the present application helps to achieve a balance between high capacity and high cycle expansion performance of an electrochemical device.

Description

[0001] This application is a divisional application of the application with the application date of March 20, 2020, the application number of 202010201979.4, and the invention name of "Negative electrode active material and electrochemical device and electronic device using the same". TECHNICAL FIELD

[0002] The present application relates to the field of energy storage, in particular to a negative electrode active material and electrochemical device and electronic device using the same. BACKGROUND

[0003] Electrochemical devices (e.g., lithium ion batteries) are widely used due to their environmental friendliness, high working voltage, large specific capacity, and long cycle life, and have become the most promising new green chemical power source in the world today. Small size lithium ion batteries are usually used as power sources for driving portable electronic communication devices (e.g., camcorders, mobile phones, or notebook computers, etc.), especially for high-performance portable devices. In recent years, medium and large size lithium ion batteries with high output characteristics have been developed and applied to electric vehicles (EV) and large-scale energy storage systems (ESS). With the wide application of lithium ion batteries, their cycle performance has become a key technical problem to be solved. Improving the active material in the electrode is one of the research directions to solve the above problems.

[0004] Therefore, it is necessary to provide an improved negative electrode active material and electrochemical device and electronic device using the same. SUMMARY

[0005] The present application provides a negative electrode active material and electrochemical device and electronic device using the same in an attempt to solve at least one problem existing in the related art, at least to some extent.

[0006] According to one aspect of the present application, the present application provides a negative electrode active material, wherein the negative electrode active material has a median particle size D 1 v50, the negative electrode active material has a median particle size D 2 v50 under a pressure of 1 t, and D 2 v50 / D 1 v50 is not less than 0.8. In some embodiments, the D 2 v50 / D 1 v50 is not less than 0.9. In some embodiments, the D 2 v50 / D 1 v50 is 0.8, 0.85, 0.9, 0.95, or 1.0.

[0007] According to an embodiment of the present application, the negative electrode active material has a specific surface area BET 1, the BET 1 is 0.6 m 2 / g to 2.0 m 2 / g, the negative electrode active material has a specific surface area BET 2 , and (BET 2 -BET 1 ) / BET 1 ≤ 1. In some embodiments, the BET 1 is 0.7 m 2 / g to 1.8 m 2 / g. In some embodiments, the BET 1 is 0.8 m 2 / g to 1.6 m 2 / g. In some embodiments, the BET 1 is 0.6 m 2 / g, 0.7 m 2 / g, 0.8 m 2 / g, 0.9 m 2 / g, 1.0 m 2 / g, 1.1 m 2 / g, 1.2 m 2 / g, 1.3 m 2 / g, 1.4 m 2 / g, 1.5 m 2 / g, 1.6 m 2 / g, 1.7 m 2 / g, 1.8 m 2 / g, 1.9 m 2 / g, or 2.0 m 2 / g.

[0008] According to embodiments of the present application, the negative electrode active material includes graphite particles that satisfy at least one of conditions (a) to (c):

[0009] (a) D 1 v50 is 10 μm to 25 μm;

[0010] (b) D 1 v90 and D 1 v10 satisfy D 1 v90 / D 1 v10 is less than 3.5;

[0011] (c) The graphite particles have a crystal size La along a horizontal direction of 160 nm to 165 nm and a crystal size Lc along a vertical direction of 30 nm to 32 nm by X-ray diffraction method.

[0012] In some embodiments, the graphite particles have a D1 v50 is 15 pm to 20 pm. In some embodiments, the graphite particles have a D 1 v50 is 10 pm, 12 pm, 15 pm, 18 pm, 20 pm, 22 pm, or 25 pm.

[0013] In some embodiments, the graphite particles have a D 1 v90 / D 1 v10 is less than 3.0. In some embodiments, the graphite particles have a D 1 v90 / D 1 v10 is less than 2.5. In some embodiments, the graphite particles have a D 1 v90 / D 1 v10 is less than 2.0.

[0014] In some embodiments, the graphite particles have a grain size La along a horizontal direction of 160 nm, 161 nm, 162 nm, 163 nm, 164 nm, or 165 nm, and a grain size Lc along a vertical direction of 30 nm, 31 nm, or 32 nm, as determined by X-ray diffraction.

[0015] According to another aspect of the present application, the present application provides an electrochemical device, comprising a negative electrode, the negative electrode including a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer including the negative electrode active material according to the present application.

[0016] According to embodiments of the present application, the negative electrode active material layer satisfies at least one of conditions (d) to (f):

[0017] (d) the negative electrode active material layer contains carbon elements and oxygen elements, and a ratio of a content of the carbon elements to a content of the oxygen elements is 2:3 to 990:1;

[0018] (e) a ratio C004 / C110 of a peak area C004 of a (004) plane and a peak area C110 of a (110) plane of the negative electrode active material layer, as determined from an X-ray diffraction pattern, is 5.7 to 18;

[0019] (f) a porosity of the negative electrode active material layer is 20% to 30%.

[0020] In some embodiments, the ratio of the content of the carbon element to the content of the oxygen element is 1:1 to 800:1. In some embodiments, the ratio of the content of the carbon element to the content of the oxygen element is 5:1 to 500:1. In some embodiments, the ratio of the content of the carbon element to the content of the oxygen element is 10:1 to 300:1. In some embodiments, the ratio of the content of the carbon element to the content of the oxygen element is 50:1 to 100:1. In some embodiments, the ratio of the content of the carbon element to the content of the oxygen element is 2:3, 1:1, 5:1, 10:1, 20:1, 50:1, 100:1, 200:1, 300:1, 400:1, 500:1, 600:1, 700:1, 800:1, 900:1, or 990:1.

[0021] In some embodiments, the C004 / C110 of the negative electrode active material layer is 6.0 to 10.0. In some embodiments, the C004 / C110 of the negative electrode active material layer is 7.0 to 8.0.

[0022] In some embodiments, the porosity of the negative electrode active material layer is 20% to 25%. In some embodiments, the porosity of the negative electrode active material layer is 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30%.

[0023] According to embodiments of the present application, the ratio C004' / C110' of the peak area of the (004) plane C004' and the peak area of the (110) plane C110' of the negative electrode active material obtained from the X-ray diffraction pattern of the electrochemical device in the full discharge state is 6.8 to 17.2. In some embodiments, the C004' / C110' of the negative electrode active material is 7.0 to 16.6. In some embodiments, the C004' / C110' of the negative electrode active material is 10.0 to 16.0. In some embodiments, the C004' / C110' of the negative electrode active material is 11.0 to 15.5.

[0024] According to embodiments of the present application, the negative electrode active material has a median particle size D a v50 under a pressure of 1 t, and the negative electrode active material has a median particle size D b v50 under a pressure of 1 t, and the negative electrode active material has a median particle size D b v50 / D a v50 is not less than 0.9. In some embodiments, the D b v50 / D a v50 is not less than 0.91. In some embodiments, the D b v50 / Da v50 is 0.92, 0.95, 0.98, or 1.0.

[0025] According to embodiments of the present application, the electrochemical device, in a full discharge state, the negative electrode active material has a median particle size D50 a v50 is 8 μm to 20 μm. In some embodiments, the negative electrode active material has a D50 a v50 is 10 μm to 15 μm. In some embodiments, the negative electrode active material has a D50 a v50 is 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, or 20 μm.

[0026] According to embodiments of the present application, the electrochemical device, in a full discharge state, the negative electrode active material has a specific surface area BET a , the negative electrode active material has a specific surface area BET b , and (BET b - BET a ) / BET a < 0.6.

[0027] According to yet another aspect of the present application, the present application provides an electronic device comprising the electrochemical device according to the present application.

[0028] Additional aspects and advantages of the present application will be described in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following description and drawings. BRIEF DESCRIPTION OF DRAWINGS

[0029] The accompanying drawings which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, will be described below.

[0030] Figure 1 The expansion percentage as a function of cycle number at 45°C is shown for lithium-ion batteries according to embodiments 22 of the present application and comparative example 1. DETAILED DESCRIPTION

[0031] Embodiments of the present application will be described in detail below. The embodiments described herein with reference to the accompanying drawings are illustrative in nature, diagrammatic and are provided to give an overall understanding of the present application. The embodiments of the present application should not be construed as limiting the present application.

[0032] In the DETAILED DESCRIPTION and in the claims, a list of items connected by the term "and" can mean one item from the list or a combination of items. For example, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, the phrase "at least one of A, B, and C" means only A; only B; only C; A and B (not C); A and C (not B); B and C (not A); or A, B, and C. Item A can include an element or a plurality of elements. Item B can include an element or a plurality of elements. Item C can include an element or a plurality of elements.

[0033] As used herein, "Dv50" means a particle size at which 50% by volume of the negative active material is accumulated from the small particle size side in a particle size distribution on a volume basis, i.e., the volume of the negative active material having a particle size smaller than this particle size accounts for 50% of the total volume of the negative active material.

[0034] As used herein, "Dv10" means a particle size at which 10% by volume of the negative active material is accumulated from the small particle size side in a particle size distribution on a volume basis, i.e., the volume of the negative active material having a particle size smaller than this particle size accounts for 10% of the total volume of the negative active material.

[0035] As used herein, "Dv90" means a particle size at which 90% by volume of the negative active material is accumulated from the small particle size side in a particle size distribution on a volume basis, i.e., the volume of the negative active material having a particle size smaller than this particle size accounts for 90% of the total volume of the negative active material.

[0036] The Dv50, Dv10, and Dv90 of the negative active material can be measured by a method known in the art, for example, using a laser particle size analyzer (e.g., Malvern particle size tester).

[0037] As used herein, "full discharge state" means a state reached by performing constant current discharge of an electrochemical device at a discharge current of 1C (i.e., a current value at which the theoretical capacity is completely discharged in 1 hour) to a voltage of 3.0 V in an environment of 25°C.

[0038] Unless otherwise specified, the electrochemical device of the present application is at 50% state of charge (SOC).

[0039] During the cycling of an electrochemical device (hereinafter exemplified by a lithium ion battery), the intercalation of lithium ions can cause the electrochemical device to swell, which is particularly severe at high temperatures. Increasing the degree of compounding of the negative active material (e.g., graphite particles) is one means of improving the cycling performance of a lithium ion battery. The primary particles of the negative active material can be compounded to form secondary particles by using a highly viscous binder or increasing the amount of the binder. The present application achieves a balance between high capacity and low thickness swelling during cycling of a lithium ion battery by improving the strength of the secondary particles.

[0040] In particular, the present application provides a negative active material, wherein the negative active material has a median particle size D 1 v50, the negative active material has a median particle size D 2 v50, and D 2 v50 / D 1 v50 is not less than 0.8. In some embodiments, the negative active material has a D 2 v50 / D 1 v50 is not less than 0.9. In some embodiments, the negative active material has a D 2 v50 / D 1 v50 is 0.8, 0.85, 0.9, 0.95, or 1.0. The negative active material has a D 2 v50 / D 1 v50 can reflect the rate of change of the particle size of the negative active material after being pressed. The greater the D 2 v50 / D 1 v50, the less the degree of particle breakage of the negative active material after being pressed, the fewer the number of broken particles, the lower the ratio of the broken particles to the total negative active material particles (i.e., the particle breakage rate), and the higher the strength of the negative active material, so that the negative active material has a reduced uncoated binder fracture surface resulting from the pressing, thereby reducing the formation of a solid electrolyte interface (SEI) film, which helps to improve the capacity, the initial efficiency, and the cycling thickness swelling rate of the lithium ion battery. When the D 2 v50 / D 1 v50 is within the above range, the negative active material has high strength, which helps to achieve a balance between high capacity and low cycling thickness swelling rate of the lithium ion battery.

[0041] The negative active material of the present application can be obtained by adding a highly viscous additive to the primary particles of the negative active material to obtain a mixture, sintering the mixture to obtain secondary particles of the negative active material, wherein the highly viscous additive comprises at least one of an oil-based pitch, a coal-based pitch, or a resinous polymer material, and the content of the highly viscous additive is not more than 30 wt% based on the total weight of the negative active material.

[0042] According to embodiments of the present application, the median particle size D 1 v50 is 10 pm to 25 pm. In some embodiments, the D 1 v50 is 15 pm to 20 pm. In some embodiments, the D 1 v50 is 10 pm, 12 pm, 15 pm, 18 pm, 20 pm, 22 pm, or 25 pm.

[0043] According to embodiments of the present application, the median particle size D 2 v50 is 8 pm to 20 pm. In some embodiments, the D 2 v50 is 10 pm to 15 pm. In some embodiments, the D 2 v50 is 8 pm, 10 pm, 12 pm, 15 pm, 18 pm, or 20 pm.

[0044] According to embodiments of the present application, the D 1 v90 and D 1 v10 satisfy D 1 v90 / D 1 v10 is less than 3.5. In some embodiments, the D 1 v90 / D 1 v10 is less than 3.0. In some embodiments, the D 1 v90 / D 1 v10 is less than 2.5. In some embodiments, the D 1 v90 / D 1 v10 is less than 2.0.

[0045] According to embodiments of the present application, the negative active material includes grains, a grain size La of the grains in a horizontal direction is 160 nm to 165 nm, and a grain size Lc of the grains in a vertical direction is 30 nm to 32 nm by X-ray diffraction method. In some embodiments, the negative active material includes grains, a grain size La of the grains in a horizontal direction is 161 nm to 164 nm, and a grain size Lc of the grains in a vertical direction is 30.5 nm to 31.5 nm by X-ray diffraction method. In some embodiments, a grain size La of the graphite particles in a horizontal direction is 160 nm, 161 nm, 162 nm, 163 nm, 164 nm, or 165 nm, and a grain size Lc of the graphite particles in a vertical direction is 30 nm, 31 nm, or 32 nm by X-ray diffraction method.

[0046] According to embodiments of the present application, the negative active material comprises graphite particles having the same D 1 v50, D 2 v50, D 1 v90, and D 1 v10. In some embodiments, the negative active material is graphite particles.

[0047] According to embodiments of the present application, the negative active material has a specific surface area BET 1 , the BET 1 is 0.6 m 2 / g to 2.0 m 2 / g, the negative active material has a specific surface area BET 2 under 1 t pressure, and (BET 2 - BET 1 ) / BET 1 ≤ 1. When the negative active material satisfies (BET 2 - BET 1 ) / BET 1 ≤ 1, the specific surface area growth rate of the negative active material after being pressed is not greater than 100% compared to the negative active material that is not pressed. The smaller the specific surface area growth rate of the negative active material, the higher the strength of the negative active material, the less uncoated binder section of the negative active material is generated by the pressing, and the less solid electrolyte interface (SEI) film is formed, which helps to improve the capacity, the first efficiency, and the cycle thickness expansion rate of the lithium ion battery.

[0048] In some embodiments, the BET 1 is 0.7 m 2 / g to 1.8 m 2 / g. In some embodiments, the BET 1 is 0.8 m 2 / g to 1.6 m 2 / g. In some embodiments, the BET 1 is 0.6 m 2 / g, 0.7 m 2 / g, 0.8 m 2 / g, 0.9 m 2 / g, 1.0 m 2 / g, 1.1 m 2 / g, 1.2 m 2 / g, 1.3 m 2 / g, 1.4 m 2 / g, 1.5 m 2 / g, 1.6 m 2 / g, 1.7 m 2 / g, 1.8 m 2 / g, 1.9 m 2 / g or 2.0 m 2 / g.

[0049] According to embodiments of the present application, the specific surface area BET of the negative active material under 1 t pressure is from 1.0 m 2 / g to 4.0 m 2 / g. In some embodiments, the specific surface area BET of the negative active material is from 1.5 m 2 / g to 3.0 m 2 / g. In some embodiments, the specific surface area BET of the negative active material is from 1.5 m 2 / g to 3.0 m 2 / g. In some embodiments, the specific surface area BET of the negative active material is from 1.5 m 2 / g to 3.0 m 2 / g, 1.5 m 2 / g, 2 m 2 / g, 2.5 m 2 / g, 3 m 2 / g, 3.5 m 2 / g or 4.0 m 2 / g.

[0050] The specific surface area of the negative active material can be obtained by the following method:

[0051] The specific surface area of the negative active material is measured by nitrogen adsorption / desorption method using a specific surface area analyzer (e.g. Tristar II 3020M): the negative active material sample is dried in a vacuum drying oven, and then loaded into a sample tube for measurement in the analyzer. The present application also provides an electrochemical device comprising a negative electrode, the negative electrode comprising a negative electrode current collector and a negative active material layer.

[0052] Negative electrode

[0053] In the electrochemical device of the present application, the negative active material layer comprises the negative active material according to the present application.

[0054] According to embodiments of the present application, the negative active material layer includes carbon elements and oxygen elements, and a ratio of a content of the carbon elements to a content of the oxygen elements is 2:3 to 990:1. In some embodiments, the ratio of the content of the carbon elements to the content of the oxygen elements is 1:1 to 800:1. In some embodiments, the ratio of the content of the carbon elements to the content of the oxygen elements is 5:1 to 500:1. In some embodiments, the ratio of the content of the carbon elements to the content of the oxygen elements is 10:1 to 300:1. In some embodiments, the ratio of the content of the carbon elements to the content of the oxygen elements is 50:1 to 100:1. In some embodiments, the ratio of the content of the carbon elements to the content of the oxygen elements is 2:3, 1:1, 5:1, 10:1, 20:1, 50:1, 100:1, 200:1, 300:1, 400:1, 500:1, 600:1, 700:1, 800:1, 900:1, or 990:1. When the ratio of the content of the carbon elements to the content of the oxygen elements in the negative active material layer is within the above range, the particle size and the graphitization degree of the negative active material particles are within a suitable range, which helps to improve the capacity and the cycle thickness expansion rate of the lithium ion battery.

[0055] According to embodiments of the present application, in the negative active material layer, a ratio C004 / C110 of a peak area C004 of a (004) plane and a peak area C110 of a (110) plane of the negative active material layer determined from an X-ray diffraction pattern is 5.7 to 11.2. The C004 / C110 value of the negative active material layer determined from the X-ray diffraction pattern can reflect the anisotropy of the negative active material particles. The smaller the C004 / C110 value, the smaller the anisotropy, which helps to improve the cycle thickness expansion rate of the lithium ion battery. In some embodiments, the C004 / C110 of the negative active material layer is 6.0 to 10.0. In some embodiments, the C004 / C110 of the negative active material layer is 7.0 to 8.0.

[0056] According to embodiments of the present application, the negative active material layer has a porosity of 20% to 30%. In some embodiments, the negative active material layer has a porosity of 20% to 25%. In some embodiments, the negative active material layer has a porosity of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30%.

[0057] According to embodiments of the present application, the ratio C004' / C110' of the peak area C004' of the (004) plane and the peak area C110' of the (110) plane of the negative electrode active material in the full discharge state is 6.8 to 17.2, as determined by X-ray diffraction pattern. In some embodiments, the C004' / C110' of the negative electrode active material is 7.0 to 16.5. In some embodiments, the C004' / C110' of the negative electrode active material is 10.0 to 15.0. In some embodiments, the C004' / C110' of the negative electrode active material is 12.0 to 14.0. When the C004' / C110' of the negative electrode active material, the anisotropy of the negative electrode active material particles in the electrochemical device in the full discharge state is still low, which can reflect that the negative electrode active material has high strength.

[0058] According to embodiments of the present application, the negative electrode active material in the full discharge state has a median particle size D a v50, the negative electrode active material has a median particle size D b v50 under a pressure of 1 t, and D b v50 / D a v50 is not less than 0.9. The D b v50 / D a v50 can reflect the degree of particle breakage of the negative electrode active material in the electrochemical device in the full discharge state after being pressed. The D b v50 / D a The greater the D b v50 / D a v50 is within the above range, the negative electrode active material in the electrochemical device in the full discharge state still has high strength, which helps to further improve the initial efficiency of the lithium ion battery and reduce the cycle thickness expansion rate thereof. In some embodiments, the D b v50 / D a v50 is 0.92, 0.95, 0.98, or 1.0.

[0059] According to embodiments of the present application, the negative electrode active material in the full discharge state has a median particle size D a v50 is 8 μm to 20 μm. In some embodiments, the D a v50 is 10 μm to 15 μm. In some embodiments, the Da v50 is 8 pm, 10 pm, 12 pm, 15 pm, 18 pm, or 20 pm.

[0060] According to embodiments of the present application, the electrochemical device in a full discharge state, the negative electrode active material has a median particle size D50 under 1 t pressure b v50 is 7.2 pm to 18 pm. In some embodiments, the negative electrode active material has a D50 under 1 t pressure b v50 is 8 pm to 15 pm. In some embodiments, the negative electrode active material has a D50 under 1 t pressure b v50 is 7.2 pm, 8 pm, 10 pm, 12 pm, 15 pm, or 18 pm.

[0061] According to embodiments of the present application, the electrochemical device in a full discharge state, the negative electrode active material has a specific surface area BET a , the negative electrode active material has a specific surface area BET b under 1 t pressure, and (BET b -BET a ) / BET a < 0.6. When the negative electrode active material satisfies (BET b -BET a ) / BET a < 0.6, the specific surface area growth rate of the negative electrode active material after being pressed is less than 60% compared to the negative electrode active material without being pressed. When the specific surface area of the negative electrode active material in the electrochemical device in a full discharge state satisfies the above relationship, it can reflect that the strength of the negative electrode active material is high.

[0062] According to embodiments of the present application, the electrochemical device in a full discharge state, the negative electrode active material has a specific surface area BET a of 0.6 m 2 / g to 2.0 m 2 / g. In some embodiments, the negative electrode active material has a BET a of 0.8 m 2 / g to 1.5 m 2 / g. In some embodiments, the negative electrode active material has a BET a of 1.0 m 2 / g to 1.2 m 2 / g. In some embodiments, the negative electrode active material has a BET a of 0.6 m 2 / g, 0.7 m 2 / g, 0.8 m 2 / g, 0.9 m 2 / g, 1.0 m 2 / g, 1.1 m2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g or 2.0m 2 / g.

[0063] According to an embodiment of this application, in the fully discharged state, the specific surface area BET of the negative electrode active material under a pressure of 1t is... b It is 0.96m 2 / g to 3.2m 2 / g. In some embodiments, the BET of the negative electrode active material 2 1.0m 2 / g to 3.0m 2 / g. In some embodiments, the BET of the negative electrode active material 2 1.5m 2 / g to 2.0m 2 / g. In some embodiments, the BET of the negative electrode active material 2 It is 0.96m 2 / g, 1.0m 2 / g, 1.2m 2 / g, 1.5m 2 / g, 1.8m 2 / g, 2.0m 2 / g, 2.2m 2 / g, 2.5m 2 / g, 2.8m 2 / g, 3.0m 2 / g or 3.2m 2 / g.

[0064] According to embodiments of this application, the negative current collector used in this application may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0065] According to embodiments of the present application, the negative electrode further includes a conductive layer. In some embodiments, the conductive material of the conductive layer can include any conductive material as long as it does not cause chemical changes. Non-limiting examples of the conductive material include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanotube, graphene, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., such as copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0066] According to embodiments of the present application, the negative electrode further includes a binder selected from at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, or nylon, etc.

[0067] According to embodiments of the present application, the negative electrode can be manufactured by any method known in the art. In some embodiments, the negative electrode can be manufactured by adding a binder and a solvent to the negative electrode active material and, if necessary, adding a thickening agent, a conductive material, a filler material, etc., forming a slurry, coating the slurry on a current collector, and drying and pressing the same.

[0068] According to embodiments of the present application, when the negative electrode includes an alloy material, the negative electrode active material layer can be formed using a vapor deposition method, a sputtering method, a plating method, etc.

[0069] Positive electrode

[0070] The positive electrode includes a positive electrode current collector and a positive electrode active material disposed on the positive electrode current collector. The specific type of the positive electrode active material is not particularly limited and can be selected as desired.

[0071] According to embodiments of the present application, the positive electrode active material includes a compound that reversibly intercalates and deintercalates lithium ions. In some embodiments, the positive electrode active material can include a composite oxide containing lithium and at least one element selected from cobalt, manganese, and nickel. In yet other embodiments, the positive electrode active material is selected from one or more of lithium cobaltate (LiCoO2), lithium nickel manganese cobalt ternary material, lithium manganate (LiMn2O4), lithium nickel manganate (LiNi 0.5 Mn 1.5 O4), lithium iron phosphate (LiFePO4).

[0072] According to embodiments of the present application, the positive electrode active material layer can have a coating layer on the surface, or can be mixed with another compound having a coating layer. The coating layer can include at least one coating element compound selected from oxides of a coating element, hydroxides of a coating element, oxyhydroxides of a coating element, oxycarbonates of a coating element, and hydroxycarbonates of a coating element. The compound used for the coating layer can be amorphous or crystalline. The coating element contained in the coating layer can include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, F, or mixtures thereof. The coating layer can be applied by any method, as long as the method does not adversely affect the performance of the positive electrode active material. For example, the method can include any coating method well known to one of ordinary skill in the art, such as spraying, dipping, etc.

[0073] According to embodiments of the present application, the positive electrode active material layer further includes a binder, and optionally further includes a positive electrode conductive material.

[0074] 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. Non-limiting examples of the binder include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, nylon, etc.

[0075] The positive electrode active material layer includes a positive electrode conductive material, thereby imparting electrical conductivity to the electrode. The positive electrode conductive material can include any conductive material, as long as it does not cause chemical changes. Non-limiting examples of the positive electrode conductive material include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0076] The positive electrode current collector for the electrochemical device according to the present application can be aluminum (Al), but is not limited thereto.

[0077] Electrolyte

[0078] The electrolyte that can be used in embodiments of the present application can be an electrolyte known in the art. The electrolyte in the electrolyte that can be used in embodiments of the present application includes, but is not limited to, inorganic lithium salts such as LiClO4, LiAsF6, LiPF6, LiBF4, LiSbF6, LiSO3F, LiN(FSO2)2, and the like; fluorine-containing organic lithium salts such as LiCF3SO3, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,3-hexafluoropropanedisulfonimide lithium, cyclic 1,2-tetrafluoroethane disulfonimide lithium, LiN(CF3SO2)(C4F9SO2), LiC(CF3SO2)3, LiPF4(CF3)2, LiPF4(C2F5)2, LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2; dicarboxylic acid complex-containing lithium salts such as lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tris(oxalato)phosphate, lithium difluorobis(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, and the like. In addition, the above electrolytes can be used singly, or two or more kinds can be used simultaneously. For example, in some embodiments, the electrolyte includes a combination of LiPF6and LiBF4. In some embodiments, the electrolyte includes a combination of an inorganic lithium salt such as LiPF6or LiBF4and a fluorine-containing organic lithium salt such as LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, and the like.

[0079] In some embodiments, the concentration of the electrolyte is in the range of 0.8 mol / L to 3 mol / L, such as in the range of 0.8 mol / L to 2.5 mol / L, in the range of 0.8 mol / L to 2 mol / L, in the range of 1 mol / L to 2 mol / L, and for example, 1 mol / L, 1.15 mol / L, 1.2 mol / L, 1.5 mol / L, 2 mol / L, or 2.5 mol / L.

[0080] The solvent in the electrolyte that can be used in embodiments of the present application includes, but is not limited to, a carbonate compound, an ester-based compound, an ether-based compound, a ketone-based compound, an alcohol-based compound, an aprotic solvent, or a combination thereof.

[0081] Examples of the carbonate compound include, but are not limited to, a chain carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound, or a combination thereof.

[0082] Examples of the chain carbonate compound include, but are not limited to, diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate compound are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof. Examples of the fluoro carbonate compound are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, trifluoromethyl ethylene carbonate, and combinations thereof.

[0083] Examples of the ester-based compound include, but are not limited to, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decalactone, valerolactone, methylvaleronolactone, hexalactone, methyl formate, and combinations thereof.

[0084] Examples of the ether-based compound include, but are not limited to, dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

[0085] Examples of the ketone-based compound include, but are not limited to, cyclohexanone.

[0086] Examples of the alcohol-based compound include, but are not limited to, ethanol and isopropanol.

[0087] Examples of the aprotic solvent include, but are not limited to, dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, formamide, dimethylformamide, acetonitrile, nitromethane, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphates, and combinations thereof.

[0088] Separator

[0089] In some embodiments, a separator is provided between the positive electrode and the negative electrode to prevent short circuiting. The material and shape of the separator that can be used in the embodiments of the present application are not particularly limited and can be any of the techniques disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance formed of a material stable to the electrolyte of the present application, etc.

[0090] For example, the separator film can include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, a film, or a composite film having a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and 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 used. The porous structure can improve the heat resistance, oxidation resistance, and electrolyte impregnation of the separator film, and enhance the adhesion between the separator film and the electrode sheet.

[0091] The surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

[0092] The inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from one or a combination of several of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from one or a combination of several of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0093] The polymer layer includes a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0094] Application

[0095] The electrochemical device according to the present application includes any device in which an electrochemical reaction occurs, and specific examples thereof include primary batteries, secondary batteries, fuel cells, solar cells, or capacitors of all kinds. In particular, the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0096] The present application also provides an electronic device including the electrochemical device according to the present application.

[0097] The use of the electrochemical device of the present application is not particularly limited, and it can be used for any electronic device known in the art. In some embodiments, the electrochemical device of the present application can be used for, but not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, portable telephones, portable facsimile machines, portable copying machines, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, hand-held cleaners, portable CD players, mini-disc players, transceivers, electronic organizers, calculators, memory cards, portable audio players, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting appliances, toys, game machines, timepieces, power tools, flashlights, cameras, home-use large storage batteries, and lithium-ion capacitors, etc.

[0098] The preparation of lithium-ion batteries is described below with examples of lithium-ion batteries and in connection with specific embodiments, and those skilled in the art will understand that the preparation methods described in the present application are only examples, and any other suitable preparation method is within the scope of the present application.

[0099] Example

[0100] The following describes the performance evaluation of examples and comparative examples of lithium-ion batteries according to the present application.

[0101] I. Preparation of lithium-ion batteries

[0102] 1. Preparation of the negative electrode

[0103] The coke was crushed to have a median particle size Dv50 in the range of 3 μm to 10 μm, and then a binder pitch having a softening point of 100-300°C was added (the amount of pitch added was 15 wt% in Examples 1-16 and 18-39, and the amount of pitch added was 5 wt% in Example 17). The mixture of the two was put into a granulation device, and granulated while being continuously stirred and heated to 500°C to 1000°C, and then subjected to a graphitization process (in which the graphitization temperature was controlled to be 2000°C to 3500°C), to obtain the graphite negative electrode active material used in the following examples.

[0104] The coke was crushed to have a median particle size Dv50 in the range of 3 μm to 10 μm, and put into a granulation device, and granulated while being continuously stirred and heated to 500°C to 1000°C, and then subjected to a graphitization process (in which the graphitization temperature was controlled to be 2000°C to 3500°C), to obtain the graphite negative electrode active material used in Comparative Example 1.

[0105] The graphite negative electrode active material prepared above, styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) are dispersed in deionized water according to a weight ratio of 97.7:1.2:1.1, and are mixed uniformly by stirring. A negative electrode slurry is obtained. The negative electrode slurry is coated on a negative electrode current collector, dried, cold-pressed to form a negative electrode active material layer, and then cut and tabbed to obtain a negative electrode.

[0106] The graphite particles of different particle sizes can be obtained by crushing and classifying the raw material using any known technique.

[0107] 2. Preparation of a positive electrode

[0108] Lithium cobalt oxide (LiCoO2), acetylene black and polyvinylidene fluoride (PVDF) are mixed uniformly by stirring in an appropriate amount of N-methyl pyrrolidone (NMP) according to a weight ratio of 96:2:2. The mixture is coated on a positive electrode current collector aluminum foil, dried, cold-pressed to form a positive electrode active material layer, and then cut and tabbed to obtain a positive electrode.

[0109] 3. Preparation of an electrolyte

[0110] Ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) are mixed in a weight ratio of 1:1:1 under a dry argon atmosphere, and LiPF6 is added and mixed uniformly. 3% of fluoroethylene carbonate is added, and the mixture is mixed uniformly to obtain an electrolyte, wherein the concentration of LiPF6 is 1.15 mol / L.

[0111] 4. Preparation of a separator

[0112] A 12 μm thick porous polyethylene (PE) polymer film is used as a separator.

[0113] 5. Preparation of a lithium ion battery

[0114] The positive electrode, the separator and the negative electrode are stacked in order, with the separator between the positive electrode and the negative electrode to play a separating role. The battery is then wound, tabbed, placed in an outer packaging foil aluminum plastic film, and injected with the electrolyte prepared above. The battery is subjected to processes such as vacuum packaging, standing, formation, shaping and capacity testing to obtain a lithium ion battery.

[0115] II. Test methods

[0116] 1. Test method for particle size of a negative electrode active material

[0117] The particle size of the negative electrode active material is measured using a Malvern particle size tester. The negative electrode active material sample is dispersed in a dispersant ethanol, and after ultrasonic treatment for 30 minutes, the sample is added to the Malvern particle size tester to test the Dv50, Dv10 and Dv90 of the negative electrode active material.

[0118] 2. Test method for specific surface area of negative active material

[0119] The specific surface area of the negative active material was measured by nitrogen adsorption / desorption method using a specific surface area analyzer (Tristar II 3020M) : The negative active material sample was dried in a vacuum drying oven, and then loaded into a sample tube to be measured in the analyzer.

[0120] 3. Test method for gram capacity of lithium ion battery

[0121] The lithium ion battery was discharged at 0.05C to 5.0 mV, at 50 μA to 5.0 mV, at 10 μA to 5.0 mV, and charged at 0.1C to 2.0 V, and the capacity of the lithium ion battery at this time was recorded as the gram capacity. 0.05C refers to the current value at 0.05 times the design gram capacity, and 0.1C refers to the current value at 0.1 times the design gram capacity.

[0122] 4. Test method for cycle thickness expansion rate of lithium ion battery

[0123] The thickness of the lithium ion battery at the initial half-charged state was measured at 45°C using a micrometer, and was recorded as H0. The lithium ion battery was charged and discharged at 1.5C rate for 500 cycles, and the thickness of the lithium ion battery at the fully charged state was measured after every 50 cycles, and was recorded as H n . The cycle thickness expansion rate of the lithium ion battery was calculated by the following equation:

[0124] Cycle thickness expansion rate corresponding to cycle number = (H n - H0) / H0 x 100%.

[0125] 5. Test method for initial efficiency of lithium ion battery

[0126] The lithium ion battery was charged at 0.5C to 4.45 V, and the initial charge capacity C was recorded, and then discharged at 0.5C to 3.0 V, and the discharge capacity D was recorded. The initial efficiency CE of the lithium ion battery was calculated by the following equation:

[0127] CE = D / C.

[0128] III. Test results

[0129] Table 1 shows the effect of the characteristics of the negative active material during the preparation of the negative active material on the gram capacity and cycle thickness expansion rate of the lithium ion battery.

[0130] Table 1

[0131]

[0132] As shown in Comparative Example 1, when no high-viscosity binder is added in the preparation of the negative electrode active material, the negative electrode active material is primary particles without being compounded to form secondary particles, and the obtained lithium ion battery has a relatively high gram capacity, but the anisotropy of the negative electrode active material is relatively large, the cycle thickness expansion rate of the lithium ion battery is relatively high, and the overall performance is relatively poor.

[0133] As shown in Examples 1-20, when an appropriate amount of high-viscosity binder is added in the preparation of the negative electrode active material, the D 2 v50 / D 1 v50 is not less than 0.8, the lithium ion battery has a relatively high gram capacity and a relatively low cycle thickness expansion rate, and a balance between high gram capacity and low cycle thickness expansion rate is achieved.

[0134] Under a certain content of the high-viscosity binder, when the median particle size D 1 v50 of the negative electrode active material gradually increases in the range of 10 μm to 25 μm, the median particle size D 2 v50 of the negative electrode active material under 1 t pressure gradually decreases, and the cycle thickness expansion rate of the lithium ion battery gradually decreases. 1 v50 of the negative electrode active material gradually decreases, the (BET 2 v50 / D 1 v50 decreases, the (BET 2 -BET 1 ) / BET 1 increases, the weight ratio of carbon element to oxygen element increases, the gram capacity of the lithium ion battery increases, and the cycle thickness expansion rate decreases. When the specific surface area of the negative electrode active material satisfies BET 1 When the specific surface area of the negative electrode active material is in the range of 0.6 m 2 / g to 2.0 m 2 / g, (BET 2 -BET 1 ) / BET 1 ≤ 1, and / or the content ratio of carbon element to oxygen element in the negative electrode active material layer is in the range of 2:3 to 990:1, a further balance between high gram capacity and low cycle thickness expansion rate can be achieved.

[0135] Table 2 shows the D 1 v90 / D 1 v10 and C004 / C110 of the negative electrode active material. Examples 21-39 are consistent with the conditions of Example 8 except for the parameters listed in Table 2.

[0136] Table 2

[0137]

[0138] The results show that when the D 1v90 / D 1 When v10 is less than 3.5, the initial efficiency of the lithium-ion battery is significantly increased. When the D 1 v90 / D 1 When v10 gradually decreases in the range of less than 3.5, the initial efficiency of the lithium-ion battery changes little, and the cycle thickness expansion rate gradually decreases. When the C004 / C110 of the negative electrode active material layer gradually decreases in the range of 5.7 to 18, the grain size La of the graphite particles decreases, the Lc increases, the porosity increases, the cycle thickness expansion rate of the lithium-ion battery gradually decreases, and the initial efficiency slightly decreases. Overall, when the negative electrode active material satisfies D 1 v90 / D 1 When v10 is less than 3.5, C004 / C110 is in the range of 5.7 to 18, La is 160 nm to 165 nm, Lc is 30 nm to 32 nm, and / or the porosity is 20% to 30%, the lithium-ion battery has a balanced initial efficiency and cycle thickness expansion rate.

[0139] Table 3 shows the influence of the properties of the negative electrode active material of the lithium-ion battery in the full discharge state on the initial efficiency and cycle thickness expansion rate of the lithium-ion battery.

[0140] Table 3

[0141]

[0142] The results show that, in the full discharge state of the lithium-ion battery, the D b v50 / D a v50 and the (BET b -BET a ) / BET a will affect the improvement of the initial efficiency of the lithium-ion battery, and will also affect the cycle thickness expansion rate of the lithium-ion battery.

[0143] Figure 1 The cycle thickness expansion rates of the lithium-ion batteries of Example 8 and Comparative Example 1 are shown. The results show that, compared with Comparative Example 1, the lithium-ion battery of Example 8 has a significantly lower cycle thickness expansion rate. The difference between the cycle thickness expansion rates of the two becomes greater as the cycle number increases.

[0144] References throughout this specification to "an embodiment", "particular embodiments", "one embodiment", "another embodiment", "certain embodiments", "some embodiments", "one example" or "an example" mean that a particular feature, structure, material or characteristic is included in at least one embodiment or example of the present application. Thus, the appearances of the phrases such as "in some embodiments", "in an embodiment", "in one embodiment", "in another embodiment", "in one example", "in a particular example" or "in some examples" in various places throughout this specification are not necessarily referring to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples.

[0145] While the illustrative embodiments have been described and illustrated, it will be understood by those skilled in the art that the above-described embodiments are not the only ways in which the present application can be practiced. Changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the application.

Claims

1. An electrochemical device comprising a negative electrode, the negative electrode including a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer including a negative electrode active material; The negative electrode active material has a median particle diameter D 1 v50, the negative electrode active material has a median particle diameter D 2 v50, and D 2 v50 / D 1 v50 is less than 1.0 and not less than 0.8, and the negative electrode active material includes graphite particles having a crystal grain size La in a horizontal direction of 160 nm to 165 nm and a crystal grain size Lc in a vertical direction of 30 nm to 32 nm by an X-ray diffraction method; and the graphite particles satisfy at least one of conditions (a) to (b): (a) D 1 v50 is from 10 to 25 μm; (b) D 1 v90 and D 1 v10 satisfies D 1 v90 / D 1 v10 is less than 3.5; wherein the electrochemical device further satisfying at least one of conditions (c) to (f): (c) the ratio C004’ / C110’ of the peak area C004’ of the 004 plane and the peak area C110’ of the 110 plane of the negative electrode active material layer determined from an X-ray diffraction pattern is 6.8 to 17.2 in a full discharge state; (d) the negative active material has a median particle size D a v50, the negative active material has a median particle size D b v50, and D b v50 / D a v50 is not less than 0.9; (e) the electrochemical device, in a full state of charge, has a median particle size D50 of the negative electrode active material of 8 pm to 20 pm a v50 is 8 pm to 20 pm; (f) said electrochemical device, in full discharge state, said negative electrode active material has a specific surface area BET a , said negative electrode active material has a specific surface area BET b after being pressed under a pressure of 1 t, and (BET b -BET a ) / BET a < 0.

6. wherein the full discharge state refers to a state reached by performing constant current discharge of the electrochemical device at a discharge current of 1 C to a voltage of 3.0 V in an environment at 25°C.

2. The electrochemical device according to claim 1, wherein the negative electrode active material has a specific surface area BET 1 , the BET 1 is 0.6 m 2 / g to 2.0 m 2 / g, the negative electrode active material has a specific surface area BET 2 after being pressed at 1 t of pressure, and (BET 2 -BET 1 ) / BET 1 ≤ 1. 3.The electrochemical device according to claim 1 or 2, wherein the negative electrode active material layer satisfies at least one of conditions (h) to (j): (h) the negative electrode active material layer contains carbon elements and oxygen elements, and the weight ratio of the content of the carbon elements to the content of the oxygen elements is 2:3 to 990:1; (i) the ratio C004 / C110 of the peak area C004 of the 004 plane and the peak area C110 of the 110 plane of the negative electrode active material layer determined from an X-ray diffraction pattern is 5.7 to 18; (j) the porosity of the negative electrode active material layer is 20% to 30%. 4.An electronic device comprising the electrochemical device according to any one of claims 1 to 3.

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