CN115321517B

CN115321517B - Negative electrode active material, negative electrode plate comprising same, electrochemical device and electricity utilization device

Info

Publication number: CN115321517B
Application number: CN202211248856.1A
Authority: CN
Inventors: 易政; 郑子桂; 谭福金; 谢远森
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2022-10-12
Filing date: 2022-10-12
Publication date: 2023-03-28
Anticipated expiration: 2042-10-12
Also published as: CN115321517A

Abstract

The application provides a negative electrode active material, a negative electrode plate comprising the same, an electrochemical device and an electric device. The negative active material includes hard carbon containing hard carbon particles having micropores with a maximum diameter d [ mu ] m of 5.0 [ mu ] m or less, the number of the hard carbon particles having micropores being greater than or equal to 50% based on the total number of the hard carbon particles. The energy density of the electrochemical device can be improved.

Description

Negative electrode active material, negative electrode plate comprising same, electrochemical device and electric device

Technical Field

The application belongs to the technical field of electrochemical cells, and particularly relates to a negative active material, a negative pole piece comprising the same, an electrochemical device and an electric device.

Background

Secondary batteries represented by lithium ion batteries have outstanding characteristics of high energy density, long cycle life, no pollution, no memory effect and the like. As a clean energy source, the application of secondary batteries has been gradually popularized from electronic products to the field of large-scale devices such as electric vehicles and the like to adapt to the sustainable development strategy of environment and energy. Thus, higher demands are also made on the energy density of the secondary battery.

At present, the commercial lithium ion battery negative electrode material is mainly graphite. Graphite has the advantages of high conductivity, high stability and the like. However, the theoretical capacity of graphite is about 372mAh/g, and in recent years, the theoretical capacity has been developed to the upper limit, and it is difficult to further increase the energy density of a lithium ion battery using graphite as a negative electrode material.

In addition, because of the scarcity of the related active material resources of the lithium ion battery, the battery cost is always high, and the battery faces the severe problems of the exhaustion of the related resources and the like, and the development of other low-cost metal ion secondary battery systems is urgently needed. Sodium ion batteries have become the popular research direction in recent years due to their advantages of low cost, abundant resources, and being similar to lithium ion battery manufacturing process. However, the energy density of the sodium ion battery is always different from that of the lithium ion battery due to the lower gram capacity and voltage platform of the current sodium ion battery cathode material, and thus the commercial application cannot be really realized.

Therefore, the development of a negative active material to increase the energy density of a secondary battery is significant for the development of the secondary battery.

Disclosure of Invention

In view of the above problems in the prior art, the present application provides a negative active material, a negative electrode sheet including the same, an electrochemical device, and an electric device, where the negative active material has a high low-voltage plateau capacity and a high reversible capacity, and can improve the energy density of the electrochemical device.

A first aspect of the present application provides an anode active material comprising hard carbon including hard carbon particles having micropores whose maximum diameter d μm or less is 5.0 μm,

the number of the hard carbon particles having micropores accounts for a ratio Q of 50% or more based on the total number of the hard carbon particles in any sufficiently large region in the negative electrode active material.

In any embodiment, 1.0 μm. Ltoreq. D μm. Ltoreq.5.0 μm.

In any embodiment, the anode active material satisfies:

and C is ₁ ≥256，

Wherein, C ₁ mAh/g represents that metallic lithium is used as a counter electrode, and the negative electrode active material is at 0V (vs Li) ⁺ /Li) to 0.2V (vs Li) ⁺ -delithiation capacity between/Li); c ₂ mAh/g represents that metallic lithium is used as a counter electrode, and the negative electrode active material is at 0V (vs Li) ⁺ (V) Li) to 1.2V (vs Li) ⁺ /Li) delithiation capacity.

In any embodiment, the anode active material satisfies:

and C is ₃ ≥180，

Wherein, C ₃ mAh/g represents that the metal sodium is used as a counter electrode, and the negative active material is at 0V (vs Na) ⁺ Na) to 0.2V (vs Na) ⁺ Na) sodium removal capacity; c ₄ mAh/g represents that the metal sodium is used as a counter electrode, and the negative active material is at 0V (vs Na) ⁺ Na) to 1.2V (vs Na) ⁺ Na) sodium removal capacity.

In any embodiment, the hard carbon particles have a particle size D _V 50 is 3 μm to 15 μm.

Optionally, the hard carbon particles have a particle size D _V 99 is 10 μm to 45 μm.

Optionally, the average molar ratio of hydrogen atoms to carbon atoms, H/C, in the hard carbon particles is from 0.02 to 0.2.

A second aspect of the present application is a method for producing the anode active material of the first aspect, comprising the steps of:

s1, uniformly mixing amylase and/or saccharifying enzyme with a water dispersion of starch, and carrying out enzymolysis reaction on the starch at an enzymolysis temperature and an enzymolysis pH value to obtain a precursor of the negative active material;

s2, placing the dried anode active material precursor in an inert atmosphere, calcining at 400-700 ℃ for 1.5-2.5 h, and crushing to obtain first particles;

s3, calcining the first particles for 1.5 to 2.5 hours at 900 to 1300 ℃ in an inert atmosphere to obtain second particles;

and S4, placing the second particles in a methane atmosphere, and performing vapor deposition at 850-950 ℃ to obtain the negative active material.

The third aspect of the present application provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises the negative electrode active material of the first aspect, or the negative electrode active material prepared by the method of the second aspect.

In any embodiment, the anode active material layer has a single-point raman spectrum satisfying: 1 < I _D /I _G Less than or equal to 1.3, wherein, I _D The representation is located at 1320cm ^-1 To 1370cm ^-1 Characteristic peak between, I _G Indicating a position of 1570cm ^-1 To 1620cm ^-1 Characteristic peaks in between.

The fourth aspect of the present application is an electrochemical device comprising the negative electrode sheet of the third aspect.

A fifth aspect of the present application is an electric device including the electrochemical device of the fourth aspect.

Drawings

FIG. 1 is a cross-sectional Scanning Electron Microscope (SEM) image of example 1-2 of the present application, at 1000 times magnification.

FIG. 2 is a cross-sectional Scanning Electron Microscope (SEM) image of example 1-2 of the present application at a magnification of 5000.

FIG. 3 is a Raman test ID/IG statistical box line for examples 1, 2 and 5 and comparative example 1 of the present application.

Fig. 4 is a charge-discharge curve diagram of button cell batteries of examples 2-8 of the present application.

Detailed Description

Embodiments of the negative electrode active material, and a negative electrode sheet, an electrochemical device, and an electric device including the same according to the present invention are specifically described below with reference to the drawings as appropriate. But a detailed description thereof will be omitted. For example, detailed descriptions of already known matters and repetitive descriptions of actually the same configurations may be omitted. This is to avoid unnecessarily obscuring the following description, and to facilitate understanding by those skilled in the art. The drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

The "ranges" disclosed herein are defined in terms of lower limits and upper limits, with a given range being defined by a selection of one lower limit and one upper limit that define the boundaries of the particular range. Ranges defined in this manner may or may not include endpoints and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3,4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise stated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 to 5" have been listed herein, and "0 to 5" is only a shorthand representation of the combination of these numbers. In addition, when a parameter is an integer of 2 or more, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12, or the like.

All embodiments and alternative embodiments of the present application may be combined with each other to form new solutions, if not specifically stated.

All technical and optional features of the present application may be combined with each other to form new solutions, if not otherwise specified.

All steps of the present application may be performed sequentially or randomly, preferably sequentially, if not specifically stated. For example, the method comprises steps (a) and (b), meaning that the method may comprise steps (a) and (b) performed sequentially, and may also comprise steps (b) and (a) performed sequentially. For example, reference to the process further comprising step (c) means that step (c) may be added to the process in any order, for example, the process may comprise steps (a), (b) and (c), may also comprise steps (a), (c) and (b), may also comprise steps (c), (a) and (b), etc.

The terms "comprises" and "comprising" as used herein mean either open or closed unless otherwise specified. For example, the terms "comprising" and "comprises" may mean that other components not listed may also be included or included, or that only listed components may be included or included.

In this application, the term "or" is inclusive, if not otherwise specified. For example, the phrase "a or B" means "a, B, or both a and B. More specifically, either of the following conditions satisfies the condition "a or B": a is true (or present) and B is false (or not present); a is false (or not present) and B is true (or present); or both a and B are true (or present).

As described in the background art, the development of a negative active material to increase the energy density of a secondary battery is significant for the development of the secondary battery.

Among the negative active materials to be developed, hard carbon materials have received great attention due to their advantages of low volume expansion rate, good rapid charge and discharge properties, high gram capacity, and the like. Moreover, the hard carbon material can be used as a negative active material of a lithium ion battery and a negative active material of a sodium ion battery, and has wide application prospect.

However, the existing hard carbon material has the defects of high irreversible capacity, unsatisfactory capacity exertion and the like, is applied to a lithium ion battery or a sodium ion battery, has very limited improvement on the energy density of the battery, and is difficult to meet the requirement of practical application.

The inventor finds that the charging and discharging voltage platform of the conventional hard carbon material is high, so that the charging and discharging voltage platform has adverse effect on the cycle performance of the battery, and the first coulomb efficiency and the energy density of the battery are directly limited to be improved. In particular, the capacity of hard carbon materials is low (less than 200 mAh/g) at low voltage platforms, which greatly limits the capacity performance of hard carbon materials.

In order to solve the above problems, the inventors have made extensive studies and extensive experiments to provide a negative active material having a high capacity at a low voltage plateau, applied to a secondary battery, and capable of allowing the secondary battery to have a high first coulombic efficiency and a high energy density.

Negative electrode active material

A first aspect of the present application provides an anode active material including hard carbon particles having micropores with a maximum diameter d [ mu ] m ≦ 5.0 [ mu ] m. For example, the micropores may have a maximum diameter d μm of 0.01 μm,0.05 μm,0.1 μm,0.5 μm,1.0 μm,1.5 μm,2.0 μm,3.0 μm,4.0 μm,5.0 μm or within a range consisting of any of the above. The number of the hard carbon particles having micropores accounts for a ratio Q of 50% or more based on the total number of the hard carbon particles in any sufficiently large region in the negative electrode active material. For example, in any sufficiently large region in the anode active material, the number of the hard carbon particles having micropores may be 50%,60%,70%,80%,90%,100% or in a range composed of any of the above values, based on the total number of the hard carbon particles.

The negative active material is composed of a plurality of hard carbon particles, which may be bound by a binder to form the negative active material, or compacted by an external force to form the negative active material. The maximum diameter of the micropores can be expressed as: in the sectional view of the hard carbon particles, the longest diameter of the micropores on the projection plane. The sufficiently large region mentioned above is intended to mean a region sufficient to reflect the distribution characteristics of the hard carbon particles in the anode active material, and the size of the region may be selected based on the particle size, volume size, or number of the hard carbon particles.

As an example, Q may be determined by a Scanning Electron Microscope (SEM) image of the anode active material, and the sufficiently large area may be selected based on the particle size of the hard carbon particles, for example, d.gtoreq.10D in the SEM image _V 50，d≥50D _V 50, or D is more than or equal to 100D _V 50, D represents the length or width of the region, in μm, D _V 50 denotes the volume average particle diameter of the hard carbon particles in units of μm, and specifically, the sufficiently large region may be a region having a size of 50 μm × 70 μm. As another example, Q may be determined by the negative electrode active material in any sufficiently large volume, based on the total number of the hard carbon particles, the number of the hard carbon particles having micropores in proportion, and the sufficiently large region may be selected based on the volume of the hard carbon particlesFor example, the sufficiently large area may be V.gtoreq.10V ₀ ，V≥50V ₀ Or V is more than or equal to 100V ₀ V denotes the volume of the region in mL, V ₀ Represents the average volume of individual hard carbon particles in mL. As still another example, Q may be determined by the ratio of the number of the hard carbon particles having micropores to the number of the hard carbon particles continuously distributed in the negative active material based on the total number of the hard carbon particles, for example, the sufficiently large area may be selected based on the number of the hard carbon particles continuously distributed in the SEM picture, for example, the sufficiently large area may be an area of 10 or more, 50 or more, or 100 or more hard carbon particles continuously distributed in the SEM picture.

Without intending to be bound by any theory or explanation, the inventors have unexpectedly found that, in the anode active material, the content of the hard carbon particles having micropores is in the above-mentioned suitable range, and the maximum diameter of the micropores in the hard carbon particles is in the above-mentioned suitable range, not only the capacity of the anode active material but also the first coulombic efficiency of the anode active material is favorably improved. Specifically, the micropores can provide capacity by accommodating active ions (e.g., lithium ions or sodium ions). When the maximum diameter of the micropores is larger, the micropores can accommodate more active ions, but the extraction of the active ions is more hindered. When the diameter of the micropores is in the smaller range, on one hand, the micropores can have a proper size, so that enough active ion adsorption sites can be provided through the micropores, and further the capacity of the negative active material, especially the capacity of a low-voltage platform, is improved; on the other hand, the method is beneficial to the smooth removal of active ions, so that the irreversible loss of the active ions can be reduced, and the irreversible capacity of the negative electrode active material is further reduced. Thus, when an appropriate amount of hard carbon particles having an appropriate pore diameter are included in the anode active material, the anode active material can have a high low plateau capacity and a high reversible capacity. Therefore, the negative electrode active material is applied to the secondary battery, so that the secondary battery can be allowed to have high energy density, and the first coulomb efficiency of the secondary battery can be improved.

In some embodiments, the negative active material may satisfy: d μm is more than or equal to 1.0 μm and less than or equal to 5.0 μm. For example, the micropores may have a maximum diameter d μm of 1.0 μm,1.5 μm,2.0 μm,2.5 μm,3.0 μm,3.5 μm,4.0 μm,4.5 μm,5.0 μm or within a range consisting of any of the above values.

Without intending to be bound by any theory or explanation, when the maximum diameter of the micropores in the negative active material, among the hard carbon particles having micropores, is within the above-mentioned suitable range, the low voltage plateau capacity of the negative active material can be further improved, the irreversible capacity of the negative active material can be reduced, and thus the energy density and the first coulombic efficiency of the secondary battery can be further improved.

In some embodiments, the negative active material may satisfy:

and C is ₁ Not less than 256, wherein, C ₁ mAh/g represents that metallic lithium is used as a counter electrode, and the negative electrode active material is at 0V (vs Li) ⁺ Li) to 0.2V (vs Li) ⁺ /Li) delithiation capacity; c ₂ mAh/g represents that metallic lithium is used as a counter electrode, and the negative electrode active material is at 0V (vs Li) ⁺ Li) to 1.2V (vs Li) ⁺ /Li) delithiation capacity.

Without intending to be bound by any theory or explanation, when C of the anode active material ₁ 、C ₂ When the above conditions are satisfied, it is considered that the negative active material is applied to a lithium ion battery and can have a high low plateau capacity. Therefore, the negative electrode active material is applied to the lithium ion battery, and is favorable for reducing the lithium removal average potential of the negative electrode in the lithium ion battery, so that the average output potential of the lithium ion battery is improved, and the energy density of the lithium ion battery is further improved. Further, in the anode active material of the present application, C ₁ 、C ₂ When the above conditions are satisfied, it is considered that the volume of the micropores is favorable for smooth extraction of active lithium ions, thereby being favorable for improvement of the reversible capacity of the negative electrode active material. Therefore, the negative electrode active material is applied to a lithium ion battery and also applied to a lithium ion batteryThe coulomb efficiency of the lithium ion battery can be further improved.

In some embodiments, the anode active material may satisfy:

and C is ₃ Not less than 180, wherein, C ₃ mAh/g represents that the metal sodium is used as a counter electrode, and the negative active material is at 0V (vs Na) ⁺ Na) to 0.2V (vs Na) ⁺ Na) sodium removal capacity; c ₄ mAh/g represents that the metal sodium is used as a counter electrode, and the negative active material is at 0V (vs Na) ⁺ Na) to 1.2V (vs Na) ⁺ Na) sodium removal capacity.

Without intending to be bound by any theory or explanation, when C of the anode active material ₃ 、C ₄ When the conditions are met, the negative active material can be considered to be applied to a sodium ion battery and can have higher low plateau capacity. From this, the negative pole active material of this application is applied to sodium ion battery, is favorable to reducing the sodium average potential that takes off of negative pole among the sodium ion battery to promote sodium ion battery's average output potential, and then promote sodium ion battery's energy density. Further, in the anode active material of the present application, C ₃ 、C ₄ When the above conditions are satisfied, it is considered that the volume of the micropores is favorable for smooth removal of active sodium ions, thereby being favorable for improving the reversible capacity of the negative electrode active material. From this, the negative electrode active material of this application is applied to sodium ion battery, can also further promote sodium ion battery's coulomb efficiency.

In some embodiments, in the anode active material, the hard carbon particles have a particle diameter D _V 50 may be 3 μm to 15 μm. For example, D _V 50 may be 3 μm,5 μm,8 μm,10 μm,12 μm,14 μm,15 μm or within a range consisting of any of the foregoing.

In some embodiments, in the anode active material, the hard carbon particles have a particle diameter D _V 99 may be 10 μm to 45 μm. For example, D _V 99 may be 10 μm,15 μm,20 μm,25 μm,30 μm,35 μm,40 μm,45 μm or any range of values thereinAnd (4) the following steps.

Without intending to be bound by any theory or explanation, the hard carbon particles have a particle size D _V 50 and/or D _V 99 in the above-mentioned suitable range, the hard carbon particles can be made to have a suitable size specific surface area and volume. Therefore, when the negative active material is applied to a secondary battery, on one hand, the area of an SEI film formed on the surface of a negative pole piece is proper, so that the irreversible loss of active ions in the primary charging process is reduced; on the other hand, the active ions can have a transmission path with a proper distance. Therefore, the first coulomb efficiency, the energy density and the cycle performance of the secondary battery can be improved.

In some embodiments, the average molar ratio of hydrogen atoms to carbon atoms, H/C, in the hard carbon particles may be 0.02 to 0.2. For example, H/C may be 0.02,0.05,0.08,0.1,0.12,0.15,0.18,0.2 or within any of the above ranges.

In the present application, the maximum diameter of the micropores of the hard carbon particles may be determined using methods and instruments known in the art. For example, a proper amount of negative active material may be adhered to a silicon wafer carrier with a conductive adhesive, and one section of the negative sample may be polished by argon ion polishing to obtain a test piece; the morphology and element distribution of the polished cross-section were analyzed by Scanning Electron Microscopy (SEM), images of hard carbon particles were screened with image processing software, and the maximum diameter of each micropore in the cross-section was tested.

In the present application, dv50, dv99 of the hard carbon particles have a meaning known in the art, wherein Dv50 denotes that 50% of the particle diameters of the hard carbon particles in the volume-based particle size distribution are smaller than this value, and Dv99 denotes that 99% of the particle diameters of the hard carbon particles in the volume-based particle size distribution are smaller than this value. The Dv50 and Dv99 of the hard carbon particles can be determined using methods and instruments known in the art. For example, it may be determined by a laser particle size analyser (e.g. Marvin Mastersizer 2000E, UK) by reference to GB/T19077-2016 particle size distribution laser diffraction.

In the present application, the average molar ratio of hydrogen atoms to carbon atoms, H/C, in the hard carbon particles has a meaning well known in the art and can be determined using methods and instruments known in the art. For example, the average molar ratio H/C of hydrogen atoms to carbon atoms in the hard carbon particles can be calculated by performing a test by an elemental analyzer and measuring the atmosphere content after sufficiently burning an appropriate amount of the hard carbon particles in oxygen.

Method for preparing negative active material

A second aspect of the present application provides a method for preparing the anode active material of the first aspect of the present application, including the following steps S1 to S4.

S1, uniformly mixing amylase and aqueous dispersion of starch, and carrying out enzymolysis reaction on the starch at an enzymolysis temperature and an enzymolysis pH value to obtain the precursor of the negative active material.

In step S1, the amylase may be selected from one or more amylases known in the art, for example, one or more amylases, β -amylases, γ -amylases (also called saccharifying enzymes) or isoamylases, and the specific types thereof may be selected according to need, and are not limited herein. The starch may be selected from one or more of the starches known in the art, for example, may be selected from plant starches, and specifically may be selected from one or more of potato starches (e.g., sweet potato starch, tapioca starch, etc.), bean starches (e.g., mung bean starch, pea starch, etc.), cereal starches (e.g., wheat starch, corn starch, etc.) or other starches (e.g., kudzu root starch, lotus root starch), etc. The enzymolysis temperature and the enzymolysis ph value can represent the temperature and the ph value which can enable the amylase to maintain the catalytic activity of the enzyme, and the specific temperature range and the specific ph value range can be selected according to the type of the amylase and the type of the starch, and are not limited herein.

And S2, placing the dried anode active material precursor in an inert atmosphere, calcining at 400-700 ℃ for 1.5-2.5 h, and crushing to obtain first particles.

In step S2, the inert atmosphere may be an atmosphere that does not substantially cause a side reaction with the anode active material precursor, and may be, for example, a nitrogen atmosphere, an argon atmosphere, or the like. In some embodiments, the crushing treatment may include crushing classification of the calcined anode active material precursor by a classifying crusher so that the first particles have a particle diameter of a suitable size. As an example, the first particles may have a particle diameter D99 of 40 μm to 50 μm after the crushing treatment.

And S3, calcining the first particles for 1.5 to 2.5 hours at 900 to 1300 ℃ in an inert atmosphere to obtain second particles.

In step S3, the inert atmosphere may represent an atmosphere that does not substantially cause a side reaction with the first particles, and may be, for example, a nitrogen atmosphere, an argon atmosphere, or the like.

Without intending to be bound by any theory or explanation, in the method of the present application, the starch is subjected to enzymolysis by amylase, and the branched chains in the starch molecules can be dissolved, so that pores are generated inside the negative electrode active material precursor, and the connectivity of micropores in the negative electrode active material is improved. Thus, the negative electrode active material precursor can be calcined and vapor-deposited to form the negative electrode active material of the first aspect of the present application. The content of the hard carbon particles having the micropores in the anode active material prepared according to the method of the present application is within an appropriate range, and the maximum diameter of the micropores in the hard carbon particles is within an appropriate range, and when applied to a secondary battery, the anode active material can not only allow the secondary battery to have a high energy density, but also improve the first coulombic efficiency of the secondary battery.

Negative pole piece

The third aspect of the present application provides a negative electrode sheet comprising a negative electrode current collector and a negative active material layer on at least one surface of the negative electrode current collector, wherein the negative active material layer comprises the negative active material of the first aspect of the present application, or the negative active material prepared by the method of the second aspect of the present application.

Without intending to be bound by any theory or explanation, the negative active material layer of the negative electrode sheet of the present application, including the negative active material of the first aspect of the present application, or the negative active material prepared according to the method of the second aspect of the present application, can have a higher low voltage plateau capacity and a high reversible capacity. From this, the negative pole piece of this application is applied to secondary battery, not only can allow secondary battery to have high energy density, can promote secondary battery's first coulomb efficiency moreover.

In some embodiments, the single-point raman spectrum of the anode active material layer may satisfy: 1 < I _D /I _G Less than or equal to 1.3, wherein, I _D Indicating that it is located at 1320cm ^-1 To 1370cm ^-1 Characteristic peak in between, I _G Indicating a position of 1570cm ^-1 To 1620cm ^-1 Characteristic peaks in between.

Without intending to be bound by any theory or explanation, in the single-point raman spectrum of the anode active material layer, I _D /I _G Within the above suitable range, the anode active material in the anode active material layer may be considered to have a suitable defect degree. Therefore, the capacity of the negative electrode active material can be improved, and the capacity of the negative electrode plate can be improved. Therefore, the negative electrode plate is applied to the secondary battery, and the secondary battery can be allowed to have higher energy density.

The application does not limit the negative current collector of the negative pole piece. Metal foils, porous metal plates or composite current collectors may be used. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a base material of a polymer material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.). As an example, the negative electrode sheet is a negative electrode sheet of a lithium ion battery, and the negative current collector may be a copper foil. As another example, the negative electrode sheet is a negative electrode sheet of a sodium ion battery, and the negative current collector may be a copper foil or an aluminum foil.

In some embodiments, the negative electrode current collector has two surfaces opposite to each other in a thickness direction thereof, and the negative electrode active material layer may be disposed on one surface of the negative electrode current collector or may be disposed on both surfaces of the negative electrode current collector. For example, the negative electrode current collector has two surfaces opposite in its own thickness direction, and the negative electrode active material layer is provided on either one or both surfaces of the two surfaces opposite to the negative electrode current collector.

In some embodiments, the negative active material layer does not exclude other negative active materials than the negative active material. The specific kind of the other anode active material is not particularly limited and may be selected as required. By way of example, other negative active materials include, but are not limited to, at least one of soft carbon, silicon-carbon composite, siO.

In some embodiments, the negative active material layer further optionally includes a binder. The binder may be selected from at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy, or nylon.

In some embodiments, the negative active material layer further optionally includes a conductive agent. The conductive agent may be selected from a carbon-based material, a metal-based material, a conductive polymer, or any combination thereof. As an example, the carbon-based material may be selected from at least one of natural graphite, artificial graphite, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The metal-based material may be selected from metal powders, metal fibers. The conductive polymer may include a polyphenylene derivative.

In some embodiments, the negative electrode active material layer may further optionally include other auxiliaries, such as a thickener (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like.

The negative pole piece in the application can be prepared according to the conventional method in the field. For example, the hard carbon, optional other negative electrode active materials, a conductive agent, a binder and a thickening agent are dispersed in a solvent, the solvent can be N-methylpyrrolidone (NMP) or deionized water, uniform negative electrode slurry is formed, the negative electrode slurry is coated on a negative electrode current collector, and the negative electrode pole piece is obtained through the working procedures of drying, cold pressing and the like.

Note that each of the anode active material layer parameters given in the present application refers to a parameter range of the one-sided anode active material layer. When the negative active material layer is disposed on both sides of the negative current collector, the parameters of the negative active material layer on either side satisfy the present application, i.e., are considered to fall within the scope of the present application.

In addition, the negative electrode sheet in the present application does not exclude other additional functional layers than the negative electrode active material layer. For example, in certain embodiments, the negative electrode sheet of the present application further comprises a conductive undercoat layer (e.g., composed of a conductive agent and a binder) interposed between the negative electrode current collector and the negative electrode active material layer, disposed on the surface of the negative electrode current collector. In some other embodiments, the negative electrode sheet of the present application further includes a protective layer covering a surface of the negative active material layer.

In the present application, in the single-point Raman spectrum of the anode active material layer, I _D /I _G The test can be carried out by the following steps: cutting a section of the negative pole piece by using an ion polishing method, placing the section on a test bench of a Raman spectrum, and testing after focusing; selecting a range of 200 μm to 500 μm during testing, setting more than 200 test points at equal intervals in the range, wherein the test range of each point is 1000m ^-1 To 2000cm ^-1 To (c) to (d); will be located at 1320cm ^-1 To 1370cm ^-1 The characteristic peak between the two is determined as D peak and is located at 1570cm ^-1 To 1620cm ^-1 The characteristic peak between the two is determined as G peak, and the I of each test point is counted _D /I _G Calculating I of a plurality of points _D /I _G Average value, I of single-point raman spectrum of negative active material layer _D /I _G 。

In the present application, for the test of various parameters of the negative electrode active material or the negative electrode active material layer, a sample may be taken during the battery preparation process, or a sample may be taken from the prepared secondary battery.

When the above test sample is taken from a prepared secondary battery, the secondary battery may be subjected to a discharge treatment (the battery is generally placed in a fully discharged state for safety) as an example; taking out the negative pole piece after the battery is disassembled, and soaking the negative pole piece for a certain time (for example, 2 to 10 hours) by using dimethyl carbonate (DMC); and taking out the negative pole piece, drying at a certain temperature and for a certain time (for example, 60 ℃ for 4 hours), and taking out the negative pole piece after drying. At this time, the dried negative electrode sheet may be sampled to test various parameters related to the negative active material layer.

Electrochemical device

A fourth aspect of the present application provides an electrochemical device, including any device in which an electrochemical reaction occurs to convert chemical energy and electrical energy into each other, specific examples of which include all kinds of lithium primary batteries, lithium secondary batteries, or sodium ion batteries. In particular, the lithium secondary battery includes a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

In some embodiments, an electrochemical device of the present application includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte.

In some embodiments, the positive electrode tab, the negative electrode tab, and the separator may be manufactured into an electrode assembly through a winding process or a lamination process.

The electrochemical device of the present application further includes an exterior package for enclosing the electrode assembly and the electrolyte. In some embodiments, the outer package may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like, or a soft bag, such as a soft bag. The soft bag can be made of plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT) and polybutylene succinate (PBS).

[ negative electrode sheet ]

The negative electrode plate of the electrochemical device of the present application is the negative electrode plate of the third aspect of the present application. The embodiments of the negative electrode sheet have been described and illustrated in detail above and will not be repeated here. It is understood that the electrochemical device of the present application can achieve the beneficial effects of any of the above-described embodiments of the negative electrode tab of the present application.

[ Positive electrode sheet ]

The materials, compositions, and methods of making the positive electrode sheets used in the electrochemical devices of the present application can include any of the techniques known in the art.

The positive pole piece comprises a positive pole current collector and a positive pole active material layer which is arranged on at least one surface of the positive pole current collector and comprises a positive pole active material. As an example, the positive electrode current collector has two surfaces opposite in its own thickness direction, and the positive electrode active material layer is disposed on either or both of the two surfaces opposite to the positive electrode current collector.

In some embodiments, the positive electrode active material layer includes a positive electrode active material, and the specific kind of the positive electrode active material is not particularly limited and may be selected as desired.

In some embodiments, the electrochemical device is a lithium ion battery. The positive active material may include one or more of lithium transition metal oxide, olivine-structured lithium-containing phosphate, and respective modified compounds thereof. In the electrochemical device of the present application, the modification compound of each positive electrode active material may be a doping modification, a surface coating modification, or a doping and surface coating modification of the positive electrode active material.

As an example, the lithium transition metal oxide may include one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds thereof. As an example, the olivine-structured lithium-containing phosphate may include one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, and a modified compound thereof. These positive electrode active materials may be used alone or in combination of two or more.

In some embodiments, the electrochemical device is a sodium ion battery. As the positive electrode active material, those known in the art for sodium ion secondary batteries can be used. As an example, the positive electrode active material may include one or more of a sodium transition metal oxide, a polyanionic type compound, and a prussian blue type compound.

Examples of the sodium transition metal oxide include: na (Na) _1-x Cu _h Fe _k Mn _l M ¹ _m O _2-y Wherein M is ¹ Is one or more of Li, be, B, mg, al, K, ca, ti, co, ni, zn, ga, sr, Y, nb, mo, in, sn and Ba, 0<x≤0.33，0<h≤0.24，0≤k≤0.32，0<l≤0.68，0≤m<0.1，h+k+l+m＝1，0≤y<0.2；Na _0.67 Mn _0.7 Ni _z M ² _0.3-z O ₂ Wherein M is ² Is one or more of Li, mg, al, ca, ti, fe, cu, zn and Ba, 0<z≤0.1；Na _a Li _b Ni _c Mn _d Fe _e O ₂ Wherein 0.67<a≤1，0<b<0.2，0<c<0.3，0.67<d+e<0.8, b, c, d, e, 1. Examples of the polyanionic compound include: a. The ¹ _f M ³ _g (PO ₄ ) _i O _j X ¹ _3-j Wherein A is ¹ Is H, li, na, K and NH ₄ One or more of, M ³ Is one or more of Ti, cr, mn, fe, co, ni, V, cu and Zn, X ¹ Is one or more of F, cl and Br, 0<f≤4，0<g≤2，1≤i≤3，0≤j≤2；Na _n M ⁴ PO ₄ X ² Wherein M is ⁴ Is one or more of Mn, fe, co, ni, cu and Zn, and X ² Is one or more of F, cl and Br, 0<n≤2；Na _p M ⁵ _q (SO ₄ ) ₃ Wherein M is ⁵ Is one or more of Mn, fe, co, ni, cu and Zn, 0<p≤2，0<q≤2；Na _s Mn _t Fe _3-t (PO ₄ ) ₂ (P ₂ O ₇ ) Wherein 0 is<s.ltoreq.4, 0. Ltoreq. T.ltoreq.3, for example t is 0, 1, 1.5, 2 or 3.

Examples of the prussian blue-based compound include: a. The ² _u M ⁶ _v [M ⁷ (CN) ₆ ] _w ·xH ₂ O, wherein A ² Is H ⁺ 、NH ₄ ⁺ One or more of alkali metal cation and alkaline earth metal cation, M ⁶ And M ⁷ Each independently is one or more of transition metal cations, 0<u≤2，0<

v≤

1，0<w≤1，0<x<6. For example A ² Is H ⁺ 、Li ⁺ 、Na ⁺ 、K ⁺ 、NH ₄ ⁺ 、Rb ⁺ 、Cs ⁺ 、Fr ⁺ 、Be ²⁺ 、Mg ²⁺ 、Ca ²⁺ 、Sr ²⁺ 、Ba ²⁺ And Ra ²⁺ One or more of, M ⁶ And M ⁷ Each independently is a cation of one or more transition metal elements of Ti, V, cr, mn, fe, co, ni, cu, zn, sn and W. Preferably, A ² Is Li ⁺ 、Na ⁺ And K ⁺ One or more of, M ⁶ Is cation of one or more transition metal elements of Mn, fe, co, ni and Cu, M ⁷ Is a cation of one or more transition metal elements of Mn, fe, co, ni and Cu.

In some embodiments, the positive electrode active material layer further optionally includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the positive electrode active material layer further optionally includes a binder. As an example, the conductive agent may be selected from a carbon-based material, a metal-based material, a conductive polymer, or any combination thereof. As an example, the carbon-based material may be selected from at least one of natural graphite, artificial graphite, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The metal-based material may be selected from metal powders, metal fibers. The conductive polymer may include a polyphenylene derivative.

In some embodiments, the positive electrode current collector may employ a metal foil or a composite current collector. As an example of the metal foil, an aluminum foil may be used as the positive electrode current collector. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may be one or more selected from aluminum, aluminum alloy, nickel alloy, titanium alloy, silver, and silver alloy. As an example, the polymeric substrate may be selected from polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, and the like.

The positive pole piece in the application can be prepared according to the conventional method in the field. For example, the positive electrode active material layer is generally formed by coating a positive electrode slurry on a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is generally formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.

The positive electrode sheet of the present application does not exclude other additional functional layers than the positive electrode active material layer. For example, in some embodiments, the positive electrode sheet of the present application further comprises a conductive undercoat layer (e.g., composed of a conductive agent and a binder) interposed between the positive electrode current collector and the positive electrode active material layer and disposed on the surface of the positive electrode current collector. In some other embodiments, the positive electrode sheet of the present application further comprises a protective layer covering the surface of the positive active material layer.

[ electrolyte ]

The electrolyte plays a role in conducting active ions between the positive pole piece and the negative pole piece. The electrolyte that can be used in the electrochemical device of the present application may be an electrolyte known in the art.

In some embodiments, the electrolyte may include an organic solvent, an electrolyte salt, and optional additives, and the kinds of the organic solvent, the lithium salt, and the additives are not particularly limited and may be selected as needed.

In some embodiments, the electrochemical device is a lithium ion battery, and the electrolyte salt may include a lithium salt. By way of example, the lithium salt includes, but is not limited to, liPF ₆ (lithium hexafluorophosphate) and LiBF ₄ Lithium tetrafluoroborate and LiClO ₄ (lithium perchlorate), liFSI (lithium bis (fluorosulfonylimide), liTFSI (lithium bis (trifluoromethanesulfonylimide)), liTFS (lithium trifluoromethanesulfonate), liDFOB (lithium difluorooxalato borate), liBOB (lithium dioxaoxalato borate), liPO2F2 (lithium difluorophosphate), liDFOP (lithium difluorooxalato phosphate) and LiTFOP (lithium tetrafluorooxalato phosphate). The lithium salt may be used singly or in combination of two or more.

In some embodiments, the electrochemical device is a sodium ion battery and the electrolyte salt may include a sodium salt. As an example, the sodium salt may be selected from NaPF ₆ 、NaClO ₄ 、NaBCl ₄ 、NaSO ₃ CF ₃ And Na (CH) ₃ )C ₆ H ₄ SO ₃ At least one of (1).

In some embodiments, the organic solvent includes, by way of example and not limitation, at least one of Ethylene Carbonate (EC), propylene Carbonate (PC), ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), butylene Carbonate (BC), fluoroethylene carbonate (FEC), methyl Formate (MF), methyl Acetate (MA), ethyl Acetate (EA), propyl Acetate (PA), methyl Propionate (MP), ethyl Propionate (EP), propyl Propionate (PP), methyl Butyrate (MB), ethyl Butyrate (EB), 1, 4-butyrolactone (GBL), sulfolane (SF), dimethylsulfone (MSM), methylethylsulfone (EMS), and diethylsulfone (ESE). The organic solvent may be used alone or in combination of two or more. Alternatively, two or more of the above organic solvents are used at the same time.

In some embodiments, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that improve certain properties of the battery, such as additives that improve the overcharge properties of the battery, additives that improve the high or low temperature properties of the battery, and the like.

By way of example, the additives include, but are not limited to, at least one of fluoroethylene carbonate (FEC), vinylene Carbonate (VC), vinyl Ethylene Carbonate (VEC), vinyl sulfate (DTD), propylene sulfate, vinyl sulfite (ES), 1, 3-Propanesultone (PS), 1, 3-Propanesultone (PST), sulfonate cyclic quaternary ammonium salts, succinic anhydride, succinonitrile (SN), adiponitrile (AND), tris (trimethylsilane) phosphate (TMSP), tris (trimethylsilane) borate (TMSB).

The electrolyte may be prepared according to a method conventional in the art. For example, an organic solvent, an electrolyte salt, and an optional additive may be uniformly mixed to obtain an electrolyte solution. The adding sequence of the materials is not particularly limited, for example, electrolyte salt and optional additives are added into an organic solvent and uniformly mixed to obtain electrolyte; or, the electrolyte salt is added into the organic solvent, and then the optional additive is added into the organic solvent to be uniformly mixed, so that the electrolyte is obtained.

[ separator ]

The isolating membrane is arranged between the positive pole piece and the negative pole piece, mainly plays a role in preventing the short circuit of the positive pole and the negative pole, and can enable active ions to pass through. The type of the separator is not particularly limited, and any known separator having a porous structure and good chemical and mechanical stability may be used.

In some embodiments, the material of the isolation film may be one or more selected from glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride, but is not limited thereto. Alternatively, the material of the isolation film may include polyethylene and/or polypropylene. The isolation film can be a single-layer film or a multi-layer composite film. When the isolating membrane is a multilayer composite film, the materials of all layers are the same or different. In some embodiments, a ceramic coating or a metal oxide coating may be further disposed on the isolation film.

Electric device

A fifth aspect of the present application provides an electric device comprising the electrochemical device of the fourth aspect of the present application.

The electronic device of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable facsimile, 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, an electric motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large household battery, a lithium ion capacitor, and the like.

Examples

Hereinafter, examples of the present application will be described. The following description of the embodiments is merely exemplary in nature and is in no way intended to limit the present disclosure. The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.

Examples 1 to 1

Adding 100 parts by weight of corn starch, 9 parts by weight of diammonium hydrogen phosphate and 3 parts by weight of citric acid into 500 parts by weight of distilled water, stirring to uniformly mix the components, and continuously stirring to obtain a mixed solution; heating the mixed solution to 55 ℃, adding 8 parts by weight of amylase while stirring, continuing stirring for 3 hours, and recording the time length of the step as the enzymolysis time length; cooling, filtering and cleaning to obtain porous enzymatic starch; drying, transferring into a box furnace, pre-calcining for 2h at 600 ℃ under the protection of nitrogen, cooling, crushing and grading to obtain first particles with D99 being 45 mu m; then, transferring the first particles into a nitrogen atmosphere protective furnace for secondary calcination at 1000 ℃ for 2 hours to obtain second particles; and (3) cooling the furnace temperature to 900 ℃, introducing methane gas, performing vapor deposition for 1h, then cutting off the methane gas, and cooling to room temperature to obtain the anode active material No. 1.

Examples 1-2 to 1-5

Based on the preparation procedures of examples 1-1, the length of enzymatic hydrolysis was adjusted to 6h,9h,12h,24h, respectively, and anode active materials 2# to 5# of examples 1-2 to 1-5 were prepared.

Examples 1-6 to 1-8

Based on the preparation process of example 1-1, the secondary calcination temperatures were adjusted to 1300 ℃,1200 ℃,1100 ℃, respectively, to prepare negative active materials # 6 to # 8 of examples 1-6 to 1-8.

Examples 1-9 to 1-10

Negative active materials # 9 of examples 1-9 were prepared based on the preparation process of example 1-1 by replacing amylase with an equal weight of saccharifying enzyme.

Negative active materials # 10 of examples 1-10 were prepared based on the preparation process of example 1-1 by replacing amylase with 8 parts by weight of amylase and 2 parts by weight of saccharifying enzyme.

Comparative examples 1 to 1

Taking 100 parts by weight of corn starch, transferring the corn starch into a box type furnace, calcining for 2 hours at 600 ℃ under the protection of nitrogen, cooling, crushing and grading to control D99 to be 45 mu m; then, transferring the classified powder into a nitrogen atmosphere protective furnace for secondary calcination, wherein the calcination temperature is 1000 ℃, and the calcination time is 2 hours; and then, cooling the furnace temperature to 900 ℃, introducing methane gas, performing vapor deposition for 1h, cutting off the methane gas, and cooling to room temperature to obtain the anode active material 11#.

Examples 2-1 to 2-10

Preparation of positive pole piece

Mixing a positive electrode active material lithium cobaltate, a conductive agent Super P and a binder polyvinylidene fluoride (PVDF) according to a mass ratio of 97; uniformly coating the positive electrode slurry on two side surfaces of an aluminum foil of a positive electrode current collector, wherein the coating thickness of one side surface is 80 microns; drying at 85 ℃, cold pressing, cutting into pieces, cutting, and drying at 85 ℃ for 4 hours under vacuum condition to obtain the positive pole piece.

Preparation of negative pole piece

Dissolving a negative electrode active material, a binder styrene butadiene rubber and sodium carboxymethylcellulose (CMC-Na) in deionized water according to a mass ratio of 97; coating the negative electrode slurry on two side surfaces of a negative electrode current collector, wherein the negative electrode current collector is a copper foil with the thickness of 6 microns, one side of the negative electrode current collector is used as a negative electrode current collector, and the coating thickness of the single side is 50 microns; drying at 85 ℃, cold pressing, cutting into pieces, cutting, and drying at 120 ℃ for 12 hours under vacuum condition to obtain the negative pole piece.

Preparation of the electrolyte

In a dry argon atmosphere glove box, ethylene Carbonate (EC), propylene Carbonate (PC), diethyl carbonate (DEC) were mixed in a mass ratio of EC: PC: DEC =1:1:1, mixing; adding 1.5wt% of 1, 3-propane sultone, fully stirring, and adding lithium salt LiPF ₆ And mixing uniformly to obtain the electrolyte. In the electrolyte, liPF ₆ The concentration of (2) is 1mol/L.

Preparation of the separator

With surface coated with Al ₂ O ₃ A Polyethylene (PE) porous polymer film having a thickness of 9 μm as a separator.

Preparation of lithium ion battery

Button cell preparation: the button cell uses metal lithium as a counter electrode, a lithium sheet with the diameter of 18mm and the thickness of 0.6mm, a separation film and a negative pole piece are sequentially assembled together, electrolyte is added, and the obtained product is packaged in a positive and negative button stainless steel shell to obtain the button cell.

Preparing a full battery: and sequentially stacking the positive pole piece, the isolating film and the negative pole piece to enable the isolating film to be positioned between the positive pole piece and the negative pole piece to play an isolating role, then winding, welding a tab, placing the tab into an outer packaging foil aluminum plastic film, injecting electrolyte, and carrying out vacuum packaging, standing, formation, shaping, capacity test and other procedures to obtain the soft package full battery.

Examples 2-11 to 2-15

Based on the preparation procedures of examples 2-1 to 2-10, the positive electrode active material was replaced with copper nickel iron manganese oxide (NaCu) of equal capacity, respectively _1/9 Ni _2/9 Fe _1/3 Mn _1/3 O ₂ ) Replacing the current collector of the negative electrode with copper foil, and replacing LiPF in the electrolyte ₆ Replacement with equal amounts of NaPF ₆ And the counter electrode in the button cell was replaced with metallic sodium, and the positive electrode sheet, negative electrode sheet, electrolyte, separator and sodium ion battery of examples 2-11 to 2-15 were prepared.

Comparative example 2-1

The kind of the negative electrode active material was adjusted, and the negative electrode sheet, the positive electrode sheet, the electrolyte, the separator and the lithium ion battery of comparative example 2-1 were prepared based on the preparation processes of the negative electrode sheet, the positive electrode sheet, the electrolyte, the separator and the secondary battery in examples 2-1 to 2-10.

Comparative examples 2 to 2

The kind of the negative electrode active material was adjusted, and the negative electrode sheet, the positive electrode sheet, the electrolyte, the separator and the sodium ion battery of comparative example 2-2 were prepared based on the preparation processes of the negative electrode sheet, the positive electrode sheet, the electrolyte, the separator and the secondary battery in examples 2-11 to 2-15.

Test section

(1) SEM test of cross section

Mixing the negative electrode active materials 1# to 11# with 3% of PVDF binder respectively, adding a proper amount of NMP to prepare slurry, coating the slurry on the surface of Cu, and drying to obtain a test piece; cutting a fresh section of the test piece by adopting an ion polishing mode, and transferring the section to a scanning electron microscope to observe the appearance of the section; the number of hard carbon particles having micropores in a test area of 50 μm × 70 μm was counted in a ratio Q based on the total number of hard carbon particles, and the maximum diameter d μm of the micropores in the test area was counted by a measurement tool provided in the system itself. The SEM images of the cross sections of examples 1-2 are shown in FIGS. 1 and 2.

(2) Dv50, dv99 test

This application uses the malvern particle size tester to measure hard carbon particle diameter: the hard carbon particulate material was dispersed in a dispersant (ethanol), and after 30 minutes of sonication, the sample was added to a malvern particle size tester and the test was started. In the volume-based particle size distribution of the hard carbon particles, the Dv50 of the hard carbon particles, which is the average particle size, is a particle size at which 50% of the volume accumulation is reached from the small particle size side; meanwhile, in the volume-based particle size distribution of the hard carbon particles, the particle size reaching 99% of the volume accumulation from the small particle size side is Dv99 of the hard carbon particles.

(3) Raman spectroscopy

Cutting a section of the negative pole piece by using an ion polishing method, then placing the section on a test bench of a Raman spectrum, testing after focusing, selecting a range of 200 micrometers to 500 micrometers during testing, arranging more than 200 test points in the range at equal intervals, wherein the test range of each point is 1000 cm ^-1 To 2000cm ^-1 To (c) to (d); will be located at 1320cm ^-1 To 1370cm ^-1 The characteristic peak between the two is determined as D peak and is located at 1570cm ^-1 To 1620cm ^-1 The characteristic peak between the two is determined as G peak, and the I of each test point is counted _D /I _G Calculating I of a plurality of points _D/ I _G Average value, I of single-point raman spectrum of negative active material layer _D /I _G . Wherein, the Raman test ID/IG statistical box plot of examples 2-1, 2-2, 2-5 and comparative example 2-1 is shown in FIG. 3.

(4) Button cell charging and discharging curve test

And (3) standing the assembled button cell for 5h in an environment at 25 ℃, and then carrying out a charge-discharge test to obtain a charge-discharge curve of the button cell. The test procedure is that 0.1mA/cm is used ² The current density is discharged to 0V in a constant current, and then the discharge is performed in a constant voltage of 0V until the current is reduced to 12 muA/cm ² (ii) a The discharge (lithium/sodium insertion) process is finished; and (3) after the mixture is placed for 5min, transferring to a charging (lithium removal/sodium removal) test, wherein the test flow comprises the following steps: at 0.1mA/cm ² The current density of (2) was constant current charged to 2V. The charge and discharge curves of the lithium button cells of examples 2-8 are shown in fig. 4.

Recording gram capacities of first discharge and first charge respectively, wherein the first coulombic efficiency of the button cell = first charge capacity/first discharge capacity 100%;

respectively record the first circleThe gram capacity and voltage in the charging and discharging process are counted, and the gram capacity distribution in each voltage interval in the lithium/sodium removing process is counted, so that C corresponding to the negative electrode active materials 1# to 11# is determined ₁ mAh/g、C ₂ mAh/g、C ₃ mAh/g and C ₄ mAh/g, wherein C ₁ =0-0.2V lithium removal specific capacity; c ₂ =0-1.2V lithium removal specific capacity; c ₃ =0-0.2V sodium removal specific capacity; c ₄ Specific sodium removal capacity of 0-1.2V; a lithium or sodium removal specific capacity of C =0-2V, i.e. the total reversible specific capacity;

(5) Testing of energy Density

Charging the full cell at a constant current of 0.2C to a voltage of 4.48V or 3.95V in an environment of 25 ℃, and then charging at a constant voltage; discharging at a constant current of 0.2 ℃ to a voltage of 2V, recording as a cycle, recording the discharge capacity and discharge energy of the first cycle, and dividing the discharge energy by the discharge capacity to obtain an average discharge voltage; testing the length, width and height of the battery cell under the SOC of 50 percent to obtain the volume of the battery cell; energy density of the full cell = discharge capacity average discharge voltage/cell volume, noted ED Wh/L.

The test results of the negative active materials 1# to 11# of examples 1-1 to 1-10 and comparative example 1-1 are detailed in table 1, and the types of the negative active materials, raman test results, and battery test results of examples 2-1 to 2-15 and comparative examples 2-1 to 2-2 are detailed in tables 2-1 to 2-2. In tables 1 and 2-1 to 2-2, "/" indicates that no corresponding treatment was performed or that the corresponding parameter could not be measured.

TABLE 1

TABLE 2-1

Tables 2 to 2

It can be seen from the results of the tests in tables 1 and 2-1 to 2-2 that, compared with comparative example 1-1, the content of the hard carbon particles having micropores in the negative active material can be increased after the pores are formed by amylase etching in examples 1-1 to 1-10, so that the low voltage plateau capacity and the total reversible capacity of the negative active material are improved. The increase of the capacity of the low-voltage platform can reduce the average potential of the negative electrode, so that the voltage of the full battery is increased, the energy density of the full battery is further improved, and meanwhile, the increase of the reversible capacity can also improve the energy density of the full battery.

It can be seen from the combination of examples 1-1 to 1-5 and examples 2-1 to 2-5, 2-11 to 2-14 that the low voltage plateau capacity of the negative active material decreases with the increase of the duration of the enzymatic hydrolysis, which is probably due to the increase of the adsorption sites and defects caused by the increase of the pores, and the increase of the high plateau stage capacity, thereby resulting in the decrease of the low voltage plateau capacity of the negative active material and the decrease of the first efficiency of the battery. Therefore, the enzymolysis time is controlled at a reasonable level, which is beneficial to improving the capacity exertion and the electrochemical performance of the negative active material, thereby being beneficial to improving the energy density and the electrical performance of the battery.

Further, as can be seen from examples 1-2, 1-6 to 1-8 and examples 2-2, 2-6 to 2-8, 2-12, 2-15, an increase in the secondary calcination temperature further increases the primary coulombic efficiency and the low voltage plateau capacity in a certain temperature range, but adversely affects the reversible capacity. Because the first efficiency, the reversible capacity and the low platform capacity proportion influence the energy density together, the energy density can be further improved by regulating and controlling the temperature of secondary calcination.

It can be seen from the comprehensive examples 1 to 9 and 1 to 10 that the pore content of the negative electrode active material can be increased by performing enzymolysis on starch by using different types of amylases, so that the low-voltage platform capacity of the negative electrode active material is remarkably improved compared with that of the negative electrode active material in the comparative example 1 to 1.

To sum up, the negative active material of the present application can have a high low-voltage platform capacity and a high reversible capacity, is applied to a secondary battery, and can significantly improve the first coulombic efficiency and energy density of the secondary battery.

The present application is not limited to the above embodiments. The above embodiments are merely examples, and embodiments having substantially the same configuration as the technical idea and exhibiting the same operation and effect within the technical scope of the present application are all included in the technical scope of the present application. Various modifications that can be conceived by those skilled in the art are applied to the embodiments and other embodiments are also included in the scope of the present application, which are configured by combining some of the constituent elements in the embodiments without departing from the scope of the present application.

Claims

1. An anode active material comprising hard carbon containing hard carbon particles having micropores with a maximum diameter d in a range of 0.5 μm or more and d μm or less and 5.0 μm or less;

the number of the hard carbon particles with micropores accounts for more than or equal to 50% of the total number of the hard carbon particles;

the preparation method of the negative active material comprises the following steps:

s1, uniformly mixing amylase and/or saccharifying enzyme with a water dispersion of starch to enable the starch to carry out enzymolysis reaction at an enzymolysis temperature and an enzymolysis pH value, thereby obtaining a precursor of a negative active material;

2. The negative electrode active material of claim 1, wherein 1.0 μm ≦ d μm ≦ 5.0 μm.

3. The anode active material according to claim 1, satisfying:

and C is ₁ ≥256，

Wherein, C ₁ mAh/g represents that metallic lithium is used as a counter electrode, and the negative electrode active material is at 0V (vs Li) ⁺ /Li) to 0.2V (vs Li) ⁺ /Li) delithiation capacity; c ₂ mAh/g represents that metallic lithium is used as a counter electrode, and the negative electrode active material is at 0V (vs Li) ⁺ Li) to 1.2V (vs Li) ⁺ /Li) delithiation capacity.

4. The anode active material according to claim 1, satisfying:

and C is ₃ ≥180，

5. The anode active material according to any one of claims 1 to 4, satisfying at least one of:

(1) The particle diameter D of the hard carbon particles _V 50 is 3 μm to 15 μm;

(2) The particle diameter D of the hard carbon particles _V 99 is 10 μm to 45 μm.

6. A negative electrode sheet comprising a negative electrode current collector and a negative active material layer on at least one surface of the negative electrode current collector, the negative active material layer comprising the negative active material according to any one of claims 1 to 5.

7. The negative electrode sheet of claim 6, the negative active material layer having a single-point Raman spectrum satisfying: 1 < I _D /I _G Less than or equal to 1.3, wherein, I _D The representation is located at 1320cm ^-1 To 1370cm ^-1 Characteristic peak between, I _G Indicating a position of 1570cm ^-1 To 1620cm ^-1 Characteristic peaks in between.

8. An electrochemical device comprising a negative electrode sheet according to claim 6 or 7.

9. An electric device comprising the electrochemical device according to claim 8.