WO2022205154A1

WO2022205154A1 - Negative electrode active material, electrochemical apparatus, and electronic apparatus

Info

Publication number: WO2022205154A1
Application number: PCT/CN2021/084631
Authority: WO
Inventors: 岳影影
Original assignee: 宁德新能源科技有限公司
Priority date: 2021-03-31
Filing date: 2021-03-31
Publication date: 2022-10-06
Also published as: CN115836408A

Abstract

Disclosed in the present application are a negative electrode active material, an electrochemical apparatus, and an electronic apparatus. The negative electrode active material of the present application comprises graphite and a coating, the coating comprising a first coating and a second coating, wherein the first coating covers at least part of the surface of the graphite, and the second coating covers at least part of the surface of the first coating, the first coating comprising a silicon material and porous carbon, and the second coating comprising an MXene material. When used as the negative electrode material of a lithium ion battery, the present negative electrode active material can increase first-cycle coulombic efficiency and reduce the capacity loss during cycling caused by polarisation.

Description

Anode active materials, electrochemical devices, and electronic devices

technical field

The present application relates to the field of lithium-ion batteries. Specifically, the present application relates to a negative electrode active material. The present application also relates to negative electrodes, electrochemical devices, and electronic devices including the negative electrode active material.

Background technique

Lithium-ion batteries have the characteristics of high voltage platform, large specific energy, and long cycle life, and are widely used in digital products, power tools and other fields. In recent years, with the development of science and technology and society, light weight and miniaturization have become the development trend of various products; at the same time, with the increasingly prominent environmental problems, energy saving and environmental protection have also become the focus of attention. The development and application of high-energy lithium-ion batteries have gradually entered people's field of vision.

At present, silicon is the material with the highest known lithium intercalation specific capacity (3579-4200mAh/g). In nature, silicon has abundant reserves, low cost, non-toxic and non-polluting, and more importantly, its lithium intercalation platform is about 0.4V, which can improve the overall output voltage of the battery while avoiding the generation of lithium dendrites. Based on the above advantages, silicon is considered to be the most promising anode material for lithium-ion batteries, and has become a hot research topic. However, silicon has low electrical conductivity (10 ^-5 -10 ^-3 S/cm) and low lithium ion diffusion coefficient (10 ^-14 -10 ^-13 cm ² /s), resulting in huge volume expansion upon electrochemical cycling (>300%), the electrochemical reaction inside the battery deteriorates rapidly, limiting its commercial application.

The traditional solutions to improve the above problems have limited effect on improving the electrochemical performance of silicon, and also bring some other problems during use, such as

1) Nano-sized silicon particles. Nano-sized particles have high specific surface area, so that nano-silicon needs to consume a large amount of electrolyte to generate SEI film, resulting in low coulombic efficiency and serious capacity fading. In addition, the tap density of nanomaterials is low. Under the same areal density, the electrode thickness is large and the ion and electron transport distance is farther. Finally, due to the poor conductivity of silicon, the polarization of the material during charging and discharging is still relatively serious.

2) Silicon-carbon composite, in order to increase the first efficiency of the negative electrode to nearly 90%, the amount of silicon added is generally below 10%, and the reversible capacity is about 600mAh/g. It is difficult to further increase the amount of silicon added.

3) Silicon compound type composite, the cycle stability of such silicon-based materials is better than that of pure silicon anode materials, but because the matrix does not undergo lithium-deintercalation reaction, the reversible capacity of such materials is generally very low.

4) Oxides of silicon, the difference in oxygen content of silicon oxide will also affect its stability and reversible capacity: with the increase of oxygen in silicon oxide, the cycle performance improves, but the reversible capacity decreases. In addition, there are still some problems with silicon oxides as anode materials for lithium-ion batteries: the formation process of Li ₂ O and lithium silicate is irreversible during the first lithium intercalation process, which makes the first Coulombic efficiency very low; at the same time, Li ₂ O Compared with elemental silicon, silicon oxide has better cycle stability as a negative electrode material, but as the number of cycles continues to increase, Its stability is still very poor.

5) Alloying (FeSi, NiSi), because the active metal itself will also appear pulverized, so the cycle performance is poor. The inactive metal in the Si-inactive metal composite material is an inert phase, which greatly reduces the reversible capacity of the silicon material.

SUMMARY OF THE INVENTION

In view of the deficiencies of the prior art, the present application provides a negative electrode active material, which has a high gram capacity as a negative electrode material for a lithium ion battery, can improve the first Coulomb efficiency of the battery, and reduce the cycle process caused by polarization Medium capacity loss.

In a first aspect, the present application provides a negative electrode active material comprising graphite, silicon material, porous carbon and MXene material.

According to some embodiments of the present application, the anode active material satisfies at least one of the following features (1) to (4): (1) Dv50 is 3 μm to 35 μm; (2) BET is 1.0 m ² /g to 3.6 m ² /g; (3) the mass content of silicon is 10% to 70% based on the mass of the negative electrode active material; (4) the mass content of the MXene material is 0.1% to 3% based on the mass of the negative electrode active material.

According to some embodiments of the present application, the graphite satisfies at least one of the following characteristics (a) to (c): (a) the degree of graphitization is 92% to 96%; (b) the Dv50 of the graphite is 3 μm to 30 μm; (c) BET is 0.8 m ² /g to 2.0 m ² /g.

According to some embodiments of the present application, the porous carbon satisfies at least one of the following features (d) to (e): (d) the pore diameter is 0.1 μm to 2.5 μm; (e) the pore wall thickness is 0.05 μm to 0.5 μm .

According to some embodiments of the present application, the Dv50 of the silicon material is 20 nm to 150 nm, and satisfies 0.3≤Dv50/Dv90≤0.7.

According to some embodiments of the present application, the general structural formula of the MXene material is M _n+1 X _n , wherein M is selected from at least one of Ti, Nb, V, Mo, Zr, Cr, W or Ta; X is at least one of C or N; n is 1, 2 or 3, and satisfies at least one of the following features (f) to (h): (f) MXene has a sheet diameter of 0.5 μm to 20 μm; (g) ) The number of lamellae of MXene ranges from 1 to 5 layers; (h) the thickness of MXene lamellae is less than or equal to 8 nm.

In a second aspect, the present application provides a negative electrode active material, the negative electrode active material includes graphite and a coating, the coating includes a first coating and a second coating, wherein the first coating The second coating covers at least a part of the surface of the graphite, the second coating covers at least a part of the surface of the first coating, the first coating comprises silicon material and porous carbon, and the second coating comprises MXene material.

According to some embodiments of the present application, the surface of the cladding material includes a second cladding layer, and the surface of the second cladding layer includes a third cladding layer; the second cladding layer and the third cladding layer include A first coating and a second coating; wherein, the surface of the second coating includes a first coating, the first coating includes silicon material and porous carbon, and the second coating includes MXene material.

According to some embodiments of the present application, the MXene material satisfies at least one of the following features (f) to (i): (f) the diameter of the MXene lamella is 0.5 μm to 20 μm; (g) the number of MXene lamellar layers 1 to 5 layers; (h) the sheet thickness of MXene≤8nm; (i) the general structural formula of MXene is M _n+1 X _n , wherein M is selected from Ti, Nb, V, Mo, Zr, Cr, At least one of W or Ta; X is at least one of C or N; n is 1, 2 or 3.

In a third aspect, the present application further provides an electrochemical device comprising a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode comprises the negative electrode active material according to the first aspect or the second aspect.

In a fourth aspect, the present application further provides an electronic device, the electronic device comprising the electrochemical device of the third aspect.

Description of drawings

Figure 1 is a schematic diagram of MXene sheet size measurement.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the implementations. example. The relevant embodiments described herein are illustrative in nature and are used to provide a basic understanding of the present application. The embodiments of the present application should not be construed as limitations of the present application. All other embodiments obtained by those skilled in the art without creative work based on the technical solutions provided in this application and the given embodiments fall within the protection scope of this application.

For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with any other lower limit to form an unspecified range, and likewise any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value may itself serve as a lower or upper limit in combination with any other point or single value or with other lower or upper limits to form a range that is not expressly recited.

In the description herein, unless otherwise stated, "above" and "below" include the numerals.

Unless otherwise specified, terms used in this application have their commonly known meanings as commonly understood by those skilled in the art. Unless otherwise specified, the values of the parameters mentioned in this application can be measured by various measurement methods commonly used in the art (for example, can be tested according to the methods given in the examples of this application).

A list of items to which the terms "at least one of," "at least one of," "at least one of," or other similar terms are linked to can mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means A only; B only; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means A only; or B only; C only; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

When there is current flowing through the battery, the phenomenon that the potential deviates from the equilibrium potential is called electrode polarization. Polarization will deteriorate the cycle performance of the battery. The capacity decay of lithium-ion batteries during cycling can be divided into two parts, one part is the capacity decay caused by the degradation of the electrode material, and the other part is the capacity decay caused by the polarization. For the anode active material system in this application, polarization is the main factor in the resulting capacity fading. The large particle size of the negative electrode material increases the diffusion channels of lithium ions to the surface, and the formation of the SEI film increases the resistance of the electrode/electrolyte interface, all of which lead to an increase in the degree of polarization. The present application provides a negative electrode active material, which uses graphite as a core, coats a porous carbon layer outside the graphite, deposits nano-silicon particles on the porous carbon layer, and uses a MXene material with good electrical conductivity to coat the outermost layer. coated to form a multi-layer coated negative electrode active silicon carbon material. The silicon carbon material of this structure can effectively solve the expansion of silicon, inhibit side reactions, and improve electronic conductivity, thereby improving the first Coulomb efficiency and reducing the capacity loss during the cycle caused by polarization.

1. Negative active material

In one aspect of the present application, the negative electrode active material provided by the present application includes graphite, silicon material, porous carbon and MXene material. The porous carbon covered by the graphite outer layer can provide sufficient buffer space for the expansion of silicon nanoparticles. The outer MXene layer not only plays the role of isolating the electrolyte, but also can withstand the extrusion stress caused by the rolling process while suppressing the occurrence of side reactions. , to ensure that the porous structure of the inner material is not damaged, it can also improve the electronic conductivity of the material, improve the first Coulomb efficiency and the capacity loss during the cycle caused by polarization, and the multi-layer coated silicon carbon material can also improve the nano-silicon The loading of the material further increases the gram capacity of the material.

According to some embodiments of the present application, the Dv50 of the negative electrode active material is 3 μm to 35 μm, such as 3 μm, 5 μm, 7 μm, 9 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 21 μm, 23 μm, 25 μm, 27 μm, 29 μm , 30μm, 32μm, 34μm and any value in between. According to some embodiments of the present application, the Dv50 of the negative electrode active material is 5 μm to 25 μm. In this application, Dv50 represents the volume distribution median particle size.

According to some embodiments of the present application, the negative electrode active material has a BET (specific surface area) of 1.0 m ² /g to 3.6 m ² /g, such as 1.2 m ² /g, 1.4 m ² /g, 1.6 m ² /g , 1.8m ² /g, 2.0m ² /g, 2.1m ² /g, 2.3m ² /g, 2.5m ² /g, 2.7m ² /g, 2.9m ² /g, 3.2m ² /g, 3.4 m ² /g and any value in between. According to some embodiments of the present application, the BET of the anode active material is 1.0 m ² /g to 3.0 m ² /g.

According to some embodiments of the present application, the mass content of silicon is 10% to 70% based on the mass of the negative electrode active material. According to some embodiments of the present application, the mass content of silicon is 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% and their any value in between.

According to some embodiments of the present application, the mass content of the MXene material is 0.1% to 3% based on the mass of the anode active material. According to some embodiments of the present application, the mass content of the MXene material is 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.2%, 2.5%, 2.7%, 2.9% and any value in between. The higher the content of MXene, the better the coating effect on the material and the smaller the polarization, but after the coating amount reaches a certain value, the effect on improving the first effect and reducing the capacity loss reaches the maximum. At this time, the coating amount is further increased. , the mass ratio of MXene to the negative electrode active material increases, while the proportion of the negative electrode active material silicon decreases, thereby reducing the gram capacity of the active material per unit mass.

According to some embodiments of the present application, the graphitization degree of the graphite is 92% to 96%, such as 93%, 94%, 95%. The charge-discharge capacity of the carbon negative electrode increases with the increase of graphitization degree, but too high graphitization degree will make the charge-discharge performance worse. The graphitization is too high, only the sp2 hybrid state exists, and it has a high lithium storage space. However, because the insertion of solvated lithium ions cannot be effectively prevented, the lithium storage space cannot be effectively utilized, so its charge-discharge performance is poor. Carbon materials with a high degree of graphitization and the existence of horizontally hybridized carbon atoms can meet the two conditions of being a negative electrode for lithium-ion batteries, namely, the formation of a beneficial SEI film and a larger lithium storage space. The graphitization is too low, the layered structure of the material is poor, the lithium ion is difficult to de-intercalate in the layered structure, and the polarization is large, resulting in fast cycle decay.

According to some embodiments of the present application, the graphite has a BET of 0.8 m ² /g to 2.0 m ² /g, such as 1.0 m ² /g, 1.2 m ² /g, 1.4 m ² /g, 1.6 m ² /g g, 1.8 m ² /g, 2.0 m ² /g, and any value in between. According to some embodiments of the present application, the graphite has a BET of 1.2 m ² /g to 2.0 m ² /g.

According to some embodiments of the present application, the graphite has a Dv50 of 3 μm to 30 μm, such as 3 μm, 5 μm, 7 μm, 9 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 21 μm, 23 μm, 25 μm, 27 μm, 29 μm, 30 μm and any value in between. The smaller the graphite particle, the smaller the van der Waals force that needs to be overcome during intercalation, the easier the intercalation is, and the smaller the particle is, the more the number of channels for lithium ion intercalation and deintercalation is relatively more, the more conducive to quickly reach the complete lithium intercalation state, but The larger the specific surface area of the particles that are too small to be in contact with the electrolyte, the greater the charge consumed by the SEI film formed during the first charge and discharge process, and the greater the irreversible capacity loss. According to some embodiments of the present application, the Dv50 of the graphite is 5 μm to 25 μm.

According to some embodiments of the present application, the pore size of the porous carbon is 0.1 μm to 2.5 μm, such as 0.2 μm, 0.4 μm, 0.5 μm, 0.7 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.3 μm, 1.5 μm, 1.7 μm μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.3 μm, and any value in between. According to some embodiments of the present application, the porous carbon has a pore wall thickness of 0.05 μm to 0.5 μm, such as 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, and any value therebetween. In some embodiments, the porous carbon has a pore wall thickness of 0.3 μm to 0.8 μm. When the pore size is large, the volume of silicon expands and shrinks with the progress of charging and discharging, which causes silicon to fall off from the pore walls of porous carbon, which affects the contact between silicon and porous carbon and reduces the electronic conductivity. When the pore size and wall thickness are suitable, although the volume of silicon will expand and contract during the cycle, the coating of the outer porous carbon layer prevents the agglomeration and electrical disconnection of the silicon particles, and the pore structure inside the carbon layer before and after the cycle. It is still stable, which helps the conduction of Li ⁺ and the release of stress. In some embodiments, the porous carbon has a pore wall thickness of 0.05 μm to 0.1 μm.

According to some embodiments of the present application, the Dv50 of the silicon material is 20 nm to 150 nm. According to some embodiments of the present application, the Dv50 of the silicon material is 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm and any value therebetween. The particle size of silicon plays a very important role in the performance of the battery. When the particle size of silicon is reduced to the order of 150 nm, the huge stress caused by the volume change of silicon can be greatly relieved. At the same time, nano-silicon can shorten the transport distance of Li ⁺ , which is beneficial to improve the dynamic properties of the material. However, due to the large specific surface area of nano-silicon particles, the SEI film easily consumes excess lithium salts, and the volume effect can easily lead to electrical dissociation between particles, resulting in a decrease in Coulombic efficiency. According to some embodiments of the present application, the Dv50 of the silicon material is 30 nm to 120 nm.

According to some embodiments of the present application, Dv50/Dv90 of the silicon material satisfies, 0.3≤Dv50/Dv90≤0.7. In some embodiments, the silicon particles have a Dv50/Dv90 of 0.4, 0.5, or 0.6.

According to some embodiments of the present application, the sheet diameter of the MXene material is 0.5 μm to 20 μm. In some embodiments, the sheet diameter of the MXene material is 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm and any value in between. The larger the lamella diameter of MXene, the more active sites, and the more conducive to the transfer of charges. However, if the lamella diameter is too large, MXene cannot be well attached to the surface of the active material during the coating process, and there are local folds. Case. According to some embodiments of the present application, the sheet diameter of the MXene material is preferably 3 μm to 15 μm.

According to some embodiments of the present application, the number of sheet layers of the MXene material is 1 to 5 layers, such as 2 layers, 3 layers or 4 layers. When the number of MXene layers is within the above range, the specific surface area is large, the active sites are many, and the electronic conductivity is good. The number of MXene layers is too low, the preparation is difficult and the cost is high. When the number of MXene layers is too large, the interlayer resistivity increases, which leads to an increase in polarization and a rapid capacity decay.

According to some embodiments of the present application, the sheet thickness of the MXene material is ≤8 nm, for example, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm or 7 nm. Too high a thickness, poor contact and reduced conductivity, resulting in increased polarization. In some embodiments of the present application, the sheet thickness of the MXene material is preferably 3 nm to 7 nm.

According to some embodiments of the present application, the lamellar spacing of the MXene material is greater than or equal to 0.5 nm, and the larger the lamellar spacing is, the more conducive to the de-intercalation of Li ⁺ , but the larger the lamellar spacing is, the greater the interlayer resistivity is. This leads to an increase in polarization and a rapid capacity decay. In some embodiments of the present application, the interlamellar spacing of the MXene material is 0.5 nm to 3 nm.

According to some embodiments of the present application, the general structural formula of the MXene is Mn ₊₁ X _n , wherein M is selected from at least one of Ti, Nb, V, Mo, Zr, Cr, W or Ta; X is At least one of C or N; n is 1, 2 or 3.

In some embodiments, the general structural formula of the MXene material is Mn ₊₁ X _n , wherein M is selected from one or more of Ti, Nb, V, Mo, Zr, Cr, W or Ta; n is 1, 2 or 3, X is C or N. In some embodiments, the general structural formula of the MXene material is (M ₁ , M ₂ ) _n+1 X _n , wherein M ₁ and M ₂ are each independently selected from Ti, Nb, V, Mo, Zr, Cr, W or One or more of Ta, n is 1, 2 or 3, X is C or N. In some embodiments, the general structural formula of the MXene material is Mn ₊₁ (X ₁ , X ₂ ) _n , wherein M is selected from one of Ti, Nb, V, Mo, Zr, Cr, W, Ta or more, n is ₁ , ₂ or 3; X1 and X2 are each independently C or N.

According to another aspect of the present application, the negative electrode active material provided by the present application includes graphite and a coating, the coating includes a first coating and a second coating, wherein the first coating coats the graphite At least a part of the surface of the first cladding is covered by a second cladding, the first cladding comprises silicon material and porous carbon, and the second cladding comprises MXene material.

According to some embodiments of the present application, the silicon material and the porous carbon coat at least a part of the surface of the graphite, and the MXene material coats at least a part of the surface of the silicon material and the porous carbon. According to some embodiments of the present application, the negative electrode active material includes graphite, a porous carbon layer coated on the surface of the graphite, nano-silicon deposited in the porous carbon, and an MXene material coated on the outside of the porous carbon and the nano-silicon. The porous carbon covered by the graphite outer layer can provide sufficient buffer space for the expansion of silicon nanoparticles, and the MXene material on the outside can isolate the electrolyte to a certain extent, inhibit the occurrence of side reactions, and at the same time can withstand the extrusion stress caused by the rolling process to ensure The porous structure of the coated layer is not damaged, and it can also improve the electronic conductivity of the material, improve the first Coulomb efficiency, and reduce the capacity loss during cycling due to polarization.

According to some embodiments of the present application, the silicon material in the first coating is attached to the porous carbon. Porous carbon can provide sufficient buffer space for the expansion of silicon particles. Although silicon undergoes volume expansion and contraction during cycling, the coating of the outer porous carbon layer prevents the agglomeration and electrical disconnection of silicon particles, while the pore structure inside the porous carbon layer remains stable before and after cycling, which helps Conduction of Li ⁺ and release of stress. According to some embodiments of the present application, the porous carbon is obtained by calcining a pore-forming agent mixed with a graphite raw material.

According to some embodiments of the present application, the number of layers of the covering is 1 to 5, such as 2 layers, 3 layers or 4 layers. Multi-layer coating can increase the loading of nano-silicon materials and further increase the gram capacity of the material, but the capacity loss during cycling caused by the excessive polarization of the number of coating layers increases.

According to some embodiments of the present application, the negative active material has a BET of 1.0 m ² /g to 3.6 m ² /g, such as 1.2 m ² /g, 1.4 m ² /g, 1.6 m ² /g, 1.8 m ² /g, 2.0m ² /g, 2.1m ² /g, 2.3m ² /g, 2.5m ² /g, 2.7m ² /g, 2.9m ² /g, 3.2m ² /g, 3.4m ² /g and any value in between. According to some embodiments of the present application, the BET of the anode active material is 1.0 m ² /g to 3.0 m ² /g.

According to some embodiments of the present application, the mass content of the MXene material is 0.1% to 3% based on the mass of the anode active material. According to some embodiments of the present application, the mass content of the MXene material is 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.2%, 2.5%, 2.7%, 2.9% and any value in between. The higher the content of MXene, the better the coating effect on the material and the smaller the polarization, but after the coating amount reaches a certain value, the effect on improving the first effect and reducing the capacity loss reaches the maximum. At this time, the coating amount is further increased. , will affect the gram capacity of the negative electrode active material to a certain extent.

According to some embodiments of the present application, the graphitization degree of the graphite is 92% to 96%, such as 93%, 94%, 95%. The charge-discharge capacity of the carbon negative electrode increases with the increase of graphitization degree, but too high graphitization degree will make the charge-discharge performance worse. The graphitization is too high, only the sp2 hybrid state exists, and it has a high lithium storage space. However, because the insertion of solvated lithium ions cannot be effectively prevented, the lithium storage space cannot be effectively utilized, so its charge-discharge performance is poor. Carbon materials with a high degree of graphitization and the existence of horizontally hybridized carbon atoms can satisfy the two conditions of being a negative electrode for lithium-ion batteries, namely, the formation of a beneficial SEI film and a larger space for lithium storage. The graphite is too low, the layered structure is poor, the lithium ion is difficult to de-intercalate in the layered structure, the polarization is large, and the cycle decay is fast.

According to some embodiments of the present application, the pore size of the porous carbon is 0.1 μm to 2.5 μm, such as 0.2 μm, 0.4 μm, 0.5 μm, 0.7 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.3 μm, 1.5 μm, 1.7 μm μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.3 μm, and any value in between. According to some embodiments of the present application, the porous carbon has a pore wall thickness of 0.05 μm to 0.5 μm, for example, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, and therebetween any value. In some embodiments, the porous carbon has a pore wall thickness of 0.3 μm to 0.8 μm. When the pore size is large, the volume of silicon expands and contracts with the progress of charging and discharging, which causes silicon to fall off from the pore walls of porous carbon, which affects the contact between silicon and porous carbon and reduces the electronic conductivity. When the pore size and wall thickness are suitable, although the volume of silicon will expand and contract during the cycle, the coating of the outer porous carbon layer prevents the agglomeration and electrical disconnection of the silicon particles, and the pore structure inside the carbon layer before and after the cycle. It is still stable, which helps the conduction of Li ⁺ and the release of stress.

According to some embodiments of the present application, the Dv50 of the silicon material is 20 nm to 150 nm. According to some embodiments of the present application, the Dv50 of the silicon material is 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm and any value therebetween. The particle size of silicon plays a very important role in the performance of the battery. When the particle size of silicon is reduced to the order of 150 nm, the huge stress caused by the volume change of silicon can be greatly relieved. At the same time, nano-silicon can shorten the transport distance of Li ⁺ , which is beneficial to improve the dynamic properties of the material. The particle size of silicon material is too small and the specific surface area is large, the SEI film is easy to consume excess lithium salt, and the volume effect is easy to cause electrical dissociation between particles, resulting in a decrease in Coulombic efficiency.

According to some embodiments of the present application, the sheet diameter of the MXene material is 0.5 μm to 20 μm. In some embodiments, the sheet diameter of the MXene material is 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm and any value in between. The larger the lamella diameter of MXene, the more active sites, and the more favorable for charge transfer. However, if the lamella diameter is too large, the MXene cannot be completely attached to the surface of the active material during the coating process, and there is a situation of local folding. . According to some embodiments of the present application, the sheet diameter of the MXene material is preferably 3 μm to 15 μm.

2. Negative electrode

According to some embodiments of the present application, the negative electrode includes a current collector and a negative electrode active material layer, and the negative electrode active material layer includes the negative electrode active material of the first aspect.

According to some embodiments of the present application, the anode active material layer further includes a binder and a conductive agent. In some embodiments, binders include, but are not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-containing Oxygen polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (esterified) styrene-butadiene rubber, epoxy resin or Nylon etc.

In some embodiments, conductive agents include, but are not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powders, metal fibers, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

In some embodiments, the current collector comprises: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, or any combination thereof.

The negative electrode of the present application can be prepared by a known method in the art. Usually, the negative electrode active material and optional conductive agent (such as carbon black and other carbon materials and metal particles, etc.), binder (such as SBR), other optional additives (such as PTC thermistor material) and other materials are mixed in Disperse together in a solvent (such as deionized water), uniformly coat the negative electrode current collector after stirring evenly, and obtain a negative electrode containing a negative electrode membrane after drying. A material such as a metal foil or a porous metal plate can be used as the negative electrode current collector.

3. Electrochemical device

Embodiments of the present application provide an electrochemical device including a negative electrode, a positive electrode, an electrolyte, and a separator.

negative electrode

The negative electrode in the electrochemical device of the present application includes the negative electrode active material of the present application.

positive electrode

Materials, compositions, and methods of making the positive electrodes that can be used in embodiments of the present application include any of those disclosed in the prior art.

In some embodiments, the positive electrode includes a current collector and a layer of positive active material on the current collector.

In some embodiments, the positive active material includes, but is not limited to: lithium cobalt oxide (LiCoO ₂ ), lithium nickel cobalt manganese (NCM) ternary material, lithium iron phosphate (LiFePO ₄ ), or lithium manganate (LiMn ₂ O ₄ ).

In some embodiments, the positive active material layer further includes a binder, and optionally a conductive material. The binder improves the bonding of the positive electrode active material particles to each other, and also improves the bonding of the positive electrode active material to the current collector.

In some embodiments, binders include, but are not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-containing Oxygen polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (esterified) styrene-butadiene rubber, epoxy resin or Nylon etc.

In some embodiments, conductive materials include, but are not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powders, metal fibers, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

In some embodiments, the current collector may include, but is not limited to, aluminum.

The positive electrode can be prepared by a preparation method known in the art. For example, the positive electrode can be obtained by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and coating the active material composition on a current collector. In some embodiments, the solvent may include, but is not limited to: N-methylpyrrolidone.

Electrolyte

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

In some embodiments, the electrolyte includes an organic solvent, a lithium salt, and an additive. The organic solvent of the electrolytic solution according to the present application may be any organic solvent known in the prior art that can be used as a solvent of the electrolytic solution. The electrolyte used in the electrolyte solution according to the present application is not limited, and it may be any electrolyte known in the prior art. The additive for the electrolyte according to the present application may be any additive known in the art as an additive for the electrolyte.

In some embodiments, the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate or ethyl propionate.

In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt.

In some embodiments, the lithium salts include, but are not limited to: lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium difluorophosphate (LiPO ₂ F ₂ ), bistrifluoromethanesulfonimide Lithium LiN(CF ₃ SO ₂ ) ₂ (LiTFSI), Lithium Bis(fluorosulfonyl)imide Li(N(SO ₂ F) ₂ )(LiFSI), Lithium Bisoxalate Borate LiB(C ₂ O ₄ ) ₂ (LiBOB) ) or lithium difluorooxalate borate LiBF ₂ (C ₂ O ₄ ) (LiDFOB).

In some embodiments, the concentration of the lithium salt in the electrolyte is: about 0.5 mol/L to 3 mol/L, about 0.5 mol/L to 2 mol/L, or about 0.8 mol/L to 1.5 mol/L.

isolation film

In some embodiments, a separator is provided between the positive electrode and the negative electrode to prevent short circuits. The material and shape of the isolation membrane that can be used in the embodiments of the present application are not particularly limited, and may be any of the techniques disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic or the like formed from a material that is stable to the electrolyte of the present application.

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

At least one surface of the base material layer is provided with a surface treatment layer, and the surface treatment layer may be a polymer layer or an inorganic material layer, or a layer formed by mixing a polymer and an inorganic material.

The inorganic layer includes inorganic particles and a binder, and the inorganic particles include aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, oxide At least one of yttrium, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. Binders include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinyl At least one of methyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene.

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

In some embodiments, the electrochemical devices of the present application include, but are not limited to, all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors.

In some embodiments, the electrochemical device is a lithium secondary battery.

In some embodiments, the lithium secondary battery includes, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

4. Electronic devices

The electronic device of the present application may be any device using the electrochemical device according to the third aspect of the present application.

In some embodiments, the electronic devices include, but are not limited to: notebook computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headsets , VCR, LCD TV, Portable Cleaner, Portable CD Player, Mini CD, Transceiver, Electronic Notepad, Calculator, Memory Card, Portable Recorder, Radio, Backup Power, Motor, Automobile, Motorcycle, Power-assisted Bicycle, Bicycle , lighting equipment, toys, game consoles, clocks, power tools, flashes, cameras, large household batteries or lithium-ion capacitors, etc.

testing method

Specific surface area test:

The negative electrode active materials in Examples and Comparative Examples were tested for specific surface area by nitrogen adsorption/desorption method measurement using a specific surface area analyzer (Tristar II 3020M). Among them, the specific test is carried out according to the national standard GB/T 19587-2017.

Particle size distribution test:

A Malvern particle size tester was used to test the particle size distribution of the negative electrode active materials in the examples and comparative examples, and the median particle diameters Dv50 and Dv90 of the negative electrode active materials were obtained. Among them, the specific test is carried out according to the national standard GB/T19077-2016.

Porous carbon pore size and pore wall thickness:

The cross-section observation method uses an ion polishing machine (model: JEOL-IB-09010CP) to cut the negative electrode along the direction perpendicular to the negative electrode current collector to obtain a cross-section. The number of voids in the measured field of view when magnified 3000 times on the cross section was read out by a scanning electron microscope (SEM), the average chord length (L) was calculated from this, and the average chord length was converted into the average void size (D). Most voids are not spherical, but close to irregular polyhedral configuration, but for the sake of convenience in the calculation process, they are still regarded as spheres with a certain diameter (D), and the relationship formula is: D=L/( 0.785) ² =L/0.616. In the formula: D is the average pore diameter of the porous body, and L is the measured average chord length of the voids. The wall thickness of the porous carbon is measured by the scale that comes with the scanning electron microscope, the wall thickness of 10-20 porous carbons is measured, and the average value is calculated to obtain the average value of the wall thickness of the porous carbon.

MXene sheet layer number, sheet diameter, sheet thickness:

The number of sheets of MXene was observed using the Tapping Model of atomic force microscope, and the sheet diameter and sheet thickness of MXene were tested with its own ruler. Since the shape of MXene is usually irregular, a line is drawn between the two points with the longest distance on the MXene surface, and the vertical bisector of the line is made. The average length of the MXene sheet in the above two directions is used as the diameter of the MXene sheet . As shown in FIG. 1 , the diameter dimension of the MXene sheet is D=(l ₁ +l ₂ )/2. The statistical quantity of one MXene sample should be no less than 100 pieces. The MXene sheet diameter is the average diameter of the MXene samples described above.

Degree of graphitization:

The degree of graphitization can be measured using X-ray diffraction (XRD). First measure the interplanar spacing d002 of graphite (002), and then use Franklin's formula (Mering-Maire formula) to calculate:

G=(0.3440–d002)/(0.3440–0.3354)×100%, where G is the degree of graphitization %, 0.3440 is the interlayer spacing of non-graphitized carbon (nm), and 0.3354 is the interlayer spacing of ideal graphite crystals (hexagonal It is half of the lattice constant of the c-axis of graphite) (nm), and d002 is the interlayer spacing (nm) of the (002) crystal plane of the carbon material.

Cycle capacity retention:

The prepared lithium-ion secondary battery was cycled at 1.5C/4C 2.8V-4.25V at 45°C. At the beginning of the cycle, a charge-discharge cycle was performed at 0.1C. The first charge capacity was recorded as C1, and the discharge capacity was recorded as C1. is D0, the first discharge capacity of 1.5C/4C is recorded as P0, and then after 49 cycles of 1.5C/4C, a 0.1C/0.1C cycle is performed, and the discharge capacity of 1.5C/4C at 499 cycles is recorded as P1, the 500th 0.1C/0.1C discharge capacity is recorded as D1, the capacity retention rate of the material after 500 cycles is R, the _total capacity loss Mtotal = 1-R, the capacity loss caused by the degradation of its own structure can be expressed as is Cap _loss =(D0-D1)/D0, the capacity loss due to polarization can be expressed as P _loss = _Mtotal -Cap _loss , since R=P1/D0,P _loss =(D1-P1)/D0, since The ratio of the capacity loss caused by polarization to the total capacity loss can be expressed as P, P=P _loss / _Mtotal =(D1-P1)/(D0-P1), and the first efficiency is denoted as T0, T0=D0/C1.

The specific test procedure is to place the lithium-ion battery in a 45°C incubator and let it stand for 30 minutes to make the lithium-ion battery reach a constant temperature. The lithium-ion battery that has reached a constant temperature is charged to 4.25V at a constant current rate of 0.1C at 45°C, charged to a constant voltage of 0.05C at 4.25V, left for 5 minutes, and then discharged to 3.0V at a constant current rate of 0.1C, and the battery is statically charged. Set for 5min; this is a 0.1C/0.1C cycle, then charge to 4.25V with 1.5C constant current, charge to 0.05C with constant voltage at 4.25V, let stand for 5 minutes, and then discharge to 3.0V with 4C rate constant current , let stand for 5min; this is a 1.5C/4C cycle, after 49 cycles of 1.5C/4C, do a 0.1C/0.1C cycle, and then use 1.5C/4C again to do 49 cycles, and the subsequent process is cycled according to this method back and forth.

The present application will be further described below with reference to the embodiments. It should be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application.

Example 1

Ethylenediaminetetraacetic acid (EDTA) and graphite raw material are mixed in a mass ratio of 2:98, wherein the Dv50 of the graphite raw material used is 18 μm, the BET is 1.31 m ² /g, the degree of graphitization is 96%, and the graphite raw material is 600 in an inert atmosphere. Sintered at ℃ for 2 h, cooled to room temperature under the protection of nitrogen atmosphere, and pulverized to obtain a graphite material coated with porous carbon. Nano-silicon particles with a Dv50 of 80 nm are deposited on the carbon, and the Dv50/Dv90 of the nano-silicon is 0.5. The amount of deposited silicon accounts for 13.8% of the mass of the negative active material (the sum of Ti ₄ N ₃ , Si, porous carbon, and graphite). ; MXene material Ti ₄ N ₃ was coated on silicon/porous carbon@graphite by spray drying method to obtain negative active material (Ti ₄ N ₃ @Si/porous carbon@graphite), wherein the sheet thickness of Ti ₄ N ₃ was 3 nm, the diameter of the lamellae is 5 μm, the number of lamellae is 3, and the mass percentage of MXene in the negative active material (here, the sum of Ti ₄ N ₃ , Si, porous carbon, and graphite) is 0.5%, and the specific surface area is used The BET of the prepared material measured by the particle size analyzer was 1.42 m ² /g, and the Dv50 of the prepared material measured by the particle size analyzer was 18.8 μm.

The prepared Ti ₄ N ₃ @Si/porous carbon@graphite negative electrode active material, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), thickener sodium carboxymethyl cellulose (CMC) according to the weight ratio of 95: 2:2:1 After fully stirring and mixing in the deionized water solvent system, it is coated on Cu foil for drying and cold pressing to obtain a negative pole piece.

The NCM811, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) were fully stirred and mixed in the N-methylpyrrolidone solvent system in a weight ratio of 94:3:3, and then coated on Al foil and dried. and cold pressing to obtain a positive pole piece.

The PE porous polymer film is used as the separator.

The positive pole piece, the separator, and the negative pole piece are stacked in sequence, so that the separator is in the middle of the positive and negative poles to play a role of isolation, and is wound to obtain a bare cell. The bare cell was placed in an aluminum-plastic film, injected with the prepared basic electrolyte (ethylene carbonate:diethyl carbonate=3:7, the addition amount of fluoroethylene carbonate was 10%, 1M lithium hexafluorophosphate) and packaged.

The charge cutoff voltage of the assembled lithium ion secondary battery was 4.25V.

Example 2 to Example 3

The preparation process of the lithium ion battery is the same as that of Example 1, except that:

On the basis of Example 1, the negative electrode active material is coated with one or two layers of Ti ₄ N ₃ @Si/porous carbon, and the specific parameters are shown in Table 1-1.

Comparative Example 1

The surface layer of the negative electrode active material is not coated with Ti ₄ N ₃ , and the specific parameters are shown in Table 1-1.

Comparative Example 2

The preparation process of lithium-ion battery is the same as that of Comparative Example 1, except that:

After preparing the composite material Si/porous carbon@graphite according to the method of Example 1, a layer of amorphous carbon was deposited on the Si/porous carbon@graphite by vapor deposition method, and the deposition time was 5h. The specific parameters are shown in Table 1-1. .

Table 1-1 shows the raw material parameters used for preparing the negative electrode active materials in Examples 1-3 and Comparative Examples 1-2.

Table 1-1

Table 1-2 shows the performance test results of the negative electrode active materials and lithium ion batteries of Examples 1-3 and Comparative Examples 1-2.

Table 1-2

According to the comparison between Example 1 and Comparative Examples 1-2 in Table 1, it can be seen that the present application coats MXene on the outermost layer of graphite, which can effectively improve the active material compared to coating other carbon layers such as amorphous carbon. The gram capacity and the first coulombic efficiency reduce the capacity loss during cycling caused by polarization. It can be seen from Example 1, Comparative Example 1, and Comparative Example 2 that the material coated with MXene can exert a higher gram capacity and first effect, and at the same time significantly reduce the loss caused by polarization. This may be because MXene has good electronic conductivity, and MXene is coated on the outer layer of the material, which can effectively reduce the contact between the silicon carbon material and the electrolyte, reduce side reactions, and thus reduce the capacity loss caused by polarization. From Examples 1, 2, and 3, it can be found that with the increase of the number of coating layers, the gram capacity of the active material increases significantly, mainly because this coating method can increase the loading of silicon material, and the gram capacity of silicon is high, The higher the loading, the higher the capacity of the active material per unit mass, so as to achieve the purpose of improving the energy density.

Example 4 to Example 9

The preparation methods of the negative electrode active materials and batteries of Examples 4 to 9 are similar to the preparation method of Example 1, but the parameter values of the graphite raw materials are adjusted, and the different parameters are shown in Table 2-1.

Table 2-1 shows the parameters of the raw materials for preparing the negative electrode active materials in Examples 4-9.

table 2-1

Table 2-2 shows the performance test results of the negative electrode active materials and lithium ion batteries of Examples 4-9.

Table 2-2

According to the comparison between Example 1 and Examples 4-6, it can be seen that under the condition that other conditions are basically unchanged, the Dv50 of graphite particles in the range of 5 μm to 25 μm has a relatively low capacity during cycling caused by polarization. loss. The smaller the graphite particle is, the smaller the van der Waals force that needs to be overcome during intercalation, the easier the intercalation is, and the smaller the particle, the more the number of channels for intercalation and deintercalation of lithium ions, which is more conducive to quickly reaching a complete lithium intercalation state. The larger the specific surface area of the particles that are too small to be in contact with the electrolyte, the greater the charge consumed by the SEI film formed during the first charge and discharge process, and the greater the irreversible capacity loss.

According to the comparison between Example 1 and Examples 7-9, it can be seen that under the condition that other conditions are basically unchanged, when the graphitization degree of graphite particles is in the range of 92% to 96%, there is a lower cycle caused by polarization capacity loss in the process. Generally speaking, the charge-discharge capacity of carbon negative electrode increases with the increase of graphitization degree, but too high graphitization degree will make the charge-discharge performance worse. The graphitization is too high, only the sp2 hybrid state exists, and it has a high lithium storage space. However, because the insertion of solvated lithium ions cannot be effectively prevented, the lithium storage space cannot be effectively utilized, so its charge-discharge performance is poor. Carbon materials with a high degree of graphitization and the existence of horizontally hybridized carbon atoms can satisfy the two conditions of being a negative electrode for lithium-ion batteries, namely, the formation of a beneficial SEI film and a larger space for lithium storage. If the graphite is too low, the layered structure is poor, and it is difficult for lithium ions to be deintercalated in the layered structure, and the polarization is large, resulting in fast cycle decay.

Example 10 to Example 18

The preparation methods of the negative electrode active materials and batteries of Examples 10 to 18 are similar to the preparation method of Example 1, but the parameter values of the silicon particles are adjusted, and the different parameters are shown in Table 3-1.

Table 3-1 shows the parameters of the raw materials for preparing the negative electrode active materials in Examples 10-18.

Table 3-1

Table 3-2 shows the performance test results of the negative electrode active materials and lithium ion batteries of Examples 10-18.

Table 3-2

According to the comparison between Example 1 and Examples 10-12, it can be seen that under the condition that other conditions are basically unchanged, the Dv50 of silicon particles in the range of 40nm to 150nm has a lower capacity loss during cycling caused by polarization . When the particle size of silicon is reduced to the order of 150 nm, the huge stress caused by the volume change of silicon can be greatly relieved. At the same time, nano-silicon can shorten the transport distance of Li ⁺ , which is beneficial to improve the dynamic properties of the material. However, due to the large specific surface area of nano-silicon particles, the SEI film is prone to consume excess lithium salts, and the volume effect can easily lead to electrical dissociation between particles, resulting in a decrease in Coulombic efficiency.

According to the comparison between Example 1 and Examples 13-15, it can be seen that under the condition that other conditions remain unchanged, when the Dv50/Dv90 of silicon particles is in the range of 0.3 to 0.7, the capacity during cycling caused by the polarization is relatively low. loss.

According to the comparison between Example 1 and Examples 16-18, it can be seen that under the condition that other conditions remain unchanged, when the content of silicon particles is in the range of 10% to 70%, there is a lower polarization caused by the cycling process. capacity loss.

Example 19 to Example 21

The preparation methods of the negative electrode active materials and batteries of Examples 19 to 21 are similar to the preparation method of Example 1, but the parameter values of the porous carbon are adjusted by adjusting the sintering temperature, and the different parameters are shown in Table 4-1.

Table 4-1 shows the parameters of the raw materials for preparing the negative electrode active materials in Examples 19-21.

Table 4-1

Table 4-2 shows the performance test results of the negative electrode active materials and lithium ion batteries of Examples 19-21.

Table 4-2

According to the comparison between Example 1 and Examples 19-21, it can be seen that under the condition that other conditions are basically unchanged, the pore size of porous carbon is in the range of 0.1 μm to 2.5 μm, and when the wall thickness is greater than 0.1 μm, it has a lower pore size. Capacity loss during cycling due to polarization. When the pore size is large, the volume of silicon expands and contracts with the progress of charging and discharging, which causes silicon to fall off from the pore walls of porous carbon, which affects the contact between silicon and porous carbon and reduces the electronic conductivity. When the pore size and wall thickness are suitable, although the volume of silicon will expand and contract during the cycle, the coating of the outer porous carbon layer prevents the agglomeration and electrical disconnection of the silicon particles, and the pore structure inside the carbon layer before and after the cycle. It is still stable, which helps the conduction of Li ⁺ and the release of stress.

Example 22 to Example 36

The preparation methods of the negative electrode active materials and batteries of Examples 22 to 36 are similar to the preparation method of Example 1, but the parameter values of the MXene material are adjusted, and the different parameters are shown in Table 5-1.

Table 5-1 shows the parameters of the raw materials for preparing the negative electrode active materials in Examples 22-36.

Table 5-1

Table 5-2 shows the performance test results of the negative electrode active materials and lithium ion batteries of Examples 22-36.

Table 5-2

According to the data in Table 5-1 and Table 5-2, it can be seen that the MXene sheet diameter, sheet number, sheet thickness and MXene content all affect the capacity loss during cycling due to polarization. Specifically, the larger the sheet diameter of MXene, the more active sites, and the more favorable for charge transport. The greater the number of MXene sheets and the greater the thickness of the sheet, the greater the interlayer resistivity, which leads to an increase in polarization and a rapid capacity decay. The higher the content of MXene, the better the coating effect on the material and the smaller the polarization, but after the coating amount reaches a certain value, the effect on the first effect and the capacity loss P reaches the maximum. At this time, the coating amount is further increased, It will affect the performance of the gram capacity of the active material, mainly because the proportion of the coating per unit mass increases, which means that the proportion of the active material decreases, and the gram capacity mainly depends on the active material.

The above is only an example of the present application, and does not limit the present application in any form. Although the present application is disclosed above with preferred embodiments, it is not intended to limit the present disclosure. Within the scope of the technical solution of the present application, any changes or modifications made by using the technical content disclosed above are equivalent to equivalent implementation cases, and are all within the scope of the technical solution of the present application.

Claims

A negative active material includes graphite, silicon material, porous carbon and MXene material.
The negative electrode active material according to claim 1, wherein the negative electrode active material satisfies at least one of the following features (1) to (4):

(1) Dv50 is 3μm to 35μm;

(2) BET is 1.0m 2 /g to 3.6m 2 /g;

(3) The mass content of silicon is 10% to 70% based on the mass of the negative electrode active material;

(4) The mass content of the MXene material is 0.1% to 3% based on the mass of the anode active material.
The negative electrode active material according to claim 1, wherein the graphite satisfies at least one of the following characteristics (a) to (c):

(a) a degree of graphitization of 92% to 96%;

(b) Dv50 of graphite is 3 μm to 30 μm;

(c) BET is 0.8 m 2 /g to 2.0 m 2 /g.
The negative electrode active material according to claim 1, wherein the porous carbon satisfies at least one of the following characteristics (d) to (e):

(d) the pore size is 0.1 μm to 2.5 μm;

(e) The pore wall thickness is 0.05 μm to 0.5 μm.
The anode active material according to claim 1, wherein Dv50 of the silicon material is 20 nm to 150 nm, and satisfies 0.3≤Dv50/Dv90≤0.7.
The negative electrode active material according to claim 1, wherein the general structural formula of the MXene material is Mn + 1Xn , wherein M is selected from Ti, Nb, V, Mo, Zr, Cr, W or Ta at least one; X is at least one of C or N; n is 1, 2, or 3; and the MXene material satisfies at least one of the following features (f) to (h):

(f) The lamellae of MXene have diameters ranging from 0.5 μm to 20 μm;

(g) the number of lamella layers of MXene is 1 to 5 layers;

(h) The sheet thickness of MXene is ≤8 nm.
A negative electrode active material, comprising graphite and a coating, the coating comprising a first coating and a second coating, wherein the first coating covers at least a part of the surface of the graphite, and the second coating The material coats at least a part of the surface of the first coating, the first coating includes silicon material and porous carbon, and the second coating includes MXene material.
The negative electrode active material according to claim 7, wherein the negative electrode active material satisfies at least one of the following features (1) to (4):

(1) Dv50 is 3μm to 35μm;

(2) BET is 1.0m 2 /g to 3.6m 2 /g;

(3) The mass content of silicon is 10% to 70% based on the mass of the negative electrode active material;

(4) The mass content of the MXene material is 0.1% to 3% based on the mass of the anode active material.
The negative electrode active material according to claim 7, wherein the graphite satisfies at least one of the following characteristics (a) to (c):

(a) a degree of graphitization of 92% to 96%;

(b) Dv50 of graphite is 3 μm to 30 μm;

(c) BET is 0.8 m 2 /g to 2.0 m 2 /g.
The negative electrode active material according to claim 7, wherein the porous carbon satisfies at least one of the following characteristics (d) to (e):

(d) the pore size is 0.1 μm to 2.5 μm;

(e) The pore wall thickness is 0.05 μm to 0.5 μm.
The anode active material according to claim 7, wherein Dv50 of the silicon material is 20 nm to 150 nm, and satisfies 0.3≤Dv50/Dv90≤0.7.
The negative electrode active material according to claim 7, wherein the general structural formula of the MXene material is Mn + 1Xn , wherein M is selected from Ti, Nb, V, Mo, Zr, Cr, W or Ta at least one; X is at least one of C or N; n is 1, 2, or 3; and the MXene material satisfies at least one of the following features (f) to (h):

(f) The lamella diameter of MXene ranges from 0.5 μm to 20 μm;

(g) the number of lamella layers of MXene is 1 to 5 layers;

(h) The sheet thickness of MXene is ≤8 nm.
An electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode comprises the negative electrode active material according to any one of claims 1 to 12.
An electronic device comprising the electrochemical device of claim 13 .