WO2017024903A1

WO2017024903A1 - Preparation method for tin-carbon composite negative electrode material

Info

Publication number: WO2017024903A1
Application number: PCT/CN2016/087181
Authority: WO
Inventors: 田东
Original assignee: 田东
Priority date: 2015-08-07
Filing date: 2016-06-25
Publication date: 2017-02-16
Also published as: CN105161671A

Abstract

Provided in the present invention is a preparation method for a tin-carbon composite negative electrode material. The tin-carbon composite negative electrode material is a tin-carbon composite negative electrode material having a core-shell structure of which the outer layer is a composite cladding layer jointly formed by asphalt, a resin, and tin powder, and the inner layer consists of graphite. The tin-carbon composite material prepared per the present method retains the high specific capacity characteristic of tin and, at the same time, provides the graphite with a modification effect, and increases the cycle stability of the material as a whole, thus increasing the energy density of the negative electrode material for a lithium-ion battery, allowing the negative electrode material to be provided with a specific capacity higher than that of a common carbon negative electrode material in commercially available lithium-ion batteries, and satisfying increasing energy density requirements that various portable electric devices have on batteries.

Description

Preparation method of tin carbon composite anode material

Technical field

The invention relates to the field of lithium ion batteries, in particular to a method for preparing a tin-carbon composite anode material for a cathode of a lithium ion battery, wherein the outer layer of the tin-carbon composite anode material prepared by the method is formed by the joint of asphalt and resin and tin powder. The composite coating layer has an inner layer of a tin-carbon composite anode material having a core-shell structure composed of graphite.

Background technique

Since Sony Corporation of Japan took the lead in developing and commercializing lithium-ion batteries in 1990, lithium-ion batteries have developed rapidly. Today, lithium-ion batteries have been widely used in various fields of civil and military applications. With the continuous advancement of technology, people have put forward more and higher requirements for the performance of batteries: the miniaturization and personalized development of electronic devices require batteries with smaller volume and higher specific energy output; aerospace energy requirements The battery has a cycle life, better low temperature charge and discharge performance and higher safety performance; electric vehicles require batteries with high capacity, low cost, high stability and safety performance.

At present, the commercial lithium ion battery anode material is made of graphite-based carbon material, has low lithium insertion/deintercalation potential, suitable reversible capacity, rich resources, and low price, and is an ideal anode material for lithium ion batteries. However, its theoretical specific capacity is only 372 mAh/g, which limits the further improvement of the specific energy of lithium-ion batteries and cannot meet the needs of the increasingly high-energy portable mobile power sources. At the same time, when graphite is used as a negative electrode material, a solid electrolyte membrane (SEI) is formed on the surface during the first charge and discharge process. The solid electrolyte membrane is formed by reacting an electrolyte, a negative electrode material, and lithium ions, and irreversibly consuming lithium ions, which is a major factor in forming an irreversible capacity. The second is that the electrolyte is easily embedded in the lithium ion intercalation process. During the process of eviction, the electrolyte is reduced, and the resulting gas product causes the graphite sheet to peel off. Especially in the electrolyte containing PC, the graphite sheet peels off and a new interface is formed, resulting in further SEI formation, irreversible capacity increase, and circulation. The stability is degraded. The amorphous carbon formed by pyrolysis of the resin-based polymer has a low degree of order and a loose structure, and lithium ions can be relatively freely embedded and extracted therein without a large influence on the structure thereof.

In addition, tin is one of the most promising anode materials for carbon materials because tin has a maximum capacity of up to 4200 mAh/g; and has a smooth discharge platform similar to graphite. However, similar to other high-capacity metals, tin has very poor cycle performance and cannot perform normal charge and discharge cycles. When tin is used as a negative electrode material, it will be accompanied by a huge volume change, resulting in collapse of the material structure and spalling of the electrode material, causing the electrode material to lose electrical contact, thereby causing a sharp drop in the cycle performance of the electrode, and finally causing electrode failure, thus in lithium It is difficult to practically use in an ion battery. Studies have shown that small-sized tin or its alloys have a great improvement in both capacity and cycle performance. When the particles of the alloy material reach the nanometer level, the volume expansion during charging and discharging is greatly reduced, and the performance is also greatly reduced. It will be improved, but the nanomaterial has a large surface energy and is prone to agglomeration, which will reduce the charge and discharge efficiency and accelerate the attenuation of the capacity, thereby offsetting the advantages of the nanoparticles; the tin film prepared by various deposition methods can To some extent, the material's cycle life is prolonged, but its high first irreversible capacity cannot be eliminated, which restricts the practical use of this material. Another research trend to improve the performance of tin anodes is to prepare composites or alloys of tin and other materials. Among them, tin/carbon composites prepared by combining the stability of carbon materials with the high specific capacity of tin have shown great application. prospect. The preparation process of the existing tin/carbon composite materials mainly has the following aspects:

(1) Mechanical ball milling: This method combines tin powder and carbon and directly ball-mills into nanocomposites. After high-efficiency mechanical ball milling, tin powder and carbon materials can be uniformly dispersed on the nanometer scale. Since the nano-sized tin powder is surrounded by the carbon material, the volume change due to lithium insertion and delithiation can be suppressed, To some extent, improve the cycle performance of tin materials. As the tin content increases, the specific capacity of the tin/carbon composite increases, but the cycle stability deteriorates. At the same time, the crystal structure, size and compatibility of the two components in the composite determine the final properties of the material. The main problem of the composite material prepared by this method is that the first irreversible capacity is large due to the large specific surface area and the inability to completely prevent the micro-oxidation during the ball milling process;

(2) High-polymer-wrapped tin powder for carbonization: This method can disperse the tin powder well in the carbon matrix and improve its cycle performance; however, due to the formation of amorphous carbon after carbonization of the polymer, it cannot be fully reflected. The stability and electrical conductivity of the graphite carbon material, and may increase the first irreversible capacity of the composite due to the amorphous structure, so the overall performance is not ideal;

(3) Asphalt as a binder to bond tin powder and graphite to carbonize: Asphalt can not only uniformly bind graphite and tin as a binder, but also acts as a surface coating after carbonization. However, the asphalt low-temperature carbonization product is also an amorphous structure, and the binder of the asphalt as a binder has limited carbon and tin, so the performance of the prepared material needs to be further improved;

(4) CVD coating: The tin or tin/carbon mixture is directly coated with a carbon film by a CVD method. After the coating, the cycle performance of tin is improved, but due to the small amount of coating, the carbon matrix is not fully reflected, and the prepared material has poor performance, but the material prepared by this method can be used to study the lithium storage of tin/carbon composite. mechanism.

As shown above, in the current coating modification treatment, only the resin hard carbon precursor or the asphalt soft carbon precursor is coated separately. The main advantage of using resin as the coating material is that the resin has good fluidity at low temperature, can not only coat the surface, but also easily penetrates into the material particles through the micropores, which is beneficial to improve the tap density and electronic conductivity of the material. It can also be cured by heating, introduction of catalyst or ultraviolet irradiation. The resin will not melt and deform during the pyrolysis process, and will not cause significant expansion. However, there are also some problems, mainly: the yield of carbon materials obtained by pyrolysis of the resin. It is low in brittleness, has many volatiles in the pyrolysis process, has a high specific surface area, and has strong adhesion to the resin. It is easy to cause the coated particles to adhere together, and the coating layer is easily destroyed during heat treatment. These problems affect the cycle efficiency, cycle stability and electrode compressibility of the resin coating material. Asphalt, petroleum tar, coal tar or a mixture thereof is used as a coating material, the pitch pyrolysis carbon has a smaller specific surface area than the resin pyrolysis carbon coating, and the affinity of the material is better, the structure is firmer, but the asphalt is coated During the heating process, it is deformed by melting. If the amount is too much, the particles of the coating material are easily bonded to each other. If the amount is too small, the coating is uneven, and the heating process is easy to expand, which affects the electrical properties of the material.

Summary of the invention

The object of the present invention is to provide a method for preparing a tin-carbon composite anode material, wherein the outer layer of the tin-carbon composite anode material is a composite coating layer formed by asphalt and a resin and tin powder, and the inner layer is composed of graphite and has a core shell. Structure of tin carbon composite anode material. The tin-carbon composite material prepared by the method maintains the high specific capacity characteristic of tin, and simultaneously modifies the graphite, increases the overall cycle stability of the material, and improves the energy density of the negative electrode material of the lithium ion battery, so that the negative electrode The material has a higher specific capacity than the carbon negative electrode materials commonly used in commercial lithium ion batteries, and meets the increasing energy density requirements of various portable electric devices for batteries.

In order to achieve the above object, the present invention is implemented by the following technical solutions.

A method for preparing a tin-carbon composite anode material, comprising the steps of:

1. Adding a pitch having a softening point between 100 ° C and 300 ° C and a resin having a softening point between 50 ° C and 150 ° C in a weight ratio of 1:1.5 to 4 to a kneading kettle having a heating and stirring device, Heating at a rate of 10 to 40 ° C / min until the asphalt and resin are both melted into a liquid;

2, then add 2% ~ 5% of the curing agent of the curing agent, under the protection of inert gas, continue to stir until the various components are evenly mixed;

3. Weigh the graphite according to the total weight of the resin and the asphalt: the weight of the graphite is 1:4-20, and add it to the mixing device with stirring and heating function, the stirring speed is 60-180 rpm, and the heating temperature is 40 ° C ~ 140 ° C, the temperature is slightly lower than the temperature of the resin softening point;

4. Weigh the tin powder and the dispersing solvent according to the ratio of graphite: tin powder: dispersing solvent=10:0.5～2:1.5～6, add the tin powder to the dispersing solvent, and uniformly disperse the ultrasonic wave, then add to the step 3 In the graphite mixing device, stirring and mixing are uniform;

5. Pass the uniformly mixed liquid in step 2 through an atomizing device, and add it to the mixing device in which graphite and tin powder are mixed in step 4. After mixing for 2 to 5 hours, stop heating and follow the rate of 5 to 20 ° C / min. Cooling to a normal temperature state, at which time the resin has completed curing;

6. The powder obtained in step 5 is heated to 700-900 ° C at a rate of 1 to 5 ° C / min under the protection of an inert gas, and then kept for 1 to 5 hours, naturally cooled, and sieved after cooling. The tin-carbon composite anode material obtained by the invention.

In the present invention, the asphalt described in the step 1 includes one or more mixtures of coal tar pitch, petroleum pitch, modified pitch, mesophase pitch, and condensed polycyclic polynuclear aromatic hydrocarbon obtained by upgrading the pitch. The softening point is above 100 °C.

In the present invention, the resin described in the step 1 is a thermoplastic resin, and one or a mixture of one or more of a furan resin, a urea resin, a pyrimidine resin, a phenol resin, an epoxy resin, and a polyoxymethylene acrylate resin.

In the present invention, the stirring time described in the step 1 is 80 to 130 minutes, and the final temperature of the heating is 30 to 40 ° C higher than the highest softening point of the pitch and the resin in the component.

In the present invention, the curing agent described in the step 2 is hexamethylenetetramine, diethylaminopropylamine, trimethylhexamethylenediamine, dihexyltriamine, and a thermosetting resin having a curing action. One or more mixtures.

In the present invention, the graphite described in the step 3 is one or a mixture of natural graphite or artificial graphite, and the average particle diameter is 5 to 30 μm, the tap density is ≥0.75 g/cm ³ , and the specific surface area is ≤6.0. m ² /g.

In the present invention, the tin powder described in the step 4 has an average particle diameter of ≤ 100 nm.

In the present invention, the dispersion solvent described in the step 4 is one of ethanol, isopropanol, carbon disulfide, toluene, xylene or distilled water with a dispersion medium.

In the present invention, the atomization in the step 5 is one of the atomization devices operating by the principle of ultrasonic atomization, centrifugal atomization, and high pressure atomization.

In the above preparation method, the inert gas is a mixture of one or both of nitrogen, argon and helium.

When graphite is used as a negative electrode material, a solid electrolyte membrane (SEI) is formed on the surface during the first charge and discharge process. The solid electrolyte membrane is formed by reacting an electrolyte, a negative electrode material, and lithium ions, and irreversibly consuming lithium ions, which is a major factor in forming an irreversible capacity. The second is that the electrolyte is easily embedded in the lithium ion intercalation process. During the process of eviction, the electrolyte is reduced, and the resulting gas product causes the graphite sheet to peel off. Especially in the electrolyte containing PC, the graphite sheet peels off and a new interface is formed, resulting in further SEI formation, irreversible capacity increase, and circulation. The stability is degraded. The amorphous carbon formed by pyrolysis of the phenolic resin has a low order degree and a loose structure, and the lithium ion can be relatively freely embedded and extracted therein without a large influence on the structure thereof, so that the powdering is not easy to occur. At the same time, the pyrolytic carbon is coated as a barrier on the periphery of the graphite, which can effectively prevent the action of the organic solvent and the graphite body, thereby preventing the graphite layer from being peeled off and pulverized by the co-insertion of the lithium ion and the electrolyte. However, due to the excessive number of small molecules in the resin during the heat treatment, excessive voids are formed on the surface of the coated material during the overflow process, resulting in an excessive surface area of the coated graphite. Causes the first irreversible capacity to be too large. The composite coating material formed by mixing asphalt and resin forms a pyrolytic carbon coating on the graphite surface, which not only utilizes the advantages of both the asphalt and the resin, but also ensures the uniformity and operability of the two, and is heat treated. After that, the pitch carbon and the resin carbon are pinned together, the complementation is insufficient, the comprehensive electrical properties of the coated graphite are improved, and the composite composite material can be prepared by adjusting the ratio of the asphalt and the resin, thereby controlling the coated graphite. The specific surface area of the particles satisfies the different requirements for cycleability and rate.

When tin powder is used as the negative electrode active material, the volume of the particles changes greatly during charge and discharge, causing the tin particles to be powdered and the electrode cycle property to be very poor. The composite coating material of the present invention through the performance of asphalt and resin can not only uniformly combine graphite and tin as a binder, but also functions as a surface coating after carbonization. This method greatly improves the cycle performance of tin.

Compared with the prior art, the beneficial effects of the present invention are:

1. The most prominent innovation of the present invention is that the cladding material precursor is composited and then coated with tin powder and graphite; the uniformity of mixing of various coating material precursors is ensured, and no solvent is needed, and the environment is Friendly; in addition, the process is simple, the cost is low, and it is easy to industrialize production;

2. The invention adds a certain amount of resin curing agent to the composite coating material, and after curing, the resin can play a skeleton supporting role to prevent the asphalt from melting during the carbonization process and causing the powder to form a sticky joint block after the carbonization, and the need The phenomenon of crushing the material to cause the coating of the material to be broken;

3. The amorphous carbon formed by the high-temperature carbonization of the resin has strong corrosion resistance to the electrolyte. At the same time, the interlayer spacing of the amorphous carbon is large, and the lithium ions can enter and exit quickly, satisfying the high-rate charge and discharge of the lithium ion battery. The requirement is that the holes and voids formed by the carbonization of the resin can buffer the volume effect of the tin powder during charging and discharging, and ensure the overall stability of the material;

4. The invention has obvious superiority as the coating material of the resin-based hard carbon precursor or the asphalt-based soft carbon precursor, and the asphalt carbon and the resin carbon are pinned together, and the complementation is insufficient. Effectively increase the strength of the coating to ensure the cycle stability of the tin-carbon composite.

detailed description

In order to make the technical means, the creative features, the workflow, and the method of use of the present invention easy to understand and understand, the present invention is further explained below.

The mesophase pitch (softening point 250 ° C) and the phenolic resin (softening point 110 ° C) were added together in a ratio of 1:3 (3.5 Kg and 10.5 Kg) to a 20 L kneading kettle, and the temperature was raised and heated to 300 ° C. After both the asphalt and the resin are melted into a liquid, 0.315 Kg of a curing agent, hexamethylenetetramine, is added in a proportion of 3% by weight of the resin, and stirring is continued until the components are uniformly mixed; according to the total weight of the asphalt and the resin: graphite weight = Weigh 126Kg of natural graphite in a ratio of 1:9, add a mixing device with stirring and heating function, stir and raise the temperature to 100 ° C; weigh 18.9 according to the ratio of graphite: tin powder: dispersing solvent = 10:1.5:3 Kg has an average particle size of 50nm tin powder and 37.8kg of alcohol solution. After adding the tin powder to the alcohol solution, it is dispersed by an ultrasonic device, and after being dispersed, it is added to the above mixed graphite device and stirred for 120 minutes. The mixed liquid of uniformly mixed asphalt, resin and curing agent is sprayed into the graphite stirring device through the ultrasonic atomizing device until the mixed liquid is completely sprayed, and after mixing for another 3 hours, the heating is stopped and according to 10 ° C / min. The temperature is lowered to the normal temperature state, at which time the resin has been solidified; finally, the uniformly mixed powder is heated to 900 ° C at a rate of 5 ° C / min, kept for 1 hour, then cooled to room temperature, and sieved to obtain the tin of the present invention. Carbon composite anode material.

The electrode material was used as the working electrode, the lithium sheet was used as the counter electrode, 1M LiPF6/DMC:EC:DEC=1:1:1, the solution was the electrolyte, the polypropylene microporous membrane was the diaphragm, and assembled into an analog battery, at 50 mA/ The current density of g is charged and discharged. The electrode material had an initial discharge capacity of 425 mAh/g, and the capacity after 100 cycles was still 394 mAh/g, and the retention rate was 92.7%.

Example 2

Coal tar pitch (softening point 120 ° C) and phenolic resin (softening point 110 ° C) were added together in a ratio of 1:3 (3 Kg and 12 Kg) to a 20 L kneading kettle, and the heating was started to be heated to 150 ° C in asphalt and resin. After being melted into a liquid, 0.675 Kg of a curing agent, trimethylhexamethylenediamine, is added in a proportion of 4.5% by weight of the resin, and stirring is continued until the components are uniformly mixed; according to the total weight of the asphalt and the resin: graphite weight = Weigh 150Kg of natural graphite in a ratio of 1:10, add a mixing device with stirring and heating function, stir and raise the temperature to 105 °C, weigh 30Kg according to the ratio of graphite: tin powder: dispersing solvent=10:2:4 The tin powder having an average particle diameter of 50 nm and a solution of 60 kg of isopropyl alcohol are added to the isopropanol solution, dispersed by an ultrasonic device, and dispersed, and then added to the apparatus for mixing the graphite, followed by stirring for 150 minutes. Then, the mixed liquid of the uniformly mixed asphalt, resin and curing agent is sprayed into the graphite stirring device through the ultrasonic atomizing device until the mixed liquid is completely sprayed, and after mixing for another 2 hours, the heating is stopped and according to 15 ° C / min. The rate is lowered to the normal temperature state, at which time the resin has been solidified; finally, the uniformly mixed powder is heated to 850 ° C at a rate of 3 ° C / min, kept for 2 hours, then cooled to room temperature, and sieved to obtain the present invention. Tin carbon composite anode material.

The electrode material test conditions were as described in Example 1, charged and discharged at a current density of 50 mA/g. The initial discharge capacity of the electrode material reached 451 mAh/g, and the capacity after 100 cycles was still 426 mAh/g, and the retention rate was 94.4%.

The basic principles, main features, and advantages of the present invention are shown and described above. It should be understood by those skilled in the art that the present invention is not limited by the foregoing embodiments, and that the present invention is only described in the foregoing description and the description of the present invention, without departing from the spirit and scope of the invention. Various changes and modifications are intended to be included within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and their equivalents.

Claims

A method for preparing a tin-carbon composite anode material, comprising the steps of:

(1) adding a pitch having a softening point between 100 ° C and 300 ° C and a resin having a softening point between 50 ° C and 150 ° C in a weight ratio of 1:1.5 to 4 to a kneading kettle having a heating and stirring device, Heating at a rate of 10 to 40 ° C / min to the asphalt and resin are melted into a liquid;

(2) then adding a curing agent in an amount of 2% to 5% by weight of the resin, and continuously stirring under the protection of an inert gas until the components are uniformly mixed;

(3) Weigh graphite according to the total weight of resin and asphalt: the weight of graphite is 1:4-20, and add it to the mixing device with stirring and heating function, stirring speed is 60-180 rpm, heating temperature 40 ° C ~ 140 ° C, the temperature is slightly lower than the temperature of the resin softening point;

(4) Weigh the tin powder and the dispersing solvent according to the ratio of graphite: tin powder: dispersing solvent=10:0.5-2:1.5-6, add the tin powder to the dispersing solvent, and uniformly disperse the ultrasonic wave, and then add to step 3 Stirring and mixing evenly in the graphite mixing device;

(5) The uniformly mixed liquid in the step 2 is passed through an atomizing device, and added to the mixing device in which the graphite and the tin powder are mixed in the step 4, and after mixing for 2 to 5 hours, the heating is stopped and the temperature is 5 to 20 ° C / min. The temperature is lowered to a normal temperature state, at which time the resin has been cured;

(6) The powder obtained in the step 5 is heated to 700-1900 ° C at a rate of 1 to 5 ° C / min under the protection of an inert gas, and then kept for 1 to 5 hours, naturally cooled, and sieved after cooling. The modified graphite anode material obtained by the present invention is used.
The invention relates to a method for preparing a tin-carbon composite anode material, characterized in that: the asphalt described in the step (1) comprises coal tar pitch, petroleum asphalt, modified asphalt, mesophase pitch, condensed polycyclic multi-core obtained by upgrading asphalt. One or more mixtures of aromatic hydrocarbons having a softening point above 100 °C.
A method for preparing a tin-carbon composite anode material, characterized in that the resin described in the step (1) is a thermoplastic resin, including furan resin, urea-formaldehyde resin, pyrimidine resin, phenolic resin, epoxy resin and polyacetal acrylic acid One or more mixtures of ester resins.
A method for preparing a tin-carbon composite anode material, characterized in that the stirring time in the step (1) is 80-130 min, and the final temperature of the heating is 30-40 higher than the highest softening point of the asphalt and the resin in the component. °C.
A method for preparing a tin-carbon composite anode material, characterized in that the curing agent described in the step (2) is hexamethylenetetramine, diethylaminopropylamine, trimethylhexamethylenediamine, and One or a mixture of one or more of a triamine, a thermosetting resin having a curing action.
A method for preparing a tin-carbon composite anode material, characterized in that the graphite described in the step (3) is one of or a mixture of natural graphite or artificial graphite, and the average particle diameter is 5 to 30 μm. The solid density is ≥0.75 g/cm 3 and the specific surface area is ≤6.0 m 2 /g.
A method for preparing a tin-carbon composite anode material, characterized in that the tin powder described in the step (4) has an average particle diameter of ≤100 nm.
A method for preparing a tin-carbon composite anode material, characterized in that the dispersion solvent described in the step (4) is one of ethanol, isopropanol, carbon disulfide, toluene, xylene or distilled water with a dispersion medium.
The invention relates to a method for preparing a tin-carbon composite anode material, characterized in that: in the step (5), one of the atomization devices working by the principle of ultrasonic atomization, centrifugal atomization and high-pressure atomization is used.