Disclosure of Invention
The invention aims to overcome the defect of difficulty in large-scale continuous production in the prior art, and provides a method for continuously preparing current collector-free silicon-carbon negative electrode paper so as to improve the production efficiency of a negative electrode.
Therefore, the invention provides the following technical scheme:
a method for continuously preparing a current collector-free silicon-carbon cathode electrode paper comprises the following steps:
a material mixing step: injecting the expanded graphite, an auxiliary carbon source and a silicon source into a mixing bin together, and mixing to obtain a mixed material;
and (3) rolling: injecting the mixed material into a forming cabin, and performing rolling treatment on the mixed material through a rolling device to prepare sheet-shaped silicon-carbon composite electrode paper;
a purification step: and transferring the silicon-carbon paper composite electrode paper into a purification cabin, and removing impurities in the silicon-carbon paper composite electrode paper by adopting a high-temperature low-pressure purification technology to obtain the current-collector-free silicon-carbon negative electrode paper.
According to the scheme, various raw materials are mixed to obtain a mixed material, then the mixed material is injected into a forming cabin, the mixed material is rolled and formed under the action of a rolling device to obtain flaky silicon-carbon composite electrode paper, the silicon-carbon composite electrode paper is transferred into a purifying cabin in a homeotropic manner, and the silicon-carbon negative electrode paper free of a current collector is obtained after impurities are removed and can be directly used as electrode paper. The whole production process is in a production line type, continuous and large-scale, so that the efficiency can be greatly improved, and continuous and reliable production can be realized.
In a further optimized scheme, in the material mixing step, the mass content of the expanded graphite is more than 65%, the mass content of the silicon source is 2-15%, and the balance is an auxiliary carbon source.
In the scheme, the mass content of the expanded graphene is limited to be more than 65%, so that the mixed material can be effectively guaranteed to be pressed into a film. The theoretical capacity of silicon is much higher than that of carbon, but the content of silicon in the material is limited to be 2-15% in consideration of the matching problem of the anode and the cathode of the battery, so that the high capacity can be kept, and the stability of circulation can be guaranteed.
In a further optimized scheme, before the step of enabling the slurry in the seasoning cabin to flow out of the discharge hole, the method further comprises the following steps of: pouring the liquid, the carbon source, the silicon source and the dispersing agent into a container in any order, stirring and crushing to obtain slurry, and then injecting the slurry into a seasoning cabin.
In one embodiment, the thickness of the silicon-carbon composite electrode paper is 0.025 to 1.0mm in the rolling step.
In a further optimized scheme, in the purification step, the temperature environment is 800-2200 ℃, and the negative pressure environment is less than 10 DEG-2Pa。
In the above scheme, through experimental analysis, the impurities can be better removed by performing purification treatment under the above environment, and the obtained negative electrode paper has better performance.
In the material mixing step, the material mixing mode is one or more of ball milling, roll pairing and jet milling. Further optimally, in the material mixing step, the material mixing mode is adopted by matching of jet milling and ball milling. The mixing uniformity of the raw materials can be promoted by combining a plurality of mixing modes.
In a further optimized scheme, before the mixing step, the method further comprises a puffing step: and injecting the expandable graphite oxide into the expansion cabin, and performing expansion treatment at the temperature of 800-.
The expanded graphite can be directly used for the existing available expanded graphite, and can be obtained by processing through an expansion step under the condition of no existing material, so that the production continuity is guaranteed.
In a further preferred embodiment, before the puffing step, the method further comprises an oxidation step: adding the purified expandable graphite into a mixture consisting of acid, strong acid salt and an oxidant, stirring at the temperature of 0-100 ℃ to achieve the aim of pre-oxidation, and drying to obtain the oxidized expandable graphite.
The current-collector-free silicon-carbon negative electrode paper can be directly used for the available oxidized expandable graphite, can be obtained by the oxidation step treatment in the absence of the available materials, further ensures the production continuity, and can be produced even under the condition of only the most original materials to be used as the electrode.
Compared with the prior art, the invention has the following advantages:
the method can be used for continuous large-scale production, is stable and reliable, effectively utilizes resources, and reduces energy consumption and production cost.
The obtained sample is directly an electrode and can be directly used, and the complicated process of preparing and coating materials in the traditional process for preparing the negative electrode with the current collector is omitted.
And a current collector is not needed, so that the weight of the battery can be greatly reduced, and the energy density is increased.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.
Before describing the method of the present invention, the production hardware system upon which the method of the present invention depends will be described.
Referring to fig. 1, the present embodiment schematically discloses a system for continuously preparing a current-collector-free silicon carbon negative electrode paper, including an oxidation reaction device, an expansion cabin 12, a mixing cabin 13, a forming cabin 15, and a purification cabin 16.
The main function of the oxidation reaction device is to realize graphite oxidation. More specifically, the oxidation reaction device comprises a container, a stirrer and a heating device, wherein the container is used for containing a mixture consisting of purified expandable graphite, acid, strong acid salt and an oxidant; the heating device can heat the container or is arranged in the container to heat the air in the container, so that the temperature reaches a specified temperature range; the stirring device stirs and purifies the mixture of the expandable graphite, the acid, the strong acid salt and the oxidant in the temperature range to promote oxidation, and the oxidized expandable graphite 11 is obtained.
It will be readily appreciated that in some embodiments, there may be a directly available oxidized expandable graphite feedstock, and that oxidation reaction equipment may not be required at this time.
The puffing chamber 12, the mixing chamber 13, the forming chamber 15 and the purifying chamber 16 respectively comprise a chamber body, and the corresponding treatment process is carried out in the chamber body.
The expansion cabin 12 mainly functions to perform expansion treatment on the expandable graphite oxide 11 to obtain expanded graphite after expansion. It will be readily appreciated that there may be, in some embodiments, expanded graphite stock available directly, and that the expansion tank 12 is not required at this time.
The mixing cabin 13 is mainly used for mixing an auxiliary carbon source, nano-silicon and expanded graphite to obtain a mixed material; the forming cabin 15 is mainly used for rolling and forming the mixed material to obtain silicon-carbon composite electrode paper; the purification cabin 16 is mainly used for purifying the silicon-carbon composite electrode paper to remove impurities, so as to obtain the current collector-free silicon-carbon negative electrode paper 17.
As shown in fig. 1, the mixing chamber 13 is provided with a feeding port, and the expanded graphite coming out of the expansion chamber 12 and the added auxiliary carbon source and silicon enter the mixing chamber 13 through the feeding port. As can be easily understood, the number of the feeding holes can be one, and the expanded graphite, the auxiliary carbon source and the silicon are sequentially added into the mixing cabin 13; the number of the feeding holes is 3, and the feeding holes are respectively an auxiliary carbon source feeding hole 18, a silicon feeding hole 19 and an expanded graphite feeding hole, so that the raw materials can be added into the mixing cabin 13 at the same time, and the time is saved.
The mixing chamber 13 is also provided with a discharge port (first discharge port described in claim 1) to facilitate the injection of the mixed material into the molding chamber 15. If the mixing compartment 13 and the shaping compartment 15 are provided separately, the shaping compartment 15 is also provided with a feed opening. As a more preferable embodiment, the mixing cabin 13 and the forming cabin 15 are connected with each other, which has the advantages that the discharge port of the mixing cabin 13 is the feed port of the forming cabin 15, thereby avoiding the additional arrangement of a communicating pipe to communicate the mixing cabin 13 with the forming cabin 15, reducing the cost, and simultaneously ensuring the stability and reliability of the connection between the mixing cabin 13 and the forming cabin 15.
A rolling device 14 is installed in the forming cabin 15 and is used for performing rolling treatment on the injected mixed material, so that the mixed material is rolled to form the sheet-shaped silicon-carbon composite electrode paper. The shaft of the rolling device 14 may be directly connected to the bulkhead of the forming chamber 15, and in order to further enhance the stability of the rolling device 14, a support frame may be erected first, and then the rolling device 14 may be mounted on the support frame. As shown in fig. 1, the rolling device 14 may comprise a plurality of sets of rollers arranged in series, and the arrangement between adjacent sets of rollers is not limited to the inclined arrangement shown in the figure. The compounding passes through the discharge gate (connect a discharging pipe in preferred discharge gate, and the mouth of pipe of discharging pipe directly aims at between two compression rollers of a set of compression roller), and two compression rollers extrude the compounding each other, can be with the bulk compounding compression moulding for flaky silicon-carbon composite electrode paper. The thickness of the obtained silicon-carbon composite electrode paper can be adjusted by adjusting the pressure applied by the two press rolls.
The molding chamber 15 is also provided with a discharge port (second discharge port in the claims) through which the obtained silicon-carbon composite electrode paper enters the purification chamber 16. Similarly, the forming cabin 15 and the purifying cabin 16 are preferably connected directly into a whole, and the silicon-carbon composite electrode paper coming out of the forming cabin 15 can directly enter the purifying cabin 16.
In the purifying cabin 16, a high-temperature low-pressure purifying technology is adopted to purify the silicon-carbon composite electrodeRemoving impurities possibly existing in the paper, and arranging a heating and vacuum-pumping device in the purification chamber 16 to provide a high-temperature environment, such as a temperature between 800--2Pa or less. The wound electrode paper material obtained after purification treatment, namely the silicon-carbon negative electrode paper 17 without the current collector, can be directly used as the negative electrode material of the lithium ion battery to assemble the battery.
The mixing cabin, the forming cabin and the purifying cabin can be respectively independent cabin bodies and are connected with each other through pipelines, but are preferably connected with each other in sequence to form a whole, and can be of a vertical structure or a horizontal structure.
The method of the present invention is explained based on a specific experimental example.
With continuing reference to fig. 1 and fig. 2, with the support of the above system, the method for continuously preparing the collector-free silicon carbon negative electrode paper provided by the present invention comprises the following steps:
an oxidation step 1: adding the purified expandable graphite into a mixture consisting of acid, strong acid salt and an oxidant, stirring at the temperature of 0-100 ℃, wherein the stirring time is variable so as to achieve the aim of pre-oxidation, and then washing and drying to obtain the oxidized expandable graphite.
In this step, the acid may be one of sulfuric acid/nitric acid/hydrochloric acid/phosphoric acid, or a mixture of a plurality of acids mixed in an arbitrary ratio. The strong acid salt can be one of sulfate/nitrate/phosphate or a mixture of a plurality of strong acid salts mixed in any proportion. The oxidant can be one of potassium permanganate, potassium dichromate and chromium trioxide, or a mixture of a plurality of oxidants in any proportion.
And (2) puffing: and (3) injecting the oxidized expandable graphite obtained in the oxidation step (1) into an expansion cabin, and performing expansion treatment at the temperature of 800-. In addition, the puffing treatment process needs to be carried out in an air or any inert gas environment, and can be carried out in an air environment for cost saving.
As shown in fig. 2, the oxidation step 1 and the expansion step 2 are indicated by dashed boxes in fig. 2, while the other steps are indicated by solid boxes, since in some cases the oxidation step 1 and/or the expansion step 2 may not need to be performed, for example in the case of expanded graphite that is ready for use, the oxidation step 1 and the expansion step 2 need not be performed. Whether the oxidation step 1 and the expansion step 2 are carried out or not depends mainly on the production conditions, and is not a step necessarily carried out in any case.
And a material mixing step 3: and injecting the expanded graphite, the auxiliary carbon source and the silicon source into a mixing bin together, and mixing to obtain a mixed material. The mixing mode can be one or more of ball milling, counter-rolling and jet milling, such as jet milling and ball milling.
In this step, as shown in fig. 1, if the expanded graphite directly flows into the mixing chamber from the expansion chamber, the auxiliary carbon source and the silicon source are injected while the mixed material flows in, so as to further improve the efficiency.
In this step, the auxiliary carbon source may be one of the commonly used carbon sources such as sugars, organic high molecular polymers, pitch, nano coal, etc., or a mixture of a plurality of carbon sources. The silicon source is preferably nano-silicon, for example, nano-silicon with a size of 50-200 nm.
In the step, in order to ensure that the mixed material can be effectively prepared into a film after being pressed in the subsequent steps, the mass content of the expanded graphite is preferably more than 65% through experimental tests. The silicon can effectively improve the theoretical capacity, but the more the silicon is, the better the silicon is, the silicon source has the mass content of 2-15 percent, and the rest is an auxiliary carbon source. Under the mixture ratio, the specific capacity of the silicon-carbon anode material is between 300-600, and the performance of the electrode can be kept for a long time.
And a rolling step 4: and (3) injecting the mixed material obtained in the mixing step (3) into a forming cabin, and performing rolling treatment on the mixed material through a rolling device to prepare the flaky silicon-carbon composite electrode paper.
In this step, as shown in fig. 1, the mixed material may directly flow into the roller pressure cabin from the mixing cabin, directly fall onto the roller pressing device, and then fall between two rollers of a group of rollers, and then the mixed material is pressed into a sheet shape by the pressure of the rollers, so as to obtain the silicon-carbon composite electrode paper. The thickness of the silicon-carbon composite electrode paper can be controlled by adjusting the pressure of the press roll and the moving speed of the silicon-carbon composite electrode paper. For example, under the conditions of pressure of 1-30MPa and linear speed of 1-50m/min, silicon-carbon composite electrode paper with thickness of 25um-1.0mm can be obtained.
And 5, a purification step: and transferring the silicon-carbon paper composite electrode paper into a purification cabin, and removing impurities in the silicon-carbon paper composite electrode paper by adopting a high-temperature low-pressure purification technology to obtain the current-collector-free silicon-carbon negative electrode paper.
In this step, the term "high temperature and low pressure" means that the temperature is 800--2Pa. The obtained wound electrode paper material can be directly used as a negative electrode material of a lithium ion battery to assemble the battery.
The preparation process can prepare the silicon-carbon cathode electrode paper without the current collector, not only does not need the current collector, but also can reliably realize large-scale continuous production and improve the production efficiency.
Two more specific experimental examples are also listed here. In the test example 1, the expandable graphite oxide, sucrose and nano silicon are directly used as raw materials; in test example 2, expanded graphite, sucrose and nano-silicon were directly used as raw materials.
Specifically, in test example 1, the procedure was as follows:
(1) injecting the oxidized expandable graphite into an expansion bin, and expanding for 5s in the air at 900 ℃ to form the vermicular expanded graphite.
(2) And simultaneously injecting the expanded graphite, the sucrose and the nano-silicon into a mixing bin for uniformly mixing, wherein the mass percentages of the expanded graphite, the sucrose and the nano-silicon are respectively 70%, 25% and 5%, and the mixing mode is air flow milling and paired rolling matching.
(3) And injecting the uniformly mixed materials into a forming cabin at the speed of 15m/min, and pressing the mixed materials by a pressing roller at the pressure of 20mPa to obtain the silicon-carbon composite electrode paper with the thickness of about 0.17 mm.
(4) And transferring the silicon-carbon paper composite electrode roll into a purification cabin, and removing impurities at 1200 ℃ in an environment with negative pressure of 0.007Pa to obtain a final product, namely the current collector-free silicon-carbon negative electrode paper.
Specifically, in test example 2, the procedure was as follows:
(1) and simultaneously injecting the expanded graphite, the sucrose and the nano-silicon into a mixing bin for uniformly mixing, wherein the expanded graphite, the sucrose and the nano-silicon are respectively 82%, 16% and 2% in mass percent, and the mixing mode is an airflow mill.
(2) And injecting the uniformly mixed materials into a forming cabin at the speed of 24m/min, and pressing the mixed materials by a pressing roller at the pressure of 20MPa to obtain the silicon-carbon composite electrode paper with the thickness of about 0.41 mm.
(3) And transferring the silicon-carbon paper composite electrode roll into a purification cabin, and removing impurities at 1600 ℃ under the negative pressure of 0.006Pa to obtain the silicon-carbon negative electrode paper free of current collector.
Through tests, the batteries prepared by taking the current collector-free silicon-carbon cathode electrode paper prepared in the two groups of test examples as a cathode material show good performance, large storage capacity and good cyclicity.
It should be noted that a large number of tests are performed in actual tests, which are not listed here, and thus are only exemplified.
The above description is only for the specific embodiments of the present invention, and the protection scope of the present invention is not limited thereto, and any person skilled in the art can easily think of the changes or substitutions within the technical scope of the present invention, and should be covered within the protection scope of the present invention.