Disclosure of Invention
In order to overcome the defects in the prior art, the main object of the present invention is to provide a lithium ion battery silicon cathode and a battery, which can solve the problem of controlling the expansion of silicon material.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a lithium ion battery silicon negative electrode comprises a silicon active material, an electrolyte material and a binder which are mixed with each other; the electrolyte material is a particle material with a three-layer composite structure, and comprises a porous core, a ceramic fast ion conductor layer in the middle layer and a protective layer in the outer layer;
the protective layer is a protective carbon layer; the protective carbon layer is deposited on the surface of the ceramic fast ion conductor layer in a thermal deposition mode of a carbon precursor;
the protective carbon layer is also provided with a polymer solid electrolyte, and the polymer solid electrolyte is of a porous structure;
the polymer solid electrolyte includes a polymer, a lithium salt, and a first conductive agent; the polymer is polyacrylate which is one or more of polymethyl methacrylate, polyethyl methacrylate, polymethyl acrylate, polyethyl methacrylate and polyethyl acrylate; the first conductive agent is a conductive carbon material.
Optionally, the porosity of the porous core is 20-95%; the pore size of the porous inner core is not more than 5 nm.
Optionally, the porous core has a void volume of 50-95%.
Optionally, the porous core is made of a porous conductive material.
Optionally, the porous core is prepared from a porous conductive carbon material.
Optionally, the silicon-based electrolyte further comprises a second conductive agent, wherein the second conductive agent is placed among the silicon active material, the electrolyte material and the binder and is uniformly mixed; the ratio of the weight of the second conductive agent to the total weight of the silicon negative electrode of the lithium ion battery is not more than 2%.
Optionally, the particle size of the porous core is 1-10 μm, and the thickness of the ceramic fast ion conductor layer is 10-500 nm; the thickness of the protective layer is 1-50 nm.
Optionally, the weight of the silicon active material accounts for 90-97% of the total weight of the silicon negative electrode of the lithium ion battery; the weight of the electrolyte material accounts for 1-5% of the total weight of the lithium ion battery silicon cathode; the weight of the binder accounts for 0.01-5% of the total weight of the lithium ion battery silicon negative electrode.
The invention also provides a lithium ion battery which comprises the lithium ion battery silicon cathode.
According to the silicon cathode of the lithium ion battery provided by the invention, the electrolyte material with a specific structure is added, the electrolyte material is provided with the porous inner core, and the electrolyte material is uniformly mixed in the silicon cathode, so that the expansion deformation generated in the expansion process of the silicon cathode is absorbed by the pores in the electrolyte material, and the problem of expansion in the use process of the silicon cathode is solved.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying 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. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a silicon negative electrode of a lithium ion battery, and generally, the material of the silicon negative electrode of the lithium ion battery can comprise a silicon active material, an electrolyte material 1 and a binder. The silicon active material, the electrolyte material 1 and the binder are uniformly mixed to prepare a solid, namely the lithium ion battery silicon cathode. The weight of the silicon active material accounts for 90-97% of the total weight of the silicon cathode of the lithium ion battery. The weight of the electrolyte material 1 accounts for 1-5% of the total weight of the silicon cathode of the lithium ion battery. The weight of the binder accounts for 0.01-5% of the total weight of the silicon cathode of the lithium ion battery. The binder may be a binder commonly used in lithium ion batteries for the purpose of increasing the bonding strength of the cured silicon negative electrode of the lithium ion battery, and may be selected as desired by those skilled in the art.
There is no particular requirement for the silicon active material selection for the silicon negative electrode, and known silicon negative electrode active materials may be used in the present invention without departing from the inventive concept, including but not limited to silicon carbon or silicon oxygen negative electrode active materials.
The binder may be one or more of polytetrafluoroethylene, styrene butadiene rubber, hydroxypropyl methylcellulose, sodium carboxymethylcellulose, hydroxyethyl cellulose, and polyvinyl alcohol.
The structural schematic diagram of the electrolyte material 1 is shown in fig. 1, and the electrolyte material 1 is a granular material with a three-layer composite structure. The three-layer composite structure of the electrolyte material 1 includes a porous core 11 at the center, a ceramic fast ion conductor layer 12 in the middle layer, and a protective layer 13 in the outer layer. The porous core 11 is a granular material having a porous structure, and the granular shape is not limited to the illustrated spherical or ellipsoidal shape, but may be other irregular granular shapes. Alternatively, the porosity of the porous core 11 is 20-95%. Preferably, the porosity of the porous core 11 is 50-95% in order to better absorb the expansion deformation during use against the silicon negative electrode. Regarding the selection of the porosity of the porous core 11, the porous cores 11 with different porosities have different abilities to absorb the expansion deformation generated in the expansion process of the silicon negative electrode, and the ability to absorb the expansion deformation is positively correlated with the porosity. When the porosity of the porous core 11 is less than 20%, the voids of the electrolyte material 1 are insufficient to absorb the expansion deformation generated during the expansion of the silicon negative electrode. When the porosity of the porous core 11 is greater than 95%, too many voids are formed in the electrolyte material 1, the preparation process is difficult, the structural strength of the particles of the electrolyte material 1 is significantly reduced, and the compactness of the negative electrode is easily insufficient.
The ceramic fast ion conductor layer 12 is fast-ion conductive ceramics (fast-ion conductive ceramics), which refers to ceramics having electron (or hole) conductivity or ion conductivity under certain conditions (temperature, pressure). The ceramic fast ion conductor layer 12 may be formed of a known ceramic fast ion conductor, which includes, but is not limited to, one or more of an oxide fast ion conductor, a sulfide fast ion conductor, and a selenide fast ion conductor, and may also be any of ceramic particles having ion conductivity, such as lithium niobate, lithium aluminum titanium phosphate, and the like.
The protective layer 13 is used to separate an electrolyte (the electrolyte is located between the positive electrode and the negative electrode of the lithium ion battery, and is used to provide transferred electrons, ions, or holes, and may be an electrolyte solution or a solid electrolyte, and the solid electrolyte is LLZO, and the like) of the lithium ion battery from the ceramic fast ion conductor layer 12, so as to prevent the electrolyte of the lithium ion battery from eroding the ceramic fast ion conductor layer 12. Specifically, the pore diameter of the porous core 11 is not more than 5 nm. The grain diameter of the porous core 11 is 1-10 μm, and the thickness of the ceramic fast ion conductor layer 12 is 10-500 nm. The thickness of the protective layer 13 is 1-50 nm. Optionally, a second conductive agent may be further added to the material of the silicon negative electrode of the lithium ion battery. The second conductive agent, the silicon active material, the electrolyte material 1 and the binder are uniformly mixed and then cured. The second conductive agent is used for increasing the conductive performance of the lithium ion battery silicon cathode. The second conductive agent may be a conductive agent commonly used in lithium ion batteries, such as a mixture of one or more of acetylene black, carbon black, graphite, carbon nanotubes, carbon nanofibers, and the like.
The protective layer 13 is a protective carbon layer. The protective layer 13 of the electrolyte material 1 can be prepared on the surface of the ceramic fast ion conductor layer 12 by a deposition method. The protective carbon layer also includes a polymer solid electrolyte. The polymer solid electrolyte is a porous structure. A protective carbon layer may be deposited on the surface of the ceramic fast ion conductor layer 12 by thermal deposition of a carbon precursor. For example, carbon precursors at 900 ℃ and C2H4Thermal deposition is carried out under an atmosphere. The thermal deposition method is a well-known manufacturing process for those skilled in the art and is not described in detail herein. The polymer solid electrolyte includes a polymer, a lithium salt, and a first conductive agent. Among them, the polymer may be polyacrylate. The polyacrylate can be one or more of polymethyl methacrylate, polyethyl methacrylate, polymethyl acrylate, polyethyl methacrylate, polyethyl ethyl acrylate, etc. The first conductive agent is a conductive carbon-based material, for example, the first conductive agent may be a mixture of one or more of acetylene black, carbon black, graphite, carbon nanotubes, carbon nanofibers, and the like. Optionally, the protective carbon layer is deposited to a thickness of 1-50nm, and an alternative method of preparing the protective carbon layer including the polymer solid electrolyte is: the polymethacrylate is generated by an in-situ polymerization method. Specifically, the electrolyte material 1 deposited with the protective carbon layer is dipped in a solution containing acrylate monomers, and after the dipping is finished, a polymer solid electrolyte is formed in the protective carbon layer in an in-situ polymerization mode.
The invention provides a silicon cathode of a lithium ion battery, which comprises the following steps: mixing a silicon active material, a binder and an electrolyte material 1 with a specific structure, stirring to form slurry with uniformly mixed components, and then drying/solidifying/curing and other processes to make the slurry become solid, namely preparing the silicon cathode of the lithium ion battery. It should be understood that the preparation method of the silicon negative electrode of the lithium ion battery of the present invention is to use the silicon negative electrode preparation method commonly used by those skilled in the art for solidification, and the focus is that the electrolyte material 1 used in the silicon negative electrode of the lithium ion battery of the present invention has a specific structure. Namely, the electrolyte material 1 is a three-layer composite structure, wherein the center of the electrolyte material is provided with a porous core 11, the middle layer is a ceramic fast ion conductor layer 12, and the outer layer is a protective layer 13. According to the silicon cathode of the lithium ion battery provided by the invention, the electrolyte material 1 is provided with the porous inner core 11 with the porosity of 20-95%, and the porous inner core 11 is uniformly mixed in the silicon cathode, so that the expansion deformation caused by the volume expansion of the silicon cathode of the lithium ion battery in the charging and discharging processes is absorbed by the electrolyte material 1, and the problem of expansion of the silicon cathode in the using process is solved.
In an alternative embodiment, the porous core 11 of the electrolyte material 1 is made of a porous conductive material. The porous inner core 11 is prepared from the conductive material, so that the electrolyte material 1 can enhance the conductivity of the lithium ion battery silicon cathode in the actual use process. Of course, the porous core 11 of the electrolyte material 1 may also be a porous structure made of a non-conductive material. When the porous core 11 is made of a non-conductive material, a second conductive agent needs to be added to the material of the lithium ion battery silicon negative electrode to enhance the conductivity of the lithium ion battery silicon negative electrode in the actual use process. Optionally, the porous core 11 is made of a porous conductive carbon material. For example, the method for preparing the porous core 11 from the porous conductive carbon material comprises the following steps: and carbonizing and activating the polymer precursor to prepare the porous conductive carbon material. The carbonization and activation processes of polymer precursors are well known to those skilled in the art. For example, the carbonization process can be carried out by heating at 800-1000 ℃ in nitrogen atmosphere to realize carbonization; the activation process may be performed under conditions of heating to 500 ℃. —, 1100 ℃ in an oxidizing atmosphere (e.g., an atmosphere of water vapor, carbon dioxide, etc.). Carbonization and activation processes for preparing porous carbon or other porous materials are known in the art and will not be described in detail herein.
The method for coating the porous core 11 with the ceramic fast ion conductor layer 12 of the electrolyte material 1 can adopt a known mechanofusion method to carry out liquid phase coating, or adopts a rotary fluidized bed coating method to coat the ceramic fast ion conductor layer 12 on the surface of the porous core 11. Optionally, the thickness of the ceramic fast ion conductor layer 12 is 10nm-500nm, preferably, the thickness of the ceramic fast ion conductor layer 12 is 30nm-100 nm. The thickness of the ceramic fast ion conductor layer 12 can be designed to be adapted to the particle size of the porous core 11 (i.e. to be a certain ratio to the particle size of the porous core 11), so that the amount of the second conductive agent can be reduced after the ceramic fast ion conductor layer 12 is added. Preferably, the ratio of the weight of the second conductive agent to the total weight of the silicon negative electrode of the lithium ion battery is not more than 2%. Further, the ratio of the weight of the second conductive agent to the total weight of the silicon negative electrode of the lithium ion battery is not more than 1%. Further, the second conductive agent is not added.
The invention also provides a lithium ion battery which comprises a battery shell, an electrode group and electrolyte. The electrode group and the electrolyte are sealed in a battery case. The electrode group includes a positive electrode, a separator, and a negative electrode. The lithium ion battery comprises a lithium ion battery silicon negative electrode as described previously.
In practical tests, the invention provides 6 lithium ion batteries with different compositions, namely, the lithium ion batteries of the examples 1 to 6. Comparative example 1 a silicon material was used directly for the negative electrode. Examples 1-6 the composition of 6 different lithium ion battery silicon negative electrodes was selected and is shown in table 1 below.
Table 1 composition of silicon negative electrode of lithium ion battery of examples 1 to 6 and comparative example
In table 1, the electrolyte refers to an electrolyte between the positive electrode and the negative electrode, and may be a solid electrolyte or an electrolytic solution. When the electrolyte is an electrolytic solution, preferably, a plasticizer is added. Wherein, inIn the invention, super-P is a conductive agent; PMMA is polymethyl methacrylate; LCO is lithium cobaltate and has the chemical formula of LiCoO2(ii) a LLZO is a garnet-type solid electrolyte; (EC + DMC +1MLiPF6) One kind of electrolyte, EC is ethylene carbonate, DMC is dimethyl carbonate, LiPF6Is lithium hexafluorophosphate. Conductive carbon-25 nm, i.e., a conductive carbon layer with a thickness of 25 nm.
Table 2 composition table of porous cores of lithium ion batteries of examples 7 to 10 and comparative examples when porosity is different
In table 2, the porosity of the porous core in the electrolyte material used for the silicon negative electrodes of the lithium ion batteries of examples 7 to 10 was selected to have different values, respectively, for performance tests.
Examples 1 to 6 and comparative examples 1 and 7 to 10 were subjected to a cycle performance test and an anode expansion growth rate test. The test results are shown in Table 3.
The test parameters and methods for the cycle performance test are as follows:
temperature: 25 +/-2 ℃;
charging to a final voltage by 1C or specified current, cutting off the current by 0.05C, and standing for 30 min;
discharging at 1C to the final discharge voltage (2.75V), recording the discharge capacity, and standing for 30 min;
and (6) circulating the first step and the second step.
The standard is as follows: discharge capacity/initial discharge capacity of 100 th cycle 100%.
Table 3 results of cycle performance test and anode expansion growth rate test of examples 1 to 10 and comparative example 1
As is clear from Table 3, examples 1 to 6 provided by the present inventionThe capacity retention rate of 100 circles of the lithium ion battery silicon cathode and the expansion growth rate of the cathode are obviously superior to those of a lithium ion battery with the cathode directly adopting silicon materials. For example, in examples 1 to 6, the addition of the electrolyte material 1 having a specific structure makes the capacity retention rate after 100 cycles not less than 90% and the expansion growth rate of the negative electrode not more than 25%. Preferably, as in example 5, the silicon active material of the silicon negative electrode of the lithium ion battery is silicon doped with 2wt% of a conductive agent; the porous core 11 of the electrolyte material 1 adopts porous conductive carbon particles with the particle size of 5 μm, the ceramic fast ion conductor layer 12 adopts lithium niobate, the protective layer 13 adopts a conductive carbon layer (protective carbon layer with conductivity) with the thickness of 25nm, and the conductive carbon layer comprises PMMA/lithium perchlorate/super-P polymer solid electrolyte; the electrolyte between the positive electrode and the negative electrode adopts (EC + DMC +1 MLiPF)6) And the anode adopts LCO. The capacity retention rate after 100 cycles is 96%, the expansion growth rate of the negative electrode is 21%, the capacity retention rate after 100 cycles is obviously better than that of the comparative example 1 is 88%, and the expansion growth rate of the negative electrode is 28%.
As can be seen from table 3, in examples 7 to 10, the porous cores 11 having different porosities are used, so that the ability of absorbing the expansion deformation generated during the expansion of the silicon negative electrode is different, and the expansion growth rate of the final negative electrode is different. When the porosity of the porous core 11 is less than 20%, the voids of the electrolyte material 1 are insufficient to absorb the expansion deformation generated during the expansion of the silicon negative electrode. When the porosity of the porous core 11 is greater than 95%, too many voids of the electrolyte material 1 are present, the preparation process is difficult, and the structural strength of the particles of the electrolyte material 1 is significantly reduced, which makes the structural strength of the silicon negative electrode of the lithium ion battery difficult to meet the requirements.
According to the lithium ion battery provided by the invention, the expansion deformation generated in the expansion process of the silicon cathode is absorbed by the electrolyte material by adding the electrolyte material 1 with a specific structure, so that the problem of expansion of the silicon cathode in the use process is solved, and the lithium ion battery has a good effect.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.