Patent Application
20170166677
The present disclosure relates to methods for making a single ion nanoconductor.
As the use of the lithium ion batteries increases greatly in new energy fields such as mobile phones, electric vehicles, and energy storage systems, safety becomes an issue. Cause based analyzes can be performed to make improvements to the safety of the lithium ion battery. One example of an improvement is to optimize the design and management of the lithium ion batteries, which include monitoring the charge and discharge processes of the lithium ion batteries in real-time and handling the safety maintenance issues of the lithium ion batteries. Another is to improve or develop new electrode materials, which increase an intrinsic safety performance of the battery. New and safer electrolytes and separators may also be used to improve the safety of the lithium ion batteries.
A separator is a critical component in a lithium ion battery. The separator prevents a short circuit between the anode and cathode electrodes and is capable of passing electrolyte ions. A conventional lithium ion battery separator is a microporous film formed by polyolefin such as polypropylene (PP) and polyethylene (PE) uses physical (such as extending) or chemical (such as extraction) methods. Commercial separator products are provided by Asahi Kasei®, Tonen, and Ube®, and Celgard®. As a matrix of the separator, polyolefin has a high strength and a good stability in acids, alkalis, and solvents. However, the melting point of polyolefin is relatively low (the melting point of PE is about 130° C., and the melting point of PP is about 160° C.), which causes a contraction and meltdown of the separator at high temperature, which could cause a burning or exploding battery.
A conventional method for improving the heat resistance of a separator is to add oxide nanoparticles such as titanium dioxide nanoparticles, silicon dioxide nanoparticles, or alumina nanoparticles to the separator. However, the nanoparticles or nanomaterials have a large specific surface area, which tend to aggregate together and become difficult to be dispersed. Therefore, the difficulty is to uniformly composite the nanoparticles with the separator, which often leads to an unsatisfactory performance of the final product.
It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. Also, the description is not to be considered as limiting the scope of the embodiments described herein.
Referring to
S1, forming a solution of nano sol through a hydrolysis reaction, the nano sol is selected from at least one of a titanium sol, an aluminum sol, a silicon sol, and a zirconium sol, wherein Si comprises:
S11, dissolving at least one of a titanium compound, an aluminum compound, a silicon compound, and a zirconium compound, capable of having a hydrolysis reaction in an organic solvent to form a first solution;
S12, forming a second solution by mixing water and another organic solvent; and
S13, mixing the first solution with the second solution and heating the mixture to form the solution of nano sol, wherein the step S12 or S13 further comprises adjusting a pH value of the second solution or the mixture of the first and second solutions to 3 to 4 or 9 to 10 by adding acid or alkali;
S2, adding a silane coupling agent containing a C═C group in the solution of nano sol, and heating in a protective gas to have a reaction thereby obtaining a solution of C═C group grafted nano sol;
S3, adding a methyl methacrylate (MMA) monomer, an acrylic acid (AA) monomer, and an initiator to the solution of C═C group grafted nano sol, and heating to have a reaction thereby forming a nano sol-P(AA-MMA) composite;
S4, heating the nano sol-P(AA-MMA) composite at an elevated pressure in a liquid phase medium of a high-pressure reactor at a temperature of 145° C. to 200° C. and a pressure of 1 MPa to 2 MPa to obtain a complete dehydroxy crystalline oxide nanoparticle-P(AA-MMA) composite, the oxide nanoparticles being at least one oxide of titanium, aluminum, silicon, and zirconium; and
S5, mixing and heating the oxide nanoparticle-P(AA-MMA) composite and lithium hydroxide in an organic solvent to obtain a transparent and clear liquid dispersion of the single ion nanoconductors.
In step S1, the nano sol is formed by hydrolyzing at least one of a titanium compound, an aluminum compound, a silicon compound, and a zirconium compound with water. The nano sol comprises a large amount of MOH groups, wherein M is titanium, aluminum, silicon, or zirconium, and the hydroxyl groups are grafted to titanium, aluminum, silicon, or zirconium.
The titanium compound, aluminum compound, silicon compound, and zirconium compound that are capable of having the hydrolysis reaction can be at least one of an organic ester compound, an organic alcohol compound, an oxysalt, and a halide, examples of which can be tetraethyl orthosilicate, tetramethyl orthosilicate, triethoxysilane, trimethoxysilane, trimethoxy(methyl)silane, methyltriethoxysilane, aluminium isopropoxide, aluminium tri-sec-butoxide, titanium sulfate (Ti(SO4)2), titanium tetrachloride (TiCl4), tetrabutyl titanate, titanium(IV) ethoxide, titanium tetraisopropanolate, titanium(IV) tert-butoxide, diethyl titanate, zirconium(IV) butoxide, zirconium tetrachloride (ZrCl4), zirconium(IV) tert-butoxide, and zirconium n-propoxide.
The acid added to the second solution can be at least one of a nitric acid, a sulfuric acid, a hydrochloric acid, and an acetic acid. The alkali added to the second solution can be at least one of sodium hydroxide, potassium hydroxide, and ammonia water. A molar ratio of the water in the second solution to titanium, aluminum, silicon, and zirconium in the first solution (H2O:M) can be 3:1 to 4:1. The organic solvent that is used in S1 can be a common choice such as ethanol, methanol, acetone, chloroform, and isopropyl alcohol. A volume ratio of the organic solvent to at least one of the titanium compound, aluminum compound, silicon compound, and zirconium compound can be 1:1 to 10:1. In step S13, the heating temperature can be 55° C. to 75° C.
In step S2, the C═C group contained silane coupling agent can be at least one of diethylmethylvinylsilane, vinyltris(tert-butylperoxy)silane, ethoxydimethylvinylsilane, vinyltri-t-butoxysilane, vinyltriisopropenoxysilane, diethoxy(methyl)vinylsilane, triethoxyvinylsilane, vinyltrimethoxysilane, dimethoxymethylvinylsilane, diethoxymethylvinylsilane, vinyltriacetoxysilane, tri(isopropoxy)vinylsilane, trimethoxy(7-octen-1-yl)silane, and vinylmethyldimethoxysilane.
The solution of nano sol can comprise water. The silane coupling agent can have a hydrolysis reaction by being added in the solution of nano sol to form SiOH group. The silane coupling agent also can have SiOR group, wherein R is hydrocarbon group, such as alkyl group. In step S2, the SiOH group (or SiOR group) reacts with the MOH group to form an Si—O—M group, thereby grafting C═C groups of the silane coupling agent onto the surface of the nano sol. In step S2, the heating temperature can be about 60° C. to about 90° C., and the protective gas can be nitrogen gas or an inert gas. A molar ratio of the nano sol to the silane coupling agent can be about 1:100 to about 1:20.
In step S3, the MMA, the AA, and the C═C groups grafted nano sol are copolymerized under the action of the initiator and the heating to form the nano sol-P(AA-MMA) composite. Specifically, the initiator causes a polymerization between the MMA and the AA to form a copolymer (P(AA-MMA), P stands for poly) while allowing the C═C double bond of the nano sol to open and copolymerize with the C═C group of the MMA and/or the AA thereby grafting/joining the nano sol to the P(AA-MMA). The process of the polymerization can be accompanied by heating and stirring, so that the nano sol can be uniformly polymerized with the MMA and the AA, and the nano sol can be evenly distributed in the obtained polymer. The initiator can be benzoyl peroxide, azobisisobutyronitrile (AIBN), or 2,2′-azobis(2,4-dimethylvaleronitrile) (ABVN).
A molar ratio of the MMA to the AA can be about 20:1 to about 10:1. A mass ratio of the nano sol to the sum of the MMA and the AA is about 10:1 to about 5:1 (i.e., nano sol:MMA-FAA=about 10:1 to about 5:1).
The polymerization in step S3 can be carried out in the heating condition, the temperature of which can be maintained at about 60° C. to about 90° C. as in the step S2.
The nano sol-P(AA-MMA) composite obtained by the steps S1 to S3 of the present invention is an inorganic-organic grafting hybrid polymer obtained by copolymerizing the AA, the MMA, and the C═C group grafted nano sol. In steps S1 to S3, the nano sol is obtained by hydrolyzing at least one of the titanium compound, aluminum compound, silicon compound, and zirconium compound. The nano sol contains a network formed by M—O bonds, and the macroscopic chemical composition of the network can be regarded as an oxide of titanium, aluminum, silicon and/or zirconium.
The oxide has an amorphous structure and is grafted with a large amount of hydroxyl groups.
In step S4, the nano sol-P(AA-MMA) composite is placed in the liquid phase medium such as water or an organic solvent and sealed in the high-pressure reactor to undergo a reaction process. This reaction process crystallizes the amorphous oxide and completely removes the hydroxyl group grafted to the oxide (e.g., dehydroxylation). By controlling the temperature and pressure of the reaction process, the oxide particles can be prevented from aggregation during the dehydroxylation, thereby forming a crystalline nanoparticles of oxide which are highly dispersed. The nanoparticles of oxide can be at least one of titanium dioxide (TiO2) nanoparticles, aluminum oxide (Al2O3) nanoparticles, silicon dioxide (SiO2) nanoparticles, and zirconium dioxide (ZrO2) nanoparticles. The nanoparticles are still grafted to the organic polymer P(AA-MMA). The polymer is coated on the surface of the nanoparticles.
In step S5, the poly acrylic acid (PAA) in the oxide nanoparticle-P(AA-MMA) composite contains a COOH group, which reacts with LiOH to form a COOLi group, thereby forming oxide nanoparticle-P(AALi-MMA), namely, the single ion nanoconductor. By carrying out the step S5 in a stepwise manner, when the oxide nanoparticle-P(AA-MMA) composite is dispersed in the organic solvent, a pale yellow opaque emulsion is formed indicating that the oxide nanoparticle-P(AA-MMA) composite has an aggregation in the organic solvent. Then LiOH is added in, and the emulsion is quickly changed into a uniform and stable transparent and clear solution by simply stirring and heating, which indicates that the energy produced by the chemical reaction helps the rapid dispersion of the oxide nanoparticles. Compared with the conventional dispersing method such as ultrasonic vibration, the present method reduces the energy consumption of dispersing the oxide nanoparticles and has a high dispersing efficiency. The transparent and clear liquid dispersion comprises the organic solvent and the single ion nanoconductors uniformly dispersed in the organic solvent. The organic solvent of step S5 can be a polar solvent, such as at least one of acetamide,
N-methyl pyrrolidone (NMP), and acetone. The liquid dispersion comprises the organic solvent and single ion nanoconductors, e.g., oxide nanoparticle-P(AALi-MMA), dispersed in the organic solvent. The oxide nanoparticle-P(AALi-MMA) does not aggregated with each other and is in a monodisperse state. A size of the oxide nanoparticle-P(AALi-MMA) is less than 10 nanometers, e.g., about 4 nanometers to about 8 nanometers. The heating temperature in step S5 can be about 60° C. to about 90° C.
Referring to
Referring to
The single ion nanoconductors can be composite with a conventional separator in the lithium ion battery to form a composite separator. The separator can be immersed in the transparent and clear liquid dispersion formed in step S5, or the liquid dispersion can be applied to the surface of the separator to obtain the composite separator having the oxide nanoparticles enhancing the separator.
The separator can be a porous film such as a polyolefin porous film or a nonwoven fabric porous film. Examples of the polyolefin porous film include a polypropylene porous film, a polyethylene porous film, and a lamination of the polypropylene porous film and the polyethylene porous film. Examples of the nonwoven fabric include a polyimide nanofiber nonwoven fabric, a polyethylene terephthalate (PET) nanofiber nonwoven fabric, a cellulose nanofiber nonwoven fabric, an aramid nanofiber nonwoven fabric, a glass fiber nonwoven fabric, a nylon nanofiber nonwoven fabric, and a polyvinylidene fluoride (PVDF) nanofiber nonwoven fabric.
In one embodiment, the single ion nanoconductors can be used in the gel polymer electrolyte lithium ion batteries. The transparent and clear liquid dispersion formed in step S5 can be mixed uniformly with a gel polymer to form a composite gel;
and the composite gel can be composited with the conventional separator to form the composite separator. The conventional separator can be immersed in the composite gel, or the composite gel can be applied to the surface of the separator to obtain the composite separator.
The gel polymer can be conventional, such as poly(methyl methacrylate), poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), polyacrylonitrile, and polyethylene oxide (PEO). A mass ratio of the single ion nanoconductors to the gel polymer can be about 1:20 to about 1:2.
The single ion nanoconductors are uniformly dispersed in the transparent and clear liquid dispersion so as to be uniformly attached to the surface and the pores of the separator, in order to improve the mechanical properties and the heat resistance of the separator. The P(AALi-MMA) matrix in the single ion nanoconductors can be uniformly mixed with varied kinds of gel polymers thereby the single ion nanoconductors can be uniformly dispersed in the composite gel. In addition, since the single ion nanoconductors are capable of providing lithium ions, the composite separator can have better ionic conductivity, thereby improving the electrochemical performance of the lithium ion battery.
10 mL of tetrabutyl titanate is mixed with 50 mL of ethanol to form a first solution. Deionized water is mixed with 50 mL of ethanol to form a second solution. The molar ratio of the deionized water to the tetrabutyl titanate is about 4:1. The second solution is slowly dropped into the first solution for mixing, the concentrated nitric acid is added to adjust the pH value to 3 to 4, and the mixture is stirred and heated at about 65° C. for about a half of an hour to obtain the titanium sol solution. The triethoxyvinylsilane is added to the titanium sol solution, and heated to about 80° C. for about 1 hour in the nitrogen gas to obtain a C═C group grafted titanium sol solution. The MMA monomer, the AA monomer, and benzoyl peroxide as the initiator are added to the C═C group grafted titanium sol solution with the reaction at about 80° C. for about 12 hours to obtain a solution of titanium dioxide nanosol-P(AA-MMA) composite. The solution of titanium dioxide nanosol-P(AA-MMA) composite is placed in an autoclave and heated at about 145° C. for about 24 hours to obtain a completely dehydroxy crystalline TiO2-P(AA-MMA) composite, which is taken out and dried to obtain a light yellow solid powder. The dried nano TiO2-P(AA-MMA) composite and LiOH are added to the organic solvent, and the mixture is stirred and heated to obtain the transparent and clear liquid dispersion.
Example 2 is the same as Example 1, except that tetrabutyl titanate is replaced with aluminium isopropoxide.
Example 3 is the same as Example 1, except that tetrabutyl titanate is replaced by zirconium(IV) butoxide.
Example 4 is the same as Example 1, except that tetrabutyl titanate is replaced by tetraethyl orthosilicate.
In the present method, the inorganic nano sol is modified first to have a C═C group. The C═C group forms a homogeneous copolymer with both acrylic acid and methyl methacrylate, so that a uniform dispersion of the inorganic nano sol in the P(AA-MMA) can be realized. The dispersion is then crystallized at certain temperature and pressure. By controlling the crystallization process, the formed oxide nanoparticles avoid aggregating together to obtain the composite having the oxide nanoparticles uniformly dispersed in the P(AA-MMA). Finally this composite and lithium hydroxide are reacted in the organic solvent, and the energy generated by the reaction disperses the oxide nanoparticles evenly to obtain the transparent and clear liquid dispersion. The liquid dispersion can be easily composited with the separator.
The embodiments shown and described above are only examples. Even though numerous characteristics and advantages of the present technology have been set forth in the foregoing description, together with details of the structure and function of the present disclosure, the disclosure is illustrative only, and changes may be made in the detail, especially in matters of shape, size, and arrangement of the parts within the principles of the present disclosure, up to and including the full extent established by the broad general meaning of the terms used in the claims. It will therefore be appreciated that the embodiments described above may be modified within the scope of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201410430209.1 | Aug 2014 | CN | national |
This application claims all benefits accruing under 35 U.S.C. §119 from China Patent Application No. 201410430209.1, filed on Aug. 28, 2014 in the State Intellectual Property Office of China, the contents of which are hereby incorporated by reference. This application is a continuation of international patent application PCT/CN2015/082727 filed Jun. 30, 2015, the content of which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CN2015/082727 | Jun 2015 | US |
| Child | 15442538 | US |
