Patent Application
20240010567
This disclosure relates to a class of multiphase rubidium titanate functional ceramic materials having unusual electrical and electrochemical properties and method for preparing/manufacturing the materials thereof.
Today, rechargeable electric energy storage (EES) devices are indispensable to human life, which are widely used in cellphones, laptops, remote control, wearable intelligent devices, electric vehicles and so on. Types of the EES devices mainly include electrochemical cells/batteries, capacitive energy storage devices and/or a combination of the two, and inductive energy storage devices that are not yet technically practicable.
Electro-chemical battery is represented by the widely used lithium batteries, whose volumetric and gravimetric energy densities are higher than other types of EES devices, reaching levels of from 250 to 700 Wh/L and from 100 to 300 Wh/kg, but these are only from 2.7% to 7.7% and from 0.77% to 2.1% of gasoline respectively, and the room for further improvement is limited. Besides, the safety related flammability, relatively low power density (charge and discharge rate), cycle life and weatherabilty, relatively high cost and so on, all these are still far away from what is expected from applications. Therefore, many efforts are continuously made to improve the lithium batteries, including the exploration of all-solid-state ones that avoid the use of electrolytic liquid, patent U.S. Pat. No. 10,249,911B2 of Toyota is one of the examples reflecting such efforts.
The representative of battery-capacitor hybrid devices is supercapacitor, and its performance falls between battery and dielectric capacitor. Its power density is from 10 to 60 times and its energy density is from 1/20 to ⅕ of that of lithium battery. There are still issues regarding safety and cost due to electrolytic liquid being still used.
Dielectric capacitor is a sort of all-solid-state physical energy storage devices with larger voltage window and advantages in power density, safety, weatherability, cycle life and cost. Its basic cell is a sandwich structure consisting of two thin conducting electrodes and a thin dielectric layer between them. Its stored electric energy is determined by the formula E=ε0ε′SV2/2d, where ε0ε′ S/d is its capacitance C (i.e. C=ε0ε′ S/d), ε0 is the permittivity (dielectric constant) of vacuum, ε′ is the relative permittivity of the dielectric layer, S is the effective area of the electrodes, d is the thickness of the dielectric layer, and V is the open circuit voltage between the electrodes. The so-called high dielectric (high-ε′) materials today have ε′≤103 only, resulting in that energy density of dielectric capacitor is far lower than the electrochemical battery. Therefore, people continually try to improve it, besides by increasing S and V, lowering loss and d (as Multilayer Ceramic Capacitor MLCC does, but currently its highest energy density is about 1 Wh/L only), mainly by developing colossal dielectric materials of ε′>103. Examples reflecting this trend include patents U.S. Pat. Nos. 10,239,792B2, 07,595,109B2 and CN106565234B etc., related to materials of colossal permittivity ε′ on the order of 104 and capacitive EES systems based on which with energy density reportedly comparable to that of the lithium battery systems.
However, it is necessary to tackle the issues such as raising the colossal permittivity from today's ε′ of from about 104 to 105 by several orders more, so that the dielectric capacitor can raise its energy density by much the same orders, before it can truly challenge the current dominance of the lithium battery. In this regard, a significant improvement reflected by Federicci R. et al. (Federicci R. et al., Rb2Ti2O5: superionic conductor with colossal dielectric constant, Physical Review Materials, 2017 1 (3), 1-6; and R. Federicci et al., The crystal structure of Rb2Ti2O5, Structural Science Crystal Engineering Materials, 2017 B73, 1142-1150) is noteworthy: a type of rubidium dititanate ceramic material has been reported, which is characterized in that the final step of preparation process of the said material is annealing at about 400° C. in the absence of air (oxygen) condition; and, only by keeping the said material tested under strictly oxygen-free and dehumidified environmental conditions, some outstanding material characteristic parameters (in terms of electrics and electrochemistry) can be measured. These parameters include a colossal relative permittivity (ε′) up to the order of 109, a high ionic conductivity circa 10−3 S/cm and a high electronic resistivity up to 108 Ω·mm etc. However, once the too strict environmental requirements for material preparation and application are not met, properties of the said material will be drastically reduced to quite inferior levels, resulting in mal applicability. These shortcomings need to be overcome, and the invention here is going to make an effective breakthrough in this aspect.
This invention provides a class of multiphase rubidium titanate functional ceramic (hereinafter referred to as MRTFC) materials, containing mainly rubidium n-titanate (Rb2TinO2n+1) phase(s), which has unusual electrical and electrochemical properties superior to the prior arts in natural ambient conditions, such as colossal permittivity ε′ up to the order of 109 at room temperature with relatively low dielectric loss, excellent insulativity with ionic conductivity up to the order of 10−3 S/cm; in addition to providing colossal dielectric solutions for high energy density storages. It also has great application potential in solid electrolytes, memory storage units, semi-conductive electronic devices, catalytic purification and other fields. The key to the preparation of such high-performance MRTFC materials lies in the preparation of highly active fine powdery precursor and/or the subsequent heat-treatment (firing/calcination etc.) processes for MRTFC powders and articles. To this end, the invention also provides methods for preparing the materials, in particular methods suitable for industrialized preparations.
The class of MRTFC materials comprises rubidium n-titanate phase(s) chemically formulated as Rb2TinO2n+1 or Rb2O·nTiO2 and titanium dioxide phase(s) chemically formulated as TiO2 (one or more among anatase, rutile, brookite or amorphous type), where n is single- or multi-valued real number no lower than 1; preferably n is from 1 to 12 including all values and subranges therebetween, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12; more preferably n is from 1.9 to 6.
The value of n in the Rb2TinO2n+1 is ranged from 1 to 12, which means that the rubidium titanate phase(s) in the present invention may comprise one or more compounds having the formula Rb2TinO2n+1. For example, the compound may be Rb2Ti2O5, Rb2Ti4O9, Rb2Ti6O13, etc. Meanwhile, the multiphase functional ceramic materials may further contain an amount of titanium dioxide to optimize the material properties and reduce raw material costs as rubidium salts are largely more expensive than that of other raw materials due to its scarcity in the Earth's crust.
Optionally, the said MRTFC materials may further comprises one or more doping elements (dopants) selected from a group consisting of niobium, indium, yttrium, bismuth, lithium, potassium, sodium and cobalt in small amount for property adjustment or improvement.
Preferably, in the said MRTFC materials, the ratio of rubidium n-titanate phase(s) to the material total mass is from 45 wt % to 99 wt %, including all values and subranges therebetween, for example, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 and 98 wt %. The ratio of titanium dioxide phase(s) to the material total mass is more preferably from 1 wt % to 55 wt %, including all values and subranges therebetween, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50 wt %.
Preferably, in the said MRTFC materials, the ratio of the sum of optional dopants to the material total mass is from zero to 2 wt %, including all values and subranges therebetween, for example, 0.1, 0.2, 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 and 1.9 wt %.
Preferably, the said MRTFC materials have at least one of the following parameters: (i) a colossal static permittivity on the order of from 108 to 109; (ii) an electronic resistivity on the order of 108 Ω·mm or more; (iii) an ionic conductivity on the order of 10−3 S/cm; and/or (iv) a quasi-static dielectric loss of no higher than one.
This invention further provides the preparation methods of the said MRTFC materials comprise a series of processes in which rubidium source, titanium source and optional dopant source are used to prepare fine and dry powdery mixture as a highly active precursor, and then get calcined (fired) into ceramic powder or articles at a temperature of from 450° C. to 1200° C.
The rubidium source of the said MRTFC precursor may be a compound that produces rubidium oxide by heating, including rubidium oxide, rubidium carbonate, rubidium hydroxide, rubidium nitrate and rubidium sulfate; preferably rubidium carbonate.
The titanium source of the said MRTFC precursor may be a compound containing titanium oxide, including titanium monoxide, titanium dioxide, wet filter cake of titanium hydroxide, and hydrated titanium dioxide, and can be metal titanium and titanium hydride; preferably titanium dioxide.
The optional dopant source of the said MRTFC precursor may be one or more selected from a group consisting of carbonate, nitrate, sulfate, oxide and hydroxide containing one or more dopant elements.
The mixing ratio between titanium and rubidium sources is based on the expected molar ratio of Rb:Ti=2:n according to Rb2O·nTiO2, but may be fine-tuned within a certain range. Considering the factors like rubidium volatilization loss in the heat treatment process, a scheme with rubidium source a little more and/or titanium source a little less may normally be chosen.
The said MRTFC fine powdery precursor may be prepared by dry synthetic methods such as solid phase mixing method and mechanical-chemical synthetic method, or by liquid and/or gas phase wet synthetic methods such as chemical deposition-precipitation method, hydrothermal method and sol-gel method. The mechanical-chemical synthetic method is preferably to use, which is conducive to large-scale industrialization and low cost preparation of the highly reactive powdery precursor, and the rubidium n-titanate phase(s) after calcination/firing still possess(s) high reactivity.
The calcination/firing process for the said MRTFC materials may be as follows: raising the temperature to a temperature of from 700° C. to 1200° C. at a heating rate of from 3° C./min to 10° C./min, holding for one hour to six hours, and then cooling to room temperature.
The calcining/firing process for the said MRTFC materials may also be as follows: the temperature rises from room temperature to a temperature of from 200° C. to 400° C. at a rate of from 3° C./min to 10° C./min, and then holds for one to four hours; then rises to a temperature of from 550° C. to 650° C. at a rate of from 3° C./min to 10° C./min, and then holds for 0.5 hour to four hours; then rises to a temperature of from 800° C. to 1200° C. at a rate of from 3° C./min to 10° C./min, and then holds for one hour to six hours; and then decreases to a temperature of from 900° C. to 700° C. at a rate of from 1° C./hour to 20° C./hour, followed by rapid decreasing to room temperature.
The rubidium n-titanate phase(s) of the calcined/fired MRTFC powder based on the precursor prepared by dry or wet methods, have a n-value approximating the expected one; but usually there also coexist certain proportion of rubidium titanates with n-value different from the expected one. The proportion of titanium dioxide phase(s) also varies within a certain range. In case there are needs to adjust the compound's phases in the application, such as adjusting the material's Rb-Ti phase ratio and making the rubidium n-titanate phase(s) shift to the desired (single) n value, several practical approaches for phase adjustment are also provided by this invention, including the dry approach to raise rubidium content, the (acid pickling dilution) wet approach to lower rubidium content, and the approach to raise titanium dioxide content, illustrated further with the corresponding examples.
The dry approach to increase Rb content ratio: an appropriate amount of rubidium carbonate or other Rb source to be newly added is evenly mixed into the highly reactive MRTFC powder obtained by previous heat treatment, and then the mixture is taken to a secondary firing at a temperature lower than the first heat treatment. The operations include: content of TiO2 in the MRTFC powder is determined by the well-established and effective methods, such as XRD quantitative analysis→based on the target molar ratio of Rb:Ti=2:n in rubidium n-titanate, the new increment of Rb source needed to convert all or a given proportion (e.g. ½) of the TiO2 existing in the MRTFC powder into the expected rubidium n-titanate is calculated out→the newly added Rb source is mixed well with the MRTFC powder→experience basic steps of secondary firing for 0.5 hour to two hours at a temperature of from 450° C. to 750° C. and so on→achieve the goals, including to raise Rb content ratio in the final product, lower down n-value of the rubidium n-titanate phase(s) and make it approach the targeted (single) n-value, etc.
The wet approach to decrease Rb content ratio: the fired highly reactive MRTFC powder is acid pickled to make the Rb components dissolved out in appropriate amount, and then the obtained solid powder is taken to a secondary firing at a temperature lower than the first firing. There is no special limit on the acid solution of pickling treatment, which may be inorganic acid like sulfuric, hydrochloric and nitric acid or organic acid like acetic acid and their combination, preferably sulfuric acid or nitric acid. The operations include: preparation of a specific mass fraction (such as 15 wt % of the MRTFC powder alkaline aqueous slurry→gradually add certain amount and concentration of acid solution to the slurry and mix, the pH of the slurry will approach the pH value corresponding to the target n-value indicated by the pH-n curve or its fitting formula (see
The approach to raise TiO2 content ratio: certain amount of TiO2 ceramic powder (ex. ceramic grade titanium dioxide) determined in advance according to the well-known ways, may be added to the fired highly reactive MRTFC powder and mixed evenly, so as to raise the ratio of TiO2 phase(s).
Compared to the prior art, the application of the MRTFC materials of the present invention will produce some prominent beneficial effects. For example in principle, inheriting the alternating laminated or wound structure of the multilayer thin film dielectric capacitors, but just replacing the existing dielectric materials with the MRTFC materials of colossal permittivity (at least from 3 to 6 orders of magnitude higher) of this invention, it is expected to form a rechargeable solid-state energy storage device with colossal specific capacitance and super-high energy storage density, while carries over the original characteristics like high charge/discharge rate, high safety, long cycle life and low cost, and even to represent a strong challenge to lithium battery.
The features and advantages of the invention will become further apparent by reading a detailed description of the exemplary examples in the following sections, and by reviewing the attached drawings, in which:
In order to make the technical solutions of the invention easy to understand, a more detailed description and explanation of the invention are given below in combination with the examples and the attached drawings. However, the invention is not limited to the following examples, and any alteration or modification of the technical ideas derived from the invention which can be easily deduced by a person familiar with the relevant technical field shall fall within the scope of the patent right for the protection claimed by the invention.
According to the stoichiometric molar ratio Ti:Rb of about n:2 in the chemical formula Rb2TinO2n+1 (in this case n is taken to be 2), an appropriate amount of dry titanium dioxide (TiO2) and rubidium carbonate (Rb2CO3) powders were separately taken as titanium and rubidium sources; the error of actual ratio between the two was controlled within 5%. After preliminarily mixing the two sources, the mixture was put in a vibrating mill further mechanically and chemically crushed/mixed for 30 minutes to form the precursor.
An appropriate amount of powdery precursor obtained according to the step 1 was put into a crucible and placed in a heat treatment furnace, and fired in air at 780° C. for 4 hours.
When the temperature was lowered close to the ambient temperature, the produced ceramic powder was taken out and isolated in a controlled atmosphere (such as in a glove box in an argon environment), because the product has a strong hygroscopicity.
Scanning electron microscopy (SEM) of the product prepared in this Example is shown in
The main test results of relevant electrical/electrochemical parameters of the material prepared in this Example are as follows: quasi-static permittivity=2.89×108, ultra-low frequency AC dielectric loss=0.79, electronic resistivity=7.7×108 Ω·mm, and ionic conductivity=3.2×10−3 S/cm.
According to the stoichiometric molar ratio Ti:Rb of about n:2 in the chemical formula Rb2TinO2n+1 (in this case n is taken to be 4), an appropriate amount of dry titanium dioxide (TiO2) and rubidium carbonate (Rb2CO3) powders were separately taken as titanium and rubidium sources with the error of actual ratio between the two being controlled within 5%, and were put in the flask, to which deionized water 4 times weight as the titanium dioxide was added and mixed evenly. The solution was concentrated by an evaporator, dried to solidify, and then ground into powder to obtain the precursor.
An appropriate amount of powdery precursor obtained according to the step 1 was put into a crucible and placed in a heat treatment furnace, and fired in air at 870° C. for 1.5 hours.
When the temperature was lowered close to the ambient temperature, the produced ceramic powder was taken out and put in a glove box in an argon environment to avoid hygroscopicity.
SEM image of the product obtained in this example is shown in
The main test results of relevant electrical/electrochemical parameters of the material prepared in this example are as follows: quasi-static permittivity=2.39×109, ultra-low frequency AC dielectric loss=0. 88, electronic resistivity=2.3×108 Ω·mm, and ionic conductivity=3.1×10−3 S/cm.
Titanium oxide (TiO2) and rubidium carbonate (Rb2CO3) powders were used as titanium source and rubidium source respectively, roasted at 100° C. for 24 hours to make them completely dehydrated. According to the stoichiometric molar ratio Ti:Rb of about n:2 in the chemical formula Rb2TinO2n+1 (in this case n is taken to be 3), the appropriate amount of titanium source and rubidium source were weighed respectively with the error of actual ratio between the two being controlled within 5%. The two were placed together in an agate mortar and ground for 20 minutes, the powder obtained was pressed by a 10-ton press for 5 minutes to obtain the precursor.
The obtained precursor was put into the crucible and placed in the heat treatment furnace, the following processes were carried out in air for heat treatment: to heat up to 315° C. and hold for 2 hours→heat up to 600° C. and hold for 0.5 hour→heat up to 930° C. and hold for 3 hours (temperature and time may be adjusted to optimize the quality of the obtained crystal)→lower down the temperature to 880° C. at a slow rate of about 5° C./hour→stop heating and quickly cool down to the room temperature. The product obtained was placed in a glove box in an argon gas environment to avoid moisture absorption.
Because the firing temperature of this method is higher, the product after partially or totally melting or sintering is easy to be bonded to the crucible wall and relatively troublesome to take out; and the product is lumpy, the subsequent crushing and grinding are needed to make it powdery.
SEM image of the product obtained in this example was shown in
The main test results of relevant electrical/electrochemical parameters of the material prepared in this example are as follows: quasi-static permittivity=2.66×109, ultra-low frequency AC dielectric loss=0.91, electronic resistivity=1.5×108 Ω·mm, and ionic conductivity=3.0×10−3 S/cm.
An appropriate amount of MRTFC powder with rubidium dititanate as the main componet made according to Example 1 was used to prepare 500 ml aqueous slurry of 15 wt %. An appropriate amount of 70 wt % nitric acid (HNO3) aqueous solution was then gradually added to it and stirred for 1 hour until the pH value was adjusted to 13.1. The slurry was filtered, separated and dried. The dry extract was then fired in a heat treatment furnace at 550° C. for 1 hour. The fired material was made into ceramic powder A with appropriate particle size by using the grinding method.
Another appropriate amount of MRTFC powder made according to Example 1 was used to prepare 500 ml aqueous slurry of 15 wt %. An appropriate amount of 70 wt % HNO3 aqueous solution was then gradually added to it and stirred for 1 hour until the pH value was adjusted to 10.9. The slurry was filtered, separated, and dried. The dried extract was then fired in a heat treatment furnace at 550° C. for one hour. The fired material was made into ceramic powder B with appropriate particle size by using the grinding method.
The XRD analysis results show that, the ratio of rubidium tetratitanate in powder A is 94 wt %, and that of rubidium hexatitanate in powder B is 93 wt %. The measured results are highly consistent with expectations, and practicability of the wet (pickling dilution) phase-control method is thus confirmed.
The MRTFC powder prepared of Example 3 was used. According to the XRD analysis result as showed above, the MRTFC powder contains 23 wt % rubidium dititanate Rb2Ti2O5 (the expected phase in this example), 42 wt % rubidium tetratitanate Rb2Ti4O9 and 35 wt % titanium dioxide TiO2. Now it is intended to convert the MRTFC powder of Example 3 into a ceramic powder of quasi single phase rubidium dititanate (n=2), i.e., rubidium dititanate as the main component.
An appropriate amount of powder F grams obtained from Example 3 was weighed, in which the TiO2 content was known to be T′=F×35 wt %. Since converting rubidium tetratitanate to rubidium dititanate will also release a certain amount of TiO2 (rubidium tetratitanate in F is 42 wt %, if they were totally converted to rubidium dititanate, the TiO2 released would figure out as F×13.2 wt %), that is, the available TiO2 source content in F is T=F×(35+13.2) wt %=F×48.2 wt % grams in fact. According to the basic molar ratio Rb:Ti=2:n (being equal to 1:1), the molar mass of Ti in T grams of TiO2 should be equal to (or slightly less than) the molar mass of the Rb element to be added, which is enough to support the newly added rubidium source (ex. rubidium carbonate) weight estimation.
The F grams of MRTFC powder of Example 3 and the rubidium carbonate newly added were evenly mixed, put into a crucible and placed in a heat treatment furnace, and fired again at 580° C. for 0.8 hour. After cooling down, the product was taken out for further crushing and grinding, the MRTFC powder after phase regulation was thus obtained.
XRD analysis of the obtained product shows the content of Rb2Ti2O5 is 90.5 wt % and that of TiO2 is 9.5 wt %, which are in line with the expected results and confirm the practicability of the phase-adjusting dry approach for increasing Rb content.
Rubidium hydroxide as rubidium source, titanium dioxide as titanium source and niobium pentaoxide as dopant source were weighed at a molar ratio of 1.8:1.5:0.07 and placed in a vibrating mill and ground for 45 minutes until the system was uniform, the powdery precursor was thus obtained.
An appropriate amount of the obtained precursor was put into the crucible and placed in the heat treatment furnace, fired in air at 750° C. for 4 hours, and taken out after cooled down to ambient temperature. The obtained product was kept in a glove box filled with argon gas to avoid moisture absorption.
XRD analysis shows that the main component of the product is Rb1.9Ti1.9Nb0.1O5, and the content is 87.5 wt %. SEM image shows that there are also a large number of whiskers with sub-micron to nanoscale diameters.
The main test results of relevant electrical/electrochemical parameters of the material prepared in this example are as follows: quasi-static permittivity=1.32×109, ultra-low frequency AC dielectric loss=0.79, electronic resistivity=1.8×108 Ω·mm, and ionic conductivity=3.0×10−3 S/cm.
According to the stoichiometric molar ratio Ti:Rb of abaout n:2 in the chemical formula Rb2TinO2n+1 (in this case n is taken to be 12), the appropriate amount of titanium source (TiO2) and rubidium source (Rb2CO3) were weighed respectively with the error of actual ratio between the two being controlled within 5%, and mixed until the system was uniform.
The obtained precursor was put into the crucible and placed in the heat treatment furnace, fired in air at 1120° C. for 4 hours, and taken out after cooled down to ambient temperature. The obtained product was kept in a glove box filled with argon gas to avoid moisture absorption.
The main test results of relevant electrical/electrochemical parameters of the material prepared in this example 7 are as follows: quasi-static permittivity=1.02×108, ultra-low frequency AC dielectric loss=0.59, electronic resistivity=9.7×109 Ω·mm, and ionic conductivity=1.03×10−3 S/cm.
While it has been shown and described several examples in accordance with the invention and use thereof, it is understood that the same is not limited thereto, but is susceptible to many changes and modifications to one possessing ordinary skill in the art, and therefore we do not wish to be limited to the details shown and described herein, but intend to cover all such modifications as are encompassed by the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202011302322.3 | Nov 2020 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2021/130707 | 11/15/2021 | WO |
