阅读说明：本技术 高温锂空气电池 (High temperature lithium air battery ) 是由 L·G·约翰逊 于 2020-04-02 设计创作，主要内容包括：本发明公开了一种可再充电锂空气电池,包含：锂基阳极,该锂基阳极包含形成包封锂金属的第一室的锂离子导电电解质；氧电极；形成第二室的固体氧离子导电电解质；和熔融电解质,该熔融电解质被容纳在该第二室中并且耦接在该氧离子导电电解质和该锂离子导电电解质之间,并且该熔融盐电解质不与空气接触。(The invention discloses a rechargeable lithium air battery, comprising: a lithium-based anode comprising a lithium ion conducting electrolyte forming a first chamber encapsulating lithium metal; an oxygen electrode; a solid oxygen ion conducting electrolyte forming a second chamber; and a molten electrolyte contained in the second chamber and coupled between the oxygen ion conducting electrolyte and the lithium ion conducting electrolyte, and the molten salt electrolyte is not in contact with air.)

1. A rechargeable lithium air battery comprising: a lithium-based anode comprising a solid lithium ion-conducting electrolyte forming a first chamber encapsulating lithium metal; an oxygen electrode; a solid oxygen ion conducting electrolyte forming a second chamber; and a molten electrolyte contained in the second chamber and coupled between the oxygen ion conducting electrolyte and the lithium ion conducting electrolyte, wherein the molten salt electrolyte is not in contact with air.

2. The rechargeable lithium-air cell of claim 1, further comprising an oxygen source, wherein the oxygen ion conducting electrolyte is exposed to the oxygen source.

3. The rechargeable lithium air cell of claim 1, further comprising a lithium source, wherein the lithium ion conducting electrolyte is exposed to the lithium source.

4. The rechargeable lithium-air cell of claim 1, wherein the solid lithium ion conducting electrolyte comprises lithium silicon phosphate (Li)₇SiPO₈)。

5. The rechargeable lithium-air cell of claim 1, wherein the molten electrolyte is a molten alkali salt electrolyte and comprises Li_9.3C₃BO_12.5LiF-LiCl-LiBr, fluorine-doped Li_9.3C₃BO_12.5And sulfur-doped Li_9.3C₃BO_12.5At least one of (a).

6. The rechargeable lithium air cell of claim 1, wherein the cell has an operating temperature of about 250 ℃ to about 650 ℃.

7. The rechargeable lithium air cell of claim 6, wherein the cell has an operating temperature of about 250 ℃ to about 400 ℃.

8. The rechargeable lithium air cell of claim 1, wherein the cell has an operating temperature of about 400 ℃ to about 650 ℃.

9. The rechargeable lithium-air cell of claim 1, wherein the solid oxygen ion conducting electrolyte is scandium-stabilized zirconia or yttria-stabilized zirconia.

10. The rechargeable lithium-air cell of claim 1, wherein the oxygen electrode is porous.

11. The rechargeable lithium-air cell of claim 1, wherein the oxygen electrode comprises a conductive metal oxide.

12. The rechargeable lithium-air cell of claim 11, wherein the oxygen electrode comprises lanthanum strontium metal oxide.

13. The rechargeable lithium-air cell of claim 1, wherein the molten electrolyte is a silane or siloxane.

Background

The modern society's need for high performance and reliable energy storage is witnessed. Lithium batteries represent a very attractive solution to these energy demands due to their excellent energy density and high performance. However, the available Li-ion storage materials limit the specific energy of conventional Li-ion batteries. Although there is any anode in which lithium has the highest specific capacity (3861mAh/g), typical cathode materials such as MnO₂、V₂O₅、LiCoO₂And (CF) n has a specific capacity of less than 200 mAh/g.

Recently, it has been proposed to convert lithium/oxygen (Li/O)₂) Or lithium air batteries as a means to avoid the limitations of current lithium ion batteries. Among these batteries, a lithium metal anode is used to maximize the anode capacity, and the cathode capacity of a lithium air battery is maximized by not storing a cathode active material in the battery. In contrast, the environment O₂Is reduced to form O on the catalytic air electrode₂ ^2-Here O₂ ^2-With Li conducted from the anode⁺The ions react. It has been found that aqueous lithium-air batteries are subject to corrosion of the Li anode by water and have a capacity below optimum due to the excess water required for efficient operation.

Abraham and Jiang (J.Electrochem.Soc.,143(1),1-5(1996)) reported a non-aqueous Li/O₂Batteries, which have an open circuit voltage close to 3V and an operating voltage of 2.0V to 2.8V, have good coulombic efficiency and some rechargeability, but have severe capacity fade, limiting the lifetime to only a few cycles. Furthermore, in non-aqueous batteries, the electrolyte must wet the lithium oxygen reaction product in order to electrolyze the product during recharging. It has been found that due to the limited solubility of the reaction products in the available organic electrolyte, an excess of electrolyte must be used to fully wet the extremely high surface area nanoscale discharge deposits produced in the cathode. Thus, the excess electrolyte required significantly reduces the high energy density that can otherwise be achieved in a lithium-oxygen battery.

Li/O₂Operation of the battery depends onDiffusion of oxygen to the air cathode. Therefore, the battery is expected to have high oxygen solubility in the electrolyte to operate under high rate discharge conditions. Read (j. electrochem. soc.,149(9) a1190-a1195(2002)) demonstrated the dependence of cathode capacity on oxygen uptake when studying the cathode of a lithium air cell. Oxygen absorption is a function of the electrolyte's intrinsic coefficient (α), electrolyte conductivity (σ) and viscosity (η). In the data of Read, the tendency of the cathode lithium reaction capacity to decrease with increasing viscosity and decreasing birth coefficient is evident. It is known that as the viscosity of the solvent increases, the lithium reaction capacity and the bunsen coefficient decrease. In addition, since the ability to dissolve the reaction products is critical, the electrolyte has an even more direct effect on the total battery capacity. This problem is always present in known batteries in one form or another.

In fact, high capacity fade rates remain a problem with non-aqueous rechargeable lithium-air batteries and have been a significant obstacle to the commercialization of these non-aqueous rechargeable lithium-air batteries. This high attenuation is primarily due to parasitic reactions occurring between the electrolyte and the moss-like lithium powder, as well as dendrites formed at the anode-electrolyte interface during battery recharge, and electrolyte and LiO during recharge₂As reduced Li between radicals₂O₂The intermediate step of (3) to (3).

During recharging, lithium ions are conducted across the electrolyte separator while lithium is plated at the anode. In contrast to dense lithium metal films, the formation of low density lithium dendrites and lithium powder complicates the recharging process. In addition to the passivation reaction with the electrolyte, the moss lithium formed during recharging can be oxidized to moss lithium oxide in the presence of oxygen. A thicker layer of lithium oxide and/or electrolyte passivation reaction product on the anode increases the resistance of the cell, thereby reducing performance. The formation of moss-like lithium with cycling can also cause a large amount of lithium to be disconnected within the cell and become ineffective. Lithium dendrites can penetrate the separator causing internal short circuits within the cell. In addition to reducing the oxygen passivation material coated on the anode surface, repeated cycling can also lead to electrolyte decomposition. This results in the formation of a layer consisting of moss lithium, lithium oxide and lithium electrolyte reaction products at the surface of the metal anode, which increases the cell impedance and consumes electrolyte, resulting in drying out of the cell.

Attempts to eliminate dendritic lithium plating using active (non-lithium metal) anodes have not been successful due to the similarity of anode and cathode structures. In such lithium air "ion" batteries, both the anode and the cathode contain carbon or another electron conductor as a medium for providing electronic continuity. Carbon black in the cathode provides electron continuity and reaction sites for lithium oxide formation. To form the active anode, graphitic carbon is included in the anode for lithium intercalation and carbon black is included for electron continuity. Unfortunately, the use of graphitic carbon and carbon black in the anode can also provide reactive sites for lithium oxide formation. At a reaction potential of about 3 volts versus the low voltage of lithium intercalation into graphite, the oxygen reaction will dominate the anode and cathode. Applying existing lithium ion battery construction techniques to lithium oxygen batteries will allow oxygen to diffuse throughout all elements of the battery structure. In the case where a lithium/oxygen reaction occurs in both the anode and the cathode, it is difficult to generate a potential difference therebetween. There will be equal oxidation reaction potentials in both electrodes, resulting in no voltage.

As a solution to the problem of dendritic lithium plating and uncontrolled oxygen diffusion, known aqueous and non-aqueous lithium air batteries have included a barrier electrolyte separator, typically a ceramic material, to protect the lithium anode and provide a hard surface onto which lithium can be plated during recharging. However, forming a reliable, cost-effective barrier is difficult. Johnson, U.S. patent No. 7,691,536, describes a lithium air battery that employs a protective solid lithium ion conductive barrier as a separator to protect the lithium in the lithium air battery. Thin film barriers have limited effectiveness in withstanding the mechanical stresses associated with stripping and plating lithium at the anode or expansion and contraction of the cathode during cycling. Furthermore, thicker lithium ion conducting ceramic plates, while providing excellent protective barrier properties, are extremely difficult to manufacture, add significantly to the quality of the battery, and are quite expensive to manufacture.

In addition, thicker lithium ion conducting ceramic plates have been used, particularly in lithium water batteries. When the thickness is in the range of 150 μm, these plates provide excellent protective barrier properties, however, they are difficult and expensive to manufacture. Furthermore, these ceramic plates significantly increase the mass of the battery, resulting in a reduction in the specific energy storage capacity. This reduction may be sufficient to offset the high energy density performance that would otherwise be obtainable using lithium-air technology.

Since it is associated with the cathode, the sharp drop in battery capacity with increasing discharge rate is attributed to the accumulation of reaction products in the cathode. At high discharge rates, oxygen entering the cathode from its surface does not have the opportunity to diffuse or otherwise migrate to reaction sites deeper within the cathode. The discharge reaction occurs at the cathode surface, resulting in the formation of a reaction product envelope that seals the cathode surface and prevents the ingress of additional oxygen. In the absence of oxygen, the discharge process cannot continue.

Another important challenge of lithium air batteries is the electrolyte stability within the cathode. The main discharge product in a lithium-oxygen battery is Li₂O₂. During recharging, the resulting lithium oxygen free radical LiO₂In the electrolysis of Li₂O₂The intermediate products produced in the process attack and decompose the electrolyte in the cathode, rendering it ineffective.

High temperature molten salts have been proposed as a replacement for organic electrolytes in non-aqueous lithium-air batteries. U.S. patent No. 4,803,134 to Sammells describes a high lithium-oxygen secondary battery in which a ceramic oxygen ion conductor is employed. The battery includes LiF-LiCl-Li as electrolyte of molten salt conducting with lithium ion₂An O-contacted lithium-containing negative electrode, the lithium ion-conducting molten salt electrolyte being separated from the positive electrode by an oxygen ion-conducting solid electrolyte. The ionic conductivity limitations of available solid oxide electrolytes require that such batteries operate in the 700 ℃ or higher range in order to have reasonable charge/discharge cycling rates. The geometry of the cell is such that discharge reaction products accumulate in the molten salt between the anode and the solid oxide electrolyte. The space required is an additional source of impedance within the cell.

Molten Nitrate also provides a viable solution and the physical properties of the Molten Nitrate electrolyte are summarized in Table 1 (Lithium Batteries Using molybdenum Nitrate Electrolytes, taken from Melvin H.Miles; (1999)).

TABLE 1 physical Properties of molten nitrate electrolytes

Molten LiNO₃Electrochemical oxidation of (2) occurs at about 1.1V (vs Ag +/Ag) or 4.5V (vs Li +/Li). LiNO₃Is generated at about-0.9V (vs Ag +/Ag), and thus the two reactions are molten LiNO at 300 deg.C₃A 2.0V electrochemically stable region is defined, and these two reactions are defined as follows:

LiNO₃→Li⁺+NO₂+1/2O₂+e^-(equation 1)

LiNO₃+2e^-→LiNO₂+O^--(equation 2)

Work with molten nitrate was not considered to be performed with lithium air batteries; however, the effective operating voltage window of the electrolyte is suitable for such applications. As indicated by the reaction potential line in scheme 1, application of a recharge voltage of 4.5V, based on the lithium anode, causes the lithium nitrate to decompose into lithium nitrite, thereby releasing oxygen. On the other hand, lithium can convert LiNO₃Reduction to Li₂O and LiNO₂. When LiNO is present₃This reaction occurs when the voltage drops below 2.5V versus lithium. As long as dissolved oxygen is present in the electrolyte, the reaction kinetics will favor the lithium oxygen reaction over LiNO₃And (4) reducing. In NaNO₃And KNO₃In the melt, the oxide ions are readily converted to peroxides (O)₂ ^2-) Ionic and corrosive superoxide (O)₂ ^-) Ions (m.h. miles et al, j.electrochem. soc.,127,1761 (1980)).

Scheme 1

In 2015, Vincent Giordani of Liox Power Inc. reported a high temperature molten salt system using nitrate. Nitrates and halide salts have the stability, high ionic conductivity and ability to dissolve the lithium oxygen and lithium carbonate reaction products required for a lithium oxygen environment. The challenges faced by these systems are primarily associated with the handling of the reaction products. Similar to nonaqueous organic electrolyte batteries, the accumulation of discharge reaction products within the battery tends to interfere with the migration of reactants to the reaction sites, thereby limiting battery performance.

There remains a need for a lithium air battery that overcomes the problems associated with the prior art.

Disclosure of Invention

A rechargeable lithium air battery according to an embodiment of the present disclosure includes: a lithium-based anode comprising a solid lithium ion-conducting electrolyte forming a first chamber encapsulating lithium metal; an oxygen electrode; a solid oxygen ion conducting electrolyte forming a second chamber; and a molten electrolyte contained in the second chamber and coupled between the oxygen ion conducting electrolyte and the lithium ion conducting electrolyte, and the molten salt electrolyte is not in contact with air.

Drawings

The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.

In the drawings:

fig. 1 is a schematic diagram of a battery cell undergoing discharge according to one embodiment of the present disclosure;

fig. 2 is a schematic diagram of a battery cell undergoing recharging according to one embodiment of the present disclosure;

FIG. 3 is an Alanikus diagram showing the lithium ion conductivities of several solid ceramic electrolytes;

FIG. 4 is an Alranimush plot showing the oxygen ion conductivity of several solid ceramic electrolytes;

FIG. 5 is a graph showing the ionic conductivity of several alkali eutectic salt electrolytes;

FIG. 6 is an Alranimush plot of lithium ion conductivity of lithium oxide;

FIG. 7 is a diagram illustrating the coarse sizing of an exemplary embodiment of the present disclosure; and is

Fig. 8 is a table of mass and volume assignments for exemplary embodiments of the present disclosure.

Detailed Description

The present disclosure relates generally to an energy storage device, and more particularly to a lithium air electrochemical cell. For the purposes of this disclosure, the terms lithium air battery cell, lithium air battery, lithium air electrochemical engine, rechargeable lithium air battery, and lithium oxygen battery are used interchangeably.

Certain terminology is used in the following description for convenience only and is not limiting. The words "proximal", "distal", "upper", "lower", "bottom", and "top" designate directions in the drawings to which reference is made. According to the present invention, the words "inwardly" and "outwardly" refer to directions toward and away from, respectively, the geometric center of the device and designated parts thereof. Unless specifically set forth herein, the terms "a," an, "and" the "are not limited to one element, but rather should be understood to mean" at least one. The terminology includes the words above, derivatives thereof and words of similar import.

It will also be understood that terms such as "first," "second," and the like are provided for clarity only. The elements or components identified by these terms and their operation are readily convertible.

Aspects of the present disclosure relate to lithium air batteries that exhibit high battery charge/discharge rates with limited capacity fade, high energy density, high power density, and the ability to operate on oxygen from ambient air. Therefore, it eliminates a significant obstacle that hinders the commercialization of lithium-air batteries. For example, by using molten lithium supplied as a flowing reactant to the anode side of a stable solid ceramic electrolyte, the formation of mossy lithium powder and dendrites at the anode-electrolyte interface during battery recharge is eliminated. A flow system for removing reaction products from the cathode is also described.

The reaction of lithium with oxygen is as follows:

2Li+O₂→Li₂O₂ E_o＝3.10V

4Li+O₂→2Li₂O E_o＝2.91V

to avoid the problems associated with past approaches to lithium air batteries, aspects of the present disclosure include lithium air batteries that operate at elevated temperatures in a wide range of about 250 ℃ to 650 ℃, more preferably about 250 ℃ to 400 ℃ or about 400 ℃ to 650 ℃, depending on the particular electrolyte contained in the battery. In particular, as described in further detail below, a lower operating temperature range is preferred when the molten electrolyte comprises siloxane, and a higher operating temperature range is preferred when the electrolyte comprises only inorganic molten salt. Operating at elevated temperatures enables faster kinetics for higher power densities, thereby eliminating the major problems associated with lithium air technology. Furthermore, operating at elevated temperatures also allows the use of high temperature organic electrolytes and inorganic molten salt electrolyte solutions with high electrochemical stability, thereby avoiding another major problem that plagues conventional methods of lithium air batteries. The selected inorganic molten salt has good solubility for the lithium/oxygen reaction products, allowing better control of the cell kinetics.

A rechargeable lithium-air battery according to an aspect of the present disclosure includes: a lithium-based anode comprising a lithium ion conducting electrolyte forming a first chamber encapsulating lithium metal; an oxygen electrode; a solid oxygen ion conducting electrolyte forming a second chamber; and a molten electrolyte contained in the second chamber and coupled between the oxygen ion conducting electrolyte and the lithium ion conducting electrolyte, wherein the molten electrolyte is not in contact with air. Each of these components will be described in more detail below.

The embodiment of the present disclosure shown in fig. 1 includes an electrolyte/reaction product housing 2 and a lithium housing 4. The lithium housing 4 is composed of a lithium ion conducting ceramic electrolyte 16 and an expansion reservoir 20. A solid lithium ion conducting electrolyte 16 extends into the reaction product housing 2. The case 4 contains molten lithium 24 and a negative electrode current collector 28. The molten lithium contained within the housing 4 extends into the lithium ion conducting electrolyte portion 16, see 26. The electrolyte housing 2 is composed of an oxygen ion conducting solid electrolyte 6 and an expansion reservoir 8. The oxygen electrode 12 is coupled to the outer surface of the oxygen ion conducting electrolyte 6 and serves as the positive electrode of the battery. Negative electrode 28 and positive electrode 12 are electrically coupled to terminal 30. A molten salt electrolyte 18 is contained within the electrolyte housing 2 and couples the oxygen ion conducting electrolyte 6 to the outer surface of the solid lithium ion conducting electrolyte 16.

Fig. 1 shows a battery in a charged state and undergoing discharge. The level of lithium 24 within reservoir 20 is high and lithium is being consumed as indicated by arrow 31 as it is oxidized along the inner surface of electrolyte 16. The resulting electrons are conducted from the electrode 28 to the terminal 30 while the lithium ions conduct through the electrolyte 16 and continue into the molten salt electrolyte 18 as indicated by arrows 34. The electrons are conducted at terminal 30 through load 40 and then to oxygen electrode 12. Oxygen gas is oxidized at the interface of the oxygen electrode 12 and the oxygen ion conducting electrolyte 6. The resulting oxygen ions are conducted through the electrolyte 6 and into the molten salt electrolyte 18 to complete the reaction with the lithium entering through the electrolyte 16 to form lithium oxide. As the lithium reaction products accumulate within the electrolyte housing 2, the level of the resulting molten salt/lithiated reaction product mixture rises, as indicated by arrow 32.

Fig. 2 shows a battery in a discharged state and undergoing recharging. It can be seen that the level of lithium-oxygen reaction products accumulated within the molten salt electrolyte 18 is much higher and the mixture now extends into the reservoir 8. The level of molten lithium metal 24 within the reservoir 20 is now low. The battery is recharged by the power source 42 as the applied voltage electrolyzes the lithium oxide dispersed within the electrolyte 18. The lithium ions are conducted through the electrolyte 16 and reduced by electrons provided from the electrodes 28 of the power supply 42. As the reduced lithium accumulates in the interior of lithium housing 4, the level of molten lithium rises, as indicated by arrow 35. Meanwhile, when electrons are extracted by the power source 42, the power source 42 reduces oxygen ions at the oxygen ion conductive electrolyte 6-electrode 12 interface. During recharging, the volume of the mixture of molten salt and lithium oxygen reaction products decreases as indicated by arrow 36. During recharging, the battery eventually returns to its original state shown in fig. 1.

Solid lithium ion conducting electrolyte 16

The solid lithium ion conducting electrolyte is preferably a ceramic material that is stable in contact with lithium metal and forms a chamber or housing for containing the lithium metal. The solid lithium ion conducting electrolyte forms the anode of the battery together with the lithium metal.

Fig. 3 is an arrhenius plot including data from Li Gaoran et al (front. energy res.,11(2015)) and M Kotobuki et al (Journal of Power Sources 1967750-7754 (2011)), and provides the conductivity of several solid lithium ion conducting electrolyte materials that can be selected for use as lithium ion conducting electrolytes.

Preferred materials for the solid lithium ion conductive electrolyte include lithium ion conductive glasses such as lithium beta alumina, lithium phosphate glass, Lithium Lanthanum Zirconium Oxide (LLZO), alumina doped LLZO (Al)₂O₃:Li₇La₃Zr₂O₁₂) Silicon lithium phosphate (Li)₇SiPO₈) Lithium Aluminum Germanium Phosphate (LAGP) and lithium titanium aluminum phosphate (LATP). The most preferred material is lithium silicon phosphate.

In a preferred embodiment, the anode chamber formed by the solid lithium ion conducting electrolyte is maintained at a relatively uniform temperature.

Solid oxygen ion conductive electrolyte 6

The solid oxygen ion conducting electrolyte forms a chamber for the molten salt electrolyte. Preferred materials for the solid oxygen ion conducting electrolyte include those composed of 3 mole% Y₂O₃(3YSZ) or 8 mol% Y₂O₃(8YSZ) stabilized ceramics such as, but not limited to, Scandium Stabilized Zirconia (SSZ) and Yttria Stabilized Zirconia (YSZ). FIG. 4 is reproduced from Ma et al (doctor theory)Herein, Stockholm, 2012), shows the oxygen ion conductivity of several materials suitable for use as solid oxygen ion conducting electrolytes in lithium air batteries described herein.

Although shown in fig. 1 and 2, the solid ion-conducting electrolyte need not be in direct contact with the molten electrolyte.

Air cathode/oxygen electrode 12

The air cathode or oxygen electrode is porous so that oxygen can flow through the pores to and from the reaction sites where it is oxidized or reduced as the cell is discharged or charged, respectively. During discharge, oxygen enters the cell by flowing to oxidation sites where it is oxidized to oxygen ions and electrons. The electrons are conducted through the load 40 to the anode electrode terminal 28. Oxygen ions are conducted through the solid electrolyte 6 into the molten electrolyte 18. The opposite occurs during charging. Oxygen ions are conducted from the molten electrolyte through the solid electrolyte 6 to reaction sites in the cathode where they are reduced to oxygen and released into the outside air.

The cathode may be composed of conductive sintered metal oxides such as lanthanum strontium iron oxide, lanthanum strontium iron cobalt oxide (LSCF), praseodymium strontium iron oxide (PSF), barium strontium cobalt iron oxide (BSCF), lanthanum strontium copper oxide (LSC), and lanthanum strontium manganese oxide (LSM). A preferred cathode material is LSM. It is also within the scope of the present disclosure for the cathode to include silver or other suitable electronically conductive material.

Molten electrolyte 18

The molten electrolyte is preferably an inorganic molten salt eutectic. FIG. 5 is a diagram of several inorganic molten salts suitable for use in the present invention, reproduced from Masset et al (Journal of Power Sources 164; 397-414 (2007)). In the eutectic salt melt shown in the figure, LiF-LiCl-LiBr (9.6-22-68.4) has the highest conductivity, 3.5S/cm at 500 ℃. Molten salts such as LiF-LiCl-LiBr have dissolved lithium-oxygen (Li)₂O and Li₂O₂) The advantages of the reaction product are of significant benefit when the battery is charged and discharged. When the discharge products in the salt are saturated,as the discharge products continue to accumulate in the molten salt 18, the discharge products will precipitate out of solution.

Alternative examples of molten electrolytes include lithium metaborate, lithium orthoborate, lithium tetraborate, bulk LiPON, lithium metaborate doped with lithium fluoride, lithium tetraborate doped with silicon, lithium carbonate doped with lithium metaborate (LiBO)₂—Li₂CO₃) Lithium carbonate (Li) doped with lithium orthoborate₃BO₃—Li₂CO₃) Lithium orthoborate doped with lithium carbonate (Li)₂CO₃—Li₃BO₃) Silica-doped Li₃BO₃—Li₂CO₃(SiO₂—Li₃BO₃—Li₂CO₃) And Li doped with lithium fluoride₃BO₃—Li₂CO₃(LiF—Li₃BO₃—Li₂CO₃). Other examples of electrolytes include molten inorganic salts, for example alkali metal nitrates such as lithium nitrate and sodium nitrate, alkali metal chlorides and bromides such as lithium chloride, lithium bromide, potassium chloride, potassium bromide, sodium chloride and sodium bromide, alkali metal carbonates such as sodium carbonate and lithium carbonate, and eutectic mixtures such as sodium nitrate-potassium nitrate (NaNO) for operation in the temperature range of 400 ℃ to 650 ℃. (the co-melting mixture is a mixture of sodium nitrate and potassium nitrate)₃-KNO₃) And lithium chloride-potassium chloride (LiCl-KCl) co-melts, as well as silanes and siloxane-based compounds, including, for example, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and dodecamethylhexasiloxane with or without polyethylene oxide groups for operation in the temperature range of 250 ℃ to 400 ℃. Particularly preferred materials include doped Li_9.3C₃BO_12.5(LCBO) such as LCBFO (LCBO doped with fluorine), LCBSO (LCBO doped with sulfur), LBCSiO (LCBO doped with silicon), LBCSiFO (LBCSiO doped with fluorine) and LBCGeO (LCBO doped with germanium), and LBCSO (LBCO doped with sulfur) for operation in the temperature range of 400 ℃ to 650 ℃.

Fig. 6 is a graph of the ionic conductivity of lithium oxide. This data is provided by Annamareddy et al (Encopy, 19,227 (2017)). Assuming an operating temperature of 500 ℃, lithium oxide will have an ionic conductivity of 10-1.5 at 500 ℃. The ionic conductivity will be the value of the mix of molten salt and solid lithium oxide reaction product mixture.

The non-aqueous electrolyte is selected to obtain stability in contact with lithium. Thus, a breach in the lithium conductive housing will not lead to a rapid reaction, especially since oxygen ingress into the cell will be controlled.

Anode

Lithium-based anodes consist of lithium contained in a sealed ceramic housing or chamber formed from a solid lithium ion conducting electrolyte. The anode comprises metallic lithium in a molten state; lithium has a melting point of about 180 ℃. Lithium metal is stable when in direct contact with a molten salt electrolyte because there is no oxygen or air within the molten salt housing. A benefit of the molten lithium anode within the ionically conductive housing is that it limits undesirable dendrite growth and shorting in the cell. The solid lithium electrolyte shell maintains the lithium in a continuous state such that all molten lithium remains in electrical contact with the anode terminal. During discharge, lithium is oxidized at the solid electrolyte interface into lithium ions and electrons. The electrons are conducted through the load 40 to the cathode electrode terminal 30. Lithium ions are conducted through the solid electrolyte 16 into the molten electrolyte 18 while oxygen ions are conducted through the oxygen ion conductive housing. The opposite occurs during charging. Lithium ions are conducted from the molten salt through the molten electrolyte 18 and are reduced to lithium metal within the reservoir 20 as electrons are coupled from the positive electrode 12 to the terminal 28.

Oxygen ions are conducted into the molten salt through the walls of the molten salt housing where the oxygen ions are conductive, and the molten salt does not contact air. There is no direct contact between the molten salt and the air so that the molten salt does not evaporate from the cell. Oxygen is oxidized to ions at the outer surface of the housing chamber and conducted through the solid housing wall into the molten salt.

Exemplary design

One exemplary design is a 1875kWh cell designed to achieve maximum power output at a 1C discharge rate, i.e., the cell is fully discharged within 1 hour. The specific energy of lithium was 11,580 Wh/kg. For a 1.875kWh cell, 162g of lithium was required. Lithium has a discharge current capacity of 3.86Ah/g, so that the ampere-hour capacity of the battery will be 625Ah, (162g 3.86Ah/g/1 hr).

Due to its operating temperature, the main reaction product of the battery is Li₂And O. The atomic mass of lithium was 6.9 g/mol. For 4Li + O₂>2Li₂O discharge the reaction product, requiring 0.5 moles of oxygen per mole of lithium. Assuming 162g (23.48 moles) of lithium, 11.74 moles (187.82g) of oxygen were required to equilibrate the reaction. Lithium oxide (Li) as a reaction product if mass of oxygen is included₂O) has a net energy density of 5,385 Wh/kg.

The air flow required to maintain the 1C discharge rate may be determined by the required oxygen flow. The oxygen content in the air was 23% by mass so that the total amount of air required for the reaction was 816.6g (187.82g O)₂/(0.23gO₂In terms of air). For 1C discharge, the air mass flow rate was 816.6g/hr or 0.23g/sec, and 0.00123g/cm was used³Air density of 187cm³Volume flow rate in sec.

Referring to fig. 7, as a rough estimate, and assuming a radius of 0.8cm for a solid lithium electrolyte container/separator 16 having an average effective height of 22cm, the average effective surface area would be 55cm². Applied at 110cm²The maximum power output current on the separator will result in 5.6A/cm²Net current density of (625Ah/1h/110 cm)²). As shown in FIG. 3, Li at 600 deg.C_3.6Si_0.6P_0.4O₄Has a lithium ion conductivity sigma of about 1x10^-0.3S/cm. A separator made of this material having a thickness t of 200 microns would have a thickness of 0.04Ohm-cm²(1/σ*t，1/10^-0.30.02 cm). The maximum power output current will have a maximum voltage drop of 0.22 volts (5.6A x 0.04Ohms) across the electrolyte 16.

As shown in fig. 5, the conductivity of the molten salt electrolyte 18 at 600 c is 4S/cm. Its average current density can be determined using its average diameter. Referring to fig. 7, the difference between the radii of the electrolyte 16 and the electrolyte 6 was 1.29 cm. Half of this thickness will be 0.645cm, which gives a radius of 1.445cm at the midpoint of the molten electrolyte. Equivalent surface area at this radiusIs 200cm²(2 π x 1.445cm x 22 cm). At a midpoint radius of 1.445cm of the molten salt, the maximum power current density will be 3.13A/cm²(625Ah/1h/200cm²). For a molten salt electrolyte having a thickness of 1.29cm and a conductivity of 4S/cm, the resistance was 0.32ohm²(1.29cm ohm/4/cm). At a current density of 3.13A/cm²The maximum power voltage drop across the molten salt will be 1 volt.

Scandium-stabilized zirconia [ (Zr2)0.9(Sc2O3)0.1, SSZ was used]As the oxygen ion-conducting electrolyte 6, the surface area at a radius of 2.09cm was 288cm²(2 π x 2.09cm x 22cm) and a maximum output current density at this radius of 2.17A/cm2(625Ah/1h/288 cm)²). According to FIG. 4, the SSZ has a conductivity of 10 at 600 deg.C^-1.69S/cm. For a thickness of 0.004cm, the resistance of the oxygen conductive enclosure will be 0.2ohms². At a current density of 2.17A/cm²The voltage drop will be 0.434 volts.

For this example, the total voltage drop with respect to the open circuit voltage during a high rate, 1 hour of full discharge would be 1.65 volts.

The energy density can be approximated by considering the mass of the components required to construct the battery. Fig. 8 shows the material and mass distribution of the various components of the batteries shown in fig. 1, 2 and 7, with the main components identified by the reference numerals in the component tables. It can be seen that the mass effect of 582 grams of molten salt electrolyte is the largest factor in determining the specific energy. In order to maintain the Li2O reaction product as a slurry suspension, an excess of electrolyte is required so that the product level within reservoir 6 can freely rise and fall with discharge and charge, respectively.

The single material that influences the bulk energy density the most is 300cm³The lithium of (1). 437cm of electrolyte have been dispensed within the electrolyte reservoirs 6 and 8³To accommodate 200cm³Plus 173cm of molten salt of³The fully discharged lithium-oxygen reaction product of (a). The evaluation assigned 200 grams for balancing equipment components that could be shared with other cells throughout the battery system including the blower and duct, thermal insulation, recuperative heat exchanger, electrode and terminal interconnects.

Based on this exemplary analysis, the approximate volumetric energy density was 3.1kWh/l (1,875Wh/604cm³) And the specific energy of complete discharge is 1.29 kWh/kg. It should be noted that reducing the molten salt distribution to 300 grams will result in a specific energy for full discharge of 1.6 kWh/kg.

It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.