Patent Application
20210043939
This application claims the benefit of European Patent Application EP18382060.4 filed on Feb. 5, 2018.
The present invention relates to the field of rechargeable batteries. In particular, it is related to a coating for Li anode protection, as well as to the coated Li anode and to a battery comprising the same.
Lithium Metal Batteries (LMB) such as Li—S, Li-air, and solid-state own the potential to surpass the limitations of Li-Ion Batteries (LIB) opening up new fields of applications with high energy storage demand (e.g. electric vehicle with long distance mobility, green energy storage). However, the intrinsic properties of metallic Li generates several issues regarding safety and device instability leading to limited cycle-life. Consequently, the successful stabilization/protection of Li anode is mandatory for a realistic development of LMB technology.
The highly reactive nature of Li triggers different processes with, generally, detrimental effect on the cycle-life of the battery such as liquid electrolyte degradation, Solid-Electrolyte-Interface (SEI) formation, corrosion of the Li anode due to the presence of minor traces of water in the electrolyte, Li dendrite formation, Li passivation through polysulfide shuttle effect in Li—S batteries.
Particularly, in Li—S batteries, the so called shuttle effect is responsible of detrimental electrochemical side-reactions between polysulfides and Li which ends with the precipitation of insulating Li2S and Li2S2 on the anode. Consequently, a premature death of the device takes place by the passivation of Li metal interface.
The different strategies that have been proposed to address all the shortcomings related to the Li anode can be classified into two main groups: 1) controlled Li+ conductive SEI formation and 2) Li coating with different materials to avoid electrolyte degradation and dendrite growth.
One of the most extended approaches to generate a stable SEI on Li anode is to induce it by adding LiNO3 in the electrolyte (cf. Zhang, S. S., “Role of LiNO3 in rechargeable lithium/sulfur battery” Electrochim. Acta, 2012, Vol. 70, p. 344-348). However, the SEI is not robust enough to prevent from moisture or dendrite formation.
On the other side, the controlled protection of Li anode with organic and/or inorganic materials has been disclosed to have a beneficial effect on the performance of the battery. Approaches based on polymeric coatings in combination with electric conductive polymers and ion conductive polymer films have been disclosed aiming at avoiding dendrite formation and protecting from moisture of the electrolyte (cf. Hu Z. et al. “Poly(ethyl α-cyanoacrylate)-Based Artificial Solid Electrolyte Interphase Layer for Enhanced Interface Stability of Li Metal Anodes” 2017, Chemistry of Materials, Vol. 29, pp. 4682-4689, US20050042515A1, and EP3136475A1). Besides, EP3093906A1 and EP3109924A1 disclose that the inclusion of certain inorganic particles on polyvinyl alcohol polymer or copolymer protection films may have an effect on mechanical properties and on the formation of dendrites on the surface of a lithium metal electrode.
Nevertheless, there is still a need to achieve better performances of lithium batteries, particularly to obtain protected lithium anodes with improved Coulombic efficiency and cycle-life.
In view of what is described above, new coating for protecting lithium-metal anodes featuring improved capacity and reversibility would represent a huge step forward in the development of next-generation energy storage devices.
The inventors have found that the incorporation of a specific amount of at least one inorganic particle having a specific average diameter and being selected from the group consisting of Al2O3, SiO2, TiO2, ZnO, Fe2O3, CuO y BaTiO3, silicates, aluminosilicates, and borosilicates in a specific polymer coating forming a protective film of a certain thickness on a lithium anode, the coating being exempt of any nitrogen-containing additive such as LiNO3 or of another metal salt such as LiTFSI, unexpectedly, allows to reach equally good battery performances in terms of Coulombic efficiency than protective coatings containing the mentioned nitrogen-containing additives. Particularly, a battery comprising the mentioned protected anode has improved Coulombic efficiency and cycle-life even in conditions where dendrite growth is avoided.
As used herein, in Li—S technology, the conditions where dendrite growth is avoided are such that low charge/discharge rates are used. A low charge/discharge rate is considered to be either at a rate below 2 C such as at 1.0, 0.5, 0.2, or 0.1, where C is the specific capacity of sulfur (1672 mAh/gS), or at current densities below 1 mA/cm2 such as at 0.75, 0.5, or 0.25 mA/cm2.
Thus, a first aspect of the invention relates to a protected anode for a lithium metal battery comprising:
wherein the protective monolayer consists of:
and wherein:
the protective monolayer has a thickness from 0.01 to 10 μm;
the inorganic particles have an average diameter from 1 to 500 nm; and
the at least one inorganic particle is in an amount from 0.01 to 30 wt %.
Surprisingly, as can be seen from the examples and comparative examples, batteries comprising the protected lithium metal anodes as defined above show a surprisingly good Coulombic efficiency, and cycle-life in conditions where dendrite growth is avoided. Unexpectedly, in spite of the protecting coating being exempt of any nitrogen-containing additive such as LiNO3 or of another metal salt such as LiTFSI, the improvement on the Coulombic efficiency is maintained above 99% for at least 120 cycles.
A second aspect of the invention relates to a process for the preparation of a lithium metal protected anode as defined above, the process comprising:
A third aspect of the invention relates to a lithium metal battery comprising:
Finally, a fourth aspect of the invention relates to the use of the lithium metal protected anode as defined above to improve Coulombic efficiency of a lithium battery, particularly in conditions where dendritic growth is avoided.
For the sake of understanding, the following definitions are included and expected to be applied throughout the description, claims and drawings.
In this specification, “(meth)acrylate” is used as a general term representing “acrylate” and “methacrylate”.
The terms “particle size”, as used herein, is in terms of diameter irrespective of the actual particle shape. The term “diameter”, as used herein, means the equivalent sphere diameter, namely the diameter of a sphere having the same diffraction pattern, when measured by laser diffraction, as the particle. The diameter of nanoparticles can be measured by Transmission Electron Microscopy (TEM). TEM measurements can be performed on JEOL 2010 F operating with 200 kV accelerating voltage. The characterization of nanoparticles can be made by deposition of a drop of highly diluted (0.1 mg/ml) nanoparticle dispersion in heptane onto a formvar coated grid, stabilized with evaporated carbon film, FCF300-Cu-25 grid from Electron Microscopy Science. The sizes of pitch, hole and bar are 84, 61, 23 μm, respectively (300 mesh). Average size and size distribution can be calculated by measuring the dimensions of a representative amount of nanoparticles by this technique. Image processing software packages are used to quantify particle size and size distribution. An example of such a software is Pebbles (cf. S. Mondini, et al., “PEBBLES and PEBBLEJUGGLER: software for accurate, unbiased, and fast measurement and analysis of nanoparticle morphology from transmission electron microscopy (TEM) micrographs”, Nanoscale, 2012, 4, 5356-5372).
All percentages used herein are by weight of the total composition, unless otherwise designated.
As used herein, the indefinite articles “a” and “an” are synonymous with “at least one” or “one or more.” Unless indicated otherwise, definite articles used herein, such as “the,” also include the plural of the noun.
As mentioned above, a first aspect relates to a protected anode for a lithium metal battery, the anode comprising a lithium metal anode and a protective monolayer disposed on at least a portion of the lithium metal anode, wherein the protective monolayer consist of one polymer and at least one inorganic particle is as defined herein above and below.
Also as mentioned above, a second aspect of the invention relates to a process for the preparation of the protected lithium metal anode as defined above, the process comprising forming a precursor solution or dispersion as defined above; spreading it onto the lithium metal anode; and evaporating the solvent and, optionally, carrying out a crosslinking reaction, in order to form a continuous, optionally cross-linked, film over the lithium metal anode.
The precursor solution or dispersion used to form the film coating on the surface of the lithium metal anode is obtained by dissolving or dispersing a polymer as defined herein above or below and at least one inorganic particle as defined herein above or below in an anhydrous solvent.
As mentioned above, polymers useful for obtaining the coated lithium anode of the invention are a polyethylene oxide (PEO) based polymer, a PEO based polymer having a cross-linking functional group, polymethylmethacrylate, polymethylacrylate, polyethylmethacrylate, polyethylacrylate, polypropylmethacrylate, polypropylacrylate, polybutylacrylate, polybutylmethacrylate, polypentylmethacrylate, polypentylacrylate, polycyclohexylmethacrylate, polycyclohexylacrylate, polyhexylmethacrylate, polyhexylacrylate, polyglycidylacrylate, polyglycidylmethacrylate, poly-2-ethylhexylmethacrylate, poly(decyl acrylate), polyethylene vinyl acetate, polyvinylidene fluoride, polyethylene oxide, polypropylene oxide, polystyrene, polystyrene sulfonate, hydrogenated polystyrene, polyvinylpyridine, polyvinyl cyclohexane, polyimide, polyamine, polyamide, polyethylene, polybutylene, polypropylene, poly(4-methyl-pentene), poly(butylene terephthalate), poly(isobutyl methacrylate), poly(ethylene terephthalate), polydimethylsiloxane, polydimethylsiloxane vinyl terminated, poly(C1 to C20 alkyl carbonate) polymaleic acid, poly(maleic anhydride), polymethacrylic acid, poly(tert-butyl vinyl ether), poly(cyclohexyl vinyl ether), polydivinylbenzene, polyacrylic acid, polymethacrylic acid, polynitrile, polyphosphazine, polydiene, polyisoprene, polybutadiene, polychloroprene, polyisobutylene, polyurethane, polybenzimidazole, polypyrrole, and copolymers thereof. These polymers are commercially available.
Particularly, PEO is an attractive building block material to form thin films on Li anodes. Due to its intrinsic ionic conductivity, the permeation of Li ions through PEO barrier is allowed while the electrolyte degradation is suppressed as the PEO interface prevents the contact between the solvent and the Li metal.
Besides, material engineering permits the modification of PEO to add functional groups that leads to the formation of a tri-dimensional net through different cross-linking chemistries. Consequently, an insoluble and mechanically stable coating can be formed which blocks the dendrite growth and homogenizes Li platting. Thus, a PEO based polymer having cross-linking functional groups comprised in the precursor solution will form a tri-dimensional matrix. The versatility of PEO based polymers can be used to design advanced materials adjusted to competitive processing methods and/or with additional functionalities (e.g. polymeric ionic liquid nature).
Thus, in a particular embodiment, the polymer is a PEO based polymer, or a crosslinked PEO based polymer. Particularly, the polymer is a PEO based polymer having a meth(acrylate) or a vinyl functional group, more particularly the polymer is poly(ethylene glycol) diacrylate (PEGDA), or poly(ethylene glycol) dimethacrylate (PEGDMA).
The cross-linking reaction necessary to obtain the final crosslinked PEO based polymer can take place through the following mechanism:
Thus, in a particular embodiment of the lithium metal anode of the invention, the polymer is a crosslinked PEO based polymer deriving from a PEO based polymer having a cross-linking functional group selected from the group consisting of meth(acrylate), vinyl, a functional group capable to induce an addition or a condensation reaction, and a functional group capable to induce a nucleophilic substitution reaction.
Particularly, examples of groups capable to induce addition/condensation reactions are a carboxylic acid group and an alcohol group, or an isocyanate group and an alcohol group. Examples of groups capable to induce nucleophilic substitution reactions are an (C1-C4)alkyl tosylate and an amine, or halogen atom such as Cl, Br or I and amine.
In a more particular embodiment of the lithium metal anode of the invention, the crosslinked PEO based polymer derives from poly(ethylene glycol) diacrylate (PEGDA), poly(ethylene glycol) dimethacrylate (PEGDMA), di(N,N′-vinyl imidazolium) dianion terminated poly(ethylenoxide), and tosylate terminated poly(ethylenoxide).
The mentioned PEO based polymers or PEO based polymers having cross-linking functional groups are used in a particular embodiment of the process of the invention.
In another particular embodiment, the PEO based polymer is PEGDA, particularly of a MW of PEG unit from 214 to 2326 g/mol (n=2-50), more particularly of 550 (n=10).
In another particular embodiment, the PEO based polymer having a cross-linking functional group is a PEO-based polymeric ionic liquid, which allows adjusting the properties and optimize the protective performance (by improving properties such as ionic conductivity, hydrophobic nature, and inorganic/carbon materials dispersion capability) of the coated Li anode in LMB. Examples of PEO-based polymeric ionic liquids include, without being limited to, di(N,N′-vinyl imidazolium) dianion terminated poly(ethylenoxide), and tosylate terminated poly(ethylenoxide).
PEO derivatives with radical cross-linking groups are sensitive to oxygen as they act as radical scavengers. Therefore, particularly the film formation process can be carried out in a glove box under oxygen and moisture free atmosphere (O2<0.1 ppm and H2O<0.1 ppm). As a result, solvent is evaporated leaving a continuous, crosslinked film with a controlled thickness.
The inorganic particles are selected from the group consisting of Al2O3, MnO, MnO2, SiO2, TiO2, ZnO, ZrO2, Fe2O3, CuO, a silicate, an aluminosilicate, a borosilicate, and an oxysalt of formula AxByOz wherein A is an alkaline metal or an alkaline-earth metal, B is selected from the group consisting of Al, Mn, Si, Ti, Zn, Zr, Fe, and Cu, and x, y, z, are the number of the corresponding atoms so that the overall charge of the oxysalt is 0, such as BaTiO3, or any one of the mentioned inorganic particles which are functionalized. Unexpectedly, these inorganic particles in addition to increase the mechanical stability of the polymeric film protecting the anode (e.g. by formation of composites), allow obtaining a battery with improved Coulombic efficiency, and cycle-life in conditions where dendrite growth is avoided.
As mentioned above, the inorganic particles are nanoparticles having an average diameter from 1 to 500 nm. In a particular embodiment of the protected anode of the invention, optionally in combination with one or more features of the particular embodiments defined above, the inorganic particles have an average diameter from 1 to 100 nm, more particularly from 1 to 10 nm. Also particularly, they have a sharp particle size distribution.
The inorganic particles are commercially available, also within the mentioned particle size ranges. Additionally, inorganic particles within the mentioned particle size range can be obtained by known mechanical methods, such as milling and/or sieving or chemical methods, such as precipitation, metal evaporation, laser pyrolysis, gas phase methods and plasma-chemical reduction method. In a particular case, metal oxide nanoparticles with controlled size and shape can be synthesized by adding basic solutions (KOH, NaOH) into a metallic salt precursor solution in the required concentrations to obtain the desired dimensions. Depending on the metal cation, metal oxide nanoparticles can be obtained directly. However, in some cases further annealing treatment is required to induce the transitions from the formed phase into the metal oxide nanoparticle. These methods are widely known and use commonly available equipment.
In a particular embodiment, optionally in combination with one or more features of the particular embodiments defined above, the inorganic particle is Al2O3.
In another particular embodiment, optionally in combination with one or more features of the particular embodiments defined above, the inorganic particles are silicates, aluminosilicates, and borosilicates. Particularly, the silicate has the formula SiaOb, the aluminosilicate is a mixture of SiaOb and Al2O3, and the borosilicate is a mixture of SiaOb and B2O3, wherein a=1-4 and b=2-8.
Although bare nanoparticles can be added, inorganic particles functionalized with molecules containing groups that can be covalently linked to the polymeric matrix are capable of being anchored to this polymeric matrix, which prevent their loss in the electrolyte. In such a way, functionalized inorganic particles are integrated in the polymer matrix to form a composite. Thus, in another particular embodiment of the process of the invention, optionally in combination with one or more features of the particular embodiments defined above, the inorganic particle is a functionalized inorganic particle. Particularly, the inorganic particle is a functionalized Al2O3.
The nanoparticles can be functionalized by anchoring different organic compounds on their surface, in order to gain additional physicochemical properties such as improved dispersability and conductivity.
The anchoring takes place, usually but not limited to, through covalent bonding created between the metal oxide and certain groups such as silane or phosphonate groups, which are part of the organic molecule (cf. M. A. Neouze and U. Schubert “Surface Modification and Functionalization of Metal and Metal Oxide Nanoparticles by Organic Ligands” Monatsh Chem, 2008, Vol. 139, pp. 183-195). Examples of typical routes to functionalize nanoparticles lie on the dissolution of the organic compound into a solvent, disperse the nanoparticles into the solution and keep the system stirring for a certain time to let the surface of the nanoparticle be coated by the organic molecule. The process may require further procedures such as filtering, purification and/or temperature treatments to obtain the final purified product. The functionalization of nanoparticles is not limited to the described procedure as different routes can be found in the state of art (cf. E. Hogue et al. “Alkylphosphonate Modified Aluminum Oxide Surfaces” J. Phys. Chem. B 2006, Vol. 110, pp. 10855-10861; P. H. Mutin et al. “Hybrid materials from organophosphorus coupling molecules” J. Mater. Chem., 2005, Vol. 15, pp. 3761-3768).
As mentioned above, the amount of inorganic particles in the polymer is from 0.01 to 30 wt %. In a particular embodiment of the anode of the invention, optionally in combination with one or more features of the particular embodiments defined above, the amount of the at least one inorganic particle in the protective layer is from 0.01 to 20 wt %, or from 0.1 to 20 wt %, or from 0.5 to 20 wt %, or from 1 to 10 wt %, or from 1.5 to 5 wt %, related to the amount of polymer.
Accordingly, as the mentioned inorganic particles can also form part of the precursor solution or dispersion used in the process for the preparation of the anode of the invention, the above mentioned amounts of particles, particle sizes, and particular inorganic particles also define particular embodiments of the process of the invention, optionally in combination with one or more features of the particular embodiments of the process defined above.
In another particular embodiment, optionally in combination with one or more features of the particular embodiments of the process defined above, the polymer is poly(ethylenoxide)diacrylate (PEGDA) and the at least one inorganic particle is in an amount from 2 to 20 wt %, or from 2 to 5 wt %, more particularly of 2.4 wt %.
As mentioned above, the precursor solution or dispersion is obtained by dissolving or dispersing the polymer and the at least one inorganic particle in the amounts defined above in an anhydrous solvent.
Examples of solvents include, without being limited to, dimethoxyethane (DME), dethylenglycol dimethylether (DEGDME), 1,3-dioxolane (DOL), and 1,4-dioxane. The evaporation can be carried out at room temperature or at higher temperature.
The specific combination of components forming the protective coating defined above provides an efficient and optimized Li protection, that allows obtaining a lithium metal battery having an improved Coulombic efficiency, and cycle-life in conditions where dendrite growth is avoided (low charge/discharge rates used in Li—S technology).
Field emission scanning electron microscope (FE-SEM) characterization was used to find out the correlation between the polymer concentration in the precursor solution and the thickness of the formed film. Particularly, the thickness of the film at each measurement point may be measured through observation of a cross-sectional view of the coated anode by using a FE-SEM (e.g., ULTRA plus ZEISS field emission scanning electron microscope).
As mentioned above, the protective monolayer has a thickness from 0.01 to 10 μm. In a particular embodiment of the protected anode of the invention, optionally in combination with one or more features of the particular embodiments defined above, the protective monolayer has a thickness from 0.05 to 5 μm, or from 0.1 to 1 μm.
Accordingly, in a particular embodiment of the process of the invention, optionally in combination with one or more features of the particular embodiments defined above, in the precursor solution or dispersion used to form the film coating on the surface of the lithium metal anode, the concentration of the polymer, particularly of the polyethylene oxide based polymer optionally comprising cross-linking functional groups, is from 0.1 to weight % with respect to the mass of the precursor solution.
Thus, as an instance, PEGDA concentration above 1 wt % with respect to the mass of the precursor solution, allows obtaining a continuous and homogeneous film of ˜100 nm whereas thicker films of ˜400 nm are obtained from 4.2% concentration solutions (see
An anode obtainable by the process mentioned above also forms part of the invention.
The anode as defined above can be used in the manufacture of a lithium battery. Thus, also form part of the invention a lithium battery comprising a lithium metal anode as defined herein above, a cathode, and an electrolyte interposed between the cathode and the anode. Particularly, the cathode comprises sulfur.
The lithium battery also comprises an electrolyte. Such electrolytes include a salt and a solvent.
As a way of example, electrolytes for Li-sulfur batteries may contain lithium salts and organic solvents. Some of the most widely used solvents are ethers such as poly(ethylene glycol), 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME) or tetra(ethylene glycol) dimethyl ether (TEGDME). Examples of the lithium salts are LiCF3SO3 (also known as LiTfO), Li(CF3SO2)2N (also known as LiTFSI), and LiNO3, among others. In yet other embodiments, the electrolyte comprises a lithium salt and an ionic liquid, such as the lithium salt LiTFSI together with the IL (N-methyl-N-propylpyrrolidone)TFSI.
When in the battery, the lithium metal anode may absorb components of the electrolyte. Thus, in a particular embodiment of the battery of the invention, the protective monolayer further comprises one or more components of the electrolyte capable of diffusing to the protective monolayer in an amount up to 2 wt %, up to 1.5 wt %, up to 1 wt %, or up to 0.5 wt %, with respect to the amount of polymer, wherein the component of the electrolyte capable of diffusing to the protective monolayer is selected from an organic solvent, a lithium salt, an ionic liquid, and mixtures thereof. Particularly, the component of the electrolyte capable of diffusing to the protective monolayer is a mixture of a lithium salt as defined above and a solvent, more particularly, a lithium salt as defined above.
Throughout the description and claims the word “comprise” and variations of the word, are not intended to exclude other technical features, additives, components, or steps.
Furthermore, the word “comprise” encompasses the case of “consisting of”. Additional objects, advantages and features of the invention will become apparent to those skilled in the art upon examination of the description or may be learned by practice of the invention. The following examples and drawings are provided by way of illustration, and they are not intended to be limiting of the present invention. Reference signs related to drawings and placed in parentheses in a claim, are solely for attempting to increase the intelligibility of the claim, and shall not be construed as limiting the scope of the claim. Furthermore, the present invention covers all possible combinations of particular and preferred embodiments described herein.
Battery grade 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) were purchased from BASF and further purified with molecular sieves 3A sigma Aldrich to keep moisture content below 20 ppm. The water content was measured by a Karl Fischer TitroLine KF Trace equipment from Schott Instruments using Hydranal-Coulomat AG reactant. It must be noted that the molecular sieves were rinsed with acetone several times and subsequently annealed at 200° C. for 6 h, previously to their use.
Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was purchased from Solvionic>99%); Lithium nitrate (LiNO3) from Aldrich 99.99%; alumina nanoparticles, 5 nm 99.99%, from US Research Nanoparticles Inc.; and poly(ethylene glycol) diacrylate 550 g/mol from Sigma-Aldrich.
For the preparation of the cathode composite, elemental sulfur (Sigma-Aldrich, 100-mesh particle size) and carbon black (Ketjenblack EC-600JD, AkzoNobel) were ball milled (Restch, PM100) for 3 h at 300 rpm. The mixture was heated at 150° C. for 6 h under argon atmosphere. Then, the temperature was increased to 300° C. and kept for 3 h to vaporize the superfluous sulfur on the outer surface of carbon spheres, diffusing entirely into the pores. After cooling down to room temperature, the sulfur-carbon composite was obtained.
Cathode was prepared by mixing sulfur-carbon composite, conductive carbon black (Super C45, Timcal) and polyvinylidene fluoride (PVDF, BASF) in a weight ratio of 50:40:10 and using N-methylpyrrolidone (NMP, Sigma-Aldrich) as solvent. The resultant slurry was cast onto carbon coated aluminum foil using the doctor blade and dried at 60° C. for 2h. The loading of the cathode was 1.60±0.05 mgsulfur·cm−2.
Cycle life of the coin cells was investigated within 1.7 V-2.6 V vs Li/Li+ at 0.1 C (1 C=1,672 mA/gS) using a battery cycler Basytec CTS system (BASYTEC GMBH, Germany) at 25° C.
The electrolyte consisted of a solution of [LiTFSI] at 0.38 M and [LiNO3] at 0.32 M in DOL:DME solvent mixture at 1:1 volume ratio.
The coating of Li anode was performed by using a precursor solution in DME of the required elements:
Lithium foil anode of 2.6 cm2 area was placed on the case of the coin cell. Subsequently, 100 μL of the precursor solution was spread over the Li anode and solvent evaporation let to dry.
The electrochemical characterization was carried out assembling CR2025 type coin cells (Hohsen Corp.) in a dry room. As the negative electrode (Anode) lithium foil (50 μm thickness, Rockwood lithium) was used (Li anode could contain a protective coating generated as previously explained), a polyethylene based separator, a positive electrode (cathode) prepared as previously explained and adding 50 μL of electrolyte.
For each system, three coin cells were tested in order to ensure the reproducibility of the approach.
Coatings on Li foils were obtained according to the “Li anode protection” disclosed above.
For each precursor solution the concentration of the corresponding components are indicated.
The Coulombic efficiency of cells containing an anode:
The thickness of the films formed from a precursor solution with a PEGDA concentration of a 2.0 wt % with respect to the mass of the precursor solution was of ˜200 nm.
Coatings on Li foils were obtained according to the “Li anode protection” disclosed above. For each precursor solution the concentration of the corresponding components are indicated.
The Coulombic efficiency of cells containing an anode:
The thickness of the films formed from a precursor solution with a PEGDA concentration of a 2.0 wt % with respect to the mass of the precursor solution was of ˜200 nm.
Similarly as in Examples 1 and 2, the Coulombic efficiency of cells containing an anode:
The thickness of the formed films was of ˜200 nm.
As it can be inferred from
The treatment of Li with PEGDA leads to higher values of Coulombic efficiency in comparison with the standard system. However, the system with PEGDA film suffers from a rapid efficiency decrease, which implies a poor robustness.
The combination of PEGDA and LiTFSI had not a particularly good performance, but showed a worst performance than the PEGDA system. Additionally, the performance of the quaternary system consisting of PEGDA, LiNO3, LiTFSI and Al2O3 was substantially inefficient as Li anode protection.
The systems of PEGDA plus LiNO3 and, optionally, LiTFSI allowed obtaining Li protection coatings with improved Coulombic efficiency with respect to the PEGDA cell. With regard to the performance of the PEGDA plus LiNO3 and LiTFSI system, it is not evident to justify its improvement, as primary results in binary PEGDA-LiTFSI system did not show any outstanding performance.
Unexpectedly, the behavior of PEGDA-Al2O3 is similar to PEGDA-LiNO3, and the incorporation of an amount of inorganic particles higher to the claimed range lead to a result similar to the unprotected anode (standard), i.e. no beneficial effect is observed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18382060.4 | Feb 2018 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/052664 | 2/4/2019 | WO | 00 |
