Dielectric thin film for solid or semi-solid lithium batteries

Abstract

Dielectric thin film for a solid-state or semi-solid-state lithium battery, wherein the lithium battery comprises a negative electrode and a positive electrode; the dielectric thin film is connected between the negative electrode and the positive electrode; the negative electrode comprises a negative electrode slurry, which is used as a binder, and a plurality of negative electrode particles dispersed in the negative electrode slurry; the positive electrode comprises a positive electrode slurry, which is used as a binder, and a plurality of positive electrode particles dispersed in the positive electrode slurry; the dielectric thin film comprises: a first, a second and a third film layer; wherein the first film layer is connected to the positive electrode and the third film layer to the negative electrode; wherein the second film layer is connected between the first film layer and the third film layer; the first film layer comprises the following: a first polymer material which is used as the base material of the first film layer; wherein the first polymer material is a mixture of PVDF-HFP (polyvinylidene fluoride hexafluoropropylene copolymer), ADN (adiponitrile), GLN (glutaronitrile) and SN (succinonitrile); wherein each of the ADN, GLN and SN is used as a plasticizer in the first polymer material and is dispersed in the PVDF-HFP to disperse a structure of the first polymer material itself; a first lithium salt dispersed in the first polymer material; wherein the first lithium salt is a mixture of LiBOB (LiB(C2O4)2, lithium bis(oxalate)borate), LiTFSI (LiN(CF3SO2)2, lithium bis(trifluoromethanesulfonyl)imide) and LiFSI (F2LiNO4S2, lithium bis(fluorosulfonyl)imide); where ADN, GLN and SN in the first polymer material serve to reduce crystal precipitation of the first polymer material and to support dissociation of the first lithium salt in the first film layer, which increases lithium ion conductivity and malleability of the first film layer; the second film layer comprises the following: a second polymer material used as the base material of the second film layer; wherein the second polymer material is a mixture of PVDF-HFP, PAN (polyacrylonitrile) and SN; wherein PAN and SN are each used as plasticizers in the second polymer material and are dispersed in the PVDF-HFP; a second lithium salt dispersed in the second polymer material; wherein the second lithium salt is a mixture of LiFSI and LiTFSI; wherein PAN and SN in the second polymer material serve to reduce crystal precipitation of the second polymer material and to promote dissociation of the second lithium salt in order to increase lithium ion conductivity of the second film layer; a second inorganic ceramic structure consisting of a plurality of first LLZO particles dispersed in the second polymer material; an outer surface of each of the first LLZO particles is coated with a first dopamine layer (DA, 3,4-dihydroxyphenethylamine); each of the first LLZO particles consists of LLZO (lithium lanthanum zirconium oxide, Li7La3Zr2O) 12 ) or from LLZO doped with at least one metal; and the third film layer comprises the following: a third polymer material, which is used as the base material of the third film layer; the third polymer material is a mixture of PEO (poly(ethylene oxide), polyethylene oxide) and PAN; the PAN in the third polymer material is used as a plasticizer and is dispersed in the PEO; a third lithium salt formed from LiTFSI and dispersed in the third polymer material; a third inorganic ceramic structure formed from a plurality of second LLZO particles dispersed in the third polymer material; an outer surface of each of the second LLZO particles is coated with a second dopamine layer; each of the second LLZO particles is formed from LLZO or doped with at least one metal; and the third inorganic ceramic structure serves to increase the lithium ion conductivity of the negative electrode.

Description

FIELD OF THE INVENTION

[0001] The invention relates to a dielectric thin film in a battery, and more particularly to a dielectric thin film for a solid or semi-solid lithium battery. BACKGROUND OF THE INVENTION

[0002] In the current state of the art, a solid-state or semi-solid-state lithium battery contains a dielectric thin film sandwiched between a negative (-) electrode and a positive (+) electrode. The dielectric thin film serves to insulate and connect the negative and positive electrodes. However, the slurries of the negative and positive electrodes easily lead to side reactions with the lithium ions, causing what is known as lithium death or lithium depletion, thus reducing the battery's electricity storage capacity. Furthermore, the lithium ion capacity of the positive and negative electrode particles is low, resulting in a reduction in the capacity of the entire positive and negative electrodes.

[0003] The conventional dielectric thin film is a single-layer structure with a rigid construction and a low concentration of lithium salt. Therefore, the stacking between the dielectric thin film and the positive electrode is not completely sealed, resulting in poor structure and bonding. The conventional dielectric thin film also cannot fill the cracks between the positive electrode and the dielectric thin film, which easily leads to a short circuit and a reduction in current efficiency. In addition, the conventional dielectric thin film has only a single specific concentration of lithium salt, resulting in poor ionic conductivity and lower overall battery performance. When a single-layer dielectric thin film is bonded to the negative electrode, the ionic conductivity is also poor, reducing the battery's storage capacity. SUMMARY OF THE INVENTION

[0004] To address the above-mentioned deficiencies in the prior art, the object of the invention is to provide a dielectric thin film for a solid-state or semi-solid-state lithium battery, wherein first and third film layers are respectively applied to two sides of a single-layer dielectric thin film to form a three-layer dielectric thin film. The first and third film layers have a soft structure that can be easily embedded into the space between the positive and negative electrodes, improving the conformation and adhesion between the dielectric thin film and the positive and negative electrodes, thus increasing battery performance, reducing the risk of short circuits, and improving battery yield. BRIEF DESCRIPTION OF THE ILLUSTRATIONS Fig. shows a schematic view of the negative electrode, the dielectric thin film and the positive electrode of the invention. Fig. shows a schematic view of the structure of the dielectric thin film of the invention. Fig. shows a schematic view depicting the first LLZO particle of the invention. Fig. shows a schematic view depicting the second LLZO particle of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0005] With reference to the Fig. The invention provides a dielectric thin film 30 for a solid-state or semi-solid-state lithium battery, wherein the lithium battery includes a negative (-) electrode 10 and a positive (+) electrode 20. The dielectric thin film 30 is connected between the negative electrode 10 and the positive electrode 20 (as in Fig. shown). The negative electrode 10 includes a negative electrode slurry 12 used as a binder and containing a plurality of negative electrode particles 15 (such as silicon carbide (SiC) particles with a tin (Sn) layer) dispersed in the negative electrode slurry 12. An outer surface of the negative electrode particles 15 receives lithium ions and functions to uniformly conduct the lithium ions in the negative electrode 10. The negative electrode particles 15 perform a side reaction with some of the lithium ions to reduce the number of usable lithium ions, which will affect the capacity of the entire lithium battery in the long run. The positive electrode 20 includes a positive electrode slurry 22 used as a binder and a plurality of positive electrode particles 26 dispersed in the positive electrode slurry 22.The positive electrode slurry 22 and the positive electrode particles 26 carry out a side reaction with the lithium ions, which pass through the positive electrode 20 and thus the lithium ions that are reacted can also be exhausted.

[0006] Referring to the Fig. The dielectric thin film 30 is disposed between the negative electrode 10 and the positive electrode 20 to insulate and simultaneously connect the negative electrode 10 and the positive electrode 20. The dielectric thin film 30 comprises the following elements: A first film layer 31, a second film layer 32, and a third film layer 33 are superimposed. The first film layer 31 is connected to the positive electrode 20, and the third film layer 33 is connected to the negative electrode 10. The second film layer 32 is connected between the first film layer 31 and the third film layer 33.

[0007] The first film layer 31 comprises the following: A first polymer material 311 is used as the base material of the first film layer 31. The first polymer material 311 consists of a mixture of PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer), ADN (adiponitrile), GLN (glutaronitrile), and SN (succinonitrile). In the first polymer material 311, the ratio of the weight of PVDF-HFP to the "total weight of ADN, GLN, and SN" is 12:1 to 8:1.

[0008] Each of the ADN, GLN, and SN in the first polymer material 311 is used as a plasticizer and dispersed in the PVDF-HFP to disperse a structure of the first polymer material 311 itself and reduce crystal precipitation of the first polymer material 311, as well as to promote the dissociation of the lithium salt (a first lithium salt 312 defined in the description below) in the first film layer 31, thus increasing lithium ion conductivity and moldability of the first film layer 31. A ratio of the weight of the ADN, the weight of the GLN, and the weight of the SN is 1:2:7 to 0.5:1:9.5.

[0009] A first lithium salt 312 is dispersed in the first polymer material 311. The first lithium salt 312 consists of a mixture of LiBOB (LiB(C2O4)2, lithium bis(oxalate)borate), LiTFSI (LiN(CF3SO2)2, lithium bis(trifluoromethanesulfonyl)imide), and LiFSI (F2LiNO4S2, lithium bis(fluorosulfonyl)imide). The ratio of the weight of the first lithium salt 312 to the weight of the first polymer material 311 is 1:2.5 to 1:5. LiTFSI and LiFSI serve to increase the conductivity of the lithium ions. The LiBOB is designed to prevent the LiTFSI and LiFSI from being corroded by water or attacked by HF (hydrofluoric acid) generated by a reaction between the water and the LiTFSI, thereby preventing performance degradation of the lithium battery and allowing the first lithium salt 312 to withstand a higher voltage difference. Therefore, the first polymer material 311 can remain relatively stable under the high-voltage action of the positive electrode 20.In the first film layer 31, a ratio of "a total weight of LiTFSI and LiFSI" and a weight of LiBOB is 2:3. A ratio of a weight of LiFSI and a weight of LiTFSI is 2:1.

[0010] The second film layer 32 comprises the following: A second polymer material 321 is used as the base material of the second film layer 32. The second polymer material 321 is a mixture of PVDF-HFP, PAN (polyacrylonitrile), and SN. In the second polymer material 321, the ratio of the weight of PVDF-HFP, the weight of PAN, and the weight of SN is 8:1.2:1 to 8:1:1.6.

[0011] PAN and SN in the second polymer material 321 are each used as a plasticizer and dispersed in the PVDF-HFP to disperse a structure of the second polymer material 321 itself, reduce crystal precipitation of the second polymer material 321, and promote dissociation of the lithium salt (a second lithium salt 322 defined in the following description) in the second polymer material 321, so as to increase the lithium ion conductivity of the second film layer 32.

[0012] A second lithium salt 322 is dispersed in the second polymer material 321. The second lithium salt 322 consists of a mixture of LiFSI and LiTFSI. In the second lithium salt 322, the ratio of the weight of LiFSI to the weight of LiTFSI is 1:2. The second lithium salt 322 serves to lower an energy level that the lithium ions must cross to conduct within the polymer material, which increases stability and conductivity. The ratio of the weight of the second lithium salt 322 to the weight of the second polymer material 321 is 1:3 to 1:9.

[0013] A second inorganic ceramic structure 323 is formed by a plurality of first LLZO particles 326 dispersed in the second polymer material 321. An outer surface of each of the first LLZO particles 326 is coated with a first dopamine layer (DA, an abbreviation for 3,4-dihydroxyphenethylamine) 324, as shown in Fig. shown. In the second film layer 32, the radial size of each of the first LLZO particles 326 is less than 100 nm. The second inorganic ceramic structure 323 serves to increase the conductivity of lithium ions and the mechanical strength of the second film layer 32. A weight fraction of the second inorganic ceramic structure 323 in the second polymer material 321 is 8 wt% to 20 wt%.

[0014] Each of the first LLZO particles 326 consists of LLZO (lithium lanthanum zirconium oxide, Li7La3Zr2O 12 ) or LLZO doped with at least one metal. Preferably, each of the first LLZO particles 326 consists of Cu-LLZO (copper-doped LLZO).

[0015] Since the PVDF-HFP in the second polymer material 321 readily reacts with the first LLZO particles 326, making the second film layer 32 difficult to form, the outer surface of each of the first LLZO particles 326 is coated with the first dopamine layer 324 to protect the first LLZO particles 326. Furthermore, since dopamine is a hydrophobic material, the first dopamine layer 324 also serves to prevent water from penetrating the first LLZO particles 326, thereby preventing the first LLZO particles 326 from easily forming alkaline byproducts upon contact with moisture and thus undergoing a lithium fluoride reaction with the PVDF-HFP. The functional group of the dopamine is highly compatible with the PAN in the second polymer material 321. In each of the first LLZO particles 326, the weight fraction of the first dopamine layer 324 in the respective first LLZO particle 326 is less than 5 wt.%. The thickness of the first dopamine layer 324 is less than 3 nm.

[0016] The third film layer 33 comprises the following: A third polymer material 331 is used as the base material of the third film layer 33. The third polymer material 331 consists of a blend of PEO (poly(ethylene oxide), polyethylene oxide) and PAN. The weight ratio of PEO to PAN is 5:1 to 8:1. The PEO exhibits high stability under the redox potential of the negative electrode 10 and has good ionic conductivity. In contrast, the PAN exhibits good electronic luminance and ionic conductivity, which in turn enhances the performance of the PEO.

[0017] The PAN in the third polymer material 331 is used as a plasticizer and is dispersed in the PEO.

[0018] An additive 332 is formed from FEC (fluoroethylene carbonate) and is dispersed in the third polymer material 331. The additive 332 serves to help the negative electrode 10 form a good ASEI (artificial solid electrolyte interphase). The weight proportion of the additive 332 in the third polymer material 331 is less than 10 wt%.

[0019] A third lithium salt 333 is formed by LiTFSI and is dispersed in the third polymer material 331. During the formation, charging, and discharging of the lithium battery, the fluorine (F) and lithium (Li) of the LiTFSI deposit on a surface of the negative electrode 10, forming LiF (lithium fluoride) to protect the electrode 10 and form the ASEI. The third lithium salt 333 serves to lower the energy level that lithium ions must cross to conduct within the polymer material. The weight ratio of the third lithium salt 333 to the weight of the third polymer material 331 is 1:3 to 1:9.

[0020] A third inorganic ceramic structure 334 is formed by a plurality of second LLZO particles 336 dispersed in the third polymer material 331. An outer surface of each of the second LLZO particles 336 is coated with a second dopamine layer 335, as shown in Fig.shown. In the third film layer 33, a radial size of each of the second LLZO particles 336 is around 200~300 nm. The third inorganic ceramic structure 334 serves to increase the lithium ion conductivity of the negative electrode 10, which reduces the deposition of dead lithium, reduces the risk of lithium crystal formation and puncture, improves mechanical properties, inhibits part of the negative electrode expansion, and generates a voltage source. A weight fraction of the third inorganic ceramic structure 334 in the third polymer material 331 is 10 to 20 wt.%. In each of the second LLZO particles 336, a weight fraction of the second dopamine layer 335 in the respective second LLZO particle 336 is less than 5 wt.%. The thickness of the second dopamine layer 335 is less than 3 nm.

[0021] Each of the second LLZO particles 336 consists of LLZO (lithium lanthanum zirconium oxide, Li7La3Zr2O 12) or LLZO doped with at least one metal. Preferably, each of the second LLZO particles 336 consists of Cu-LLZO (copper-doped LLZO).

[0022] The first film layer 31 has no inorganic ceramic structure and is made of a soft material, ensuring better adhesion to the positive electrode 20. The first polymer material 311 of the first film layer 31 is a soft material that is filled into a gap between the dielectric thin film 30 and the positive electrode 20. The first lithium salt 312 of the first film layer 31 can reduce the energy level gap to increase the conductivity of the lithium ions.

[0023] A concentration (molar concentration) of the first lithium salt 312 of the first film layer 31 is higher than a concentration (molar concentration) of the second lithium salt 322 of the second film layer 32 and a concentration (molar concentration) of the third lithium salt 333 of the third film layer 33, which reduces the energy level that the lithium ions must cross to become conductive in the first, second and third polymer materials 311, 321, 331 and thus increases the overall conductivity.

[0024] In the invention, the lithium salt concentration in the first, second, and third film layers 31, 32, 33 decreases progressively from the first film layer 31 to the third film layer 33. That is, the concentration (molar concentration) of the first lithium salt 312 of the first film layer 31 is higher than the concentration (molar concentration) of the second lithium salt 322 of the second film layer 32; and the concentration of the second lithium salt 322 of the second film layer 32 is higher than the concentration (molar concentration) of the third lithium salt 333 of the third film layer 33.

[0025] The normal polymer material cannot effectively form chains to form a film structure if the concentration of the polymer material is too high. To solve this problem, the invention incorporates plasticizers (ADN, GLN, SN, and PAN) into the first, second, and third polymer materials 311, 321, and 331. These plasticizers can prevent crystals of the first, second, and third polymer materials 311, 321, and 331 from settling, while supporting the structure of the first, second, and third polymer materials 311, 321, and 331, and improving the structural properties of the first, second, and third polymer materials 311, 321, and 331. The plasticizers in the first, second and third polymer materials 311, 321, 331 are highly polar plasticizers, which enable easier dissociation of the first, second and third lithium salts 312, 322, 333 to increase the amount of free lithium ions, resulting in better lithium ion conductivity.As a result, the second and third inorganic ceramic structures 323, 334 in the second and third film layers 32, 33 can increase the lithium ion conductivity and the mechanical properties.

[0026] The sum of the thickness of the first film layer 31, the thickness of the second film layer 32, and the thickness of the third film layer 33 is 12 µm to 24 µm. The thickness of the second film layer 32 is 10 µm to 18 µm. The thickness of the first film layer 31 and the third film layer 33 is each 1 µm to 3 µm.

[0027] The first film layer 31 and the third film layer 33 are used as connecting layers between the interfaces for connecting the positive electrode 20 and the negative electrode 10, respectively.

[0028] The invention thus relates to a dielectric thin film for a solid-state or semi-solid-state lithium battery, wherein the dielectric thin film is connected between a negative electrode and a positive electrode of the lithium battery. The dielectric thin film comprises a first film layer connected to the positive electrode, a third film layer connected to the negative electrode, and a second film layer connected between the first film layer and the third film layer. The first film layer comprises a first polymer material and a first lithium salt. The second film layer comprises a second polymer material, a second lithium salt, and a second inorganic ceramic structure. The third film layer comprises a third polymer material, a third lithium salt, and a third inorganic ceramic structure.

[0029] Having described the invention, it will be obvious that it may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all modifications obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims

[1] A dielectric thin film for a solid-state or semi-solid-state lithium battery, the lithium battery comprising a negative electrode and a positive electrode; the dielectric thin film is connected between the negative electrode and the positive electrode; the negative electrode comprises a negative electrode slurry used as a binder and a plurality of negative electrode particles dispersed in the negative electrode slurry; the positive electrode comprises a positive electrode slurry used as a binder and a plurality of positive electrode particles dispersed in the positive electrode slurry; the dielectric thin film comprises: a first, a second, and a third film layer; wherein the first film layer is connected to the positive electrode and the third film layer is connected to the negative electrode; wherein the second film layer is connected between the first film layer and the third film layer; wherein the first film layer comprises: a first polymer material used as the base material of the first film layer; wherein the first polymer material is a mixture of PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer), ADN (adiponitrile), GLN (glutaronitrile), and SN (succinonitrile); wherein each of ADN, GLN, and SN is used as a plasticizer in the first polymer material and is dispersed in the PVDF-HFP to disperse a structure of the first polymer material itself; a first lithium salt dispersed in the first polymer material; wherein the first lithium salt is a mixture of LiBOB (LiB(C2O4)2, lithium bis(oxalate)borate), LiTFSI (LiN(CF3SO2)2, lithium bis(trifluoromethanesulfonyl)imide), and LiFSI (F2LiNO4S2, lithium bis(fluorosulfonyl)imide); wherein ADN, GLN and SN in the first polymer material serve to reduce crystal precipitation of the first polymer material and promote dissociation of the first lithium salt in the first film layer, which increases lithium ion conductivity and formability of the first film layer; wherein the second film layer comprises: a second polymer material used as the base material of the second film layer; wherein the second polymer material is a mixture of PVDF-HFP, PAN (polyacrylonitrile), and SN; wherein PAN and SN are each used as plasticizers in the second polymer material and are dispersed in the PVDF-HFP; a second lithium salt dispersed in the second polymer material; wherein the second lithium salt is a mixture of LiFSI and LiTFSI; wherein PAN and SN in the second polymer material serve to reduce crystal precipitation of the second polymer material and promote dissociation of the second lithium salt to increase lithium ion conductivity of the second film layer; a second inorganic ceramic structure consisting of a plurality of first LLZO particles dispersed in the second polymer material; an outer surface of each of the first LLZO particles is coated with a first dopamine layer (DA, 3,4-dihydroxyphenethylamine); each of the first LLZO particles consists of LLZO (lithium lanthanum zirconium oxide, Li7La3Zr2O 12 ) or of LLZO doped with at least one metal; and wherein the third film layer comprises: a third polymer material used as the base material of the third film layer; the third polymer material is a mixture of PEO (poly(ethylene oxide), polyethylene oxide) and PAN; the PAN in the third polymer material is used as a plasticizer and is dispersed in the PEO; a third lithium salt formed from LiTFSI and dispersed in the third polymer material; a third inorganic ceramic structure formed from a plurality of second LLZO particles dispersed in the third polymer material; an outer surface of each of the second LLZO particles is coated with a second dopamine layer; each of the second LLZO particles is formed from LLZO or doped with at least one metal; and the third inorganic ceramic structure serves to increase the lithium ion conductivity of the negative electrode. [2] The dielectric thin film according to claim 1, wherein, in the first film layer, a ratio of a weight of the ADN, a weight of the GLN, and a weight of the SN is 1:2:7 to 0.5:1:9.5; a ratio of a weight of the PVDF-HFP and “a total weight of the ADN, GLN, and SN” is 12:1 to 8:1; a ratio of the weight of the first lithium salt 312 and the weight of the first polymer material 311 is 1:2.5 to 1:5; a ratio of a “total weight of the LiTFSI and LiFSI” and a weight of the LiBOB is 2:3; and a ratio of a weight of the LiFSI and a weight of the LiTFSI is 2:

1. [3] The dielectric thin film according to claim 1, wherein in the second film layer, a ratio of a weight of the PVDF-HFP, a weight of the PAN, and a weight of the SN is 8:1.2:1 to 8:1:1.6; a ratio of a weight of the LiFSI and a weight of the LiTFSI is 1:2; a ratio of a weight of the second lithium salt and a weight of the second polymer material is 1:3 to 1:9; a weight ratio of the second inorganic ceramic structure in the second polymer material is 8 wt% to 20 wt%. [4] The dielectric thin film according to claim 1, wherein in the second film layer, a radial size of each of the first LLZO particles is less than 100 nm; in each of the first LLZO particles, a weight fraction of the first dopamine layer in the respective first LLZO particle is less than 5 wt%; and the thickness of the first dopamine layer is less than 3 nm. [5] The dielectric thin film according to claim 1, wherein in the third film layer, a ratio of a weight of the PEO and a weight of the PAN is 5:1 to 8:1; and a ratio of a weight of the third lithium salt and a weight of the third polymer material is 1:3 to 1:

9. [6] The dielectric thin film according to claim 1, wherein the third film layer further comprises an additive formed from FEC (fluoroethylene carbonate) and dispersed in the third polymer material; and the additive serves to help the negative electrode form an ASEI (artificial solid electrolyte interphase). [7] The dielectric thin film according to claim 6, wherein a weight proportion of the additive in the third polymer material is less than 10 wt%. [8] The dielectric thin film according to claim 1, wherein each of the first LLZO particles is formed of Cu-LLZO (copper-doped LLZO); each of the second LLZO particles is formed of Cu-LLZO (copper-doped LLZO). [9] The dielectric thin film according to claim 1, wherein a radial size of each of the second LLZO particles is 200~300 nm; and a weight ratio of the third inorganic ceramic structure in the third polymer material is 10 wt% to 20 wt%. [10] The dielectric thin film according to claim 1, wherein a concentration of the first lithium salt of the first film layer is higher than a concentration of the second lithium salt of the second film layer; and the concentration of the second lithium salt of the second film layer is higher than a concentration of the third lithium salt of the third film layer. [11] The dielectric thin film according to claim 1, wherein the sum of the thickness of the first film layer, the thickness of the second film layer, and the thickness of the third film layer is 12 µm to 24 µm; the thickness of the second film layer is 10 µm to 18 µm; and the thickness of the first film layer and the third film layer is each 1 µm to 3 µm. [12] The dielectric thin film according to claim 1, wherein the first film layer and the third film layer are used as interface connection layers for connecting the positive electrode and the negative electrode, respectively.

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