Additives for electrolytes

Abstract

To provide additives for electrolytes. [Solution] The use of an additive comprising at least one organic catalyst in an electrolyte for a battery is provided. Also provided is a method for preventing contact between the anode and residual water in a battery and / or reducing the level of gas in the battery. Furthermore, an electrolyte for a battery comprising an additive comprising at least one organic catalyst is provided. Moreover, a battery comprising an electrolyte comprising an additive comprising at least one organic catalyst is provided. The electrolyte of the present invention can be used in a battery in which the anode comprises a reactive group.

Description

[Technical Field]

[0001] Field of Invention This invention generally relates to additives for electrolytes. More specifically, it relates to the use of an organic catalyst as an additive in an electrolyte containing a carbonate. The electrolyte of this invention can be used in a battery in which the anode contains a reactive group. The organic catalyst promotes the reaction between the reactive group and the carbonate, thereby forming a protective layer on the surface of the anode, thus preventing contact between the anode and residual water in the battery, and also preventing the decomposition of the carbonate in the electrolyte. Batteries using the electrolyte of this invention are more stable and safer. [Background technology]

[0002] Background of the Invention Water is a residual contaminant of battery electrodes. For example, during the cycle of a battery where the anode is lithium titanium oxide (LTO), water comes into contact with the LTO to produce hydrogen and oxygen. Typically, in such a battery, the cathode is LiMPO4 based with M being Fe, Co, Ni, Mn, etc., and the electrolyte is a mixture of linear and cyclic carbonates as solvents and salts which may be LiPF6, LiFSI, LiTFSI, LiBOB, LiBF4, or any other suitable commercially available salt containing lithium. This is because the anode is titanium hydrogen oxide (HTO), TiO2, Si, SiO2 x This also occurs in batteries containing materials such as tin and graphite. Furthermore, it can occur in batteries where the cathode is a high-energy cathode.

[0003] During the cycle of such a battery, for example, a battery with an LTO anode, the electrolyte (carbonate) can react with residual water in the presence of the anode to form CO2, CO, H2, O2, and hydrocarbons. These products cause the expansion of pouch cells. These are publicly known and could pose a safety problem [1-3].

[0004] One industrial approach to address this problem involves removing water from the cathode and anode. Since the active material is generally hydrophilic, the electrodes must be carefully dried. This generally requires a large amount of energy and therefore increases costs.[4]

[0005] Another approach is to allow the formation of a protective coating at the interface on the electrode. This coating can prevent contact between the electrolyte and the active surface of the electrode. For example, an additive is used in the electrolyte, and a film is formed by the decomposition of the additive [6]. Alternatively, a shell can be formed directly on the active material before assembling the cell to create a protective layer on the LTO anode [7]. A method is still needed to prevent the anode from coming into contact with residual water inside the battery. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Belharouak, I.; Amine, K.; Koenig, G.; Tan, T.; Yumoto, H.; Ota, N. In gassing and performance degradation in Li4Ti5O12 based Li-ion batteries, 29th International Battery Seminar and Exhibit 2012: Primary and Secondary Batteries - Other Technologies, 2012; pp 874-887. [Non-Patent Document 2] Wu, K.; Yang, J.; Liu, Y.; Zhang, Y.; Wang, C.; Xu, J.; Ning, F.; Wang, D., Investigation on gas generation of Li4Ti5O12 / LiNi1 / 3Co1 / 3Mn1 / 3O2 cells at elevated temperature. Journal of Power Sources 2013, 237(0), 285-290.

Non-Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

[0007] Summary of the Invention The inventors have discovered the use of an organic catalyst as an additive in an electrolyte containing carbonate. The electrolyte of the present invention can be used in batteries in which the anode contains a reactive group. The organic catalyst promotes the reaction between the reactive group and the carbonate, thereby forming a protective layer on the surface of the anode, which prevents contact between the anode and residual water in the battery and also prevents the decomposition of the carbonate in the electrolyte. Batteries using the electrolyte of the present invention are more stable and safer.

[0008] Therefore, according to its embodiments, the present invention provides the following: (1) Use of an additive containing at least one organic catalyst in an electrolyte for a battery. (2) Use of an additive comprising at least one organic catalyst in an electrolyte comprising at least one carbonate. (3) Use of an additive comprising at least one organic catalyst in a battery in which the anode comprises a reactive group and the electrolyte comprises at least one carbonate. (4) Additives comprising at least one organic catalyst, wherein the anode is lithium titanium oxide (LTO), titanium hydrogen oxide (HTO), TiO2, Si, SiO x Use in a battery comprising a material selected from the group consisting of Sn, graphite, and combinations thereof, wherein the electrolyte comprises at least one carbonate. (5) Use of an additive comprising at least one organic catalyst in a battery comprising a material in which the anode is lithium titanium oxide (LTO) and the electrolyte comprises at least one carbonate. (6) A method for preventing contact between the anode and residual water in a battery and / or reducing the level of gas in the battery, wherein the method includes using an electrolyte comprising at least one organic catalyst. (7) A method for preventing contact between the anode and residual water and / or reducing the gas level in a battery in which the electrolyte comprises at least one carbonate, wherein the method comprises adding at least one organic catalyst to the electrolyte. (8) A method for preventing contact between the anode and residual water and / or reducing the gas level in a battery in which the anode comprises a reactive group and the electrolyte comprises at least one carbonate, wherein the method comprises adding at least one organic catalyst to the electrolyte. A method including the addition of a medium. (9) A method for preventing contact between the anode and residual water in a battery, and / or reducing the gas level in the battery, and / or preventing the decomposition of carbonate in the electrolyte, wherein the anode is lithium titanium oxide (LTO), titanium hydrogen oxide (HTO), TiO2, Si, SiOx A method comprising a material selected from the group consisting of Sn, graphite and combinations thereof, wherein the electrolyte comprises at least one carbonate, and the method comprises adding at least one organic catalyst to the electrolyte. (10) A method for preventing contact between the anode and residual water in a battery, and / or reducing the level of gas in the battery, and / or preventing the decomposition of carbonate in the electrolyte, wherein the anode comprises a material in which lithium titanium oxide (LTO) is the anode, and the electrolyte comprises at least one carbonate, and the method comprises adding at least one organic catalyst to the electrolyte. (11) An electrolyte for a battery comprising an additive containing at least one organic catalyst. (12) The anode is lithium titanium oxide (LTO), titanium hydrogen oxide (HTO), TiO2, Si, SiO x An electrolyte for a battery comprising a material selected from the group consisting of sn, graphite, and combinations thereof, wherein the electrolyte comprises an additive comprising at least one organic catalyst. (13) An electrolyte for a battery comprising a material in which the anode is lithium titanium oxide (LTO), wherein the electrolyte comprises an additive comprising at least one organic catalyst. (14) A battery comprising an additive which contains at least one organic catalyst as the electrolyte. (15) A battery in which the electrolyte comprises at least one carbonate, and the electrolyte further comprises an additive comprising at least one organic catalyst. (16) A battery in which the anode comprises a reactive group and the electrolyte comprises at least one carbonate, wherein the electrolyte further comprises an additive comprising at least one organic catalyst. (17) The anode is lithium titanium oxide (LTO), titanium hydrogen oxide (HTO), TiO2, Si, SiO x A battery comprising a material selected from the group consisting of sn, graphite and combinations thereof, wherein the electrolyte comprises at least one carbonate, and the electrolyte further comprises an additive comprising at least one organic catalyst. (18) A battery in which the anode contains a material of lithium titanate oxide (LTO), the electrolyte contains at least one carbonate, and the electrolyte further contains an additive containing at least one organic catalyst. (19) The use according to any one of (1) to (5) above, or the method according to any one of (6) to (10) above, or the electrolyte according to any one of (11) to (13) above, or the battery according to any one of (14) to (18) above, wherein the organic catalyst is an alkaloid compound. (20) The use according to any one of (1) to (5) above, or the method according to any one of (6) to (10) above, or the electrolyte according to any one of (11) to (13) above, or the battery according to any one of (14) to (18) above, wherein the organic catalyst is an amidine compound. (21) The use according to any one of (1) to (5) above, or the method according to any one of (6) to (10) above, or the electrolyte according to any one of (11) to (13) above, or the battery according to any one of (14) to (18) above, wherein the organic catalyst is 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). (22) The use according to (3) above, or the method according to (8) above, or the battery according to (16) above, wherein the reactive group is OH, SH, or a combination thereof. (23) The use according to any one of (1) to (5) above, or the method according to any one of (6) to (10) above, or the electrolyte according to any one of (11) to (13) above, or the battery according to any one of (14) to (18) above, wherein the carbonate is a saturated or unsaturated linear, branched, or cyclic carbonate. (24) The carbonate has the following general formula I

Chemical formula

[0009] Other objects, advantages, and features of the present invention will become more apparent by reading the following non-limiting description relating to specific embodiments, which are given merely as examples, with reference to the accompanying drawings.

[0010] The attached drawings are as follows: [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 generally illustrates the chemical reaction between the reactive groups of the anode and the electrolyte carbonate, catalyzed by an organic catalyst, on the surface of the anode.

[0012] [Figure 2] Figure 2 shows the chemical reaction between a hydroxyl group and a carbonate on the surface of a lithium titanium oxide (LTO) anode, catalyzed by 1,8-diazabicyclo[5.4.0]undeca-7-ene (DBU).

[0013] [Figure 3] Figure 3 shows the HPLC-MS TOF of the model system.

[0014] [Figure 4] Figure 4 shows the volume of gas in the cell quantified by GC. Blue represents hydrogen, red represents propylene, light blue represents methane, green represents carbon dioxide, and yellow represents oxygen.

[0015] [Figure 5] Figure 5 shows a hypothetical mechanism illustrating the formation of the protective layer on the LTO anode surface.

[0016] [Figure 6] Figure 6 shows the FTIR spectrum of the anode containing the additive.

[0017] [Figure 7] Figure 7 shows a) a scanning electron microscope (SEM) image and b) a deep profile at m / z=59, where this fragment corresponds to propylene oxide, and the fragment at m / z=47.869 represents titanium.

[0018] [Figure 8] Figure 8 shows the thermogravimetric analysis of the anode.

[0019] [Figure 9] Figure 9 shows the effect of the additive on gas suppression.

[0020] [Figure 10] Figure 10 shows the stray current during a stray test at 45°C.

[0021] [Figure 11] Figure 11 shows the discharge / DC resistance (DCR) at various temperatures.

[0022] [Figure 12] Figure 12 shows the changes in volume retention and DCR during a cyclic test at 45°C.

[0023] [Figure 13] Figure 13 shows the changes in volume retention and DCR during a cycle test at -10°C. [Modes for carrying out the invention]

[0024] Illustrative Examples and Description of Embodiments Before further describing the present invention, it should be understood that the invention is not limited to these embodiments, as variations of the specific embodiments described below may be fabricated and still fall within the scope of the appended claims. It should also be understood that the terminology used is intended to describe specific embodiments and not to limit them. Instead, the scope of the invention is established by the appended claims.

[0025] To provide a clear and consistent understanding of the terms used herein, some definitions are provided below. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art in which this invention pertains.

[0026] As used herein, the term “organic catalyst” is intended to refer to an organic catalyst containing carbon, hydrogen, sulfur, and other nonmetallic elements found in organic compounds.

[0027] As used herein, the term “reactive group” is intended to refer to a chemical group that can react with carbonates to form stable compounds such as polymers.

[0028] The use of the words “a” or “an” may mean “one” when used with the term “including” in the claims and / or herein, but also coincides with the meanings of “one or more,” “at least one,” and “one or more.” Similarly, the word “another” may mean at least a second or more.

[0029] When used herein and in the claims, the words “comprising” (as well as “comprise” and “comprises”) "Having" (and any forms of "having," such as "have" and "has"), "including" (and any forms of "including," such as "include" and "includes"), or "containing" (and any forms of "containing," such as "contain" and "contains") are inclusive or open-ended words and do not exclude additional, unlisted elements or process steps.

[0030] As used herein, the term “about” is used to indicate that a value includes inherent variations in the error of the apparatus or method used to determine that value.

[0031] The present invention relates to the use of an organic catalyst as an additive in an electrolyte for a battery. Such an organic catalyst is, for example, as described by Nederberg et al. [8], the details of which are incorporated herein by reference. Further disclosures are available. In fact, it is well known in the art that the reaction of cyclic carbonates in the presence of 1,8-diazabicyclo[5.4.0]undeca-7-ene (DBU) is an attractive method for preparing poly(carbonates).

[0032] In embodiments of the present invention, the electrolyte comprises a carbonate. The electrolyte may further comprise a salt, preferably a lithium salt.

[0033] In embodiments of the present invention, the organic catalyst is an alkaloid. In other embodiments, the organic catalyst is an amidine compound such as DBU.

[0034] The electrolyte of the present invention can be used in a battery in which the anode contains a reactive group. In embodiments of the present invention, the reactive group is an OH group or an SH group, preferably an OH group.

[0035] Referring to Figure 1, the organic catalyst (10) promotes the reaction between the reactive group (12) on the surface of the anode (20) and the carbonate (14) in the electrolyte. This forms a protective layer (16) on the surface of the anode (20). The protective layer (16) prevents contact between the anode (20) and residual water in the battery. In particular, according to embodiments of the present invention, the protective layer (16) is made from a polymer material (18) formed as shown in the figure. Batteries using the electrolyte of the present invention are more stable and safe.

[0036] In one embodiment of the present invention, an organocatalyst, for example, 1,8-diazabicyclo[5.4.0]undeca-7-ene (DBU), is used for ring-opening polymerization (ROP) of cyclic carbonates on the surface of a lithium titanium oxide (LTO) anode (where R is saturated or unsaturated C1-C). 12which may be a linear, branched or cyclic alkyl group). This is shown in FIG. 2. In fact, the hydroxyl groups on the surface of the LTO anode act as initiators, preferentially causing the formation of the polymer on the LTO anode surface rather than on any other surface of the battery. Thus, the LTO anode is coated (protected), thereby substantially restricting the generation of gas within the battery. Accordingly, an undesirable reaction between the electrolyte and residual water on the surface of the LTO anode, which involves gas formation, is prevented. Also, as illustrated in FIG. 5, the organic catalyst DBU can trap any HF, CO2 and / or water formed during the cycling of the battery. Further, the decomposition of carbonate within the electrolyte can be prevented.

[0037] As will be understood by those skilled in the art, other carbonates can also be used. The carbonate may be linear, branched, saturated or unsaturated. In embodiments of the present invention, the carbonate may be a compound of general formula I. [Chemical formula] In the formula, R is a C1-C 12 linear, branched or cyclic alkyl group, and n is an integer from 1 to 6.

[0038] As will be understood by those skilled in the art, other organic catalysts can also be used. Such an organic catalyst may be any suitable organic catalyst known in the art, including carbon, hydrogen, sulfur and other non-metallic elements found in organic compounds.

[0039] The inventors evaluated the behavior of DBU by 1 1H NMR and HPLC-MS in a model system. The model consisted of a mixture of PC-DBU heated at 45 °C for 12 hours to simplify the analysis. FIG. 3 shows the spectra obtained. The chain is initiated by DBU from one insertion of PC by ROP. Also, 1 the 1H NMR spectrum shows signals characteristic of a small amount of poly(propylene carbonate) due to the presence of a large excess of PC and DBU.

[0040] Adding 0.5% or less of DBU to the electrolyte can reduce the total gas volume by 20%. Specifically, as determined by gas chromatography (GC), the levels of hydrogen, oxygen, and propylene decrease, while the level of carbon dioxide increases. Figure 4 shows the gas levels and distribution within the cell.

[0041] Based on the results obtained, a hypothesis can be formulated regarding the estimated mechanism of protective layer formation on the anode. An overview of this hypothesis is shown in Figure 5. As those skilled in the art will understand, different mechanisms can be considered to be responsible for the formation of the protective layer.

[0042] In the first step, propylene carbonate decomposes to produce CO2 and poly(propylene oxide) (PPO) in a cationic and radical form. Simultaneously, DBU may neutralize HF. In the second step, polymerization of propylene oxide fragments occurs, initiated by hydroxyl groups stabilized by DBU and located on the surface of the LTO anode. These cations are stimulated to react with LTO or PPO, forming a stable layer on the surface of the LTO anode, while the radicals likely react with DBU [8-10]. The formation of PPO is also confirmed by FTIR with ATR-diamond analysis of the anode. The spectrum shows no bands (1735cm²) due to the vibration of the carbonyl group. -1 ) is not shown, and therefore the inventors can discard the presence of poly(propylene carbonate) (Figure 6).

[0043] The formation of a solid electrolyte interface (SEI) occurs during the first stage of the cycle. Thus, extensive decomposition of the electrode is avoided. The mechanism of this formation is unclear, but it is thought that the reaction proceeds probably by reduction of the electrolyte, forming radicals that can initiate the formation of an SEI [11,12]. Based on this mechanism, the use of DBU is considered compatible with graphite anodes, since DBU can react with radicals to form a stable SEI. As will be understood by those skilled in the art, the use of DBU may also be compatible with other anodes, including materials such as titanium hydrogen oxide (HTO), TiO2, Si, SiOx, and Sn.

[0044] Furthermore, surface analysis using mass spectrometry (MS) and scanning electron microscopy (SEM) coupled with a time-of-flight (TOF) detector confirmed the deposition of a polymer layer on the anode surface. This layer has a thickness of approximately 350 nm. This protective layer is confirmed by the presence of polymer-related organic fragments on the anode surface. The presence of titanium derived from LTO, compared to the reference, also suggests the presence of a coating on the LTO anode surface. Figure 7a shows the SEM image, and Figure 7b shows the deep profile at m / z=59, where this fragment corresponds to propylene oxide, and the fragment at m / z=47.869 represents titanium.

[0045] This demonstrated that the formation of linear polymers was promoted by using a lithium salt as a catalyst

[13] . Furthermore, after washing the anode with deuterated chloroform for NMR analysis, there was virtually no DBU residue in the leachate. As a result, the inventors concluded that this absence of DBU was due to the formation of an insoluble polymer film. In addition, although a large proportion of fluoride was present in the polymer, this fluoride did not appear to be in the LiF form, which is the usual form on the surface of the LTO anode. The inventors hypothesized that the fluoride was in an acidic form and reacted with DBU, thus avoiding the formation of gaseous HF inside the cell (not shown in Figure 7)

[10] . This was also supported by thermogravimetric analysis of the anode (Figure 8).

[0046] The addition of DBU promotes the formation of a coating on the LTO anode surface rather than on the poly(ethylene) separator. This may be desirable because it prevents the pores of the separator from becoming clogged with this polymer. This was confirmed by visual inspection of the separator (cells with DBU) and by the cyclability of the cells after a 5-day floating test at 45°C and 2.4V. Normally, cells without DBU (see our reference) cannot be circulated after this process because the pores of the separator are completely filled with polymer resulting from the decomposition of the cyclic carbonate.

[0047] The inventors can divide the spectrum into different temperature ranges that may be related to the decomposition of different components. The first range lies on the plane line, between 30 and 60°C, which the inventors believe is related to the evaporation of HF. This range is only visible in the anode-plus-additive curve. It is likely related to the trapping of hydrogen fluoride. The second range is defined between 260 and 600°C, which corresponds to the decomposition of the polymer. The anode with the additive has 0.8 wt% more polymer, corresponding to the weight loss. Finally, as is already known, oxidation of LTO occurs at temperatures above 800°C. This process involves the reaction of hydroxyl groups located on the surface of the LTO anode, which leads to the decomposition of the electrolyte. The inventors have already discussed the initiation of polymerization by these groups, and as a result, the mechanism is confirmed by the reduction of oxidation of the anode with the additive. The inventors observe a decrease of 1.2 wt%. Therefore, the addition of DBU promotes the formation of a coating on the surface of the LTO anode, which is initiated by hydroxyl groups and stabilized by DBU (see Figure 4).

[0048] Therefore, no polymer was observed on the poly(ethylene) separator, which constitutes one advantage as it prevents the polymer from clogging the separator's pores. This was confirmed by visual inspection of the separator (cells with DBU) and the cyclability of the cells after a 5-day flotation test at 45°C and 2.4V. Normally, cells without DBU (see our reference) cannot be circulated after this process because the separator becomes completely filled with polymer resulting from the decomposition of the cyclic carbonate. Gas suppression effect

[0049] Vinylenine carbonate (VC) is widely used in graphite-based lithium-ion batteries to suppress degradation and extend lifespan. For example, when 2% VC was added to the electrolyte, 20% of the generated gas was suppressed (Figure 9). Furthermore, 0.5% DBU showed the same level of gas suppression. Small amounts of DBU may be highly effective. Suppression of short circuits during floating tests

[0050] Figure 10 shows the stray current during the stray test. The current shows a sharp increase in the reference cell without the organic catalyst or additive, which indicates a micro-short circuit within the cell. In contrast, the cell with DBU shows a continuous low stray current, which indicates higher stability under high temperature conditions of 45°C. Effect on the internal resistance of the cell

[0051] Figure 11 shows the DC resistance (DCR) of the cell at various temperatures. The values ​​were obtained after 10 seconds of discharge at 1 ItA and 3 ItA.

[0052] Typically, additives or protective coatings increase the initial resistance of a cell instead of inhibiting degradation. The results show no significant resistance increase in cells with DBU added. In other words, DBU does not impair the power performance of the cell over a wide temperature operating range. Cycle performance at various temperatures

[0053] High Temperature of 45°C: Figure 12 shows the cycle performance at 45°C. Cells with DBU show better capacity retention, indicating less degradation in high-temperature environments compared to the reference cell without the organic catalyst. This can greatly improve the long-term stability of the battery and its system. The DCR remains at the same level as or below that of the reference DCR, indicating that DBU does not impair battery performance.

[0054] Low Temperature of -10°C: Figure 13 shows the cycle performance at -10°C. The DCR value was obtained at 23°C using the same method as described above. Both capacity retention and DCR variation in the cell with added DBU were at the same level as the reference. In this temperature range, the inventors do not anticipate many side reactions such as gas generation, so it is reasonable that no significant difference is observed. As can be seen from this, DBU does not impair power performance.

[0055] Regarding the properties outlined above, DBU can suppress gas even when added in small amounts and maintains sufficient battery performance over a wide temperature operating range.

[0056] Although the present invention has been described above with respect to specific embodiments thereof, it can be modified without departing from the spirit and essence of the invention as set forth in the appended claims.

[0057] This specification references several sources, the contents of which are incorporated herein by reference.

[0058] References

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Claims

[Claim 1] Stray current.

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