Electrolyte, niobium battery containing electrolyte, and method for producing same

Abstract

The present invention relates to a secondary battery and a method for making the secondary battery, the secondary battery comprising a positive electrode, a negative electrode comprising a niobium metal oxide, a separator between the positive electrode and the negative electrode, and an electrolyte comprising a solvent composition comprising a dinitrile solvent and at least one second solvent selected from the list consisting of a mononitrile solvent, a carbonate solvent, an ester solvent, or an ether solvent, the dinitrile being present in an amount of at least 0.1 weight percent based on the total weight of the solvent composition. The electrolyte suppresses gas generation from the reaction between the electrolyte and the niobium metal oxide in the negative electrode, improving the safety of the battery.

Description

[Technical field]

[0001] Related Applications This application claims priority to and the benefit of GB2201480.7, filed on February 4, 2022 (04.02.2022), the contents of which are incorporated herein by reference in their entirety.

[0002] The present invention relates to a secondary battery and a method for making the secondary battery. [Background technology]

[0003] During storage of niobium batteries, undesirable gassing can occur. Thus, there remains a need for improved materials for niobium-based batteries that have reduced gas formation. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US2017 / 0244135 [Patent Document 2] JP2013 / 152825 [Patent Document 3] WO2020 / 047228 Summary of the Invention [Means for solving the problem]

[0005] The present invention generally relates to a secondary battery comprising an electrolyte, the electrolyte comprising: Multi-nitrile solvents having two or more nitrile groups, and At least one second solvent selected from the group consisting of mononitrile solvents, carbonate solvents, ester solvents, or ether solvents. A solvent composition comprising: The multi-nitrile solvent is present in an amount of at least 0.1 weight percent based on the total weight of the solvent composition; A secondary battery is provided.

[0006] In a first aspect of the present invention, A positive electrode and a negative electrode comprising niobium oxide or a niobium metal oxide; a separator between the positive electrode and the negative electrode; an electrolyte comprising a solvent composition; A secondary battery comprising: Multi-nitrile solvents having two or more nitrile groups, and At least one second solvent selected from the group consisting of mononitrile solvents, carbonate solvents, ester solvents, and ether solvents. Including, The multi-nitrile solvent is present in an amount of at least 0.1 weight percent based on the total weight of the solvent composition; A secondary battery is provided.

[0007] In a second aspect of the present invention, there is provided a method for producing a secondary battery, comprising the steps of: providing a positive electrode; providing a negative electrode comprising niobium oxide or a niobium metal oxide; providing a separator between the positive electrode and the negative electrode; Multi-nitrile solvents having two or more nitrile groups, and At least one second solvent selected from the group consisting of mononitrile solvents, carbonate solvents, ester solvents, or ether solvents. providing an electrolyte comprising a solvent composition comprising the multinitrile is present in an amount of at least 0.1 weight percent based on the total weight of the solvent composition; contacting the positive electrode, the negative electrode, and the separator with an electrolyte to produce a secondary battery; A method is provided, comprising:

[0008] In some embodiments, the multi-nitrile solvent is a di-nitrile solvent or a tri-nitrile solvent, such as a di-nitrile solvent.

[0009] In some embodiments, the electrolyte further comprises a lithium salt.

[0010] In some embodiments, the negative electrode comprises niobium metal oxide.

[0011] In certain embodiments, the multi-nitrile solvent is a di-nitrile solvent, the electrolyte comprises a lithium salt, and the negative electrode comprises a niobium metal oxide.

[0012] In some embodiments, the invention provides a secondary battery comprising a positive electrode, a negative electrode comprising a niobium metal oxide, a separator between the positive electrode and the negative electrode, and an electrolyte comprising a solvent composition, wherein the solvent composition comprises a dinitrile solvent, and at least one of a carbonate solvent, an ester solvent, or an ether solvent, and the dinitrile is included in an amount of at least 0.1 weight percent based on the total weight of the solvent composition and the lithium salt.

[0013] In some embodiments, the present invention provides a method of producing a secondary battery comprising the steps of: providing a positive electrode; providing a negative electrode comprising a niobium metal oxide; providing a separator between the positive electrode and the negative electrode; providing an electrolyte comprising a solvent composition and a lithium salt, the solvent composition comprising a dinitrile solvent, and at least one of a carbonate solvent, an ester solvent, or an ether solvent, wherein the dinitrile is present in an amount of at least 0.1 weight percent based on the total weight of the solvent composition; and contacting the positive electrode, the negative electrode, and the separator with the electrolyte to produce the secondary battery.

[0014] The above and other features are illustrated by the following figures and detailed description.

[0015] The following figures are exemplary embodiments in which like elements are numbered alike: [Brief description of the drawings]

[0016] [Figure 1]1 is a graph showing the volume of gas evolved in a lithium nickel cobalt aluminum oxide (NCA) / niobium tungsten oxide (NWO) pouch cell during storage of the cell at 60° C. for 7 days. [Diagram 2] 1 is a pie chart showing the composition of gas evolved in an NCA / NWO pouch cell containing salt-free electrolyte. [Diagram 3] 1 is a graph showing the volume of gas evolved over time (weeks) in NCA / NWO pouch cells containing electrolytes with different lithium salts. [Figure 4] 1 is a graph showing the volume of gas evolved and percent capacity lost in LCO / NWO pouch cells containing different electrolytes after 14 days of cell storage at 60° C. [Diagram 5] 1 is a graph showing the volume of gas evolved and percent capacity lost in LCO / NWO pouch cells containing different electrolytes after 7 days of cell storage at 60° C. [Figure 6] FIG. 1 is a graph showing cell volume increase for LCO / NWO pouch cells containing different electrolyte compositions (Examples 5.1-5.5) after 2 weeks of storage at 60° C. The black crosses correspond to the average volume increase and the shaded area corresponds to the standard deviation of the volume increase. [Figure 7] FIG. 1 is a graph showing capacity retention in LCO / NWO pouch cells containing different electrolyte compositions (Examples 5.1-5.5) after 2 weeks storage at 60° C. The black crosses correspond to the average capacity retention and the shaded area corresponds to the standard deviation of the capacity retention. [Figure 8] FIG. 1 is a graph showing cell volume increase in LCO / NWO pouch cells containing different electrolyte compositions (Examples 5.2, 5.4, 5.6 and 5.7) after 6 weeks of storage at 60° C. The black crosses correspond to the average volume increase and the shaded area corresponds to the standard deviation of the volume increase. [Figure 9] FIG. 1 is a graph showing capacity retention in LCO / NWO pouch cells containing different electrolyte compositions (Examples 5.2, 5.4, 5.6 and 5.7) after 6 weeks of storage at 60° C. The black crosses correspond to the average capacity retention and the shaded area corresponds to the standard deviation of the capacity retention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Secondary batteries containing niobium oxide or niobium metal oxide negative electrodes generate large amounts of gas when the cell is in a charged state. It has been found that gassing is influenced by the composition of the electrolyte. For example, when the electrolyte contains a cyclic carbonate (e.g., ethylene carbonate), reduction of the cyclic carbonate can occur in the presence of a niobium-based negative electrode. Interaction between the electrolyte and the niobium-based negative electrode can result in reduction of the electrolyte and evolution of hydrogen and oxygen, especially when the cell is kept in a charged state and / or at high temperatures. In cells containing niobium oxide or niobium metal oxide negative electrodes, decomposition of the electrolyte can be autocatalytic, involving reaction of fluorinated salts with residual alcohol or water in the electrolyte solvent and reduction of the cyclic carbonate (if present), resulting in gassing. The evolved hydrogen and oxygen can accumulate in the battery and become dangerous.

[0018] Cells where the negative electrode potential can be reduced to a voltage suitable for forming a solid-electrolyte interface (SEI) avoid this problem. For example, in cells with graphite-based negative electrodes, this gassing problem does not occur when the negative electrode potential relative to lithium is less than 0.2 volts (V) vs. Li, because the solid-electrolyte interface (SEI) is formed. It is understood that the SEI passivates the negative electrode surface and prevents the reduction of the electrolyte. However, this strategy is not available for niobium-based electrodes, because the SEI is also decomposed or removed at larger potentials, and niobium-based electrodes operate at potentials above 0.2 V vs. Li.

[0019] Also, the use of sacrificial additives in the electrolyte to promote the formation of the SEI (e.g., vinylene carbonate or 1,3-propane sultone) is insufficient for niobium-based anodes because as the cell is charged and discharged, it is cycled through a range of reduction-oxidation potentials, which leads to the decomposition of the SEI. Furthermore, the SEI forms a resistive barrier that inhibits charge and discharge rates, thereby adversely affecting one of the important properties of niobium-based anodes.

[0020] Disclosed herein are electrolytes that reduce gassing and improve safety in lithium-ion secondary batteries that include niobium oxide or niobium metal oxide negative electrodes. In particular, it has been discovered that an electrolyte that advantageously includes a multi-nitrile solvent (e.g., dinitrile or trinitrile) in combination with one or more of a carbonate, ester, and / or ether solvent effectively reduces the amount of gassing. It is believed that the multi-nitrile component inhibits decomposition of the electrolyte in the niobium metal oxide cell, thus reducing the amount of gassing.

[0021] In some embodiments, the electrolyte further comprises a lithium salt, such as a lithium salt selected from LiBF, LiPF, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or combinations thereof, and additionally or alternatively lithium difluoro(oxalato)borate (LiDOFB).

[0022] Additionally, electrolytes comprising a multi-nitrile solvent (e.g., di- or tri-nitrile) in combination with a lithium salt (e.g., LiBF4, LiPF6, or LiDFOB) and one or more carbonate, ester, and / or ether solvents have been found to further reduce the amount of gas evolved. It is believed that the multi-nitrile solvent and the lithium salt act synergistically to further reduce electrolyte decomposition and gas evolution.

[0023] As a result of the reduced electrolyte decomposition, the present invention also results in improved capacity retention of secondary batteries, especially after extended storage at elevated temperatures and / or in a charged state.

[0024] Some secondary batteries and electrolytes are known and are discussed below.

[0025] US2017 / 0244135 describes an electrochemical cell and a system for restoring capacity to the cell. The document describes electrolytes containing various solvents such as carbonates, esters and ethers, lithium salts, and additives such as dinitriles. An example describes a cell containing a graphite anode and an electrolyte of ethylene carbonate and LiTFSA (see

[0315] ). Graphite anodes are known to be less susceptible to gassing. US2017 / 0244135 does not describe a niobium metal oxide anode in combination with an electrolyte containing multi-nitriles. The document does not discuss electrolyte gassing, nor does it suggest that a particular combination of a multi-nitrile electrolyte solvent and a niobium (metal) oxide anode may reduce gassing.

[0026] JP2013 / 152825 is concerned with reducing electrolyte decomposition and gassing. The document suggests that gassing can be reduced by using an electrolyte and / or positive electrode containing a phosphorus compound that can form a phosphorus oxide film on the anode during cell cycling. The general disclosure refers to a lithium titanium niobium oxide anode in combination with a phosphorus compound, and an electrolyte containing various nitrile compounds. The examples do not disclose cells containing both a niobium metal oxide anode and a dinitrile-containing electrolyte, instead focusing on Li metal electrodes with polymer electrolytes. There is no suggestion that dinitriles are particularly effective in reducing gassing in niobium-based anodes. Rather, JP2013 / 152825 teaches the use of phosphorus additives to form an SEI on the Li metal electrode. This is in contrast to the present invention, which avoids the need for an SEI to allow for better high-rate performance of the battery.

[0027] WO2020 / 047228 relates to coated cathode materials for secondary lithium-ion cells. This document does not provide any examples of complete batteries, only cathode materials. The general disclosure refers to electrodes containing lithium niobate and electrolytes containing nitrile solvents. However, niobium metal oxide anodes and dinitrile-containing electrolytes used in combination are not disclosed, and the use of electrolyte compositions to reduce gas generation is not mentioned. This document only refers to cathode coatings or pressure relocation systems to address gas formation.

[0028] electrolyte The electrolyte disclosed herein comprises a solvent composition comprising a multi-nitrile solvent and at least one second solvent selected from the list consisting of a mono-nitrile solvent, a carbonate solvent, an ester solvent, or an ether solvent.

[0029] Typically, the electrolyte is non-aqueous, that is, it is substantially free of water.

[0030] In some embodiments, the electrolyte comprises a lithium salt.

[0031] Multi-nitrile solvents are nitrile-containing compounds that have two or more nitrile groups per molecule. Multi-nitriles are C3-C 20 It may be an aliphatic multinitrile. Typically, the multinitrile contains 2 to 5 nitrile groups, preferably 2 to 4 nitrile groups, more preferably 2 or 3 nitrile groups. The multinitrile may be a dinitrile or a trinitrile.

[0032] Dinitriles are C3-C 10 Aliphatic dinitriles, preferably C3-C 10 It is an aliphatic linear dinitrile. C3~C 10 The aliphatic group of the aliphatic dinitrile is a substituted or unsubstituted C3-C 10 Alkyl, alkenyl, or alkynyl groups, or preferably linear C3-C10 It may be an alkyl, alkenyl, or alkynyl group. 10 Examples of aliphatic linear dinitriles include glutaronitrile (GN; pentanedinitrile), adiponitrile (ADN; hexanedinitrile), pimelonitrile (PMN; heptanedinitrile), suberonitrile (SUN; octanedinitrile), azelanitrile (AZN; nonanedinitrile), sebaconitrile (SEN; decanedinitrile), or combinations thereof, and additionally or alternatively succinonitrile (SN; butanedinitrile).

[0033] Trinitrile is C4-C 10 Aliphatic trinitriles, preferably C4-C 10 It is an aliphatic linear trinitrile. C4~C 10 The aliphatic group of the aliphatic trinitrile is a substituted or unsubstituted C4-C 10 Alkyl, alkenyl, or alkynyl groups, such as linear C4-C 10 It may be an alkyl, alkenyl, or alkynyl group. 10 Examples of aliphatic linear trinitriles include 1,3,6-hexanetricarbonitrile.

[0034] The carbonate solvent includes C3 to C9 linear carbonates, examples of which include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), methyl iso-propyl carbonate, ethyl propyl carbonate (EPC), ethyl iso-propyl carbonate, ethyl methyl carbonate (EMC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), isobutylene carbonate, monofluoroethylene carbonate (FEC), 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, or combinations thereof.

[0035] In some embodiments, the solvent composition comprises a multi-nitrile solvent and at least one carbonate solvent. Preferably, the carbonate solvent comprises ethylene carbonate (EC), ethyl methyl carbonate (EMC), propylene carbonate (PC) or a combination thereof. More preferably, the solvent composition comprises a mixture of ethylene carbonate and ethyl methyl carbonate, or propylene carbonate and ethyl methyl carbonate.

[0036] In some embodiments, the weight ratio of ethylene carbonate to ethyl methyl carbonate is 30:70 to 50:50. In some embodiments, the weight ratio of propylene carbonate to ethyl methyl carbonate is 30:70 to 50:50. Preferably, the weight ratio is about 30:70.

[0037] Preferably, the solvent composition comprises propylene carbonate (PC) solvent. In some such embodiments, the propylene carbonate is included in an amount of at least 1 weight percent, based on the total weight of the solvent composition.

[0038] Ether solvents include dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or combinations thereof.

[0039] The ester solvent includes a C3 to C9 linear ester, examples of which include methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, gamma-butyrolactone, 5-decanolide, gamma-valerolactone, dl-mevalonolactone, gamma-caprolactone, or a combination thereof.

[0040] The multi-nitrile solvent (e.g., dinitrile or trinitrile solvent) is included in the solvent composition in an amount of at least 0.1 weight percent (wt%), such as at least 0.5 wt%, or at least 1 wt%, or at least 5 wt%, or at least 10 wt%. In one embodiment, the dinitrile solvent is included in the solvent composition in an amount of 0.1 wt% to 55 wt%, or 0.2 wt% to 50 wt%, or 1 wt% to 45 wt%, or 5 wt% to 40 wt%, or 5 wt% to 30 wt%, or 10 wt% to 30 wt%, or 10 wt% to 25 wt%, or 10 wt% to 20 wt%, based on the total weight of the solvent composition.

[0041] Preferably, the dinitrile solvent is present in the solvent composition in an amount of at least 0.1 weight percent (wt%), such as at least 0.5 wt%, or at least 1 wt%, or at least 5 wt%, or at least 10 wt%. In one embodiment, the dinitrile solvent is present in the solvent composition in an amount of 0.1 wt% to 55 wt%, or 0.2 wt% to 50 wt%, or 1 wt% to 45 wt%, or 5 wt% to 40 wt%, or 5 wt% to 30 wt%, or 10 wt% to 30 wt%, or 10 wt% to 25 wt%, or 10 wt% to 20 wt%, based on the total weight of the solvent composition.

[0042] In one embodiment, the multi-nitrile solvent is included in the solvent composition in an amount of 10 weight percent to 50 weight percent, preferably 20 weight percent to 40 weight percent, based on the total weight of the solvent composition.

[0043] In another embodiment, the multi-nitrile solvent is present in the solvent composition in an amount from 1 weight percent to 10 weight percent, preferably from 2 weight percent to 5 weight percent, and more preferably about 5 weight percent, based on the total weight of the solvent composition.

[0044] In one embodiment, the total amount of the mononitrile solvent, carbonate solvent, ester solvent, and / or ether solvent contained in the solvent composition is 1 wt% to 99.8 wt%, or 20 wt% to 99.8 wt%, or 30 wt% to 99 wt%, or 40 wt% to 95 wt%, or 50 wt% to 95 wt%, or 70 wt% to 90 wt%, or 75 wt% to 90 wt%, or 80 wt% to 90 wt%, based on the total mass of the solvent composition.

[0045] In one embodiment, the weight ratio of the dinitrile solvent to the total amount of the mononitrile solvent, the carbonate solvent, the ester solvent, and / or the ether solvent may be 5:1 to 1:20, or 3:1 to 1:20, or 2:1 to 1:10, or 1:1 to 1:10, or 1:2 to 1:10, or 1:3 to 1:10.

[0046] In one embodiment, the solvent composition includes a carbonate solvent. In one embodiment, the carbonate solvent includes PC, EMC, or a combination thereof. In one embodiment, the carbonate solvent consists of PC, EMC, or a combination thereof. In one embodiment, the carbonate includes EC or PC, and the EC or PC is included in an amount of at least 1 weight percent based on the total weight of the solvent composition. In one embodiment, the EC or PC is included in an amount of at least 1 wt%, at least 5 wt%, at least 10 wt%, or at least 20 wt%, based on the total weight of the solvent composition. In one embodiment, the EC or PC is included in an amount of 1 wt% to 60 wt%, or 5 wt% to 45 wt%, or 10 wt% to 40 wt%, based on the total weight of the solvent composition.

[0047] In one embodiment, the solvent composition includes a mononitrile solvent. In one embodiment, the mononitrile solvent includes a C2-C8 aliphatic mononitrile. The aliphatic group of the C2-C8 aliphatic mononitrile may be a linear or branched C2-C8 alkyl, alkenyl, or alkynyl group, and in one embodiment is a linear C2-C8 alkyl, alkenyl, or alkynyl group. Examples of mononitriles include methoxypropionitrile, butyronitrile, ethanenitrile, propanenitrile (proprionitrile), acetonitrile, or a combination thereof. In one embodiment, the mononitrile solvent is contained in the solvent composition in an amount of 1 wt% to 95 wt%, or 5 wt% to 90 wt%, or 10 wt% to 85 wt%, or 10 wt% to 75 wt%, or 20 wt% to 50 wt%, based on the total mass of the solvent composition. In one embodiment, the mononitrile solvent is included in the solvent composition in an amount of 5 wt % to 50 wt %, or 10 wt % to 40 wt %.

[0048] In one embodiment, the solvent composition includes a dinitrile solvent and a mononitrile solvent, and the total amount of carbonate solvent, ether solvent, and ester solvent in the solvent composition is 0.01 wt% to 10 wt%, or 0.05 wt% to 5 wt%, or 0.1 wt% to 1 wt%, based on the total weight of the solvent composition. In one embodiment, the solvent composition includes a dinitrile solvent and a mononitrile solvent, and is substantially free of carbonate solvent, ester solvent, or ether solvent.

[0049] In one embodiment, the solvent consists of PC or EC, EMC, and ADN. In one embodiment, the solvent composition comprises or consists of 30 wt% PC or EC, 60 wt% EMC, and 10 wt% ADN.

[0050] In a preferred embodiment, the solvent composition comprises, for example consists of, PC or EC, EMC, and ADN, SN or TN. In such an embodiment, the solvent composition comprises, or consists of, PC or EC and EMC in a mass ratio of 30:70 to 50:50, and ADN, SN or TN in an amount of 2 to 5 wt.% based on the mass of the electrolyte composition.

[0051] In a particularly preferred embodiment, the solvent composition comprises, for example consists of, PC, EMC, and ADN, SN, or TN, In such an embodiment, the solvent composition comprises, or consists of, PC and EMC in a mass ratio of 30:70 to 50:50, and ADN, SN, or TN in an amount of 2 to 5 wt.% based on the mass of the electrolyte composition.

[0052] In another preferred embodiment, the solvent composition comprises, for example consists of, PC, EMC, and ADN or SN. In such an embodiment, the solvent composition comprises, or consists of, PC and EMC in a mass ratio of 30:70 to 50:50, and ADN or SN in an amount of 2 to 5 wt.% based on the mass of the electrolyte composition. In an even more preferred embodiment, the dinitrile is SN.

[0053] In some embodiments, the electrolyte comprises a lithium salt.

[0054] In some such embodiments, the lithium salt in the electrolyte comprises LiBF4, LiPF6, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or combinations thereof, and additionally or alternatively lithium difluoro(oxalato)borate (LiDOFB). The concentration of the lithium salt in the (e.g., non-aqueous) electrolyte is, for example, 0.01 molar (M) to 2.0 M, 0.05 M to 1.8 M, 0.1 M to 1.6 M, 0.5 M to 1.4 M, 0.5 M to 1.3 M, or 0.8 M to 1 M, based on the total weight of the electrolyte. In one embodiment, the lithium salt comprises 0.01 to 1 M LiBF4 and 0.1 M to 0.3 M LiPF6. In another embodiment, the lithium salt comprises 0.1 to 0.3 M LiBF4, e.g., 0.2 M LiBF4. In a further embodiment, the lithium salt comprises 0.05 to 0.2 M LiDFOB, such as 0.1 M LiDFOB.

[0055] In one embodiment, the electrolyte comprises 0.5M to 3M lithium salt and is substantially free of PF6-. In one embodiment, the electrolyte comprises less than 0.1M, or less than 0.05M, or less than 0.02M, or less than 0.01M, or less than 0.005M PF6 - In one embodiment, the electrolyte comprises PF6 - Does not include.

[0056] The solvent composition may be prepared by combining a dinitrile solvent and at least one of a carbonate solvent, an ester solvent, or an ether solvent. The electrolyte may be prepared by contacting the solvent composition with a lithium salt, if present, and dissolving the lithium salt in the solvent composition.

[0057] secondary battery Also disclosed is a secondary battery comprising the electrolyte described herein. In particular, the secondary battery comprises a positive electrode, a negative electrode comprising niobium metal oxide, a separator between the positive electrode and the negative electrode, and an electrolyte. Typically, the battery comprises one or more electrochemical cells. In general, a secondary battery refers to a battery in which the cell reaction is reversible, and thus the battery is typically rechargeable.

[0058] The negative electrode comprises a negative electrode active material on a current collector. The negative electrode active material comprises niobium oxide or a niobium metal oxide. Typically, the negative electrode active material consists essentially of niobium oxide or a niobium metal oxide.

[0059] Niobium metal oxides are typically represented by the formula Nb x M y O z wherein x is 2 to 34, y is 1 to 20, z is 8 to 115, and M is Na, Mg, Al, Si, P, S, K, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Y, Zr, Mo, In, Sn, Sb, Ta, W, or a combination thereof. In one embodiment, M is V, Cr, Mo, Ta, W, P, S, or a combination thereof. In one embodiment, the niobium metal oxide comprises niobium, tungsten or molybdenum, and optionally calcium, chromium, cobalt, magnesium, manganese, nickel, potassium, phosphorus, sodium, sulfur, or a combination thereof. In one embodiment, the niobium metal oxide is niobium tungsten oxide or niobium molybdenum oxide. In one embodiment, the niobium metal oxide comprises niobium, tungsten or molybdenum, and oxygen. An example of a niobium tungsten oxide is Nb 14 W3O 44 , Nb 16 W5O 55 , Nb 18 W8O 69 , Nb2WO8, Nb 18 W 16 O 93 , Nb 22 W 20 O 115 , Nb2Mo3O 14 , Nb 14 Mo3O44 , Nb 12 MoO 44 In one embodiment, the niobium metal oxide comprises Nb 16 W5O 55 Includes.

[0060] Niobium oxides are typically represented by the formula Nb x1 O z1 In the formula, x1 is 2 to 25, and z1 is 2 to 62. Examples of niobium oxide include Nb2O5, NbO2, and Nb 12 O 29 Or Nb 25 O 62 or a combination thereof.

[0061] Niobium oxide is also doped to give the formula Nb x M1 y1 M2 y2 O z Also mentioned is an embodiment of producing a compound of the formula: wherein M1 is W or Mo, M2 is V, Cr, Mo, Ta, W, P, S, or a combination thereof, x is 2 to 34, (y1+y2) is 1 to 20, z is 8 to 115, and 0≦y1≦20, and 0≦y2≦20.

[0062] The negative electrode active material may further include additional active materials. Examples of additional negative electrode active materials include tungsten oxide, lithium titanium oxide, or a combination thereof.

[0063] The negative electrode may be formed from a negative electrode composition including a negative electrode active material. In addition to the negative electrode active material, the negative electrode composition may further include a binder, a solvent, a conductive agent, or a combination thereof. The binder may include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, or a combination thereof. The conductive agent may include conductive carbon such as carbon nanotubes, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fibers, or powder or fiber of metals such as copper, nickel, aluminum, or silver.

[0064] In one embodiment, the negative electrode comprises a negative electrode composition deposited on an aluminum current collector, the negative electrode composition comprising Nb as the negative electrode active material. 16 W5O 55 , SBR as a binder, and conductive carbon as a conductive agent, or alternatively consisting of these.

[0065] Alternatively, the negative electrode current collector may include copper, nickel, stainless steel, carbon steel, titanium, or combinations thereof.

[0066] The negative electrode may be formed by coating a layer of the negative electrode composition onto a negative electrode current collector, or alternatively, the negative electrode composition may be cast onto a separate support and the film peeled from the separate support and laminated onto a metal current collector. The method of making the negative electrode is not so limited, and any other method suitable for making a negative electrode may also be used.

[0067] The positive electrode includes a positive electrode active material. The positive electrode may be lithium cobalt oxide (LCO), lithium nickel cobalt aluminum oxide (NCA), lithium manganese oxide (LMO), lithium nickel manganese oxide (LNMO), lithium nickel cobalt manganese oxide (NMC) (e.g., LiNi 0.8 Co 0.10 Mn 0.10 O2; The positive electrode active material may include lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), or a combination thereof. Preferably, the positive electrode active material includes LCO, NCA, or NMC.

[0068] The positive electrode may be formed from a positive electrode composition including a positive electrode active material. In addition to the positive electrode active material, the positive electrode composition may further include a binder, a solvent, a conductive agent, or a combination thereof. The conductive agent may include carbon nanotubes, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, powders or fibers of metals such as copper, nickel, aluminum, or silver, or a combination thereof. The binder in the positive electrode composition may include polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, or a combination thereof. In one embodiment, the positive electrode comprises a positive electrode composition on an aluminum current collector, the positive electrode composition comprising or consisting of NMC or LCO as a positive electrode active material, PVDF as a binder, and carbon nanotubes, carbon black, and / or Ketjen black as a conductive agent.

[0069] The positive electrode may further include a positive electrode current collector comprising aluminum, titanium, stainless steel, carbon, or combinations thereof.

[0070] The positive electrode can be prepared in a manner similar to that described above for the negative electrode.

[0071] The secondary battery includes a separator between the positive and negative electrodes. The separator is not limited and may be any separator suitable for use in lithium ion batteries. The separator includes separator materials that are electrically insulating, chemically unreactive with the positive and negative active materials, chemically unreactive with the electrolyte, and insoluble in the electrolyte. Furthermore, the separator material is selected to have sufficient porosity to allow the electrolyte to pass through during the electrochemical reaction of the cell. The separator may be a porous polymer membrane, or may be a non-woven or woven fabric. The separator may include, for example, polypropylene (e.g., Celgard® 2500), polyethylene, polyamide (nylon), polysulfone, polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hydrofluoropropylene (PVDF-HFP), tetrafluoroethylene-ethylene copolymer (PETFE), chlorotrifluoroethylene-ethylene copolymer, or combinations thereof. In one embodiment, the separator may include two or more layers of alternating materials, for example, a polypropylene / polyethylene / polypropylene tri-layer separator. The separator may be impregnated with an electrolyte.

[0072] Method of preparation The cell is manufactured by providing a non-aqueous electrolyte and adding the non-aqueous electrolyte to an assembly including a positive electrode, a negative electrode, and a separator between the positive and negative electrodes.

[0073] The secondary battery can be of any configuration, such as a cylindrically wound cell, a prismatic cell, a rigid laminate cell, or a flexible pouch, envelope, or bag cell.

[0074] Secondary batteries comprising niobium metal oxide as a negative electrode active material and an electrolyte disclosed herein exhibit reduced gas generation. In particular, a relatively low amount of gas is generated by the secondary battery during long-term storage at temperatures between 50°C and 70°C, or between 55°C and 65°C, or at 60°C. The disclosed secondary battery has a gas generation volume of less than 10 vol%, or less than 8 vol%, or less than 5 vol%, or less than 3 vol%, or less than 1 vol%, or less than 0.1 vol% based on the total volume of the cell after storage of the secondary battery for 6 days at 60°C. The disclosed secondary battery also has a gas generation volume of 0.001 vol%, 0.01 vol%, or 0.1 vol% to 1 vol%, 5 vol%, or 10 vol% based on the total volume of the cell after storage for 14 days at 60°C. In one embodiment, the gas volume is less than 10% of the total cell volume after storage for 3 months at 60°C.

[0075] The present disclosure is further illustrated by the following non-limiting examples.

[0076] Other Advantages Any and all compatible combinations of the above-described embodiments are expressly disclosed herein as if each and every combination was individually and explicitly recited.

[0077] Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure.

[0078] "And / or," as used herein, is considered a specific disclosure of each of the two specified features or components with or without the other. For example, "A and / or B" is considered a specific disclosure of (i) A, (ii) B, and (iii) each of A and B, as if each were individually set forth herein.

[0079] Unless the context indicates otherwise, the above feature descriptions and definitions are not limited to any particular aspect or embodiment of the present invention, but apply equally to all aspects and embodiments described.

[0080] Certain aspects and embodiments of the invention will now be described, by way of example and with reference to the figures described above.

[0081] The compositions, methods, and articles can alternatively comprise, consist of, or consist essentially of any suitable materials, steps, or ingredients disclosed herein. The compositions, methods, and articles can additionally, or alternatively, be designed to be free, or substantially free, of any materials (or species), steps, or ingredients that are not necessary to the function or accomplishment of the purpose of the compositions, methods, and articles.

[0082] When an element is referred to as being "on" another element, it will be understood that it can be directly on the other element, or there may be intervening elements, whereas when an element is referred to as being "directly on" another element, there are no intervening elements present.

[0083] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other (e.g., a range of "up to 25 wt.%, or more specifically, 5 wt.% to 20 wt.%" includes the endpoints of the range "5 wt.% to 25 wt.%", and all intermediate values, etc.). "Combination" includes blends, mixtures, alloys, reaction products, and the like. Terms such as "first", "second", and the like do not denote any order, amount, or importance, but are used to distinguish one element from another. The terms "a", "an", and "the" do not denote quantitative limitations, and should be construed to encompass both the singular and the plural, unless otherwise specified herein or clearly contradicted by context. "Or" means "and / or" unless expressly stated otherwise. Throughout the specification, references to "some embodiments", "embodiments", and the like mean that the specific element described in connection with an embodiment is included in at least one embodiment described herein and may or may not be present in other embodiments. Further, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments. "Combinations thereof" is open ended and includes any combination containing at least one of the recited components or features, optionally with similar or equivalent unrecited components or features.

[0084] Unless otherwise defined, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in this application contradicts or conflicts with a term in an incorporated reference, the term from this application shall take precedence over the conflicting term from the incorporated reference.

[0085] Compounds are described using standard nomenclature. For example, any position not substituted by any group shown is understood to have the valence filled by a bond as shown, or by a hydrogen atom. A dash ("-") that is not between two letters or symbols is used to indicate the point of attachment of a substituent. For example, -CHO is attached through the carbon of a carbonyl group.

[0086] "Aliphatic" or "aliphatic group" means a saturated or unsaturated linear or branched hydrocarbon group. An aliphatic group can be an alkyl, alkenyl, or alkynyl group, e.g., "nitrile" or "mononitrile" means a compound having the formula R-CN, where R is a substituted or unsubstituted C-C 20 "Dinitrile" means a compound having the formula CN-R-CN, where R is a substituted or unsubstituted C-C 20 It is an aliphatic group.

[0087] "Cyclic carbonate" refers to a carbonate compound having at least one ring in which the carbonate group (-O(C=O)O-) forms part of the ring. "Acyclic carbonate" refers to a carbonate compound in which the carbonate group (-O(C=O)O-) does not form part of a ring. Acyclic carbonates can include linear hydrocarbon chains, branched hydrocarbon chains, or both.

[0088] The term "alkyl" means a branched or straight-chain unsaturated aliphatic hydrocarbon group, such as methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl, t-butyl, n-pentyl, s-pentyl, and n- and s-hexyl.

[0089] "Alkenyl" means a linear or branched monovalent hydrocarbon radical having at least one carbon-carbon double bond, such as ethenyl (-HC=CH2).

[0090] "Alkylene" means a straight-chain or branched saturated divalent aliphatic hydrocarbon radical, such as methylene (-CH2-) or propylene (-(CH2)3-).

[0091] "Substitution" refers to, instead of hydrogen, independently, halogen (e.g., F-, Cl-, Br-, I-), hydroxyl, alkoxy, nitro, cyano, amino, azido, amidino, hydrazino, hydrazono, carbonyl, carbamyl, thiol, C1-C6 alkoxycarbonyl, ester, carboxyl or a salt thereof, sulfonic acid or a salt thereof, phosphoric acid or a salt thereof, C1-C 20 Alkyl, C2-C 16 Alkynyl, C6-C 20 Aryl, C7-C 13 Aryl alkyl, C1-C4 oxy alkyl, C1-C 20 Heteroalkyl, C3-C 20 Heteroaryl (i.e., a group containing at least one aromatic ring in which at least one ring member is other than carbon), C3-C 20 Heteroarylalkyl, C3-C 20 Cycloalkyl, C3-C 15 Cycloalkenyl, C6-C 15 Cycloalkynyl, C5-C 15 Heterocycloalkyl means a compound or moiety substituted with at least one (e.g., 1, 2, 3, 4, 5, 6 or more) substituents selected from heterocycloalkyl, or a combination comprising at least one of the above, provided that the valence does not exceed the normal valence of the substituted atom.

[0092] While particular embodiments have been described, presently unforeseen or unforeseen alternatives, modifications, variations, improvements, and substantial equivalents may occur to applicant or those skilled in the art. Accordingly, the appended claims, as submitted and as they may be amended, are intended to cover all such alternatives, modifications, variations, improvements, and substantial equivalents.

[0093] Description of the invention The following numbered paragraphs contain descriptions of broad combinations of technical features in accordance with various aspects of the invention disclosed herein.

[0094] 1. A positive electrode; a negative electrode comprising niobium metal oxide; a separator between the positive electrode and the negative electrode; an electrolyte comprising a solvent composition and a lithium salt; A secondary battery comprising: The solvent composition comprises a dinitrile solvent and at least one of a mononitrile solvent, a carbonate solvent, an ester solvent, or an ether solvent, the dinitrile being present in an amount of at least 0.1 weight percent based on the total weight of the solvent composition; Secondary battery.

[0095] 2. Dinitrile is C3-C 10 2. The secondary battery of paragraph 1, wherein the compound is an aliphatic linear dinitrile.

[0096] 3. C3~C 10 3. The secondary battery of paragraph 2, wherein the aliphatic linear dinitrile comprises glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelanitrile, sebaconitrile, or a combination thereof.

[0097] 4. C3~C 10 3. The secondary battery of paragraph 2, wherein the aliphatic linear dinitrile is adiponitrile.

[0098] 5. The secondary battery according to any one of paragraphs 1 to 4, wherein the dinitrile is contained in an amount of 0.2 mass percent to 50 mass percent based on the total mass of the solvent composition.

[0099] 6. The secondary battery of any one of paragraphs 1 to 5, wherein the carbonate solvent comprises dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethyl methyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, monofluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, or a combination thereof.

[0100] 7. The secondary battery described in paragraph 6, wherein the carbonate solvent comprises propylene carbonate, the propylene carbonate being contained in an amount of at least 1 weight percent based on the total weight of the solvent composition.

[0101] 8. The secondary battery of any one of paragraphs 1 to 7, wherein the ester solvent comprises methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, gamma-butyrolactone, 5-decanolide, gamma-valerolactone, dl-mevalonolactone, gamma-caprolactone, or a combination thereof.

[0102] 9. The secondary battery of any one of paragraphs 1 to 8, wherein the ether solvent comprises dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof.

[0103] 10. The secondary battery according to any one of paragraphs 1 to 9, wherein the mononitrile solvent comprises a C2 to C8 aliphatic mononitrile.

[0104] 11. The secondary battery according to paragraph 9, wherein the C2 to C8 aliphatic mononitrile comprises butyronitrile, ethanenitrile, proprionitrile, acetonitrile, or a combination thereof.

[0105] 12. The secondary battery according to paragraph 10, wherein the C2 to C8 aliphatic mononitrile is contained in an amount of 30 to 90 mass percent based on the total mass of the solvent composition.

[0106] 13. The secondary battery of any one of paragraphs 1 to 12, wherein the lithium salt comprises LiBF4.

[0107] 14. The secondary battery according to any one of paragraphs 1 to 13, wherein the lithium salt is contained in the electrolyte at a concentration of 0.5 to 3 molar.

[0108] 15. The secondary battery according to paragraph 14, wherein the electrolyte contains 0.01 to 0.3 molar LiBF4.

[0109] 16. The secondary battery according to paragraph 14, wherein the electrolyte comprises 0.8 Molar to 3 Molar LiPF6.

[0110] 17. The electrolyte has a PF6 of less than 0.1 molar. - 15. The secondary battery of paragraph 14, comprising:

[0111] 18. The electrolyte is PF6 - 15. The secondary battery of paragraph 14, not comprising:

[0112] 19. Niobium metal oxide is Nb 14 W3O 44 , Nb 16 W5O 55 , Nb 18 W8O 69 , Nb2WO8, Nb 18 W 16 O 93 , Nb 22 W 20 O 115 , Nb2Mo3O 14 , Nb 14 Mo3O 44 , Nb 12 MoO 44 19. The secondary battery of any one of paragraphs 1 to 18, wherein the secondary battery is a

[0113] 20. Niobium metal oxide is Nb 16 W5O 55 20. The secondary battery according to paragraph 19,

[0114] 21. A method for producing a secondary battery, comprising: providing a positive electrode; providing a negative electrode comprising niobium metal oxide; providing a separator between the positive electrode and the negative electrode; providing an electrolyte comprising a solvent composition and a lithium salt, the solvent composition comprising: a dinitrile solvent and at least one of a carbonate solvent, an ester solvent, or an ether solvent, the dinitrile being present in an amount of at least 0.1 weight percent based on the total weight of the solvent composition; contacting the positive electrode, the negative electrode, and the separator with an electrolyte to produce a secondary battery; A method comprising: EXAMPLES

[0115] The following examples are provided to further illustrate the present invention and are not intended to limit the scope of the invention.

[0116] Example 1 Lithium nickel cobalt aluminum oxide (LiNi x Co y Al z O2, where x≧0.8, z≦0.05 and x+y+z=1, NCA), and niobium tungsten oxide Nb 16 W5O 55 A multi-layer pouch cell containing NWO was filled with an electrolyte containing 1 M LiPF6 and the solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a 30:70 EC:EMC mass ratio and charged to 3 V. The electrode stack was removed from the charged complete cell and separated into individual anode layers, each with a capacity of about 80 mAh. At this state, the NWO anode was fully lithiated and at a potential of about 1.1 V vs. lithium.

[0117] The first negative electrode layer (1) was not rinsed and placed in a pouch with fresh electrolyte, the second negative electrode layer (2) was rinsed and placed in a pouch with fresh electrolyte, and the third negative electrode layer (3) was rinsed and placed in a pouch with only 30:70 EC:EMC solvent, i.e., no LiPF6 salt.

[0118] FIG. 1 shows the gas volume generated by interaction between the NWO anode and the other materials contained within the pouch, namely the electrolyte in the case of layers (1) and (2) and the solvent in the case of layer (3). Layer (1), which was not rinsed and therefore had a higher salt concentration, produced the highest volume of gas. Layer (2), which was rinsed and then contacted with the 30:70 EC:EMC electrolyte, produced a lower volume of gas, which was still greater than the volume produced by layer (3). Thus, a decrease in salt concentration (1>2>3) resulted in a decrease in gas volume, since the autocatalytic decomposition of LiPF6 was less pronounced.

[0119] Example 2 The composition of the gas produced by the salt-free pouch (third anode layer) in Example 1 was measured by gas chromatography to determine the role of the solvent in salt-independent gas evolution. The results are shown in Figure 2 and show that a significant percentage of the gas was composed of ethylene (the gas was composed of 90% hydrogen, 3% carbon dioxide, and 7% ethylene), indicating a reduction of the electrolyte solvent EC. From these experiments, it was concluded that benefits could be gained by using a salt and solvent package designed to reduce interactions with the NWO anode.

[0120] Example 3 The effect of lithium salts on gassing was evaluated. Multi-layer 0.6 ampere-hour (Ah) NCA / NWO pouch cells were fabricated and filled with one of the following electrolytes: 1M LiPF6 and 30:70 EC:EMC, 1M LiFSI and 30:70 EC:EMC, or 1M LiBF4 and 30:70 EC:EMC. The cells were charged to 3V so that the NWO anode was fully lithiated and had a potential of approximately 1.1V vs. lithium. The cells were stored in an oven at 60°C and the gas volume was measured periodically as described in Example 1.

[0121] The results (Figure 3) show that the use of LiBF4 salt significantly reduces gassing compared to LiPF6 or LiFSI.

[0122] Example 4 The effect of electrolyte solvent on gassing was evaluated. Multi-layer 0.16 Ah LCO / NWO pouch cells were filled with electrolyte containing 1.1 M of 20% LiBF4 / 80% LiPF6 salt in different solvents, molded, and charged to 3.35 V or 3.25 V. A mixture of LiBF4 / LiPF6 was used instead of pure LiBF4 to provide improved electrolyte conductivity while avoiding gassing. Solvents adiponitrile (ADN), proprionitrile (PN), and propylene carbonate (PC) were tested based on their stability to low voltage versus reduction with Li. The electrolyte compositions tested are shown in Table 1 below. Once the pouches were assembled, they were stored at 60° C. for 14 days and the gas volume was measured as described in Example 1. The capacity of the cells was also measured by discharging to 1.3 V at C / 2 and compared to the initial capacity.

[0123] [Table 1]

[0124] As shown in Figure 4, cells charged to 3.35 V exhibit significantly less gassing and less capacity loss when the solvent is 20:40:40 PC:EMC:ADN, indicating the stability of this solvent system. Cells containing a 45:45:10 PC:EMC:ADN blend have less gassing and less capacity loss when charged to 3.25 V than cells containing a 30:70 EC:EMC blend. These cells also have less gassing and less capacity loss than a 50:50 PC:EMC blend, indicating that ADN significantly improves solvent stability.

[0125] To reduce the viscosity, 10% of the EMC in 45:45:10 PC:EMC:ADN was replaced with PN. The cells were stored at 60° C. for 7 days with minimal gassing and capacity loss. The results in FIG. 5 show that PN improves the electrochemical performance of cells containing PC and ADN.

[0126] As demonstrated in the examples, the use of selected salt and solvent combinations provides reduced gassing of niobium oxide or niobium metal oxide negative electrodes.

[0127] Example 5 Additional studies were performed to test electrolyte compositions using alternative electrode materials and alternative nitrile solvents.

[0128] In Examples 5.1 to 5.7, lithium cobalt oxide (LiCoO2, LCO) was used as the positive electrode active material (cathode during discharge) and niobium tungsten oxide (Nb 16 W5O 55 Multi-layer 0.12 ampere hour (Ah) pouch cells were fabricated using NWO, polyethylene separators, and electrolyte. The electrodes were each placed on an aluminum current collector and assembled into a pouch cell with a separator. The pouch cells were filled with the electrolyte composition and vacuum sealed.

[0129] The electrolytes included a base solvent that was a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and / or propylene carbonate (PC) in the mass ratios listed in Table 2. Example 5.1 was made without any additional electrolyte additives. Example 5.2 included a lithium salt (LiBF4) as an additive present in the electrolyte at a molar concentration of 0.2M (see Table 2). Examples 5.3-5.7 included a dinitrile solvent selected from adiponitrile (ADN) and succinonitrile (SN), or a trinitrile solvent (TN) that was 1,3,6-hexanetricarbonitrile. The amount of nitrile solvent included is shown in Table 2 as a percentage by mass of the total electrolyte solution.

[0130] [Table 2]

[0131] The pouch cells had initial external dimensions of 50 mm x 34 mm x 3 mm. The initial volume of the cell was determined by measuring the total displacement of the cell in fluid (Archimedes' principle). The cell was then charged to 3.15 V at room temperature and discharged to 1.3 V at a C rate of C / 2 to determine the initial discharge capacity.

[0132] The cell was recharged to 3.15 V and stored in a 60° C. oven for 6 weeks.

[0133] The gas volume in the cells was measured after 2 weeks and 6 weeks of storage. To measure the gas volume, the cells were removed from the oven and cooled to room temperature. The volume of the cells was then measured as described above. The cell volume increase (%) was calculated by comparing the cell volume at 2 weeks or 6 weeks to the initial volume.

[0134] Figure 6 shows the cell volume increase for Examples 5.1 to 5.5 after 2 weeks of storage at 60° C. The black crosses correspond to the average volume increase and the shaded area corresponds to the standard deviation.

[0135] Figure 8 shows the cell volume increase for Examples 5.2, 5.4, 5.6 and 5.7 after 6 weeks of storage at 60°C. The black crosses correspond to the average volume increase and the shaded area corresponds to the standard deviation.

[0136] After two weeks, Example 5.1 (no additive) had a volume increase of over 14%. In contrast, Examples 5.3, 5.4 and 5.5 (2% ADN, SN and TN) only showed an 8-12% volume increase over two weeks. The dinitrile and trinitrile additives are believed to inhibit gassing and therefore prevent large cell volume increases. The dinitriles ADN and SN have been shown to inhibit cell volume increase better than the trinitrile additive.

[0137] After 6 weeks, Example 5.4 (2% SN) showed a volume increase of 35%, while Examples 5.6 and 5.7 (both 5% SN) had lower volume increases of about 23% and 4%, respectively. The inclusion of higher amounts of dinitrile (SN) was shown to further suppress gassing, thus resulting in a smaller cell volume increase. In particular, the combination of PC / EMC-based solvent with 5% SN additive (Example 5.7) was shown to substantially reduce cell volume increase over 6 weeks to only 4%.

[0138] Example 5.2 (0.2M LiBF4) showed low volume gain of about 4% over 2 weeks and about 10% over 6 weeks. However, the volume gain seen in Example 5.7 (PC / EMC and 5% SN) was lower and the capacity retention of Example 5.2 was lower than all of the dinitrile / trinitrile containing electrolytes over 6 weeks, as discussed below.

[0139] The discharge capacity of the cells was measured after 2 weeks and 6 weeks of storage. To measure the discharge capacity, the cells were removed from the oven and cooled to room temperature. The cells were discharged to 1.3 V at a C rate of C / 2 to determine the discharge capacity. The discharge capacity retention (%) was calculated by comparing the 2-week or 6-week discharge capacity with the initial discharge capacity.

[0140] Figure 7 shows capacity retention for Examples 5.1-5.5 after 2 weeks storage at 60° C. The black crosses correspond to the mean capacity retention and the shaded area corresponds to the standard deviation.

[0141] Figure 9 shows the capacity retention for Examples 5.2, 5.4, 5.6 and 5.7 after 6 weeks of storage at 60° C. The black crosses correspond to the mean capacity retention and the shaded area corresponds to the standard deviation.

[0142] After two weeks, Example 5.1 (no additive) had a capacity retention of about 16%. Examples 5.3, 5.4 and 5.5 (2% ADN, SN and TN) showed much better capacity retention of 64%, 71% and 54%, respectively. In particular, the capacity retention of Example 5.4 (2% SN) was higher than all other examples over two weeks. This is believed to be due to the dinitrile and trinitrile additives that suppress electrolyte gassing.

[0143] Over a 6 week period, Example 5.4 (2% SN) showed a volume retention of 39%, while Examples 5.6 and 5.7 (both 5% SN) had higher volume retention of 62% and 64%, respectively. The inclusion of higher amounts of dinitrile (SN) has been shown to further suppress gassing and result in improved volume retention.

[0144] Example 5.2 (0.2M LiBF4) showed reasonable capacity retention (69%) over two weeks, but this decreased to only 25% after six weeks. Examples containing nitrile additives such as Examples 5.4, 5.6 and 5.7 all had better capacity retention over the longer six week period (39%, 62% and 64%, respectively).

[0145] The examples show that the addition of a dinitrile or trinitrile solvent to the electrolyte provides a good balance of properties (both lower cell volume increase and higher capacity retention) over longer storage periods of the cell. However, the examples (e.g., Example 4) also show that the addition of both a lithium salt and a dinitrile or trinitrile solvent provides further improvements in electrolyte gassing and capacity retention.

[0146] References Certain publications have been cited above in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Full citations for these references are provided below. The entire contents of each of these references are incorporated herein. US2017 / 0244135 JP2013 / 152825 WO2020 / 047228

Claims

1. Positive electrode and, A negative electrode containing niobium oxide or niobium metal oxide, A separator between the positive and negative electrodes, A multinitrile solvent having two or more nitrile groups, and A second solvent selected from the group consisting of mononitrile solvents, carbonate solvents, ester solvents, and ether solvents. A solvent composition comprising an electrolyte and A secondary battery comprising the following: a secondary battery comprising a multinitrile solvent in an amount of at least 0.1 mass percent based on the total mass of the solvent composition.

2. The secondary battery according to claim 1, wherein the multinitrile solvent is a dinitrile solvent or a trinitrile solvent, preferably a dinitrile solvent.

3. Multinitrile solvents, ３ ~C １０ Aliphatic dinitrile, preferably C ３ ~C １０ The secondary battery according to claim 1, wherein the aliphatic linear dinitrile is used.

4. C ３ ~C １０ The secondary battery according to claim 3, wherein the aliphatic dinitrile includes glutalonitrile, adiponitrile, pimeronitrile, suberonitrile, azelanitrile, sebaconitrile, succinonitrile, or a combination thereof.

5. C ３ ~C １０ The secondary battery according to claim 3, wherein the aliphatic dinitrile is adiponitrile or succinonitrile.

6. The multi-nitrile solvent is C ４ to C １０ The secondary battery according to claim 1, which is an aliphatic trinitrile.

7. C ４ ~C １０ The secondary battery according to claim 6, wherein the aliphatic trinitrile solvent is 1,3,6-hexanetricarbonite.

8. The secondary battery according to claim 1, wherein the total amount of the multinitrile solvent contained in the electrolyte is 0.2% to 50% by mass, preferably 2% to 40% by mass, based on the total mass of the solvent composition.

9. The secondary battery according to claim 1, wherein the total amount of the multinitrile solvent contained in the electrolyte is 1% to 10% by mass, preferably 2% to 5% by mass, based on the total mass of the solvent composition.

10. The secondary battery according to claim 1, wherein the total amount of the multinitrile solvent contained in the electrolyte is 10% to 50% by mass, preferably 20% to 40% by mass, based on the total mass of the solvent composition.

11. The secondary battery according to claim 1, wherein the second solvent is a carbonate solvent.

12. The secondary battery according to claim 1, wherein the carbonate solvent is dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, ethyl isopropyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, monofluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, or a combination thereof.

13. The secondary battery according to claim 1, wherein the carbonate solvent is ethylene carbonate, ethyl methyl carbonate, propylene carbonate, or a combination thereof.

14. The secondary battery according to claim 13, wherein the carbonate solvent comprises ethylene carbonate and ethyl methyl carbonate, or a mixture of propylene carbonate and ethyl methyl carbonate.

15. The secondary battery according to claim 14, wherein the mass ratio of ethylene carbonate to ethyl methyl carbonate or the mass ratio of propylene carbonate to ethyl methyl carbonate is 30:70 to 50:

50.

16. The secondary battery according to claim 1, wherein the carbonate solvent is propylene carbonate, and the total amount of propylene carbonate contained in the electrolyte is at least 1 mass percent based on the total mass of the solvent composition.

17. The secondary battery according to claim 1, wherein the second solvent is an ester solvent, for example, methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, 5-decanolide, γ-valerolactone, dl-mevalonolactone, γ-caprolactone, or a combination thereof.

18. The secondary battery according to claim 1, wherein the second solvent is an ether solvent, for example, dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof.

19. The second solvent is a mononitrile solvent, for example, a mononitrile solvent is C ２ ~C ８ A secondary battery according to claim 1, comprising an aliphatic mononitrile.

20. C ２ ~C ８ The secondary battery according to claim 19, wherein the aliphatic mononitrile includes butyronitrile, propionitrile, acetonitrile, methoxypropionitrile, or a combination thereof.

21. C in electrolytes ２ ~C ８ The secondary battery according to claim 19, wherein the total amount of aliphatic mononitrile is 30 to 90 percent by mass based on the total mass of the solvent composition.

22. The secondary battery according to claim 1, wherein the electrolyte further comprises a lithium salt.

23. Lithium salts, LiBF ４ LiPF ６ Alternatively, lithium difluoro(oxalato) borate, preferably LiBF ４ or LiPF ６ , more preferably LiBF ４ A secondary battery according to claim 22, including the following:

24. The secondary battery according to claim 22, wherein the lithium salt comprises LiBF4, LiPF6, LiFSI, LiTFSI, or a combination thereof.

25. The secondary battery according to claim 22, wherein the total lithium ion concentration in the electrolyte is 0.5 to 3 molars.

26. Electrolytes in a LiPF of 0.8 Molar to 3 Molar ６ A secondary battery according to claim 22, including the following:

27. Electrolyte levels less than 0.1 Mohlers ６ － It contains, preferably, an electrolyte, PF ６ － A secondary battery according to claim 22, which does not include the following.

28. The secondary battery according to claim 1, wherein the negative electrode contains a niobium metal oxide.

29. The secondary battery according to claim 1, wherein the niobium metal oxide has the formula Nb x My y O z, where x is 2 to 34, y is 1 to 20, z is 8 to 115, and M is Na, Mg, Al, Si, P, S, K, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Y, Zr, Mo, In, Sn, Sb, Ta, W, or a combination thereof.

30. The secondary battery according to claim 29, wherein M is V, Cr, Mo, Ta, W, P, S, or a combination thereof, preferably M is V, Cr, Mo, Ta, W, or a combination thereof.

31. The secondary battery according to claim 1, wherein the niobium metal oxide is niobium tungsten oxide or niobium molybdenum oxide.

32. Niobium metal oxide, Nb １４ W ３ O ４４ , Nb １６ W ５ O ５５ Nb １８ W ８ O ６９ , Nb ２ WO ８ Nb １８ W １６ O ９３ Nb ２２ W ２０ O １１５ , Nb ２ Mo ３ O １４ Nb １４ Mo ３ O ４４ Nb １２ MoO ４４ , or a combination thereof, preferably Nb １６ W ５ O ５５ Or Nb １８ W １６ O ９３ , or a combination thereof, more preferably Nb １６ W ５ O ５５ The secondary battery according to claim 1.

33. The secondary battery according to claim 1, wherein the niobium oxide has the formula Nb x1 O z1, where x1 is 2 to 25 and z1 is 2 to 62.

34. The secondary battery according to claim 1, wherein the niobium oxide is Nb₂O₅, NbO₂, Nb₁₂O₂₇, Nb₂₅O₂₇, or a combination thereof.

35. A method for manufacturing a secondary battery, The process of providing the positive electrode, A step of providing a negative electrode containing niobium oxide or niobium metal oxide, A step of providing a separator between the positive electrode and the negative electrode, The process involves providing an electrolyte containing a solvent composition, wherein the solvent composition is A multinitrile solvent having two or more nitrile groups, and A second solvent selected from the group consisting of mononitrile solvents, carbonate solvents, ester solvents, or ether solvents. A step comprising: including, and containing multinitrile in an amount of at least 0.1 mass percent based on the total mass of the solvent composition; The process of manufacturing a secondary battery involves bringing the positive electrode, negative electrode, and separator into contact with an electrolyte. Methods that include...

36. The method according to claim 35, wherein the electrolyte comprises a lithium salt.

37. The method according to claim 35, wherein the multinitrile solvent is a dinitrile or trinitrile solvent, preferably a dinitrile solvent.

38. The method according to claim 35, wherein the negative electrode contains a niobium metal oxide.

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