Electrolyte and energy storage battery

Abstract

The invention provides an electrolyte and an energy storage battery. The electrolyte comprises a phosphamide additive. The phosphamide additive is added into the electrolyte, the additive is of a chain structure and contains two F atoms with strong polarity, the viscosity of the electrolyte can be reduced, the wettability of the electrolyte to a pole piece can be improved, the length of a molecular chain of the phosphamide additive can be limited by limiting the structures of R1 and R2, and the service life of the phosphamide additive can be prolonged. Fluorine atoms, hydroxyl groups and carboxyl groups can be further introduced through R1 and R2, so that the battery performance is further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to an electrolyte and an energy storage battery. Background Art

[0002] As the size of energy storage batteries becomes larger and larger, the size, surface density and compaction density of the pole pieces are also increasing. The wetting problem of the pole pieces in the central area of ​​the core package has become a bottleneck for improving the performance of large batteries.

[0003] The electrolyte additives generally selected in the related art include vinylene carbonate (VC), fluoroethylene carbonate (FEC) and diethylene sulfate (DTD), but these additives are not suitable for large batteries (batteries with large electrode size, surface density and compaction density, such as electrode area > 500cm 2 , positive electrode surface density ≥ 220g / cm 2 , positive electrode compaction density ≥ 2.50g / cm 3 , negative electrode surface density ≥100g / cm 2 , negative electrode compaction density ≥1.50g / cm 3 ) is not wettable enough, which results in regular black spots and lithium deposition in the center of the electrode when the battery is fully charged and disassembled after formation. Summary of the invention

[0004] The embodiments of the present invention provide an electrolyte and an energy storage battery, which can improve the technical problem of insufficient wettability of the existing electrolyte in large batteries.

[0005] In a first aspect, an embodiment of the present invention provides an electrolyte, including a phosphoramide additive, wherein the phosphoramide additive has a structural formula of

[0006]

[0007] Among them, R1 is a carbon chain with 1 to 3 carbon atoms that is singly substituted by a first substituent or unsubstituted, R2 is a carbon chain with 1 to 3 carbon atoms or a hydrogen atom that is substituted by a second substituent or unsubstituted, the first substituent includes one of a fluorine atom and a carboxyl group, and the second substituent includes one or more of a fluorine atom and a hydroxyl group.

[0008] In one embodiment, the phosphoramide additive includes

[0009]

[0010] One or more of the .

[0011] In one embodiment, the mass content of the phosphoramide additive in the electrolyte is 0.5%-4.0%.

[0012] In one embodiment, the electrolyte includes a lithium salt, and the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide salt, and lithium dioxalatoborate; and / or

[0013] The electrolyte includes lithium salt, and the concentration of the lithium salt is 0.5 mol / L to 2.0 mol / L.

[0014] In one embodiment, the electrolyte further includes a solvent, and the solvent includes one or more of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, propylene carbonate and dimethyl carbonate.

[0015] In one embodiment, the electrolyte further includes 1,3-propane sultone.

[0016] In one embodiment, the mass content of the 1,3-propane sultone in the electrolyte is 0.1% to 2.0%.

[0017] In one embodiment, the electrolyte further comprises vinylene carbonate, and the mass content of the vinylene carbonate in the electrolyte is 0.5% to 2.0%.

[0018] In a second aspect, an embodiment of the present invention provides an energy storage battery, comprising a positive electrode sheet, a negative electrode sheet and the above-mentioned electrolyte.

[0019] In one embodiment, the active material of the positive electrode sheet includes lithium iron phosphate; and / or

[0020] The active material of the negative electrode sheet includes graphite and silicon carbon; and / or

[0021] The surface density of the positive electrode sheet is 220 g / cm 2 ~260g / cm 2 The compaction density of the positive electrode sheet is 2.55 g / cm 3 ~2.70g / cm 3 ; and / or

[0022] The surface density of the negative electrode sheet is 100 g / cm 2 ~130g / cm 2 The compaction density of the negative electrode sheet is 1.50 g / cm 3 ~1.65g / cm 3 .

[0023] In an embodiment of the present invention, by adding a phosphoramide additive into the electrolyte, the additive has a chain structure and contains two highly polar F atoms, the viscosity of the electrolyte can be reduced and the wettability of the electrolyte to the electrode can be improved; by limiting the structure of R1 and R2, the length of the molecular chain of the phosphoramide additive can be limited, thereby controlling the viscosity of the phosphoramide additive, and fluorine atoms, hydroxyl groups and carboxyl groups can be further introduced through R1 and R2, thereby further improving the battery performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 is the structural formula of the phosphoramide additive provided by an embodiment of the present invention;

[0026] Figure 2 is the structural formula of the phosphoramide additive provided in Example 1 of the present invention;

[0027] Figure 3 is the structural formula of the phosphoramide additive provided in Example 2 of the present invention;

[0028] Figure 4 is the structural formula of the phosphoramide additive provided in Example 3 of the present invention;

[0029] Figure 5 is the structural formula of the phosphoramide additive provided in Example 4 of the present invention;

[0030] Figure 6 It is the structural formula of the additive provided in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention. In addition, it should be understood that the specific implementation methods described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention. In the present invention, unless otherwise specified, the directional words used, such as "upper" and "lower", generally refer to the upper and lower parts of the device in actual use or working state, specifically the drawing direction in the drawings; while "inside" and "outside" refer to the outline of the device.

[0032] The technical solution of this application is as follows:

[0033] In a first aspect, an embodiment of the present application provides an electrolyte, including a phosphoramide additive, wherein the phosphoramide additive has a structural formula of

[0034]

[0035] Wherein, R1 is a carbon chain with 1 to 3 carbon atoms which is substituted by a first substituent or is not substituted, R2 is a carbon chain with 1 to 3 carbon atoms or a hydrogen atom (-H) which is substituted by a second substituent or is not substituted, the first substituent includes one of a fluorine atom (-F) and a carboxyl group (-COOH), and the second substituent includes one or more of a fluorine atom (-F) and a hydroxyl group (-OH).

[0036] In the present application, by adding a phosphoramide additive to the electrolyte, the additive has a chain structure and contains two strongly polar F atoms, which can reduce the viscosity of the electrolyte, improve the wettability of the electrolyte to the electrode, and thus improve the cycle performance of the battery; the two F atoms on the phosphoramide of the additive have strong electronegativity, which can improve the ionic conductivity of the electrolyte, thereby improving the kinetic performance, low temperature performance and cycle performance of the battery; by limiting the structure of R1 and R2, the length of the molecular chain of the phosphoramide additive can be limited, thereby controlling the viscosity of the phosphoramide additive, and fluorine atoms, hydroxyl groups and carboxyl groups can be further introduced through R1 and R2, thereby further improving the battery performance; the phosphoramide structure of the additive can generate a stable solid electrolyte interface film (solid electrolyte interface, referred to as SEI film) at the negative electrode, thereby improving the cycle performance of the battery.

[0037] When R1 contains a carboxyl group, in the battery ester electrolyte, the presence of the carboxyl group has an important influence on the ionic conductivity and stability of the electrolyte, specifically in the following aspects:

[0038] Improved ion conductivity: The carboxyl group has good ion exchange capacity and can quickly exchange with ions in the electrolyte, thereby improving the ion conductivity of the electrolyte. This allows the battery to transfer charge faster during charging and discharging, thereby improving the performance of the battery.

[0039] Optimizing electrolyte performance: The carboxyl group can interact with other components in the electrolyte to optimize the performance of the electrolyte. For example, it can form hydrogen bonds with solvent molecules in the electrolyte, increase the polarity of the electrolyte, and thus improve the solubility of the electrolyte.

[0040] When R2 contains a hydroxyl group, in the ether electrolyte of a lithium battery, the presence of a hydroxyl group can promote the migration of lithium ions and improve battery performance and safety. As a hydrophilic functional group, the hydroxyl group can increase the degree of freedom of lithium ions by forming hydrogen bonds with lithium ions, thereby accelerating the migration speed of lithium ions. The phosphoramide additives of the present application can improve the electrolyte wettability of thick electrodes, thereby reducing the lithium precipitation phenomenon of the battery, improving the liquid retention coefficient of thick electrode batteries, and allowing the battery to have sufficient electrolyte to transport charges during long cycles, thereby improving the long cycle life of the battery.

[0041] In one embodiment, the phosphoramide additive includes

[0042]

[0043] In this way, the wettability of the electrolyte to the electrode sheet can be better improved, and then the electrolyte can improve the cycle performance of the battery.

[0044] In some embodiments, the mass content of the phosphoramide additive in the electrolyte is 0.5%-4.0%, for example, it can be 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, etc. In this way, the wettability of the electrolyte to the pole piece can be effectively improved, and the cycle performance of the battery can be improved. If the addition amount is too low, the wettability of the electrolyte to the pole piece will be poor, and black spots and lithium precipitation will easily appear in the central area of ​​the pole piece. If the addition amount is too much, the regularity of the SEI film will be reduced, resulting in an increase in the loss of active lithium, thereby reducing the cycle performance of the battery.

[0045] In some embodiments, the electrolyte includes a lithium salt, and the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LIFSI), and lithium borate bis(oxalate) (LiBOB).

[0046] In some embodiments, the concentration of lithium salt is 0.5 mol / L to 2.0 mol / L, for example, 0.5 mol / L, 0.7 mol / L, 0.9 mol / L, 1.1 mol / L, 1.3 mol / L, 1.4 mol / L, 1.7 mol / L, 1.9 mol / L, 2.0 mol / L, etc.

[0047] In some embodiments, the electrolyte further includes a solvent, and the solvent includes one or more of ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), propylene carbonate (PC) and dimethyl carbonate (DMC).

[0048] In some embodiments, the solvent includes ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1.

[0049] In some embodiments, the electrolyte further includes vinylene carbonate (VC).

[0050] In some embodiments, the mass content of vinylene carbonate (VC) in the electrolyte is 0.5% to 2.0%, for example, 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.4%, 1.7%, 1.9%, 2.0%, etc.

[0051] In some embodiments, the electrolyte further includes 1,3-propane sultone (PS). In this way, 1,3-propane sultone can promote the formation of a stable SEI film, improve the stability of the battery at high temperatures, reduce the gas production of the battery, and thus improve the wettability of the electrolyte to the electrode. High gas production of the battery will reduce the effect of the phosphoramide additive on the improvement of the electrolyte wettability.

[0052] In some embodiments, the mass content of 1,3-propane sultone (PS) in the electrolyte is 0.1% to 2.0%, for example, 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.4%, 1.7%, 1.9%, 2.0%, etc.

[0053] In a second aspect, an embodiment of the present application provides an energy storage battery, comprising a positive electrode sheet, a negative electrode sheet and the above-mentioned electrolyte.

[0054] In some embodiments, the active material of the positive electrode sheet includes lithium iron phosphate.

[0055] In some embodiments, the active material of the negative electrode sheet includes graphite and silicon carbon.

[0056] In the present application, graphite includes artificial graphite and natural graphite.

[0057] In some embodiments, the surface density of the positive electrode sheet is 220 g / cm 2 ~260g / cm 2 , for example, it can be 220g / cm 2 , 225g / cm 2 , 230g / cm 2 , 235g / cm 2 , 240g / cm 2 , 245g / cm 2 , 250g / cm 2 , 255g / cm 2 , 260g / cm 2 The compaction density of the positive electrode is 2.55g / cm 3 ~2.70g / cm 3 , for example, it can be 2.55 g / cm3 , 2.57g / cm 3 , 2.59g / cm 3 , 2.61g / cm 3 , 2.63g / cm 3 , 2.65g / cm 3 , 2.67g / cm 3 , 2.69g / cm 3 , 2.70g / cm 3 In this way, under the condition that the positive electrode sheet has a high surface density and a high compaction density, the electrolyte of the present application can still have good wettability to the positive electrode sheet.

[0058] In some embodiments, the surface density of the negative electrode sheet is 100 g / cm 2 ~130g / cm 2 , for example, 100 g / cm 2 , 105g / cm 2 , 110g / cm 2 , 115g / cm 2 , 120g / cm 2 , 125g / cm 2 , 130g / cm 2 The compaction density of the negative electrode sheet is 1.50g / cm 3 ~1.65g / cm 3 , for example, it can be 1.50 g / cm 3 , 1.52g / cm 3 , 1.54g / cm 3 , 1.56g / cm 3 , 1.58g / cm 3 , 1.60g / cm 3 、1.62g / cm 3 , 1.64g / cm 3 , 1.65g / cm 3 In this way, under the condition that the negative electrode sheet has a high surface density and a high compaction density, the electrolyte of the present application can still have good wettability to the negative electrode sheet.

[0059] Example 1

[0060] An electrolyte and a preparation method thereof, comprising the following steps:

[0061] LiPF6, vinylene carbonate (VC), 1,3-propane sultone (PS), phosphoramide additives (whose structural formula is shown in the attached Figure 2As shown in the figure, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) are mixed together and dispersed evenly, wherein the volume ratio of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) is 1:1:1, to obtain an electrolyte, in which the concentration of LiPF6 is 1.0 mol / L, the mass content of vinylene carbonate (VC) is 1.5%, the mass content of 1,3-propane sultone (PS) is 1.0%, and the mass content of phosphoramide additives is 1.0%.

[0062] Example 2

[0063] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the structural formula is as shown in the attached figure. Figure 2 The phosphoramide additive shown in the figure is replaced by the structural formula as shown in the attached Figure 3 The phosphoramide additives shown.

[0064] Example 3

[0065] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the structural formula is as shown in the attached figure. Figure 2 The phosphoramide additive shown in the figure is replaced by the structural formula as shown in the attached Figure 4 The phosphoramide additives shown.

[0066] Example 4

[0067] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the structural formula is as shown in the attached figure. Figure 2 The phosphoramide additive shown in the figure is replaced by the structural formula as shown in the attached Figure 5 The phosphoramide additives shown.

[0068] Example 5

[0069] This embodiment is substantially the same as Embodiment 1, except that the mass content of the phosphoramide additive in this embodiment is 1.5%.

[0070] Example 6

[0071] This embodiment is substantially the same as Embodiment 1, except that the mass content of the phosphoramide additive in this embodiment is 2.0%.

[0072] Example 7

[0073] This embodiment is substantially the same as Embodiment 1, except that the mass content of the phosphoramide additive in this embodiment is 3.0%.

[0074] Example 8

[0075] This embodiment is substantially the same as Embodiment 1, except that the mass content of the phosphoramide additive in this embodiment is 4.0%.

[0076] Example 9

[0077] This embodiment is substantially the same as Embodiment 1, except that the mass content of the phosphoramide additive in this embodiment is 0.5%.

[0078] Example 10

[0079] This embodiment is substantially the same as Embodiment 1, except that the mass content of the phosphoramide additive in this embodiment is 5.0%.

[0080] Comparative Example 1

[0081] This comparative example is substantially the same as Example 1, except that no phosphoramide additive is added in this comparative example.

[0082] Comparative Example 2

[0083] This comparative example is basically the same as Example 1, except that in this comparative example, the structural formula is as shown in the attached figure. Figure 2 The phosphoramide additive shown in the figure is replaced by the structural formula as shown in the attached Figure 6 Additives as indicated.

[0084] The electrolyte obtained in the embodiment and the comparative example was injected into the battery cell to obtain an energy storage battery, wherein the positive electrode active material of the battery cell was lithium iron phosphate, and the positive electrode surface density was 245 g / cm 2 The positive electrode compaction density is 2.68g / cm 3 The negative electrode active material of the battery cell is artificial graphite, and the negative electrode surface density is 120g / cm 2 The compacted density of the negative electrode is 1.63 g / cm 3 .

[0085] Test Example: The energy storage batteries and electrolytes obtained in the embodiments and comparative examples were subjected to performance tests, and the test data are shown in Table 1.

[0086] Test method:

[0087] Ion conductivity of electrolyte: The ion conductivity of the electrolytes obtained in the examples and comparative examples was tested using a conductivity tester.

[0088] Viscosity: The viscosity of the electrolytes obtained in the examples and comparative examples was tested using a viscometer.

[0089] Contact angle: 100 μl of the electrolyte obtained in the embodiment and the comparative example was dripped onto the surface of the negative electrode sheet, the surface image was captured by a high-precision camera of the contact angle meter, and then the contact angle of the droplet was calculated by a computer algorithm.

[0090] Capacity retention rate: The energy storage batteries obtained in the examples and comparative examples were charged and discharged at 1C / 1C at 25°C, and the charge and discharge data were collected.

[0091] Table 1

[0092]

[0093] From Table 1, we can see that:

[0094] Compared with Example 1 to Example 4 and Comparative Example 2, the electrolyte of Example 3 has higher ion conductivity, lower viscosity, smaller contact angle with the negative electrode sheet, and higher battery capacity retention rate. It can be seen that the additive of Example 3 contains carboxyl groups, which can improve the ion conductivity of the electrolyte in the ester electrolyte, thereby improving the performance of the battery. The ion conductivity of the electrolyte of Example 1 to Example 4 is higher than that of Comparative Example 2, the viscosity of the electrolyte of Example 1 to Example 4 is lower than that of Comparative Example 2, the contact angle of the electrolyte of Example 1 to Example 4 with the negative electrode sheet is lower than that of Comparative Example 2, and the battery capacity retention rate of Example 1 to Example 4 is higher than that of Comparative Example 2. It can be seen that the structure of the additive will affect the performance of the electrolyte and the battery. The additive of the present application is a chain structure, which has a smaller viscosity than the ring structure of Comparative Example 2, so that it can better reduce the viscosity of the electrolyte, thereby improving the wettability of the electrolyte to the electrode sheet.

[0095] Compared with Example 1, Example 5-Example 10, as the amount of phosphoramide additive added increases, the ionic conductivity of the electrolyte increases, the viscosity decreases, and the contact angle with the negative electrode sheet becomes smaller, indicating that the phosphoramide additive can improve the wettability of the electrolyte to the thick electrode sheet. However, the capacity retention rate of the battery in Example 5 is the highest, which shows that the amount of phosphoramide additive added affects the cycle performance of the battery. Compared with Example 9, Example 8 has a higher amount of phosphoramide additive added to the electrolyte of Example 8, and a lower amount of phosphoramide additive added to the electrolyte of Example 9. The capacity retention rate of the battery in Example 8 for 2000 cycles is higher than that in Example 9, and the capacity retention rate of the battery in Example 8 for 3000 cycles is lower than that in Example 9. The reason is that when the amount of phosphoramide additive added is high, the SEI film will grow too thick, thereby reducing the battery cycle performance. The capacity retention rate of the battery of Example 8 after 2000 cycles is higher than that of Example 9 because there are other additives in the electrolyte that can protect the negative electrode, thereby preventing the SEI film from growing too fast. By 3000 cycles, since other additives are basically consumed, the high content of phosphoramide additives causes the SEI film to grow too thick, and the battery cycle performance decreases. The early 2000 cycles are better than Example 8 because there are other additives in the electrolyte that can protect the negative electrode and prevent the crazy growth of SEI. At 3000 cycles, other additives are basically consumed. When the content of the selected additives is too high, it will cause excessive growth of SEI and reduce battery performance.

[0096] Therefore, the additive content of 0.5% in Example 8 is also included in the protection scope of the claims.

[0097] Compared with Comparative Example 1, the electrolyte of the embodiment has higher ion conductivity, lower viscosity, smaller contact angle with the negative electrode sheet, and higher battery capacity retention rate. It can be seen that the phosphoramide additive of the present application can effectively reduce the viscosity of the electrolyte and improve the cycle performance of the battery.

[0098] The embodiments of the present invention are described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. An electrolyte, characterized in that: It includes a phosphoramide additive, and the structural formula of the phosphoramide additive is: Among them, R1 is a carbon chain with 1 to 3 carbon atoms that is singly substituted by a first substituent or unsubstituted, R2 is a carbon chain with 1 to 3 carbon atoms or a hydrogen atom that is substituted by a second substituent or unsubstituted, the first substituent includes one of a fluorine atom and a carboxyl group, and the second substituent includes one or more of a fluorine atom and a hydroxyl group.

2. The electrolyte according to claim 1, characterized in that The phosphoramide additives include One or more of the .

3. The electrolyte according to claim 1, characterized in that The mass content of the phosphoramide additive in the electrolyte is 0.5%-4.0%.

4. The electrolyte according to claim 1, characterized in that The electrolyte further includes a lithium salt, wherein the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide salt, and lithium bis(oxalatoborate); and / or The electrolyte also includes a lithium salt, and the concentration of the lithium salt is 0.5 mol / L to 2.0 mol / L.

5. The electrolyte according to claim 1, characterized in that The electrolyte also includes a solvent, and the solvent includes one or more of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, propylene carbonate and dimethyl carbonate.

6. The electrolyte according to claim 1, characterized in that The electrolyte also includes 1,3-propane sultone.

7. The electrolyte according to claim 6, characterized in that The mass content of the 1,3-propane sultone in the electrolyte is 0.1% to 2.0%.

8. The electrolyte according to claim 1, characterized in that The electrolyte further comprises vinylene carbonate, and the mass content of the vinylene carbonate in the electrolyte is 0.5% to 2.0%.

9. An energy storage battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet and an electrolyte as claimed in any one of claims 1 to 8.

10. The energy storage battery according to claim 9, characterized in that: The active material of the positive electrode sheet includes lithium iron phosphate; and / or The active material of the negative electrode sheet includes graphite and silicon carbon; and / or The surface density of the positive electrode sheet is 220 g / cm 2 ~260g / cm 2 The compaction density of the positive electrode sheet is 2.55 g / cm 3 ~2.70g / cm 3 ; and / or The surface density of the negative electrode sheet is 100 g / cm 2 ~130g / cm 2 The compaction density of the negative electrode sheet is 1.50 g / cm 3 ~1.65g / cm 3 .

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