Electrolyte and energy storage battery

Abstract

The application provides an electrolyte and an energy storage battery, and the electrolyte comprises a phosphoramide additive. In the application, the phosphoramide additive is added into the electrolyte, the additive has a chain structure, contains two strong polar F atoms, can reduce the viscosity of the electrolyte, improve the wettability of the electrolyte to the pole piece, the length of the molecular chain of the phosphoramide additive can be limited by limiting the structures of R1 and R2, so that the viscosity of the phosphoramide additive is controlled, and the fluorine atoms, the hydroxyl groups and the carboxyl groups can be further introduced through R1 and R2, so that the performance of the battery is further improved.

Description

TECHNICAL FIELD

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

[0002] With the increasing size of the energy storage battery, the size, surface density and compaction density of the pole piece are also increasing, and the pole piece in the center area of the core package has become a bottleneck for performance improvement of large batteries.

[0003] The electrolyte additives in the related art are generally selected from vinylene carbonate (VC), fluoroethylene carbonate (FEC) and vinyl sulfate (DTD), but these additives have insufficient wettability in large batteries (batteries with large pole piece size, surface density and compaction density, such as pole piece area > 500 cm 2 , positive pole piece surface density ≥ 220 g / cm 2 , positive pole piece compaction density ≥ 2.50 g / cm 3 , negative pole piece surface density ≥ 100 g / cm 2 , and negative pole piece compaction density ≥ 1.50 g / cm 3 ), resulting in regular strip-shaped black spots and lithium precipitation in the center area of the pole piece when the battery is disassembled after formation. SUMMARY

[0004] Embodiments of the present application 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, embodiments of the present application provide an electrolyte, comprising a phosphoramide additive, the structural formula of the phosphoramide additive is

[0006]

[0007] wherein R1 is a carbon chain with 1-3 carbon atoms which is singly substituted by a first substituent or unsubstituted, R2 is a carbon chain with 1-3 carbon atoms which is substituted by a second substituent or unsubstituted, or a hydrogen atom, 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 an embodiment, the phosphoramide additive includes one or more of

[0009]

[0010]

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

[0012] In an embodiment, the electrolyte comprises a lithium salt, the lithium salt comprising one or more of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium bis(oxalato)borate; and / or

[0013] The electrolyte comprises a lithium salt, the concentration of the lithium salt being 0.5 mol / L-2.0 mol / L.

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

[0015] In an embodiment, the electrolyte further comprises 1,3-propane sultone.

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

[0017] In an embodiment, the electrolyte further comprises vinylene carbonate, the mass content of the vinylene carbonate in the electrolyte being 0.5%-2.0%.

[0018] In a second aspect, embodiments of the present application provide an energy storage battery, comprising a positive electrode sheet, a negative electrode sheet and the electrolyte described above.

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

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

[0021] The areal density of the positive electrode sheet is 220 g / cm 2 -260 g / cm 2 , and the tap density of the positive electrode sheet is 2.55 g / cm 3 -2.70 g / cm 3 ; and / or

[0022] The areal density of the negative electrode sheet is 100 g / cm 2 -130 g / cm 2 , and the tap density of the negative electrode sheet is 1.50 g / cm 3 -1.65 g / cm 3 .

[0023] In the embodiment of the present application, by adding the phosphoramide additive in the electrolyte, the additive is a chain structure, and contains two strong polar F atoms, the viscosity of the electrolyte can be reduced, and the electrolyte wettability of the electrode sheet is improved; by limiting the structure of R1 and R2, the length of the molecular chain of the phosphoramide additive can be limited, so as to control the viscosity of the phosphoramide additive, and the fluorine atom, the hydroxyl group and the carboxyl group can be further introduced through R1 and R2, so as to further improve the battery performance. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort.

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

[0026] Figure 2 is a structural formula of the phosphoramide additive provided by the embodiment 1 of the present application;

[0027] Figure 3 is a structural formula of the phosphoramide additive provided by the embodiment 2 of the present application;

[0028] Figure 4 is a structural formula of the phosphoramide additive provided by the embodiment 3 of the present application;

[0029] Figure 5 is a structural formula of the phosphoramide additive provided by the embodiment 4 of the present application;

[0030] Figure 6 is a structural formula of the additive provided by the comparative example 2 of the present application. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort belong to the scope of protection of the present application. In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application. In the present application, the orientation words such as "upper" and "lower" generally refer to the upper and lower of the device in the actual use or working state, and specifically refer to the direction of the drawing surface in the drawings; and "inner" and "outer" refer to the outline of the device.

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

[0033] In a first aspect, the embodiments of the present application provide an electrolyte, comprising a phosphoramide additive, the structural formula of the phosphoramide additive is

[0034]

[0035] wherein R1 is a carbon chain with 1-3 carbon atoms which is singly substituted by a first substituent or unsubstituted, R2 is a carbon chain with 1-3 carbon atoms which is substituted by a second substituent or unsubstituted, or a hydrogen atom (-H), the first substituent includes one of a fluorine atom (-F) and a carboxyl group (-COOH), and the second substituent includes one or several 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 strong polar F atoms, which can reduce the viscosity of the electrolyte, improve the wettability of the electrolyte to the electrode sheet, and further 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 structures 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 the fluorine atom, the hydroxyl group and the carboxyl group 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 (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, stability and other aspects of the electrolyte, which has the following effects:

[0038] Improving ionic conductivity: the carboxyl group has good ion exchange ability and can quickly exchange with ions in the electrolyte, thereby improving the ionic conductivity of the electrolyte. This enables the battery to transfer charges 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 thereby improve the solubility of the electrolyte.

[0040] When R2contains a hydroxyl group, the presence of the hydroxyl group can promote the migration of lithium ions, improve the performance and safety of the battery in the ether electrolyte of the lithium battery. As a hydrophilic functional group, the hydroxyl group can increase the freedom of lithium ions by forming hydrogen bonds with lithium ions, thereby accelerating the migration speed of lithium ions. The phosphoramide additive of the present application can improve the electrolyte wettability of the thick electrode, thereby reducing the lithium precipitation phenomenon of the battery and improving the liquid retention coefficient of the thick electrode battery, so that the battery has sufficient electrolyte to transport charge during long cycle process, thereby improving the long cycle life of the battery.

[0041] In an embodiment, the phosphoramide additive comprises one or more of

[0042]

[0043] Thereby, the electrolyte can better improve the wettability of the electrode sheet, and in turn 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. Thereby, the wettability of the electrolyte to the electrode sheet can be effectively improved, and the cycle performance of the battery is improved. If the addition amount is too low, the wettability of the electrolyte to the electrode sheet will not be good, and black spots and lithium precipitation phenomenon are prone to occur in the center area of the electrode sheet. If the addition amount is too high, the regularity of the SEI film will be reduced, the loss of active lithium will be increased, and the cycle performance of the battery will be reduced.

[0045] In some embodiments, the electrolyte comprises a lithium salt, and the lithium salt comprises one or more of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide salt (LIFSI), and lithium bis(oxalato)borate (LiBOB).

[0046] In some embodiments, the concentration of the lithium salt is 0.5 mol / L-2.0 mol / L, for example, it can be 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 comprises a solvent, and the solvent comprises 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 comprises 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 comprises vinylene carbonate (VC).

[0050] In some embodiments, the mass content of vinylene carbonate (VC) in the electrolyte is 0.5%-2.0%, for example, can be 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 comprises 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 temperature, reduce the gas production of the battery, and thus improve the wettability of the electrolyte to the electrode sheet. High gas production of the battery will reduce the effect of phosphoramidate additives on the wettability of the electrolyte.

[0052] In some embodiments, the mass content of 1,3-propane sultone (PS) in the electrolyte is 0.1%-2.0%, for example, can be 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, the embodiments of the present application provide a 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 comprises lithium iron phosphate.

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

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

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

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

[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), and a phosphoramide additive (the structural formula of which is shown in the attached drawing) Figure 2Ethylene carbonate (EC), methyl ethyl carbonate (EMC) and dimethyl carbonate (DMC) are mixed together and uniformly dispersed, wherein the volume ratio of ethylene carbonate (EC), methyl ethyl 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 additive is 1.0%.

[0062] Example 2

[0063] This example is basically the same as Example 1, except that in this example, the phosphoramide additive with the structural formula as shown in the following Figure 2 is replaced by the phosphoramide additive with the structural formula as shown in the following Figure 3 .

[0064] Example 3

[0065] This example is basically the same as Example 1, except that in this example, the phosphoramide additive with the structural formula as shown in the following Figure 2 is replaced by the phosphoramide additive with the structural formula as shown in the following Figure 4 .

[0066] Example 4

[0067] This example is basically the same as Example 1, except that in this example, the phosphoramide additive with the structural formula as shown in the following Figure 2 is replaced by the phosphoramide additive with the structural formula as shown in the following Figure 5 .

[0068] Example 5

[0069] This example is basically the same as Example 1, except that in this example, the mass content of the phosphoramide additive is 1.5%.

[0070] Example 6

[0071] This example is basically the same as Example 1, except that in this example, the mass content of the phosphoramide additive is 2.0%.

[0072] Example 7

[0073] This example is basically the same as Example 1, except that in this example, the mass content of the phosphoramide additive is 3.0%.

[0074] Example 8

[0075] This example is basically the same as Example 1, except that the mass content of the phosphoramidate additive in this example is 4.0%.

[0076] Example 9

[0077] This example is basically the same as Example 1, except that the mass content of the phosphoramidate additive in this example is 0.5%.

[0078] Example 10

[0079] This example is basically the same as Example 1, except that the mass content of the phosphoramidate additive in this example is 5.0%.

[0080] Comparative Example 1

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

[0082] Comparative Example 2

[0083] This comparative example is basically the same as Example 1, except that the phosphoramidate additive with the structural formula as shown in the following Figure 2 is replaced by an additive with the structural formula as shown in the following Figure 6 .

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

[0085] Test Example: The energy storage batteries and electrolytes obtained in the examples and comparative examples are tested for performance, and the test data are shown in Table 1.

[0086] Test Method:

[0087] Ionic conductivity of electrolyte: The ionic conductivity of the electrolytes obtained in the examples and comparative examples is tested by using a conductivity tester.

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

[0089] Contact angle: 100 μl of the electrolytes obtained in the examples and comparative examples is added dropwise on the surface of a negative electrode sheet, the surface image is photographed by using a high-precision camera of a contact angle meter, and then the contact angle of the liquid drop is calculated by using a computer algorithm.

[0090] Capacity retention: the energy storage batteries obtained in the examples and the comparative example were subjected to 1C / 1C charge-discharge at 25°C, and the charge-discharge data were collected.

[0091] Table 1

[0092]

[0093] From Table 1, it can be seen that:

[0094] Compared with Example 1-Example 4 and Comparative Example 2, the electrolyte of Example 3 has higher ionic conductivity, lower viscosity, smaller contact angle with the negative electrode sheet, and higher battery capacity retention. It can be seen that the additive of Example 3 can improve the ionic conductivity of the electrolyte due to the carboxyl group contained therein, thereby improving the performance of the battery. The ionic conductivity of the electrolyte of Example 1-Example 4 is higher than that of Comparative Example 2, the viscosity of the electrolyte of Example 1-Example 4 is lower than that of Comparative Example 2, the contact angle of the electrolyte of Example 1-Example 4 with the negative electrode sheet is smaller than that of Comparative Example 2, and the capacity retention of the battery of Example 1-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 performance of the battery. The additive of the present application has a chain structure, which has smaller viscosity than the cyclic structure of Comparative Example 2, thereby better reducing the viscosity of the electrolyte and improving the wettability of the electrolyte to the electrode sheet.

[0095] Compared with Example 1, Example 5-Example 10, as the amount of the phosphoramide additive 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 of the battery of Example 5 is the highest, indicating that the amount of the phosphoramide additive affects the cycle performance of the battery. Compared with Example 9, the amount of the phosphoramide additive in the electrolyte of Example 8 is higher, and the amount of the phosphoramide additive in the electrolyte of Example 9 is lower. The capacity retention of the battery of Example 8 at 2000 cycles is higher than that of Example 9, and the capacity retention of the battery of Example 8 at 3000 cycles is lower than that of Example 9. The reason is that when the amount of the phosphoramide additive is high, the SEI film grows too thick, thereby reducing the cycle performance of the battery. The capacity retention of the battery of Example 8 at 2000 cycles is higher than that of Example 9 because there are other additives in the electrolyte that can protect the negative electrode, thereby avoiding the rapid growth of the SEI film. At 3000 cycles, the other additives are basically consumed, and the high content of the phosphoramide additive causes the SEI film to grow too thick, thereby reducing the cycle performance of the battery.

[0096] Compared with Comparative Example 1, the electrolyte of the examples has higher ionic conductivity, lower viscosity, smaller contact angle with the negative electrode sheet and higher battery capacity retention rate, which shows that the phosphoramide additive of the application can effectively reduce the viscosity of the electrolyte and improve the cycle performance of the battery.

[0097] The above has described the embodiments of the application in detail, and the principles and implementation manners of the application have been described by applying specific examples. The above description of the embodiments is only used to help understand the method of the application and its core idea. Meanwhile, for those skilled in the art, the specific implementation manners and application ranges will be changed according to the idea of the application. In summary, the content of the specification should not be understood as a limitation of the application.

Claims

1. An electrolyte, characterized by, The phosphoramide additive comprises The structural formula of the phosphoramide additive is: ， wherein R1 is a carbon chain with 1-3 carbon atoms which is singly substituted by a first substituent or unsubstituted, R2 is a carbon chain with 1-3 carbon atoms which is substituted by a second substituent or unsubstituted, or a hydrogen atom, the first substituent comprises one of a fluorine atom and a carboxyl group, and the second substituent comprises one or more of a fluorine atom and a hydroxyl group; The mass content of the phosphoramide additive in the electrolyte is 0.5%-4.0%.

2. The electrolyte according to claim 1, characterized in that, The phosphoramide additive comprises , , , , and one or more of 3. The electrolyte of claim 1, wherein The electrolyte further comprises a lithium salt, the lithium salt comprises one or more of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, and lithium bis(oxalato)borate; and / or The electrolyte further comprises a lithium salt, the concentration of the lithium salt is 0.5mol / L-2.0mol / L.

4. The electrolyte of claim 1, wherein The electrolyte further comprises a solvent, the solvent comprises one or more of vinyl carbonate, methyl ethyl carbonate, diethyl carbonate, propylene carbonate, and dimethyl carbonate.

5. The electrolyte of claim 1, wherein The electrolyte further comprises 1,3-propane sultone.

6. The electrolyte according to claim 5, characterized in that The mass content of the 1,3-propane sultone in the electrolyte is 0.1%-2.0%.

7. The electrolyte of claim 1, wherein The electrolyte further comprises vinylene carbonate, and the mass content of the vinylene carbonate in the electrolyte is 0.5%-2.0%.

8. An energy storage cell, characterized by The positive electrode sheet, the negative electrode sheet, and the electrolyte as claimed in any one of claims 1-7.

9. The energy storage cell of claim 8, wherein, The active material of the positive electrode sheet comprises lithium iron phosphate; and / or The active material of the negative electrode sheet comprises graphite and silicon-carbon; and / or The active material of the negative electrode sheet comprises graphite and silicon-carbon; and / or The areal density of the positive electrode is 220 g / cm³. 2 ~260g / cm 2 The compaction density of the positive electrode sheet is 2.55 g / cm³. 3 ~2.70g / cm 3 ; and / or The face density of the negative electrode sheet is 100 g / cm 2 130 g / cm 2 The compacted density of the negative electrode sheet is 1.50 g / cm 3 1.65 g / cm 3 .

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