Negative pole piece, preparation method thereof and secondary battery

Abstract

The invention provides a negative pole piece, a preparation method thereof and a secondary battery. The negative pole piece comprises a current collector layer, and a modified layer and a negative active material layer which are sequentially stacked on at least one side of the current collector layer; and the material of the modified layer comprises a polymer of benzodifuran and derivatives thereof. The negative pole piece provided by the invention not only can effectively reduce the nucleation overpotential of lithium ion deposition, but also can inhibit the growth of lithium dendrites, so that the electrochemical performance of the lithium metal secondary battery is improved.

Description

Technical Field

[0001] The present invention belongs to the field of negative electrode materials, and in particular relates to a negative electrode sheet and a preparation method thereof, and a secondary battery. Background Art

[0002] Lithium metal anode is considered to be one of the ideal anode materials in high-energy-density battery systems because of its low reduction potential (-3.04V vs. standard hydrogen electrode) and extremely high theoretical specific capacity (3860mAh / g). Copper current collectors are usually used as anodes in lithium metal secondary batteries. However, copper has poor affinity for lithium ions, which leads to excessively high nucleation potential when lithium ions are deposited on the surface of copper current collectors, which easily induces the formation of lithium dendrites, thereby damaging the electrochemical performance and safety of lithium metal secondary batteries. The above factors have seriously hindered the commercial application of lithium metal secondary batteries.

[0003] In view of the above problems, designing a conductive coating is an effective method to improve the performance of lithium metal negative electrodes. For example, CN108713267A discloses a negative electrode including multiple protective layers of conductive polymers. The multiple protective layers prevent lithium dendrites from growing on the electrode surface, and since the protective layer itself does not act as a resistance layer, it does not cause overpotential during charging and discharging. Therefore, it can prevent battery performance from decreasing and ensure stability when operating the battery. Conductive polymers can be divided into p-type conductive polymers and n-type conductive polymers according to the type of doping. Although the p-type conductive polymers currently used can achieve ultra-high conductivity, such as polyacetylene, the conductivity of the material after doping can reach more than 1000S / cm, but lithium metal is more conducive to n-type doping due to its strong reducibility. However, the conductivity of conventional n-type conductive polymers is generally low, and the conductivity of the material after doping is usually less than 100S / cm. In addition, the lithium metal negative electrode obtained by modifying the above conventional conductive polymer cannot effectively solve the technical problem of lithium dendrites in lithium metal secondary batteries.

[0004] Therefore, it is urgent to develop a lithium metal negative electrode material to solve the above problems. Summary of the invention

[0005] In view of the shortcomings of the prior art, the object of the present invention is to provide a negative electrode plate and a preparation method thereof and a secondary battery. The negative electrode plate provided by the present invention can not only effectively reduce the nucleation overpotential of lithium ion deposition, but also inhibit the growth of lithium dendrites, thereby improving the electrochemical performance of lithium metal secondary batteries.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a negative electrode plate, the negative electrode plate comprising a current collector layer and a modified layer and a negative electrode active material layer sequentially stacked on at least one side of the current collector layer;

[0008] The material of the modified layer includes polymers of benzodifuran and its derivatives.

[0009] The present invention designs the structure and composition of the negative electrode plate, and arranges a conductive polymer modified layer containing benzodifuran and its derivatives on at least one side of the current collector layer. The material of the conductive polymer modified layer is an n-type conductive polymer formed by in-situ polymerization. At the same time, since lithium metal has extremely high reducibility, it can realize the electron transfer process between the main chain of the n-type conductive polymer. This process greatly improves the n-type doping efficiency of the polymer in the modified layer, and finally forms a polymer modified layer with high conductivity, thereby effectively reducing the nucleation overpotential in the lithium ion deposition process, and inducing lithium ions to deposit more uniformly.

[0010] The secondary battery assembled by using the negative electrode plate provided by the present invention benefits from the excellent characteristics of the negative electrode plate, so that its coulombic efficiency is significantly improved.

[0011] In the present invention, the modified layer is disposed on the surface of at least one side of the current collector layer, and the negative electrode active material layer is disposed on the surface of the modified layer away from the current collector layer.

[0012] Preferably, the structural formula of the benzodifuran and its derivatives is as shown in Formula I:

[0013]

[0014] Wherein, the dotted line is selected from a single bond or a double bond, when the dotted line is selected from a single bond, R1 is selected from any one of -H or methyl; when the dotted line is selected from a double bond, R1 is selected from a carbonyl group;

[0015] R2 is selected from any one of -H, methyl, alkylamine group, alkanoyl group or halogen atom, and R3 is selected from any one of -H, methyl, alkylamine group, alkanoyl group or halogen atom.

[0016] Preferably, the benzodifuran and its derivatives include at least one compound as shown below:

[0017]

[0018]

[0019] Among them, the CAS number of compound 1 is 81926-24-1; the CAS number of compound 2 is 30272-74-3; the CAS number of compound 3 is 178557-13-6; the CAS number of compound 4 is 774160-87-1; the CAS number of compound 5 is 733720-95-1; the CAS number of compound 6 is 219986-80-8; the CAS number of compound 7 is 178557-19-2; and the CAS number of compound 8 is 94883-25-7, so the above compounds can be purchased commercially.

[0020] Preferably, the thickness of the modified layer is 2-10 μm, preferably 5 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm. The present invention adjusts the thickness of the modified layer so that the modified lithium metal negative electrode can have both high conductivity and high lithium affinity, thereby reducing the deposition overpotential of lithium ions and ultimately inhibiting the formation of lithium dendrites. If the thickness of the modified layer is low, the lithium affinity of the lithium metal negative electrode will be insufficient and the deposition overpotential of lithium ions will be high. Conversely, the conductivity of the lithium metal negative electrode will be low and the deposition overpotential of lithium ions will be high.

[0021] Preferably, the material of the negative electrode active material layer includes lithium metal.

[0022] In a second aspect, the present invention provides a method for preparing the negative electrode sheet according to the first aspect, the method comprising the following steps:

[0023] Applying a solution containing benzodifuran and its derivatives on at least one side of the current collector layer to obtain a modified layer after a polymerization reaction;

[0024] A negative electrode active material layer is compounded on the surface of the modified layer to obtain the negative electrode plate.

[0025] Preferably, the solution containing benzodifuran and its derivatives further comprises an oxidant and a solvent.

[0026] Preferably, the oxidant comprises any one of p-benzoquinone, tetramethylbenzoquinone, tetrahydroxybenzoquinone or p-dimethylquinone, preferably tetramethylbenzoquinone.

[0027] Preferably, the solvent comprises a polar aprotic solvent.

[0028] Preferably, the polar aprotic solvent includes any one of dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP) or N,N-dimethylformamide (DMF).

[0029] Preferably, the mass ratio of the benzodifuran and its derivatives to the oxidant is 1:(1-2), preferably 1:1.5, for example, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, etc. The present invention adjusts the mass ratio of benzodifuran and its derivatives to the oxidant so that the modified layer obtains suitable conductivity. If the mass ratio of benzodifuran and its derivatives to the oxidant is low, it will lead to incomplete polymerization, resulting in low conductivity of the modified layer. On the contrary, it will cause more oxidants to remain in the system, which will also lead to low conductivity of the modified layer.

[0030] In the present invention, the coating method exemplarily includes any one of blade coating, wire rod coating, micro gravure coating, dip coating, spin coating or spray coating.

[0031] Preferably, the polymerization reaction is carried out under an inert atmosphere, which exemplarily includes at least one of argon or nitrogen.

[0032] Preferably, the polymerization reaction temperature is 100-120°C, for example, 100°C, 105°C, 110°C, 115°C, 120°C, etc., and the reaction time is 1-3h, for example, 1h, 1.5h, 2h, 2.5h, 3h, etc.

[0033] In the present invention, after the polymerization reaction is completed, washing and drying treatment is also included. Specifically, the collector after the polymerization reaction is taken out and washed with ether for 3 times, and then vacuum dried. The vacuum drying temperature is 40-60°C, preferably 50°C, for example, it can be 40°C, 45°C, 50°C, 55°C, 60°C, etc.; the time is 4-6h, preferably 5h, for example, it can be 4h, 4.5h, 5h, 5.5h, 6h, etc.

[0034] Preferably, the thickness of the negative electrode active material layer is 1-20 μm, preferably 10 μm, for example, 1 μm, 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, etc.

[0035] In a third aspect, the present invention provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the negative electrode sheet comprises the negative electrode sheet according to the first aspect.

[0036] The secondary battery assembled by using the negative electrode plate provided by the present invention benefits from the excellent characteristics of the negative electrode plate, so that its coulombic efficiency is significantly improved.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The present invention provides a negative electrode plate. The present invention designs the structure and composition of the negative electrode plate, and arranges a conductive polymer modified layer containing benzodifuran and its derivatives on at least one side of the current collector layer. The material of the conductive polymer modified layer is an n-type conductive polymer formed by in-situ polymerization. At the same time, since lithium metal has extremely high reducibility, it can realize the electron transfer process between the main chain of the n-type conductive polymer. This process greatly improves the n-type doping efficiency of the polymer in the modified layer, and finally forms a polymer modified layer with high conductivity, thereby effectively reducing the nucleation overpotential in the lithium deposition process, and inducing lithium ions to deposit more uniformly.

[0039] The secondary battery assembled by using the negative electrode plate provided by the present invention benefits from the excellent characteristics of the negative electrode plate, so that its coulombic efficiency is significantly improved. DETAILED DESCRIPTION

[0040] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0041] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0042] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0043] Example 1

[0044] This embodiment provides a negative electrode plate, which includes a copper current collector layer and a modified layer and a lithium metal layer stacked in sequence on one side of the copper current collector layer; the material of the modified layer includes a polymer of compound 1 (CAS: 81926-24-1).

[0045] This embodiment also provides a method for preparing the above-mentioned negative electrode sheet, which comprises the following steps:

[0046] S1. Add 4 g of compound 1 (CAS: 81926-24-1) and 6 g of tetramethylbenzoquinone into 100 mL of dimethyl sulfoxide (DMSO), respectively, and stir to obtain a solution containing benzodifuran and its derivatives;

[0047] S2, coating the solution containing benzodifuran and its derivatives on the surface of the copper current collector by wire rod coating, and maintaining the polymerization reaction at 100°C in an argon atmosphere for 1 hour. After the polymerization reaction is completed, the current collector is taken out and washed with ether three times, and dried at 50°C under vacuum for 5 hours to obtain a copper current collector with a modified layer with a thickness of 5 μm;

[0048] S3, rolling a lithium ribbon onto the surface of the modified layer on the copper current collector obtained in step S2 to obtain a negative electrode sheet with a lithium metal layer having a thickness of 10 μm.

[0049] Example 2

[0050] This embodiment provides a negative electrode plate, which includes a copper current collector layer and a modified layer and a lithium metal layer stacked in sequence on one side of the copper current collector layer; the material of the modified layer includes a polymer of compound 2 (CAS: 30272-74-3).

[0051] This embodiment also provides a method for preparing the above-mentioned negative electrode sheet, which comprises the following steps:

[0052] S1. Add 4 g of compound 2 (CAS: 30272-74-3) and 6 g of tetramethylbenzoquinone into 100 mL of dimethyl sulfoxide (DMSO), respectively, and stir to obtain a solution containing benzodifuran and its derivatives;

[0053] S2, coating the solution containing benzodifuran and its derivatives on the surface of the copper current collector by wire rod coating, and maintaining the polymerization reaction at 100°C in an argon atmosphere for 1 hour. After the polymerization reaction is completed, the current collector is taken out and washed with ether three times, and dried at 50°C under vacuum for 5 hours to obtain a copper current collector with a modified layer with a thickness of 5 μm;

[0054] S3, rolling a lithium ribbon onto the surface of the modified layer on the copper current collector obtained in step S2 to obtain a negative electrode sheet with a lithium metal layer having a thickness of 10 μm.

[0055] Example 3

[0056] The difference between this embodiment and embodiment 1 is that in step S1, compound 1 is replaced by compound 3 (CAS: 178557-13-6) of equal mass, and the rest is the same as embodiment 1.

[0057] Example 4

[0058] The difference between this embodiment and embodiment 1 is that in step S1, compound 1 is replaced by compound 5 (CAS: 733720-95-1) of equal mass, and the rest is the same as embodiment 1.

[0059] Example 5

[0060] The difference between this embodiment and embodiment 1 is that in step S1, compound 1 is replaced by compound 8 (CAS: 94883-25-7) of equal mass, and the rest is the same as embodiment 1.

[0061] Example 6

[0062] The difference between this embodiment and embodiment 1 is that in step S1, half the mass of compound 1 is replaced by an equal mass of compound 2 (CAS: 30272-74-3), and the rest is the same as embodiment 1.

[0063] Example 7

[0064] The difference between this embodiment and embodiment 1 is that the thickness of the modified layer is 2 μm, and the rest is the same as embodiment 1.

[0065] Example 8

[0066] The difference between this embodiment and embodiment 1 is that the thickness of the modified layer is 10 μm, and the rest is the same as embodiment 1.

[0067] Comparative Example 1

[0068] This comparative example provides a method for preparing a negative electrode sheet, and the specific steps are as follows:

[0069] S1. Add 4 g of polyaniline into 100 mL of dimethyl sulfoxide (DMSO) and stir to obtain a polyaniline solution;

[0070] S2, coating the polyaniline solution on the surface of the copper current collector by wire rod coating, and drying at 100° C. for 2 h under vacuum to obtain a copper current collector provided with a polyaniline layer;

[0071] S3, rolling a lithium ribbon onto the surface of the polyaniline layer on the copper current collector obtained in step S2 to obtain a negative electrode sheet with a lithium metal layer having a thickness of 10 μm.

[0072] Comparative Example 2

[0073] This comparative example provides a method for preparing a negative electrode sheet, and the specific steps are as follows:

[0074] S1. Add 4 g of polypyrrole into 100 mL of dimethyl sulfoxide (DMSO) and stir to obtain a polypyrrole solution;

[0075] S2, coating the polypyrrole solution on the surface of the copper current collector by wire rod coating, and drying at 100° C. for 2 h under vacuum to obtain a copper current collector provided with a polypyrrole layer;

[0076] S3, rolling a lithium ribbon onto the surface of the polypyrrole layer on the copper current collector obtained in step S2 to obtain a negative electrode sheet with a lithium metal layer having a thickness of 10 μm.

[0077] Comparative Example 3

[0078] This comparative example provides a method for preparing a negative electrode sheet, and the specific steps are as follows:

[0079] The lithium strip was rolled onto an unmodified copper current collector to obtain a negative electrode sheet with a lithium metal layer having a thickness of 10 μm.

[0080] Test conditions

[0081] The negative electrode sheets provided in Examples 1-8 and Comparative Examples 1-3 were subjected to performance tests, and the test methods were as follows:

[0082] by 2400 is used as a diaphragm, the electrolyte is LiFSI with a concentration of 1.2 mol / L dissolved in a mixed solution of DME and TTE, DME:TTE=1:1 (volume ratio), the negative electrode provided in Example 1 is used as a working electrode, and the lithium sheet is used as a counter electrode to assemble a button battery with a model number of 2032, which is named Application Example 1, and then Examples 2-8 and Comparative Examples 1-3 are assembled into button batteries with a model number of 2032 according to the above method, which are named Application Examples 2-8 and Comparative Application Examples 1-3 respectively.

[0083] Test method (using application example 1 as an example): ① 0.5mA / cm 2 ② Deposit 10 mAh of lithium onto the negative electrode provided in Example 1 at a current density of 0.5 mA / cm 2 10 mAh of lithium was deposited onto the negative electrode sheet provided in Example 1 at a current density of 0.5 mA / cm 2 ④ At a current density of 0.5 mA / cm 2 The deposited lithium is stripped off at a current density of 10000 Nm and charged to 1 V (capacity Qs);

[0084] Average coulombic efficiency = (200 + Qs) / (200 + 10) × 100%.

[0085] The test results are shown in Table 1:

[0086] Table 1

[0087]

[0088]

[0089] It can be seen from Table 1 that the lithium metal secondary battery using the negative electrode plate provided by the present invention can effectively reduce the nucleation overpotential of lithium deposition, induce uniform deposition of lithium ions, and inhibit the formation of lithium dendrites, thereby obtaining high coulombic efficiency.

[0090] Application Examples 1-5 show that the modified layer prepared by using benzodifuran and its derivatives with specific structures and substituent groups of the present invention has high conductivity and lithium affinity, so that the assembled lithium metal secondary battery has both low overpotential and high coulombic efficiency. In addition, Application Example 6 shows that the combination of multiple benzodifuran and its derivatives can further improve the comprehensive performance of lithium metal secondary batteries.

[0091] Application Examples 7-8 show that the present invention adjusts the thickness of the modified layer so that the modified lithium metal negative electrode can have both high conductivity and high lithium affinity, thereby reducing the deposition overpotential of lithium ions and ultimately inhibiting the formation of lithium dendrites.

[0092] Comparing Application Example 1 and Comparative Application Example 1-2, it can be seen that since Comparative Application Example 1-2 uses p-type conductive polymer, and highly reducing lithium has a poor doping effect on it, resulting in low conductivity of the modified layer and high deposition overpotential, the assembled lithium metal secondary battery exhibits a lower coulombic efficiency.

[0093] By comparing Application Example 1 and Comparative Application Example 3, it can be seen that when no modification layer is provided, the deposition overpotential of lithium on the surface of the bare copper current collector layer is relatively high, which is extremely unfavorable for the uniform deposition of lithium ions, resulting in the worst coulombic efficiency of the assembled lithium metal secondary battery.

[0094] The applicant declares that the present invention illustrates the process method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A negative electrode plate, characterized in that: The negative electrode plate includes a current collector layer and a modified layer and a negative electrode active material layer stacked in sequence on at least one side of the current collector layer; The material of the modified layer includes polymers of benzodifuran and its derivatives.

2. The negative electrode sheet according to claim 1, characterized in that: The structural formula of the benzodifuran and its derivatives is shown in Formula I: Wherein, the dotted line is selected from a single bond or a double bond, when the dotted line is selected from a single bond, R1 is selected from any one of -H or methyl; when the dotted line is selected from a double bond, R1 is selected from a carbonyl group; R2 is selected from any one of -H, methyl, alkylamine group, alkanoyl group or halogen atom, and R3 is selected from any one of -H, methyl, alkylamine group, alkanoyl group or halogen atom.

3. The negative electrode sheet according to claim 2, characterized in that: The benzodifuran and its derivatives include at least one compound as shown below:

4. The negative electrode sheet according to any one of claims 1 to 3, characterized in that: The thickness of the modified layer is 2-10 μm, preferably 5 μm; Preferably, the material of the negative electrode active material layer includes lithium metal.

5. A method for preparing a negative electrode sheet according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: Coating a solution containing benzodifuran and its derivatives on at least one side of the current collector layer to obtain a modified layer after a polymerization reaction; A negative electrode active material layer is compounded on the surface of the modified layer to obtain the negative electrode plate.

6. The method according to claim 5, characterized in that The solution containing benzodifuran and its derivatives also includes an oxidant and a solvent; Preferably, the oxidant comprises any one of p-benzoquinone, tetramethylbenzoquinone, tetrahydroxybenzoquinone or p-dimethylquinone, preferably tetramethylbenzoquinone; Preferably, the solvent comprises a polar aprotic solvent; Preferably, the polar aprotic solvent includes any one of dimethyl sulfoxide, N-methylpyrrolidone or N,N-dimethylformamide.

7. The method according to claim 6, characterized in that The mass ratio of the benzodifuran and its derivatives to the oxidant is 1:(1-2), preferably 1:1.

5.

8. The method according to any one of claims 5 to 7, characterized in that: The polymerization reaction is carried out under an inert atmosphere; Preferably, the polymerization reaction temperature is 100-120° C. and the time is 1-3 h.

9. The method according to any one of claims 5 to 8, characterized in that: The thickness of the negative electrode active material layer is 1-20 μm, preferably 10 μm.

10. A secondary battery, characterized in that: The secondary battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, and the negative electrode sheet comprises the negative electrode sheet according to any one of claims 1 to 4.

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