CN112467147A

CN112467147A - Lithium metal battery negative electrode current collector for inhibiting dendritic crystal growth and modification method thereof

Info

Publication number: CN112467147A
Application number: CN202110134452.9A
Authority: CN
Inventors: 黄现礼; 庄冬梅; 陈志辉; 王涛; 何建平
Original assignee: Nanjing University of Aeronautics and Astronautics
Current assignee: Nanjing University of Aeronautics and Astronautics
Priority date: 2021-02-01
Filing date: 2021-02-01
Publication date: 2021-03-09
Anticipated expiration: 2041-02-01
Also published as: CN112467147B

Abstract

The invention discloses a lithium metal battery negative electrode current collector for inhibiting dendrite growth and a modification method thereof, and belongs to the field of lithium battery negative electrode dendrite growth inhibition. The Cu current collector is treated accordingly to reduce "lithium dendrites" The formation of "dead lithium" and the formation of "dead lithium" can improve the coulombic efficiency and cycle life of lithium metal anodes. The present invention uses a spin coating method to modify a layer of PES film on the surface of the current collector. The PES film contains a large number of polar functional groups O=S=O. During the lithium deposition process, the polar functional groups can induce the uniform nucleation of lithium ions. In this way, the growth of lithium dendrites is inhibited; at the same time, the wettability of the electrode interface is improved, the impedance of the anode and the solid-liquid phase interface of the electrolyte is reduced, and the transport of lithium ions at the interface is improved; and the PES polymer is covered on the copper foil, which can also The direct contact between the electrode and the electrolyte is blocked, preventing the consumption of the electrolyte during the cycle.

Description

Lithium metal battery negative electrode current collector for inhibiting dendritic crystal growth and modification method thereof

Technical Field

The invention belongs to the field of dendritic crystal growth inhibition of a negative electrode of a lithium battery, and particularly relates to a negative electrode current collector of a lithium metal battery for inhibiting dendritic crystal growth and a modification method thereof.

Background

With the rapid development and application of portable charging and discharging equipment, in mobile energy storage equipment, a long-time charging interval is a new requirement for a high-energy-density battery. The lithium metal as the negative pole of the battery has extremely high theoretical specific capacity (3860 mAh^-1) 10 times or more than that of the carbon material; the new generation rechargeable battery using the metallic lithium as the negative electrode has important research value and wide application prospect. The application of lithium metal batteries with higher energy density, lithium air batteries and lithium oxygen batteries is necessary to be premised on a mature lithium metal negative electrode technology.

The main current problem of the lithium metal negative electrode is that the electrons obtained by the lithium ions under the reduction potential of lithium are transformed from an ionic state to a metallic state and deposited on a current collector, and dendritic lithium metal, namely dendritic lithium metal, is formed due to the inherent characteristics of the lithium metal and the uneven distribution of current density. The lithium dendrites often break during multiple deposition/stripping cycles to form "dead lithium" which results in loss of the lithium metal negative active material and electrolyte, resulting in a sharp decrease in reversible capacity and a rapid decay in coulombic efficiency. Meanwhile, the dendrite in the deep part of the electrolyte often reduces the strength of an electrolyte interface film (SEI) on the surface of the lithium metal negative electrode, influences the stability of the battery structure and greatly shortens the service life of the battery. In the current method for inhibiting lithium dendrite, the regulation and control of electrolyte components and the use of electrolyte additives are the most convenient schemes, however, in the actual operation process of the battery, the additives can continuously generate irreversible chemical reactions, and the effect of the additives can continuously decline. The solid electrolyte has higher Young modulus, can inhibit the growth of lithium dendrite, and can effectively improve the safety performance of the lithium cathode, but the ionic conductivity of the solid electrolyte is far lower than that of a liquid electrolyte, so that the impedance of the battery is obviously increased, and the efficiency of the battery is low.

Disclosure of Invention

The invention provides a lithium metal battery negative current collector for inhibiting dendritic crystal growth and a modification method thereof, which are used for correspondingly treating a current collector Cu, reducing the generation of 'lithium dendritic crystals' and the formation of 'dead lithium', and improving the coulombic efficiency and the cycle life of a lithium metal battery.

In order to achieve the purpose, the invention adopts the following technical scheme:

a lithium metal battery negative electrode current collector for inhibiting dendritic crystal growth is characterized in that a layer of polysulfone polar polymer film containing a polar functional group O = S = O is modified on the surface of the current collector.

A modification method of a negative electrode current collector of a lithium metal battery for inhibiting dendritic crystal growth comprises the following steps:

step 1: cutting the processed current collector into a proper size;

step 2: adding the polysulfone polar high-molecular polymer into N-N-dimethylformamide or N-methylpyrrolidone, isolating air and moisture, and naturally dissolving and standing to form a polysulfone polar high-molecular polymer-DMF or NMP mixed solution;

and step 3: uniformly coating the polysulfone polar high molecular polymer-DMF or NMP mixed solution obtained in the step 2 on the surface of the current collector obtained in the step 1;

and 4, step 4: and (3) quenching the current collector coated in the step (3) and then drying the current collector in vacuum to obtain the current collector with the surface covered by the polymer film containing the polar functional group O = S = O.

In the above step, the polysulfone polar high-molecular polymer in step 2 is Polysulfone Ether (PES), bisphenol a Polysulfone (PSU) or polyphenylene sulfone (PPSU), and the concentration of the mixed solution of the polysulfone polar high-molecular polymer and DMF or NMP is 1.3-66.7 mg/mL, preferably 3.3 mg/mL;

and 3, coating the surface of the current collector by using a spin coating method, wherein the rotation speed of the spin coating is 3500r/min, and the amount of the spin coating is 2-5 mL.

In the step 4, the quenching temperature is 100 ℃, the quenching time is 30min, the vacuum drying temperature is 80 ℃, and the drying time is 24 h.

The method for modifying the current collector is applied to a battery system taking lithium metal as a negative electrode, and comprises the following steps: lithium metal batteries, lithium sulfur batteries, lithium air battery systems.

Has the advantages that: the invention provides a lithium metal battery negative electrode current collector for inhibiting dendritic crystal growth and a modification method thereof, wherein an artificial polymer film on the surface of the current collector is adopted to protect a lithium negative electrode and inhibit dendritic crystal growth, and the distribution of lithium ion current is induced by utilizing the polar functional group S = O = S of the polymer; the method has obvious effect, and the modified negative electrode has good consistency and is convenient to operate. Modifying a layer of polysulfone polar high-molecular polymer film on the surface of the Cu electrode by using a spin-coating method, wherein the polysulfone polar high-molecular polymer film contains a large number of polar functional groups O = S = O, and the polar functional groups can induce the uniform nucleation of lithium ions in the electrodeposition process, so that the growth of lithium dendrites is inhibited; meanwhile, the wettability of an electrode interface is improved, the impedance of a negative electrode and an electrolyte solid-liquid phase interface is reduced, and the transmission of interface lithium ions is improved; and the PES high polymer covers the copper foil, so that direct contact between the electrode and the electrolyte can be prevented, the consumption of the electrolyte in the circulation process is prevented, and the coulomb efficiency and the circulation life of the battery are greatly improved. The spin-coated PES protective film is very stable, can well protect the sensitive area of the electrode from ineffective consumption of electrolyte, and is beneficial to improving the stability of the lithium metal electrode. The lithium metal half cell assembled by the current collector of the invention is at 0.5 mA cm^-2， 0.5 mAh cm^-2The charge and discharge are carried out, the average coulombic efficiency reaches 90%, and the cycle can be stably carried out for 220 circles, which is three times that of a control group; increasing the charge-discharge current density to 2.0 mA cm^-2The battery can stably circulate for 120 circles; 3.0 mA cm^-2The cell was able to cycle stably for 100 cycles. For a Li/Li symmetric cell, the Cu-PES structure has a small and stable impedance value and a longer cell cycle life of 1mA cm^-2, 1 mAh cm^-2Can be stably charged and discharged for 500 h under the condition.

Drawings

FIG. 1 is SEM images of the growth of lithium on negative electrodes of examples and comparative examples of the present invention, wherein (a) is an unmodified Cu current collector lithium deposition topography, and (b) is a Cu-PES composite current collector lithium deposition topography;

FIG. 2 is a graph showing the cycle efficiency after the current collectors of the example of the present invention and the comparative example, in which (a) is current density, were assembled into a batteryThe degree is 0.5 mA cm^-2The electric quantity is 0.5 mAh cm^-2A graph of the discharge efficiency of the cell at that time, and (b) a graph of the current density of 1.0 mA cm^-2The electric quantity is 1.0 mAh cm^-2A discharge efficiency chart of the time cell, wherein (c) is a current density of 1.0 mA cm^-2The electric quantity is 1.0 mAh cm^-2Time lithium/lithium symmetrical battery charging and discharging curve chart.

Detailed Description

The invention is described in detail below with reference to the following figures and specific examples:

preparing a Polysulfone Ether (PES), bisphenol A Polysulfone (PSU) or polyphenylene sulfone (PPSU) -DMF or NMP mixed solution:

0.04 g, 0.1 g, 0.16 g, 0.3 g, 2 g of Polysulfone Ether (PES), bisphenol A type Polysulfone (PSU) or polyphenylene sulfone (PPSU) was weighed and added to 30 mL of N-N-Dimethylformamide (DMF) or NMP, respectively, to form a Polysulfone Ether (PES), bisphenol A type Polysulfone (PSU) or polyphenylene sulfone (PPSU) -DMF or NMP mixed solution having a mass concentration of 1.3 mg/mL, 3.3 mg/mL, 5.3 mg/mL, 10 mg/mL, 66.7 mg/mL, respectively, to be dissolved naturally.

Modifying a current collector:

cutting a copper foil with a polished single surface and a clean and tidy surface into a square with the side length of 5 cm, spin-coating Polysulfone Ether (PES), bisphenol A Polysulfone (PSU) or polyphenylene sulfone (PPSU) -DMF or NMP mixed solution with different concentrations on the surface of the copper foil, putting the copper foil in a muffle furnace for quenching at 100 ℃, transferring a sample into a vacuum drying oven after 30min, and drying at 80 ℃ for 24h to cover the surface of the copper with a polymer film containing a polar functional group O = S = O;

preparation of lithium metal battery:

under the protection of an Ar atmosphere glove box, assembling the modified copper current collector composite electrode into a half cell, and dropwise adding 70 microliter of 1mol/L LiPF₆The EC/DMC electrolyte of (1) is charged for the first time at a given current, followed by a charge-discharge cycle.

Example 1

In the embodiment, the PES precursor solution subjected to spin coating is a polyether sulfone-DMF mixed solution with the mass concentration of 1.3 mg/mL; after drying under vacuum, at that concentrationThe modified Cu-PES composite electrode is used as a substrate, and the anode is a lithium sheet; the current density of the cathode of the half cell is 0.5 mA cm^-2(ii) a Electricity 1 mAh cm^-2。

Example 2

In the embodiment, the PES precursor solution subjected to spin coating is a polyether sulfone-DMF mixed solution with the mass concentration of 3.3 mg/mL; after vacuum drying, taking the Cu-PES composite electrode modified under the concentration as a substrate, and taking a lithium sheet as an anode; the current density of the cathode of the half cell is 0.5 mA cm^-2(ii) a Electricity 1 mAh cm^-2。

Example 3

In the embodiment, the PES precursor solution subjected to spin coating is a polyether sulfone-DMF mixed solution with the mass concentration of 5.3 mg/mL; after vacuum drying, taking the Cu-PES composite electrode modified under the concentration as a substrate, and taking a lithium sheet as an anode; the current density of the cathode of the half cell is 0.5 mA cm^-2(ii) a Electricity 1 mAh cm^-2。

Example 4

In this embodiment, the PES precursor solution for spin coating is a polyethersulfone-DMF mixed solution with a mass concentration of 66.7 mg/mL; after vacuum drying, taking the Cu-PES composite electrode modified under the concentration as a substrate, and taking a lithium sheet as an anode; the current density of the cathode of the half cell is 0.5 mA cm^-2(ii) a Electricity 1 mAh cm^-2。

Example 5

In this example, the spin-coated bisphenol a Polysulfone (PSU) precursor solution was a bisphenol a polysulfone-DMF mixed solution with a mass concentration of 3.3 mg/mL; after vacuum drying, taking the Cu-PSU composite electrode modified under the concentration as a substrate, and taking a lithium sheet as an anode; the current density of the cathode of the half cell is 0.5 mA cm^-2(ii) a Electricity 1 mAh cm^-2。

Example 6

In this embodiment, the PES precursor solution for spin coating is a mixed solution of polyethersulfone-N-methylpyrrolidone (NMP) with a mass concentration of 3.3 mg/mL; after vacuum drying, taking the Cu-PES composite electrode modified under the concentration as a substrate, and taking a lithium sheet as an anode; the current density of the cathode of the half cell is 0.5 mA cm^-2(ii) a Electricity 1 mAh cm^-2。

Example 7

In this embodiment, the screwThe coated PES precursor solution is a polyether sulfone-DMF mixed solution with the mass concentration of 3.3 mg/mL; after vacuum drying, taking the Cu-PES composite electrode modified under the concentration as a substrate, and taking a lithium sheet as an anode; the current density of the cathode of the half cell is 1mA cm^-2(ii) a Electricity 1 mAh cm^-2。

Example 8

In the embodiment, the PES precursor solution subjected to spin coating is a polyether sulfone-DMF mixed solution with the mass concentration of 3.3 mg/mL; after vacuum drying, taking the Cu-PES composite electrode modified under the concentration as a substrate, and taking a lithium sheet as an anode; the current density of the cathode of the half cell is 2 mA cm^-2(ii) a Electric quantity of 2 mAh cm^-2. The rest is the same as example 1.

Comparative example 1

Preparation of lithium metal battery:

under the protection of an Ar atmosphere glove box, a commercial copper current collector and a lithium sheet are assembled into a half cell, and 70 microliter of 1mol/L LiPF is dropwise added₆The EC/DMC electrolyte of (1) is charged for the first time at a given current, followed by a charge-discharge cycle.

In the comparative example, the copper foil surface is coated with the DMF mixed solution without polyether sulfone; the current density of the cathode of the half cell is 0.5 mA cm^-2(ii) a Electricity 1 mAh cm^-2。

Comparative example 2

Preparation of lithium metal battery:

In the present comparative example, in the present example, the surface of the copper foil was not subjected to any treatment; the current density of the cathode of the half cell is 0.5 mA cm^-2(ii) a Electricity 1 mAh cm^-2。

The lithium growth topography of the current collectors of the above examples and comparative examples is shown in fig. 1, fig. 1(a) is an unmodified Cu current collector lithium deposition topography, and fig. 1(b) is a Cu-PES composite current collector lithium deposition topography obtained by spin coating with a polyethersulfone-DMF mixed solution with a mass concentration of 3.3 mg/mL. The current density was 1mA cm^-2Electric quantity is1 mAh cm^-2It can be seen that a large number of dendritic lithium dendrites grew over the unmodified Cu current collector; the Cu-PES composite current collector modified by the polyether sulfone-DMF mixed solution is subjected to electrodeposition, dendritic lithium dendrites are not generated, and compact nano-particle columnar lithium is formed, so that polyether sulfone can induce uniform nucleation of lithium ions, and the growth of the lithium dendrites is well inhibited.

The battery cycling efficiency is shown in FIG. 2, and it can be seen that the current density is 0.5 mA cm^-20.5 mAh cm of electric quantity^-2In the case (as shown in fig. 2 (a)), the coulombic efficiency of the Li-Cu half cell assembled by the unmodified Cu current collector is reduced sharply when the Li-Cu half cell circulates for 60 cycles, while the cell assembled by the copper foil modified by the polyethersulfone-DMF mixed solution has higher discharge efficiency and longer service life, the PES concentration is 3.3 mg/mL, the cell can stably circulate for 230 cycles, and the number of effective charge-discharge cycles is more than 3 times that of the unmodified half cell. The current density was 1mA cm^-2(ii) a Electricity 1 mAh cm^-2In this case (see FIG. 2 (b)), it can be seen that the cycle life and cycle efficiency of the Cu-PES composite current collector modified by the polyethersulfone-DMF mixed solution with the mass concentration of 3.3 mg/mL are also the best. For a lithium symmetric cell (as shown in fig. 2 (c)), it can be found that the voltage polarization rapidly increases and the cell fails when the control system is cycled for 220 h, while the Cu-PES structure has a more stable impedance value and a longer battery cycle life of 1mA cm^-2， 1 mAh cm^-2Can be stably charged and discharged for 500 h under the condition. In conclusion, the Cu-PES composite current collector obtained by spin-coating the polyether sulfone-DMF mixed solution provided by the invention has an active effect on uniform deposition of a metal lithium cathode, can better inhibit dendritic crystal growth in a lithium ion deposition stripping process, enables electrodeposition of lithium metal on a cathode to be more uniform, and can greatly improve the coulombic efficiency and stability of the lithium metal battery cathode.

While the foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. a method for modifying the negative electrode current collector of a lithium metal battery for suppressing dendrite growth, is characterized in that, comprises the following steps:

Step 1: Cut the processed current collector to an appropriate size;

Step 2: Add the polysulfone polar polymer to N-N-dimethylformamide or N-methylpyrrolidone, isolate the air and moisture, and let it dissolve naturally and stand to form a polysulfone with high polarity. Molecular polymer-DMF or NMP mixed solution;

Step 3: evenly coat the polysulfone polar polymer-DMF or NMP mixed solution obtained in step 2 on the surface of the current collector obtained in step 1;

Step 4: The current collector coated in step 3 is quenched and then vacuum-dried to obtain a current collector whose surface is covered with a polymer film containing polar functional groups O=S=O.

2 . The method for modifying the negative electrode current collector of a lithium metal battery for inhibiting dendrite growth according to claim 1 , wherein the polysulfone polar polymer is polysulfone ether, bisphenol A type poly Sulfone, polyphenylene sulfone.

3. The method for modifying the negative electrode current collector of a lithium metal battery for suppressing dendrite growth according to claim 2, wherein the concentration of the polysulfone polar polymer-DMF or NMP mixed solution described in step 2 1.3~66.7 mg/mL.

4. The method for modifying the negative electrode current collector of a lithium metal battery for suppressing dendrite growth according to claim 3, wherein the concentration of the polysulfone polar polymer-DMF or NMP mixed solution described in step 2 was 3.3 mg/mL.

5 . The method for modifying the negative electrode current collector of a lithium metal battery for inhibiting dendrite growth according to claim 1 , wherein in step 3, the surface of the current collector is coated by a spin coating method. 6 .

6 . The method for modifying the negative electrode current collector of a lithium metal battery for suppressing dendrite growth according to claim 5 , wherein the rotational speed of the spin coating is 3500 r/min, and the amount of the spin coating solution is 2˜5 mL. 7 .

7. The method for modifying the negative electrode current collector of a lithium metal battery for suppressing dendrite growth according to claim 1, wherein in step 4, the quenching temperature is 100°C, the quenching time is 30min, and the vacuum drying temperature is 80°C, Drying time is 24h.

8. The negative electrode current collector of a lithium metal battery for inhibiting dendrite growth prepared by any one of the methods of claims 1-7, wherein the surface of the current collector is modified with a layer of polymer film containing polar functional groups O=S=O .

9 . The negative electrode current collector for lithium metal batteries for inhibiting dendrite growth according to claim 8 , wherein the polymer is a polysulfone-based polar polymer. 10 .

10 . The negative electrode current collector of lithium metal battery for inhibiting dendrite growth according to claim 9 is applied to a lithium metal battery, a lithium sulfur battery or a lithium air battery system. 11 .