CN113097647B

CN113097647B - High-voltage lithium ion battery

Info

Publication number: CN113097647B
Application number: CN202110193143.9A
Authority: CN
Inventors: 吕东生; 伍思泳; 李灿煌; 丘奕靖
Original assignee: South China Normal University
Current assignee: South China Normal University
Priority date: 2021-02-20
Filing date: 2021-02-20
Publication date: 2022-06-07
Anticipated expiration: 2041-02-20
Also published as: CN113097647A

Abstract

The invention discloses a high-voltage lithium ion battery, which adopts a lithiated porous PVDF (polyvinylidene fluoride) based diaphragm, wherein the diaphragm can absorb and adsorb electrolyte oxidation products from a high-voltage positive electrode so as to prevent the electrolyte oxidation products from migrating to a negative electrode, ensure that the negative electrode can normally insert and remove lithium ions, prolong the cycle life of the battery, and improve the interface performance of the electrode/electrolyte because the porous PVDF diaphragm has good compatibility with carbonate electrolyte.

Description

High-voltage lithium ion battery

The technical field is as follows:

the invention relates to a lithium ion battery, in particular to a high-voltage lithium ion battery.

Background art:

lithium nickel manganese (LiNi) as positive electrode material of lithium ion battery_0.5Mn_1.5O₄) High energy density (650W.h/Kg) and long cycle life at high voltage (4.9V, vs Li/Li +), and is considered to be a potential cathode material for future development. The working voltage of the lithium ion battery formed by the lithium ion battery and the carbon cathode can reach about 4.6V, and the energy density is 20-30% higher than that of the common lithium ion battery. However, the current commercial carbonate electrolyte can be oxidized and decomposed on a high-voltage positive electrode, and the decomposition product is transferred to a negative electrode and reduced, so that the negative electrode cannot normally insert and remove lithium ions, and finally, the capacity of the battery is rapidly reduced.

To address the above issues, current strategies include material coatings, electrolyte additives, and new electrolytes. The existing research results show that the cycle life of the lithium nickel manganese oxide/lithium metal half battery can be prolonged to a certain extent by coating the surface of the lithium nickel manganese oxide, but the cycle life of the high-voltage lithium nickel manganese oxide/carbon lithium ion battery cannot be effectively prolonged. The effect of the electrolyte additive enhancement is also limited. The novel electrolyte mainly refers to polymer electrolyte, high-concentration lithium salt electrolyte and the like, and the comprehensive properties (such as cost, interface stability, viscosity and the like) of the electrolyte cannot meet the requirements of practical application.

The commonly used lithium ion battery diaphragm is polypropylene (PP), Polyethylene (PE) or a combined diaphragm, the combination property of the diaphragm is strong, but the thermal stability and the electrolyte affinity of the diaphragm still have a space for improving. More importantly, the commercial separator does not have functionality, and cannot solve the problems existing in the commercialization of the high-voltage lithium ion battery, such as electrolyte decomposition at the cathode, nickel and manganese ions in the anode dissolving out, and migration to the cathode, and SEI film on the surface being damaged. Many scholars modify commercial membranes and hope to make up for the deficiencies.

The Jeahao Lin coats the CoP/C on the PP to ensure that the PP has functionality, the porous structure of the CoP/C increases the specific surface and can provide a position for capturing polysulfide, and the polar CoP/C can be chemically bonded with sulfur through cobalt to effectively reduce the shuttle effect 1. The MinaHan produced a uniform film on the PE by plasma induced grafting. The graft polymer has amphiphilicity, the positive charge enhances the conductivity of lithium ions through repulsion, and the negative charge attraction can facilitate lithium ion migration, thereby protecting the stability of the SEI film 2. After all, the connection capacity between the membrane and the coating is not very tight after the modification is carried out on the basis of the original commercial membrane. Also, non-uniform thickness at the surface is a common problem, too thick increasing the internal resistance of the cell, and too thin not functioning during long cycling.

In recent years, it is also a trend to make the separator electrolyte all solid. The Panlong Guo fixes lithium salt in hydrogen bond supermolecular polymer, and can prepare self-repairing, flame-retardant and high-conductivity solid electrolyte. Since the electrostatic interaction between the charged imidazole groups and the TFSI-groups in the lithium salt can repair mechanical damage in the copolymer. Although the solid electrolyte has good safety performance and is not inflammable, the growth of lithium dendrite of the cathode is reduced, and the energy density is high. However, the solid electrolyte has weak fluidity, low ion mobility and excessively high interfacial resistance, so that the solid electrolyte is obviously insufficient for high-rate charge and discharge, and meanwhile, the material cost is higher, and the solid electrolyte has long road resistance for a commercial road.

The invention content is as follows:

the invention aims to provide a high-voltage lithium ion battery, which adopts a lithiated porous PVDF (polyvinylidene fluoride) -based diaphragm, wherein the diaphragm can absorb and adsorb electrolyte oxidation products from a high-voltage positive electrode so as to prevent the electrolyte oxidation products from migrating to a negative electrode, ensure that the negative electrode can normally insert and remove lithium ions, and prolong the cycle life of the battery.

The invention is realized by the following technical scheme:

a high-voltage lithium ion battery comprises a lithium nickel manganese oxide positive electrode, a graphite negative electrode, electrolyte and a diaphragm, wherein the diaphragm is prepared by the following method: dissolving polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP) and an additive in N-methyl pyrrolidone, magnetically stirring in a water bath kettle at 60 ℃ until the PVDF, the PVP and the additive are completely dissolved, clarifying and transparent the solution, pouring the solution on the smooth surface of an aluminum foil, coating by using a 100-micrometer scraper, standing for 4-6min, soaking in distilled water by a phase transfer method, soaking for 24h, taking out, placing in a vacuum drying oven at 60 ℃ for more than 8h, and cutting into a diaphragm with the diameter of 14 mm; placing the prepared diaphragms in a glove box, activating each diaphragm by 1mL of n-butyllithium for 12h, taking out, washing by n-hexane and dimethyl carbonate respectively, waiting for 3h to completely volatilize the solvent, and assembling into a battery; the mass ratio of polyvinylidene fluoride (PVDF) to polyvinylpyrrolidone (PVP) is 10: 1-10: 3; the additive is selected from one of benzoic acid, terephthalic acid, trimesic acid, anthraquinone, 1-aminoanthraquinone, 1, 8-dihydroxyanthraquinone, titanium dioxide, tin dioxide, nickel oxide, cobalt oxide, ferric oxide, manganese dioxide, titanium sulfide and iron sulfide, and the mass fraction of the additive is 1-5%.

The electrolyte is 1mol L^-1LiPF₆Dissolving in a mixed solvent of ethylene carbonate EC and ethyl methyl carbonate EMC with a volume ratio of 3:7 to obtain the product.

Polyvinylpyrrolidone PVP is used as a pore-forming agent, the PVP is very soluble in water in the phase transfer process, and small holes with the aperture of 2um are left on PVDF after the PVP is removed and dissolved in water. In fact, the dissolution of PVDF in NMP is carried out in two steps, the first step: the PVDF has hydrogen bonds between molecules and C-H-F. When the PVDF and the NMP are mixed and heated to 60 ℃, most of hydrogen bonds in the PVDF and among molecules are broken by heat, meanwhile, the NMP moving speed of solvent molecules is higher than that of polymer molecules, and the NMP molecules rapidly move among the PVDF molecules, so that the volume is increased, and the swelling phenomenon is generated. And O in the NMP molecule can form a new hydrogen bond with H of PVDF, and the F atom with stronger electronegativity can only form a new hydrogen bond with H of other PVDF molecules. By analogy, taking F as a bridge, the cross-linked chain of PVDF begins. As more and more NMP hydrogen bonds with PVDF, whose F hydrogen bonds with other molecules, dissolve the PVDF in NMP. And secondly, when the coated PVDF membrane enters an aqueous phase, the NMP molecules are quickly dissolved in water, and hydrogen bond chains of the PVDF molecules with C as a framework are broken and dispersed into a plurality of small molecules. The common PVDF film is formed, and the surface porosity is low. When the additive is added, the additive can prevent the crosslinking of PVDF and NMP in the first step, similar to the action of water in the second step, and break the hydrogen bond of PVDF molecule with C as the skeleton, so that the crosslinking performance of PVDF is weakened and the porosity is enhanced.

The diaphragm is white before activation, the thickness is basically 20-30 mu m, the affinity to electrolyte is good, and the diaphragm becomes light earthy yellow after the activation of n-butyl lithium, because the n-butyl lithium and the additive of the diaphragm have chemical reaction, and taking benzoic acid as an example, the n-butyl lithium can replace hydrogen on the carboxyl of benzoic acid to generate-OLi bond, so that the diaphragm has strong reducibility. The quinone group reacts with a strong reducing agent (n-butyllithium), and the C ═ O double bond is broken, resulting in a reduced product having a — OLi bond. The membrane has strong reducibility and can convert Mn into Mn²⁺Reduced to and attached to the membrane.

The invention has the following beneficial effects:

1) the invention adopts a lithiated porous PVDF (polyvinylidene fluoride) based diaphragm, and the diaphragm can absorb and adsorb electrolyte oxidation products from a high-voltage positive electrode so as to prevent the electrolyte oxidation products from migrating to a negative electrode, ensure that the negative electrode can normally embed and remove lithium ions and prolong the cycle life of a battery.

2) The contact angle can reflect the wettability of the diaphragm to the electrolyte, the contact angle of the commercial diaphragm Celgard2500 to the electrolyte is 50.74 degrees, the contact angle of the lithiated porous PVDF (polyvinylidene fluoride) -based diaphragm is 27.58-33.13 degrees, and because the lithiated porous PVDF (polyvinylidene fluoride) -based diaphragm has good compatibility with the carbonate electrolyte, the compatibility with the electrolyte is obviously superior to Celgard2500, the diaphragm has affinity with the electrolyte, the liquid absorption rate is saturated in a short time, the liquid absorption amount is basically twice of that of Celgard2500, and the interface performance of an electrode/the electrolyte is also improved.

3) The lithiated porous PVDF (polyvinylidene fluoride) -based separator of the present invention has a relatively wide range of service temperatures. Thermogravimetric testing of the thermochemical behavior of the lithiated porous PVDF (polyvinylidene fluoride) -based separator showed no change in the mass of the separator as it rose from 40 c to 400 c, but Celgard2500 decreased in mass from 250 c to 0g in mass at 400 c. The PVDF composite membrane has a wider range of service temperature.

Description of the drawings:

fig. 1 is a graphical representation of lithiated porous PVDF-based separator membranes containing various additives.

Wherein (a) contains no additives; (b)1 wt% benzoic acid; (c)1 wt% terephthalic acid; (d)1 wt% trimesic acid

The specific implementation mode is as follows:

the following is a further description of the invention and is not intended to be limiting.

Example 1:

0.4g of PVDF, 0.04g of polyvinylpyrrolidone and 0.004g of benzoic acid are weighed into a 20ml beaker, 2.3ml of LN-methyl pyrrolidone is added, and the mixture is magnetically stirred in a water bath kettle at the temperature of 60 ℃ until the mixture is completely dissolved, and the solution is clear and transparent. And then pouring the solution on the smooth surface of an aluminum foil, coating by using a 100um scraper, standing for 5min, soaking in 500mL of distilled water by a phase transfer method, soaking for 24h, taking out, and placing in a vacuum drying oven at 60 ℃ for more than 8 h. Cut into a diaphragm with a diameter of 14 mm. The prepared membranes are placed in a glove box, each membrane is activated by 1mL n-butyllithium for 12h, taken out and then washed by n-hexane and dimethyl carbonate respectively, and the solvent is completely volatilized after 3 h.

Lithium nickel manganese oxide is used as a positive electrode, graphite is used as a negative electrode, and the electrolyte is 1mol L^-1LiPF₆Dissolving in mixed solvent of ethylene carbonate EC and ethyl methyl carbonate EMC at volume ratio of 3:7 to obtain the final product according to the following formula of negative electrode shell-spring piece-gasket-negative electrode-electrolyte-diaphragm-electrolyte-positive electrodeAfter the batteries are sequentially arranged in the pole-positive shell, the batteries are activated on a battery system by 0.1C current, and then are circulated by 0.3C current. The specific capacity of Celgard2500 after 200 cycles is 80mAh g^-1The specific capacity of the PVDF composite membrane after lithiation of the invention is 82.8-100.8mAh g after 200 cycles^-1。

Manganese ion interception detection experiment is carried out on the Celgard2500 and the lithiated PVDF composite membrane, and the Celgard2500 interception effect is 1.420mg L from the mother solution^-1To 1.309mg L of lixivium^-1The PVDF composite membrane after lithiation is 1.022mg L from mother liquor^-1To 0.063mg L of the leach solution^-1Obviously, the PVDF composite membrane after lithiation has obvious effect of intercepting lithium ions.

Example 2:

reference example 1 except that the additive was terephthalic acid;

example 3:

reference example 1 was repeated except that the additive was trimesic acid.

Example 4:

reference example 1 with the exception that the additive was ferric oxide.

Example 5:

reference example 1 is made with the exception that the additive is titanium sulfide.

Claims

1. The high-voltage lithium ion battery is characterized by comprising a lithium nickel manganese oxide positive electrode, a graphite negative electrode, an electrolyte and a diaphragm, wherein the diaphragm is prepared by the following method: dissolving polyvinylidene fluoride, polyvinylpyrrolidone and an additive in N-methyl pyrrolidone, magnetically stirring in a 60 ℃ water bath until the polyvinylidene fluoride, the polyvinylpyrrolidone and the additive are completely dissolved, clarifying and transparent the solution, pouring the solution on the smooth surface of an aluminum foil, coating by using a 100um scraper, standing for 4-6min, soaking in distilled water by a phase transfer method, soaking for 24h, taking out, placing in a 60 ℃ vacuum drying oven for more than 8h, and cutting into a diaphragm with the diameter of 14 mm; placing the prepared diaphragms in a glove box, activating each diaphragm by 1mL of n-butyllithium for 12h, taking out, washing by n-hexane and dimethyl carbonate respectively, and assembling into a battery after the solvent is completely volatilized; the mass ratio of the polyvinylidene fluoride to the polyvinylpyrrolidone is 10: 1-10: 3; the additive is selected from one of benzoic acid, terephthalic acid, trimesic acid, anthraquinone, 1-aminoanthraquinone, 1, 8-dihydroxyanthraquinone, titanium dioxide, tin dioxide, nickel oxide, cobalt oxide, ferric oxide, manganese dioxide, titanium sulfide and iron sulfide, and the mass fraction of the additive is 1-5%.

2. The high voltage lithium ion battery of claim 1, wherein the electrolyte is 1mol L^-1LiPF₆Dissolving in a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3: 7.