CN1750296A - Negative electrode of lithium ion secondary battery, preparation method thereof, and lithium ion secondary battery comprising the negative electrode - Google Patents

Abstract

The invention discloses a negative electrode of a lithium ion secondary battery, a preparation method of the negative electrode and the lithium ion secondary battery comprising the negative electrode. The negative electrode thereof comprises: orthorhombic black phosphorus with an orthorhombic structure; artificially applying an inorganic solid electrolyte crystalline film having a thickness of 20-5000 AA and comprising an ionic conductivity of at least 1 x 10 on black phosphorus^－10S/cm of a lithium ion conductive material. The cathode can be prepared relatively easily by deposition. And preparing the lithium ion secondary battery containing the cathode by corresponding anode and electrolyte. The negative electrode of the invention is easy to prepare and is an ideal material for replacing graphite, the produced battery has high capacity, and the specific capacity of the negative electrode material of the invention can reach more than 700 mAh/g.

Description

Negative electrode of lithium ion secondary battery and preparation method thereof, and lithium ion secondary battery comprising the negative electrode

technical field

The invention relates to a negative pole of a lithium ion secondary battery, a preparation method thereof, and a lithium ion secondary battery containing the negative pole. In particular, it relates to an artificially applied inorganic solid electrolyte crystalline film, the crystalline film has good lithium ion conductivity and can form an effective SEI film negative pole of a lithium ion secondary battery with the existing lithium ion carbonate electrolyte Preparation method and lithium ion secondary battery comprising the negative electrode.

Background technique

Today's society is a society where information is developing rapidly, and fast, accurate, and massive storage and transmission of information are the requirements of the information age. The development of portable electronic devices such as mobile phones, notebook computers, and handheld computers has put forward higher requirements for lithium-ion secondary batteries with light weight and large capacity. What current commercial lithium-ion secondary battery anode material usually adopts is graphite carbon material, and its shortcoming is: 1), its theoretical specific capacity is only 372mAh/g, thereby has limited the further improvement of specific capacity of lithium-ion secondary battery; 2) The small tap density results in low volume specific energy, and its tap density is generally 0.8g/cm ³ .

Contents of the invention

The technical problem to be solved by the present invention is to provide a negative electrode of a lithium ion secondary battery, a preparation method thereof and a lithium ion secondary battery comprising the negative electrode. Inorganic solid electrolyte crystal film with good liquid compatibility. The negative electrode of the lithium ion secondary battery can be prepared by a simple method.

Technical solutions of the present invention are as follows:

A negative electrode of a lithium ion secondary battery, comprising: orthorhombic black phosphorus with an orthogonal structure; artificially applying a layer of inorganic solid electrolyte crystal film on the black phosphorus, the crystal film has a thickness of 20-5000 Å and includes a A lithium ion conducting material with an ion conductivity of at least 1×10 ^-10 S/cm.

The lithium ion conductive material is Li _x PO _y , where 2<X<4 and 3<Y<5.

The lithium ion conductive substance is Li ₃ PO ₄ .

The lithium ion conducting material is Li _a PO _b N _C where a is 2-4, b is 3-5, and c is 0.1-0.9.

The lithium ion conductive substance is Li _2.9 PO _3.3 N _0.46 .

A method for preparing a negative electrode of a lithium-ion secondary battery. In a strong oxidant solution, black phosphorus is oxidized and reacted with a lithium-containing compound to deposit a solid electrolyte crystal film. The crystal film contains an ionic conductivity At least 1×10 ^-10 s/cm lithium ion conductive material; strong oxidizing agent is selected from ammonium persulfate, nitric acid, hydrogen peroxide and sulfuric acid; lithium-containing compound is selected from n-butyllithium, tert-butyllithium, hexa Lithium fluorophosphorus, lithium tetrafluoroborate, lithium citrate, lithium naphthalene, and lithium hydroxide.

The aforementioned lithium ion conductive substance is Li _x PO _y , where 2<X<4 and 3<Y<5.

The aforementioned lithium ion conductive substance is Li ₃ PO ₄ .

A lithium ion secondary battery, the negative electrode of which is deposited on a black phosphorus substrate with a thickness of 20-5000 Å and contains a lithium ion conductive material with an ion conductivity of at least 1×10 ^-10 s/cm Crystal film; the positive electrode includes any one selected from lithium cobalt oxide, lithium nickel oxide, lithium manganate, lithium cobalt nickel oxide, lithium nickel manganese oxide, lithium iron phosphate, lithium cobalt phosphate, or any ratio of two or more Combination; the main salt of the electrolyte can be one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, and lithium perfluoroalkylsulfonate; the solvent component can be ethylene carbonate, dimethyl carbonate ester, diethyl carbonate, propylene carbonate, ethyl methyl dicarbonate, methyl propyl carbonate, diethoxyethane, 2-methyltetrahydrofuran, or a combination of two or more in any proportion.

The outstanding effects of the present invention are: 1), compared with the traditional carbon negative electrode, its specific capacity can be greatly improved up to 700mAh/g; 2), the tap density is high, and the density is generally 1.27g/cm ³ , which is convenient for the battery Can increase volume specific energy.

Description of drawings

Fig. 1 is the charge-discharge curve figure when the black phosphorus negative pole of the present invention has no crystal film;

Fig. 2 is the second charge-discharge curve figure after Li _a PO _b N _C crystal film is deposited on black phosphorus negative electrode of the present invention;

Fig. 3 is the XRD spectrum after charge and discharge of black phosphorus negative pole amorphous film of the present invention;

Fig. 4 is the XRD spectrum of the black phosphorus negative electrode amorphous film before charge and discharge of the present invention;

Fig. 5 is the second charge and discharge curve of the black phosphorus negative electrode of the present invention after depositing a Li ₃ PO ₄ crystal film.

Detailed ways

Example 1

Put 5 grams of black phosphorus powder sieved through 200 meshes into 100 milliliters of strong oxidizing agent concentration and carry out oxidation treatment in 10% nitric acid (HNO ₃ ) solution at room temperature for 10 hours, then wash with distilled water, and then put into a drying box Dry at 120°C for 12 hours. Then take vinylidene fluoride as binder, N-methylpyrrolidone as organic solvent, and acetylene black as conductive agent, mix and stir the slurry evenly according to the ratio of black phosphorus: acetylene black: vinylidene fluoride=90:4:6 Coated on the current collector copper foil, and dried at 120°C for 16 hours. Then immerse in any ratio of lithium-containing compound n-butyllithium/ethane solution for 12 hours, then wash with dimethoxyethane, put it into a vacuum drying oven, heat up to 160°C, and keep it warm for 48 hours to get this product. Invention of the required lithium ion secondary battery negative electrode.

The lithium ion secondary battery negative electrode that above-mentioned makes, positive electrode material is lithium cobaltate, electrolyte is lithium hexafluorophosphate, solvent is ethylene carbonate and diethyl carbonate, volume ratio is 1: 1, diaphragm is CeLgrd2300 microporous film, makes A 063048 battery was formed, and the capacity of the battery was determined to be 1385mAh.

Example 2

The negative electrode of the lithium ion secondary battery prepared above, the positive electrode material is lithium manganate, the electrolyte is lithium hexafluoroborate, the solvent is ethylene carbonate and diethyl carbonate with a volume ratio of 1:3, and the diaphragm is CeLgrd2300 microporous membrane , made of 063048 batteries. , The measured capacity of the battery is 1345mAh.

Example 3

With the lithium ion secondary battery negative electrode that above-mentioned makes, anode material is lithium nickelate, electrolytic solution is lithium chlorate, solvent solvent is ethylene carbonate and diethyl carbonate, volume ratio is 1: 1, diaphragm is CeLgrd2300 micron The porous film is made into a 063048 battery, and the measured capacity of the battery is 1425mAh.

Example 4:

A target is used to deposit crystals on a black phosphorus electrode under an inert gas atmosphere, said crystal film comprising a lithium ion conducting material with a lithium ion conductivity of at least 1 x 10 ^-10 S/cm.

The lithium ion conductive substance is a compound represented by Li _x PO _y , where 2<X<4 and 3<Y<5, and it is stable under a nitrogen atmosphere.

The lithium ion conducting material is Li _a PO _b N _C where a is 2-4, b is 3-5, and c is 0.1-0.9.

The inert gas is selected from helium, neon and argon, because none of these gases react chemically with black phosphorus to produce by-products.

The target may be Li ₃ PO ₄ or a mixture of Li ₂ O and P ₂ O ₅ mixed in an appropriate mixing ratio.

A layer of Li ₃ PO ₄ crystalline film was formed by depositing a 4-inch diameter Li ₃ PO ₄ target on the black phosphorus electrode for 10 minutes at a pressure of 5 mTorr, an RF power of 300 W, and an argon atmosphere

The deposition process is carried out by suitable methods, such as: plating, electron beam evaporation, vacuum thermal evaporation, laser ablation, chemical vapor deposition, thermal evaporation, plasma chemical vapor deposition, laser chemical vapor deposition or jet vapor deposition deposition. Those skilled in the relevant art can understand that the deposition is not limited to the above-mentioned methods, and it includes any conventional methods.

Use untreated black phosphorus as the negative electrode, the metal lithium sheet as the counter electrode, the separator as the CeLgrd2300 microporous membrane, the electrolyte as 1.0mol/L, LiPF6/EC:DEC, and the solvent volume ratio as 1:1. A simulated battery was made in a 1% glove box, and the charging and discharging performance of black phosphorus was measured. The results are shown in Figure 1. In Fig. 1, since no effective SEI film is formed at 0.8 volts, co-intercalation of solvent molecules occurs, and the discharge capacity diagram shows zero.

The black phosphorus electrode prepared by the above method is used as the negative electrode, the metal lithium sheet is used as the counter electrode, the separator is a CeLgrd2300 microporous membrane, the electrolyte is 1.0mol/L, LiPF6/EC: DEC, and the solvent volume ratio is 1: 1. A mechanical simulated battery was made in a glove box with a humidity of 1% and the charging and discharging performance of black phosphorus was measured. The results are shown in Fig. 2 and Fig. 5 . It can be seen from Figures 2 and 5 that the negative electrode of the present invention can perform effective charge-discharge cycles, and the discharge capacity in Figure 2 is 630mAh/g. In Fig. 5, V represents the voltage, and C represents the specific capacity.

Test Conditions:

Charge and discharge current density, charge current 1mA/cm ² , discharge current 1mA/cm ² cut-off voltage 0-1.0 volts. The experimental results show that after the black phosphorus electrode is artificially deposited with a crystal film, a voltage plateau is formed at 0.8 volts when it is charged for the first time, corresponding to a dense and effective SEI film attached to the crystal film. Since the formation of this SEI film prevents the co-intercalation of organic molecules, the discharge capacity is greater than 650mAh/g. The black phosphorus electrode without deposited crystal film does not form an effective SEI film, and the solvent molecules are co-embedded, which fundamentally destroys the structure of black phosphorus, and the discharge capacity is zero. Fig. 3 is the XRD pattern after charging without depositing crystal film.

Working principle: Black phosphorus has a layered structure like graphite. The atoms in the layer are superimposed with σ covalent bonds and are firmly combined with each other. The two layers are only connected by weak van der Waals force. This mixed bond type crystal structure makes it have The special chemical properties mean that some atoms and molecules can be embedded between the layers of such crystals without destroying the covalent bonds of the stacking, but only changing the interlayer spacing to form interlayer compounds. In graphite, a carbon atom forms a σ covalent bond with a coordination number of 3, and only one P electron is left to participate in the formation of a delocalized π bond, while in black phosphorus, after a phosphorus atom forms a σ covalent bond with a coordination number of 3, There is a pair of lone P electrons participating in the formation of delocalized π bonds. This shows that black phosphorus can provide more bonding electrons to coordinate with lithium ions. Black phosphorus has the potential to have a higher specific capacity than graphite. In the carbonate electrolyte system such as propylene carbonate and ethylene carbonate, the black phosphorus negative electrode cannot form an effective SEI film for the first time, resulting in co-embedding of solvent molecules, which fundamentally destroys the crystal structure of black phosphorus, making black phosphorus The electrodes are thus deactivated. But orthorhombic black phosphorus of orthorhombic structure; artificially applied a layer of inorganic solid electrolyte crystalline film on black phosphorus, said crystalline film has a thickness of 20-5000 Å and includes an ionic conductivity of at least 1×10 ^-10 S/ cm Li-ion conductive material, the experiment proves that the negative electrode that deposits crystal film on the surface of black phosphorus substrate for the first time can form an effective SEI film, preventing the collapse of black phosphorus structure caused by the co-intercalation of solvent lithium ions. Instead, it allows lithium ions to pass through it.

In Example 1 of the present invention, the black phosphorus powder will form phosphorus oxides and acids on the surface under the action of a strong oxidizing agent. After washing with distilled water, the oxides remaining on the surface of the black phosphorus are heated and dried in the presence of water and oxygen. , a small amount of phosphoric acid will be generated on its surface, and a layer of Li ₃ PO ₄ crystal film will be formed on the surface of black phosphorus particles due to the action of phosphoric acid and lithium-containing compounds.

Claims (9)

1, a kind of negative pole of lithium rechargeable battery is characterized in that: comprising: the oblique side's black phosphorus with orthohormbic structure; Manually apply one deck inorganic solid electrolyte crystal film on black phosphorus, described crystal film has the thickness of 20-5000 and comprises a kind of ionic conductivity at least 1 * 10 ^-10The lithium ion conduction material of S/cm.

2, according to right 1 described negative pole, it is characterized in that: the lithium ion conduction material is Li _xPO _y, wherein, 2＜X＜4 and 3＜Y＜5.

3, negative pole according to claim 2 is characterized in that: the lithium ion conduction material is Li ₃PO ₄

4, negative pole according to claim 1 is characterized in that: the lithium ion conduction material is Li _aPO _bN _CA is 2-4 herein, and b is 3-5, and c is 0.1-0.9.

5, negative pole according to claim 4 is characterized in that: the lithium ion conduction material is Li _2.9PO _3.3N _0.46

6, a kind of method for preparing lithium ion secondary battery negative pole, it is characterized in that: in strong oxidant solution, black phosphorus is advanced oxidation processes, with the compound deposition one deck solid electrolyte crystal film that contains lithium, described crystal film contain that a kind of ionic conductivity is at least 1 * 10 ^-10S/cm lithium ion conduction material; Strong oxidizer is selected from and comprises ammonium persulfate, nitric acid, hydrogen peroxide and sulfuric acid; Lithium-containing compound is selected from and comprises n-BuLi, tert-butyl lithium, hexafluoro phosphorus lithium, LiBF4, lithium citrate, lithium naphthalene and lithium hydroxide.

7, according to right 6 described methods, it is characterized in that: the lithium ion conduction material is Li _xPO _y, wherein, 2＜X＜4 and 3＜Y＜5.

8, method according to claim 6 is characterized in that: the lithium ion conduction material is Li ₃PO ₄

9, a kind of lithium rechargeable battery is characterized in that: its negative pole is to deposit one deck to have the thickness of 20-5000 and contain a kind of ionic conductivity and be at least 1 * 10 on the black phosphorus base material ^-10The crystal film of the lithium ion conduction material of S/cm; Positive pole comprises a kind of combination that is selected from by cobalt acid lithium, lithium nickelate, LiMn2O4, cobalt lithium nickelate, nickel LiMn2O4, LiFePO4, cobalt phosphate lithium any or two or more arbitrary proportions wherein; The main salt of electrolyte can be wherein a kind of of lithium hexafluoro phosphate, LiBF4, hexafluoroarsenate lithium, lithium perchlorate, perfluoro alkyl sulfonic acid lithium; Solvent composition can be the combination of one or more arbitrary proportions in vinyl carbonate, dimethyl carbonate, diethyl carbonate, propylene carbonate, two methyl ethyl carbonates, carbonic acid first propyl ester, diethoxyethane, the 2-methyltetrahydrofuran.

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