Ultrathin lithium composite and preparation method and use thereof

Abstract

A method for preparing an ultrathin Li complex includes the steps of preparing an organic transition layer on a substrate in advance, and contacting the substrate having transition layer with molten Li in argon atmosphere with H.sub.2O≤0.1 ppm and O.sub.2≤0.1 ppm. The molten Li spreads rapidly on the surface of the substrate to form a lithium thin layer. The ultrathin Li layer stores lithium on the current collector beforehand. It can be used as a safe lithium anode to inhibit dendrites.

Claims

1. A method for forming a lithium layer, comprising: coating a mixture solution of polyvinylidene fluoride and polyethyleneimine on a piece of planar copper substrate to form an organic transition layer on the substrate; and contacting the piece of planar copper substrate having the organic transition layer with a molten lithium in an argon atmosphere having H.sub.2O≤0.1 ppm and O.sub.2≤0.1 ppm for 10-120 s at a temperature of the molten lithium of 180-300° C., thereby spreading molten lithium on the substrate to form the lithium layer having a thickness of 5-50 μm, and peeling the lithium layer off the piece of planar copper substrate.

2. The method according to claim 1, wherein the mixture solution of polyvinylidene fluoride and polyethyleneimine comprises a solvent of N-methyl-2-pyrrolidone.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a photograph showing the wettability of molten Li on porous Cu foam substrate with a transition layer in Example 1.

(2) FIG. 2A is a Scanning Electron Microscopy (SEM) image of the ultrathin Li layer on Cu foam substrate with a transition layer in Example 1.

(3) FIG. 2B is an SEM image at high magnitude of the ultrathin Li on Cu foam substrate with a transition layer in Example 1.

(4) FIG. 2C is a cross-sectional SEM image of the ultrathin Li on the Cu foam substrate with a transition layer in Example 1.

(5) FIG. 2D is a plot showing the areal capacity of the ultrathin Li on the Cu foam substrate in Example 1.

(6) FIG. 3 is a photograph showing the poor wettability of molten Li on porous Cu foam substrate without a transition layer in Comparative Example 1.

(7) FIG. 4A is a photograph showing the wettability of molten Li on carbon fiber felt substrate with a transition layer in Example 2.

(8) FIG. 4B is an X-Ray diffraction (XRD) diagram of the ultrathin Li on carbon fiber felt substrate in Example 2.

(9) FIG. 5A is an SEM image of the ultrathin Li on carbon fiber felt substrate with a transition layer in Example 2.

(10) FIG. 5B is an SEM image at high magnitude of the ultrathin Li on carbon fiber felt substrate with a transition layer in Example 2.

(11) FIG. 5C is a cross-sectional SEM image of the ultrathin Li on carbon fiber felt substrate with a transition layer in Example 2.

(12) FIG. 5D is a plot showing the areal capacity of the ultrathin Li on carbon fiber felt substrate in Example 2.

(13) FIG. 6 is a photograph showing the poor wettability of molten Li on carbon fiber felt substrate without a transition layer in Comparative Example 2.

(14) FIG. 7 is an SEM image of the ultrathin Li infused into the inside pores of the carbon fiber felt in Example 3.

BEST MODE FOR CARRYING OUT THE INVENTION

(15) The present invention is further explained in examples with specific embodiments, but it is not limited by the following examples. The reagents and materials used in the following examples, if there is no particular statement, can be obtained from commercial.

Example 1

(16) Preparation of Ultrathin Li on Cu Foam Substrate

(17) 5 g abietic resin was weighed and dissolved in 95 g ethanol to form a homogeneous resin solution. A copper foam was soaked in the solution for 1 minute, and the solvent ethanol was fully volatilized and dried, thus a homogeneous transition layer was formed on the surface of the copper foam. The sample was transferred into an argon-filled glove box with an oxygen and moisture level <0.1 ppm. Li metal was heated to 250° C. in a stainless steel container to form molten Li, and then the Cu foam with transition layer contacted with molten Li for 20 s. The results show that after the contact of Cu foam with molten Li, the molten lithium spread quickly on the surface of the Cu foam with the transition layer, so as to form a relatively uniform ultrathin layer of lithium, as shown in FIG. 1. As can be seen from FIG. 1, the area of the lithium metal layer is relatively large, which can be obtained at one time. Comparing with the electrodeposited lithium in button cell, the preparation method is simple, efficient and practical. The morphology of the ultrathin Li anode was characterized and the areal capacity was measured. The morphology of the ultrathin Li on Cu foam was observed by using scanning electron microscope (SEM). The transition layer formed from the abietic resin solution (5 wt %) can make the metal lithium to generate an independent layer, and the molten Li cannot be detected in the copper foam, as shown in FIG. 2A and FIG. 2C. The thickness of the ultrathin Li layer is about 30 μm, which is illustrated in FIG. 2C. Referring to FIG. 2D, the capacity of the ultrathin Li layer is about 6 mAh.Math.cm.sup.−2 as measured by using electrochemical testing. A symmetrical battery was assembled using the ultrathin Li anode in combination with a commercial lithium sheet that was used as a counter electrode, and the polarization performance was measured. The polarization voltage finally stabilized at 40 mV after 100 cycles with a current density of 1 mA.Math.cm.sup.−2 and a capacity of 1 mAh.Math.cm.sup.−2. When a symmetrical battery is assembled with two commercial lithium sheets as the electrode materials, the polarization voltage stabilizes at 80 mV under the same current density. The comparison shows that the ultrathin Li prepared in the present invention exhibits excellent performance as a lithium metal battery material.

Comparative Example 1

(18) Li metal was heated to 250° C. in a stainless steel container to form molten Li, then a Cu foam substrate without transition layer contacts with the molten Li for 20 s. The results show that the wettability of molten Li on Cu foam without a transition layer is relatively poor. As shown in FIG. 3, molten Li presents on the Cu foam substrate in form of spherical granules, which indicates a highly lithiophobic of molten Li on Cu substrate.

Example 2

(19) Preparation of Ultrathin Li on Carbon Felt Substrate

(20) 10 g citric acid was weighed and dissolved in 90 g ethanol to form a homogeneous solution. A carbon felt was soaked in the solution for 1 minute, and the solvent ethanol was fully volatilized and dried, thus a homogeneous transition layer was formed on the surface of the carbon felt. The sample was transferred into an argon-filled glove box with an oxygen and moisture level <0.1 ppm. Li metal was heated to 250° C. in a stainless steel container to form molten Li, and then the carbon felt with transition layer contacted with molten Li for 20 s. The results show that after the contact of carbon felt with molten Li, the molten lithium spread quickly on the surface of the carbon felt with the transition layer so as to form a relatively uniform ultrathin layer of lithium, as shown in FIG. 4A.

(21) The crystal structure of the product was confirmed by the powder X-ray diffractometer (Rigaku DmaxrB, CuK ray), as shown in FIG. 4B. It can be seen from the XRD that there is no impurity peak beside the peaks of lithium and carbon felt, which indicates that the purity of the lithium metal is quite high.

(22) The morphology of ultrathin Li anode was characterized and the areal capacity was measured. The morphology of ultrathin Li on Cu foam was observed by using scanning electron microscope (SEM). The transition layer formed from the citric acid solution (5 wt %) can make the metal lithium to generate an independent layer, and the molten Li cannot be detected in the carbon felt, as shown in FIG. 5A and FIG. 5C. The thickness of the ultrathin Li layer is about 40 μm, which is illustrated in FIG. 5C. Referring to FIG. 5D, the capacity of the ultrathin Li layer is about 8 mAh.Math.cm.sup.−2 as measured by using electrochemical testing. A symmetrical battery was assembled using the ultrathin Li anode in combination with a commercial lithium sheet that was used as a counter electrode, and the polarization performance was measured. The polarization voltage finally stabilized at 30 mV after 100 cycles, with a current density of 1 mA.Math.cm.sup.−2 and a capacity of 1 mAh.Math.cm.sup.−2. When a symmetrical battery is assembled with two commercial lithium sheets as the electrode materials, the polarization voltage stabilizes at 80 mV under the same current density. The comparison shows that the ultrathin Li prepared in the present invention exhibits excellent performance as a lithium metal battery material.

Comparative Example 2

(23) Li metal was heated to 250° C. in a stainless steel container to form molten Li, and then a carbon felt without transition layer contacted with the molten Li for 20 s. The results show that the wettability of molten Li on carbon felt without a transition layer is relatively poor. As shown in FIG. 6, the contact angles of molten Li on carbon felt are relatively large (>90°), which indicates a highly lithiophobic of molten Li on carbon felt.

Example 3

(24) Preparation of Ultrathin Li Infused into Carbon Felt

(25) 30 g citric acid was weighed and dissolved in 70 g water to form a homogeneous solution. A carbon felt was soaked in the solution for 1 minute, and the solvent water was fully volatilized and dried, thus a homogeneous transition layer was formed on the surface and inside of the carbon felt. The sample was transferred into an argon-filled glove box with an oxygen and moisture level <0.1 ppm. Li metal was heated to 250° C. in a stainless steel container to form molten Li, and then the carbon felt with transition layer contacted with the molten Li for 20 s. As shown in FIG. 7, the molten Li infused into the carbon felt so as to generate a high areal capacity of up to 30 mAh.Math.cm.sup.−2 for molten Li. A symmetrical battery was assembled using the Li anode in combination with a commercial lithium sheet that was used as a counter electrode, and the polarization performance was measured. The polarization voltage finally stabilized at 30 mV after 100 cycles with a current density of 1 mA cm.sup.−2 and a capacity of 1 mAh.Math.cm.sup.−2. When a symmetrical battery is assembled by two commercialized lithium sheets as the electrode materials, the polarization voltage stabilizes at 80 mV under the same current density. The comparison shows that the ultrathin Li prepared in the present invention exhibits excellent performance as a lithium metal battery material. Compared with Example 2, the higher the concentration of the functional group-containing material in the transition layer is, the thicker the lithium layer in unit time can be obtained under the same preparation condition.

Example 4

(26) Preparation of Ultrathin Li Formed onto Carbon Felt

(27) 20 g lactic acid was weighed and dissolved in 80 g water to form a homogeneous solution. A layer of the solution was coated on the surface of a carbon felt, and the solvent water was fully volatilized and dried before the substrate was transferred into an argon-filled glove box with an oxygen and moisture level <0.1 ppm. Li metal was heated to 250° C. in a stainless steel container to form molten Li, and then the carbon felt with transition layer contacted with molten Li for 20 s. The metal lithium generated an independent layer, and the molten Li could not be detected in the carbon felt. The thickness of the Li layer is about 30 and the areal capacity is about 6 mAh.Math.cm.sup.−2. Compared with Example 2, upon altering the type of the transition layer and controlling the concentration of the solution, a good wettability can also be achieved. A symmetrical battery was assembled using the prepared Li complex in combination with a commercial lithium sheet, and the polarization performance was measured. The polarization voltage finally stabilized at 50 mV after 100 cycles with a current density of 1 mA.Math.cm.sup.−2 and a capacity of 1 mAh.Math.cm.sup.−2. When a symmetrical battery is assembled with two commercial lithium sheets as the electrode materials, the polarization voltage stabilizes at 80 mV under the same current density. The comparison shows that the ultrathin Li prepared in this invention exhibits excellent performance as a lithium metal battery material.

Example 5

(28) Preparation of Li with a Thickness of 30 μm Formed onto Carbon Felt

(29) 10 g citric acid was weighed and dissolved in 90 g ethanol to form a homogeneous solution. A carbon felt was soaked in the solution for 1 minute, and the solvent ethanol was fully volatilized and dried, thus a uniform transition layer was coated on the surface of the carbon felt. Then the substrate was transferred into an argon-filled glove box with an oxygen and moisture level <0.1 ppm. Li metal was heated to 250° C. in a stainless steel container to form molten Li, and then the carbon felt with transition layer contacted with the molten Li for 60 s. The thickness of the resulting ultrathin Li layer is about 30 and the areal capacity is about 6 mAh.Math.cm.sup.−2. Compared with Example 2, the thickness could also be controlled by controlling the contacting time. A symmetrical battery was assembled using the prepared Li complex in combination with a commercial lithium sheet, and the polarization performance was measured. The polarization voltage finally stabilized at 30 mV after 100 cycles with a current density of 1 mA cm.sup.−2 and a capacity of 1 mAh.Math.cm.sup.−2. Compared with Example 3, the polarization voltage varies not very much, since the factors determining the polarization voltage are mainly related to the type of the transition layer. When a symmetrical battery is assembled with two commercial lithium sheets as the electrode materials, the polarization voltage stabilizes at 80 mV under the same current density. The comparison shows that the ultrathin Li prepared in this invention exhibits excellent performance as a lithium metal battery material.

Example 6

(30) Preparation of Ultrathin Li on a Planar Cu Substrate

(31) 5 g citric acid was weighed and dissolved in 94 g ethanol to form a homogeneous solution. Then 1 g phenolic resin was added, and the solution was stirred evenly for using as the source of the transition layer. A layer of the solution was coated on the surface of a planar Cu substrate. After natural drying, it was put into a vacuum drying box at 80° C. for fully dryness. The planar Cu substrate coated with transition layer was transferred into an argon-filled glove box with an oxygen and moisture level <0.1 ppm. Li metal was heated to 250° C. in a stainless steel container to form molten Li, and then the planar Cu with transition layer contacted with molten Li for 10 s. The thickness of the resulting Li layer is about 10 μm, and the areal capacity is about 2 mAh.Math.cm.sup.−2. A symmetrical battery was assembled using the prepared Li complex in combination with a commercial lithium sheet, and the polarization performance was measured. The polarization voltage finally stabilized at 50 mV after 100 cycles with a current density of 1 mA cm.sup.−2 and a capacity of 1 mAh.Math.cm.sup.−2. When a symmetrical battery is assembled with two commercial lithium sheets as the electrode materials, the polarization voltage stabilizes at 80 mV under the same current density. The comparison shows that the ultrathin Li prepared in this invention exhibits excellent performance as a lithium metal battery material.

Example 7

(32) Preparation of Ultrathin Li on Planar Cu Substrate with Imide-Based Organic Matter as a Transition Layer

(33) 1 g polyethyleneimine (PEI) was weighed and dissolved in 99 g ethanol to form a homogeneous PEI solution. The solution was stirred evenly to serve as the source of the transition layer. A layer of the solution was coated on the surface of a planar Cu substrate. After natural drying, it was put into a vacuum drying box at 40° C. for fully dryness. The planar Cu substrate coated with the transition layer was transferred into an argon-filled glove box with an oxygen and moisture level <0.1 ppm. Li metal was heated to 250° C. in a stainless steel container to form molten Li, and then the planar Cu with transition layer contacted with molten Li for 15 s. The thickness of the resulting Li layer is about 7.5 μm, and the areal capacity is about 1.5 mAh.Math.cm.sup.−2. A symmetrical battery was assembled using the prepared Li complex in combination with a commercial lithium sheet, and the polarization performance was measured. The polarization voltage finally stabilized at 35 mV after 100 cycles with a current density of 1 mA cm.sup.−2 and a capacity of 1 mAh.Math.cm.sup.−2. When a symmetrical battery is assembled with two commercial lithium sheets as the electrode materials, the polarization voltage stabilizes at 80 mV under the same current density. The comparison shows that the ultrathin Li prepared in this invention exhibits excellent performance as a lithium metal battery material.

Example 8

(34) Preparation of Ultrathin Li on Planar Cu Substrate with Benzoic Acid as a Transition Layer

(35) 3 g benzoic acid was weighed and dissolved in 97 g ethanol to form a homogeneous solution for using as the source of the transition layer. A layer of the solution was coated on the surface of a planar Cu substrate. After natural drying, it was put into a vacuum drying box at 80° C. for fully dryness. The planar Cu substrate coated with the transition layer was transferred into an argon-filled glove box with an oxygen and moisture level <0.1 ppm. Li metal was heated to 250° C. in a stainless steel container to form molten Li, and then the planar Cu with transition layer contacted with molten Li for 10 s. The thickness of the resulting Li layer is about 10 μm, and the areal capacity is about 2 mAh.Math.cm.sup.−2. A symmetrical battery was assembled using the prepared Li complex in combination with a commercial lithium sheet, and the polarization performance was measured. The polarization voltage finally stabilized at 55 mV after 100 cycles with a current density of 1 mA.Math.cm.sup.−2 and a capacity of 1 mAh.Math.cm.sup.−2. When a symmetrical battery is assembled with two commercial lithium sheets as the electrode materials, the polarization voltage stabilizes at 80 mV under the same current density. The comparison shows that the ultrathin Li prepared in this invention exhibits excellent performance as a lithium metal battery material.

Example 9

(36) Preparation of Ultrathin Li on Planar Cu Substrate with Rosin Glyceride as a Transition Layer

(37) 3 g rosin glyceride was weighed and dissolved in 97 g ethanol to form a homogeneous solution for using as the source of the transition layer. A layer of the solution was coated on the surface of a planar Cu substrate. After natural drying, it was put into a vacuum drying box at 80° C. for fully dryness. The planar Cu substrate coated with the transition layer was transferred into an argon-filled glove box with an oxygen and moisture level <0.1 ppm. Li metal was heated to 250° C. in a stainless steel container to form molten Li, and then the planar Cu with transition layer contacted with molten Li for 10 s. The thickness of the Li layer is about 10 μm, and the areal capacity is about 2 mAh.Math.cm.sup.−2. A symmetrical battery was assembled using the prepared Li complex in combination with a commercial lithium sheet, and the polarization performance was measured. The polarization voltage finally stabilized at 40 mV after 100 cycles with a current density of 1 mA.Math.cm.sup.−2 and a capacity of 1 mAh.Math.cm.sup.−2. When a symmetrical battery is assembled with two commercial lithium sheets as the electrode materials, the polarization voltage stabilizes at 80 mV under the same current density. The comparison shows that the ultrathin Li prepared in this invention exhibits excellent performance as a lithium metal battery material.

Example 10

(38) Preparation of Ultrathin Li on Planar Cu Substrate with Methyl Anthranilate as a Transition Layer

(39) 3 g methyl anthranilate was weighed and dissolved in 97 g ethanol to form a homogeneous solution for using as the source of the transition layer. A layer of the solution was coated on the surface of a planar Cu substrate. After natural drying, it was put into a vacuum drying box at 80° C. for fully dryness. The planar Cu substrate coated with the transition layer was transferred into an argon-filled glove box with an oxygen and moisture level <0.1 ppm. Li metal was heated to 250° C. in a stainless steel container to form molten Li, and then the planar Cu with transition layer contacted with molten Li for 10 s. The thickness of the Li layer is about 10 μm, and the areal capacity is about 2 mAh.Math.cm.sup.−2. A symmetrical battery was assembled using the prepared Li complex in combination with a commercial lithium sheet, and the polarization performance was measured. The polarization voltage finally stabilized at 30 mV after 100 cycles with a current density of 1 mA cm.sup.−2 and a capacity of 1 mAh.Math.cm.sup.−2. When a symmetrical battery is assembled with two commercial lithium sheets as the electrode materials, the polarization voltage stabilizes at 80 mV under the same current density. The comparison shows that the ultrathin Li prepared in this invention exhibits excellent performance as a lithium metal battery material.

Example 11

(40) Preparation of Ultrathin Li on Planar Cu Substrate with 2 Naphthalenesulfonic Acid as a Transition Layer

(41) 3 g naphthalenesulfonic acid was weighed and dissolved in 97 g ethanol to form a homogeneous solution for using as the source of the transition layer. A layer of solution was coated on the surface of a planar Cu substrate. After natural drying, it was put into a vacuum drying box at 80° C. for fully dryness. The planar Cu substrate coated with the transition layer was transferred into an argon-filled glove box with an oxygen and moisture level <0.1 ppm. Li metal was heated to 250° C. in a stainless steel container to form molten Li, and then the planar Cu with transition layer contacted with molten Li for 10 s. The thickness of the Li layer is about 15 μm, and the areal capacity is about 3 mAh.Math.cm.sup.−2. A symmetrical battery was assembled using the prepared Li complex in combination with a commercial lithium sheet, and the polarization performance was measured. The polarization voltage finally stabilized at 55 mV after 100 cycles with a current density of 1 mA.Math.cm.sup.−2 and a capacity of 1 mAh.Math.cm.sup.−2. When a symmetrical battery is assembled with two commercial lithium sheets as the electrode materials, the polarization voltage stabilizes at 80 mV under the same current density. The comparison shows that the ultrathin Li prepared in this invention exhibits excellent performance as a lithium metal battery material.

Example 12

(42) Preparation of Ultrathin Li on Planar Cu Substrate with Polyvinyl Alcohol as a Transition Layer

(43) 3 g polyvinyl alcohol was weighed and dissolved in 97 g ethanol to form a homogeneous solution for using as the source of the transition layer. A layer of the solution was coated on the surface of a planar Cu substrate. After natural drying, it was put into a vacuum drying box at 80° C. for fully dryness. The planar Cu substrate coated with the transition layer was transferred into an argon-filled glove box with an oxygen and moisture level <0.1 ppm. Li metal was heated to 250° C. in a stainless steel container to form molten Li, and then the planar Cu with transition layer contacted with molten Li for 10 s. The thickness of the Li layer is about 20 μm, and the areal capacity is about 4 mAh.Math.cm.sup.−2. A symmetrical battery was assembled using the prepared Li complex in combination with a commercial lithium sheet, and the polarization performance was measured. The polarization voltage finally stabilized at 50 mV after 100 cycles, with the current density of 1 mA cm.sup.−2 and the capacity of 1 mAh.Math.cm.sup.−2. When a symmetrical battery is assembled with two commercial lithium sheets as the electrode materials, the polarization voltage stabilizes at 80 mV under the same current density. The comparison shows that the ultrathin Li prepared in this invention exhibits excellent performance as a lithium metal battery material.

Example 13

(44) Preparation of Ultrathin Li on Planar Cu Substrate with a Fluorine-Containing Organic Compound as a Transition Layer

(45) 3 g polyvinylidene fluoride was weighed and dissolved in 97 g ethanol to form a homogeneous solution for using as the source of the transition layer. A layer of the solution was coated on the surface of planar Cu substrate. After natural drying, it was put into a vacuum drying box at 80° C. for fully dryness. The planar Cu substrate coated with the transition layer was transferred into an argon-filled glove box with an oxygen and moisture level <0.1 ppm. Li metal was heated to 250° C. in a stainless steel container to form molten Li, and then the planar Cu with transition layer contacted with molten Li for 10 s. The thickness of the Li layer is about 15 μm, and the areal capacity is about 3 mAh.Math.cm.sup.−2. A symmetrical battery was assembled using the prepared Li complex in combination with a commercial lithium sheet, and the polarization performance was measured. The polarization voltage finally stabilized at 25 mV after 100 cycles, with a current density of 1 mA cm.sup.−2 and a capacity of 1 mAh.Math.cm.sup.−2. When a symmetrical battery is assembled with two commercial lithium sheets as the electrode materials, the polarization voltage stabilizes at 80 mV under the same current density. The comparison shows that the ultrathin Li prepared in this invention exhibits excellent performance as a lithium metal battery material.

Example 14

(46) Preparation of Ultrathin Li on Planar Cu Substrate with a Mixture of a Fluorine-Containing

(47) Organic Compound and an Imide Based Polymer as a Transition Layer 2 g polyvinylidene fluoride and 1 g PEI were weighed and dissolved in 97 g N-methyl-2-pyrrolidone (NMP) to form a homogeneous solution for using as the source of the transition layer. A layer of the solution was coated on the surface of a planar Cu substrate. After natural drying, it was put into a vacuum drying box at 80° C. for fully dryness. The planar Cu substrate coated with the transition layer was transferred into an argon-filled glove box with an oxygen and moisture level <0.1 ppm. Li metal was heated to 250° C. in a stainless steel container to form molten Li, and then the planar Cu with transition layer contacted with molten Li for 10 s. The thickness of the Li layer is about 15 μm, and the areal capacity is about 3 mAh.Math.cm.sup.−2. A symmetrical battery was assembled using the prepared Li complex in combination with a commercial lithium sheet, and the polarization performance was measured. The polarization voltage finally stabilized at 20 mV after 100 cycles with a current density of 1 mA.Math.cm.sup.−2 and a capacity of 1 mAh.Math.cm.sup.−2. When a symmetrical battery is assembled with two commercial lithium sheets as the electrode materials, the polarization voltage stabilizes at 80 mV under the same current density. The comparison shows that the ultrathin Li prepared in this invention exhibits excellent performance as a lithium metal battery material.

Example 15

(48) Preparation of Ultrathin Li on Planar Cu Substrate with a Mixture of Polyvinylidene Fluoride and Benzoic Acid as a Transition Layer

(49) 2 g polyvinylidene fluoride and 1 g benzoic acid were weighed and dissolved in 97 g NMP to form a homogeneous solution for using as the source of the transition layer. A layer of solution was coated on the surface of a planar Cu substrate. After natural drying, it was put into a vacuum drying box at 80° C. for fully dryness. The planar Cu substrate coated with the transition layer was transferred into an argon-filled glove box with an oxygen and moisture level <0.1 ppm. Li metal was heated to 250° C. in a stainless steel container to form molten Li, and then the planar Cu with transition layer contacted with molten Li for 10 s. The thickness of the Li layer is about 15 μm, and the areal capacity is about 3 mAh.Math.cm.sup.−2. A symmetrical battery was assembled using the prepared Li complex in combination with a commercial lithium sheet, and the polarization performance was measured. The polarization voltage finally stabilized at 30 mV after 100 cycles with a current density of 1 mA.Math.cm.sup.−2 and a capacity of 1 mAh.Math.cm.sup.−2. When a symmetrical battery is assembled with two commercial lithium sheets as the electrode materials, the polarization voltage stabilizes at 80 mV under the same current density. The comparison shows that the ultrathin Li prepared in this invention exhibits excellent performance as a lithium metal battery material.

Example 16

(50) Preparation of Ultrathin Li on Planar Cu Substrate with Polytetrafluoroethylene Emulsion as a Transition Layer

(51) A polytetrafluoroethylene emulsion with a concentration of 30% was used as the source of the transition layer. A layer of the emulsion was coated on the surface of a planar Cu substrate. After natural drying, it was put into a vacuum drying box at 80° C. for fully dryness. The planar Cu substrates coated with the transition layer were transferred into an argon-filled glove box with an oxygen and moisture level <0.1 ppm. Li metal was heated and held at 180, 200, 220, 240, 260, 280 and 300° C. respectively in a stainless steel container to form molten Li, then the planar Cu with transition layer contacted with molten Li for 20 s. The thickness of the Li layers is in the range of 5-20 μm. The thickness of the lithium layer obtained at 180° C. and 200° C. is about 5 μm, and the thickness of the lithium layer is about 10 μm at 220° C., 240° C. and 260° C. The thickness of the lithium layer obtained at 280° C. is about 20 μm, and the thickness of the lithium layer obtained at 300° C. is about 15 μm. This is because the melting rate of the transition layer and the reaction activity increased with the elevation of temperature, which results in an accelerated spreading rate of molten lithium. However, when the temperature is increased to a certain extent, the reaction rate between the transition layer and the molten lithium is accelerated, the decomposition rate of transition layer increases, and the content of effective transition layer is reduced. Therefore, the temperature of the molten lithium has an important effect on the control of the thickness of the ultrathin lithium layer. A symmetrical battery was assembled using the prepared Li complex in combination with a commercial lithium sheet at 260° C. with a capacity of 2 mA.Math.h.Math.cm.sup.−2, and the polarization performance was measured. The polarization voltage finally stabilized at 20 mV after 100 cycles with a current density of 1 mA.Math.cm.sup.−2 and a capacity of 1 mAh.Math.cm′. When a symmetrical battery is assembled with two commercial lithium sheets as the electrode materials, the polarization voltage stabilizes at 80 mV under the same current density. The comparison shows that the ultrathin Li prepared in this invention exhibits excellent performance as a lithium metal battery material.

(52) TABLE-US-00001 TABLE 1 Performance of products in the examples Polarization Number Substrate Transition layer Contact Wettability voltage Example 1 Cu foam abietic resin 20 s good 40 mV (5 wt %) Comparative Cu foam None 20 s poor — Example 1 Example 2 Carbon citric acid 20 s good 30 mV felt (10 wt %) Comparative Carbon None 20 s poor — Example 2 Example 3 Carbon citric acid 20 s good 30 mV felt (30 wt %) Example 4 Carbon lactic acid 20 s good 50 mV felt (20 wt %) Example 5 Carbon citric acid 60 s good 30 mV felt (10 wt %) Example 6 Planar Cu Citric acid 10 s good 50 mV (5 wt %) Example 7 Planar Cu PEI 10 s good 35 mV (1 wt %) Example 8 Planar Cu benzoic acid 10 s good 55 mV (3 wt %) Example 9 Planar Cu rosin and glycerol 10 s good 40 mV ester (3 wt %) Example 10 Planar Cu methyl anthranilate 10 s good 30 mV (3 wt %) Example 11 Planar Cu naphthalenesulfonic 10 s good 55 mV acid (3 wt %) Example 12 Planar Cu Polyvinyl alcohol 10 s good 50 mV (3 wt %) Example 13 Planar Cu PVDF (3 wt %) 10 s good 25 mV Example 14 Planar Cu PVDF (2 wt %) and 20 s good 20 mV PEI (1 wt %) Example 15 Planar Cu PVDF (2 wt %) and 10 s good 30 mV benzoic acid (l wt %) Example 16 Planar Cu PVDF emulsion 20 s good 20 mV (30 wt %)

(53) From the above-mentioned examples, it is clear that there are many factors that influence the thickness of ultrathin lithium layer, including the concentration of the transition solution, the type of the transition layer solution, the contact time between molten lithium and the transition layer, and the temperature of molten lithium. The higher the concentration of the transition layer is, the higher the wettability of the molten lithium on the substrate can be achieved, and thereby the thickness of the lithium layer increases. An independent ultrathin metal lithium layer can be obtained by controlling the concentration of the solution for forming the transition layer. The Li complex prepared according to the present invention can be used as anode in secondary lithium battery, or can also be used in the prelithiation technology for anodes. Through the patterned design of the transition layer on the substrate, a highly controllable ultrathin Li can be obtained, which is useful in electronic devices and has a broad application prospect and a profound influence on the large-scale application of lithium metal.

(54) In conclusion, a universal method for preparing ultrathin lithium and its application is provided via the preparation of an organic transition layer on various substrates for improving the wettability of molten Li. The preparation method of the invention is easy to control, and the transition layer has the advantages of a wide range of raw materials and a low cost. The ultrathin lithium layer prepared in the present invention can either be separated from the substrate or be combined with a current collector, which is useful in lithium metal secondary battery for saving lithium metal consumption and inhibiting lithium dendrites. The ultrathin Li prepared in the present invention can also be used in the prelithiation technology for anodes. Furthermore, controllable ultrathin Li can be obtained through patterned design of the transition layer on the substrate, for further application in electronic devices. As the method is simple and feasible, it is applicable to many substrates. The transition layer can be selected in a wide range with a low cost, thus the method is suitable for large-scale production and has broad application prospects.

(55) The above contents are only preferred examples of the invention and are not used to restrict the scope of the invention. According to the main conception and spirit of the invention, those skilled in the field can easily adapt or modify the examples. As a result, the scope of the invention shall be based on the protection scope requested by the claims.