Method for improving purity and ionic conductivity of LATP solid electrolyte

Abstract

The invention belongs to the field of solid electrolyte of a solid-state battery, and relates to the field of lithium titanium aluminum phosphate solid-state dielectric media, in particular to a method for improving the purity and ionic conductivity of an LATP solid-state electrolyte. By introducing the sintering aid Bi2O3, the raw materials are crystallized at a relatively low temperature, so that the volatilization of lithium in the sintering process is inhibited, the generation of impure phases such as AlPO4 is reduced, and the purity of the product is improved. In addition, Se is introduced as a dopant for Ti-site doping, so that the unit cell volume is increased, an ion transport channel is expanded, and the ionic conductivity of LATP is improved.

Description

Technical Field

[0001] The present invention belongs to the field of solid electrolytes for solid-state batteries. Further, it relates to the field of lithium aluminum titanium phosphate solid electrolytes. Specifically, it relates to a method for improving the purity and ionic conductivity of LATP solid electrolytes. Background Art

[0002] Today, with the rapid development of new energy technologies, lithium battery technologies have been widely applied. Not only small electronic devices such as mobile phones, cameras, and watches use lithium batteries, but even automobiles widely use lithium batteries as energy storage devices. However, the currently widely used lithium batteries are liquid batteries, and the safety of liquid batteries has always been plagued by problems. Especially in the field of new energy vehicles, once a lithium battery catches fire, it will be a tragedy of vehicle destruction and human casualties. In addition to safety issues, liquid batteries have low energy density and poor low-temperature performance, which also limit their further development space.

[0003] Compared with liquid batteries, solid-state batteries use solid electrolytes and have no risk of combustion or explosion even when pierced, showing good safety. At the same time, their characteristics of high energy density, good low-temperature performance, and fast charge and discharge rates can almost solve all the drawbacks of liquid batteries. Among them, lithium aluminum titanium phosphate batteries (LATP) have become one of the most promising solid-state batteries for mass production due to advantages such as low cost, simple production process, and large electrochemical window.

[0004] However, the calcination temperature of LATP often remains above 800 °C. Such a high temperature will cause the volatilization of Li in LATP, thus forming impurity phases such as AlPO 4 etc. This will not only lead to the formation of microcracks but also reduce the ionic conductivity of LATP. It is often difficult to suppress the formation of impurity phases by improving the sintering process, which limits the development and application of LATP. In addition, due to the too small size of the lithium ion channels in the LATP electrolyte, the free migration of lithium ions in three-dimensional space is restricted, resulting in low ionic conductivity and limiting the practical application of LATP. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to solve the problems of easy generation of impurity phases and low ionic conductivity in the preparation process of LATP solid electrolytes.

[0007] The concept of the present invention is to introduce a sintering aid Bi 2 O 3 , enabling the raw materials to complete crystallization at a lower temperature, thereby suppressing the volatilization of lithium during sintering and reducing the formation of impurity phases such as AlPO 4 etc., thus improving the purity of the product. In addition, by introducing Se as a dopant and performing Ti-site doping, the unit cell volume is increased, the ion transport channels are expanded, and the ionic conductivity of LATP is improved.

[0008] A preparation method of LATP solid electrolyte, comprising the following steps: Mix a lithium source, an aluminum source, a titanium source, a phosphorus source, and a modifier, and then ball-mill them; The ball-milled material is sintered and then ball-milled again to obtain; The modifier is one or both of selenium and / or a flux.

[0009] The weight ratio of the lithium source, aluminum source, titanium source, and phosphate is formulated according to the molecular formula, and the lithium source is in an excess of 5-25%; The molecular formula is; ; ; ; d = 3;.

[0010] The flux is Bi 2 O 3 .

[0011] The mass percentage range of the flux in the solid electrolyte is 2-4%, and the stoichiometric number of selenium in the molecular formula of the solid electrolyte is 0.01-0.05.

[0012] The lithium source is one or a mixture of several of lithium carbonate, lithium hydroxide, lithium oxide, lithium nitrate, lithium dihydrogen phosphate, oxalic acid, and lithium halide.

[0013] The aluminum source is aluminum nitrate, aluminum hydroxide, aluminum oxide, or aluminum chloride.

[0014] The titanium source is titanium dioxide, titanium oxalate, titanium nitrate, or titanium chloride.

[0015] The phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphorus chloride.

[0016] The conditions for the sintering treatment are 700-950 °C and the time is 5-20 h.

[0017] The solid electrolyte obtained by the above method.

[0018] A lithium-ion battery, which contains the above solid electrolyte.

[0019] The beneficial effects of the present invention are: by introducing Bi 2 O 3 as a sintering aid during the calcination of LATP, not only the problem of easy generation of impurity phases in the traditional solid-phase method is solved, but also the energy consumption in the reaction process is effectively reduced, and the cost is reduced. In addition, by introducing the Se element to dope the Ti site of LATP, the unit cell volume becomes larger and the ion migration channel is expanded, effectively solving the problem of low ionic conductivity of the LATP solid electrolyte. Description of the Drawings

[0021] Figure 1X-ray diffraction pattern of the LATP crystal prepared in Example 1; Figure 2 Electrochemical impedance spectroscopy diagram of the LATP wafer prepared in Example 1.

[0022] Figure 3 X-ray diffraction pattern of the LATP crystal prepared in Example 2.

[0023] Figure 4 X-ray diffraction pattern of the LATP crystal prepared in Example 3; Figure 5 Electrochemical impedance spectroscopy diagram of the LATP wafer prepared in Example 3.

[0024] Figure 6 X-ray diffraction pattern of the LATP crystal prepared in Example 4; Figure 7 Electrochemical impedance spectroscopy diagram of the LATP wafer prepared in Example 4. Detailed implementation manners

[0025] The present invention provides a method for improving the purity and ionic conductivity of LATP solid electrolyte, including: The raw material components of the LATP solid electrolyte include a lithium source, a titanium source, an aluminum source and a phosphorus source, and the molecular formula is; ; ; ; d = 3; ; Weighing according to the ratio in the molecular formula. Among them, the lithium source is in excess by 15%.

[0026] The lithium source is one or more of lithium carbonate, lithium hydroxide, and lithium acetate; The titanium source is one or more of titanium dioxide, titanium oxalate, titanium nitrate, and titanium chloride; The aluminum source is one or more of aluminum nitrate, aluminum hydroxide, aluminum oxide, and aluminum chloride; The phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphorus chloride.

[0027] In order to reduce the sintering temperature to improve the purity, Bi 2 O 3 is used as a sintering aid, and the addition amount is 2-4% of the raw material mass.

[0028] In order to increase the unit cell volume and expand the ion transport channels, Se is used as a dopant for Ti-site doping, and the stoichiometric number is 0.01-0.05, and weighing is carried out according to this ratio.

[0029] Its preparation method includes: (1) Weigh the raw materials proportionally and conduct preliminary mixing with a powder grinder. The purpose is to break up the large-sized raw materials and conduct preliminary mixing. Place the mixed powder in a planetary ball mill. The ball mill tank is made of zirconia, and the balls are zirconia balls, which have the characteristics of high hardness and good wear resistance. Use isopropanol as the dispersant. The ratio of the material, balls, and dispersant is 1:1:1.5, and ball mill at a rate of 350 r / min for 10 h. The ball-milled material is dried through a rotary evaporator, and the recovered isopropanol can be reused after filtration.

[0030] (2) Place the dried powder in a mullite crucible. The crucible is flat, which is conducive to uniform heating of the raw materials. Place the crucible in a sintering furnace and heat it up to 600 °C at a rate of 2 °C / min, with a holding time of 4 h. This can cause the raw materials to decompose fully and release gases such as NH 3 etc., to avoid affecting the full reaction between the materials due to expansion during sintering. At the same time, since harmful gases are generated during the calcination process, an inert gas is introduced into the furnace and the harmful gases are recovered through a washing bottle.

[0031] (3) The pre-calcined material is a light white block with many internal voids. Crush and sieve the preliminarily calcined material through a powder grinder, place the powder in a planetary ball mill, and conduct ball milling and refinement at a rate of 500 r / min for 20 h. Dry the ball-milled slurry through a rotary evaporator.

[0032] (4) Place the dried powder in a sintering furnace and heat it up to 800 °C at a rate of 5 °C / min, with a holding time of 8 h. The calcination temperature of LATP generally needs to reach 900 °C to cause the raw materials to react fully. However, when the temperature exceeds 900 °C, part of the lithium in the raw materials and the synthesized LATP will volatilize to form impurities such as AlPO 4 etc., which will block the ion migration channels and generate microcracks, reducing the density of the sintered sheet. The Bi 2 O 3 sintering aid introduced in the present invention can reduce the sintering temperature of the raw materials to 800 °C, thereby achieving full reaction of the materials at a lower temperature and reducing the volatilization of lithium and the formation of impurities.

[0033] (5) Crush the sintered material into small pieces through a crusher and grind it into powder through a powder grinder. Further, ball mill the powder through a planetary ball mill at a rate of 500 r / min for 20 h, and use isopropanol as the dispersant. Dry the ball-milled slurry through a rotary evaporator, and the dried powder is the pure-phase LATP. Example 1

[0034] A preparation method of an LATP solid electrolyte specifically includes the following steps: (1) Lithium carbonate, titanium dioxide, aluminum hydroxide and ammonium dihydrogen phosphate were prepared in a ratio of 0.65:1.7:0.3:3, with an excess of 15% lithium carbonate. The raw materials were preliminarily mixed by a powder grinder, and then ball milled at a rate of 350 r / min for 10 h in a planetary ball mill. The ball mill jar and balls were made of zirconium oxide, the dispersant was isopropanol, and the ratio of raw materials, balls, and isopropanol was 1:1:1.5. The slurry after ball milling was dried by a rotary evaporator.

[0035] (2) Place the mixed raw materials in a sintering furnace, heat them to 600 °C at a rate of 2 °C / min and keep them at that temperature for 4 h. Pre-sintering promotes the NH 3 and CO 2 release to suppress the adverse effects caused by expansion.

[0036] (3) The pre-burned material is crushed by a powder grinder, and the crushed material is sieved through a 100-mesh screen. The sieved powder is placed in a planetary ball mill and ball-milled at a rate of 500 r / min for 20 h. Isopropyl alcohol is used as a dispersant. The ball-milled slurry is dried by a rotary evaporator.

[0037] (4) Place the dried powder in a sintering furnace and heat it to 800-900 °C at a rate of 5 °C / min. Set the holding time to 8 h and cool it down naturally.

[0038] (5) The calcined material was crushed by a jaw crusher, and the broken pieces were ground into powder by a powder mill and passed through a 100-mesh screen. The sieved material was refined by a planetary ball mill at a ball milling rate of 500 r / min for 20 h. The ball-milled slurry was dried by a rotary evaporator, and the dried LATP powder was subjected to XRD phase analysis. The XRD analysis results are shown in Figure 1 As shown in Figure 2, whether calcined at 800 °C or 900 °C, AlPO 4 Mixed phase.

[0039] (6) Add PVB as a binder to the refined LATP powder, then place the powder in a mold with a diameter of 16 mm and press it at 100 MPa for 5 min on a tablet press. Place the thin slice in a small crucible and cover it with a layer of LATP mother powder for calcination. The calcination temperature is 1000 °C, the holding time is 10 h, and the heating rate is 10 °C / min. The main purpose of burying the powder is to inhibit the volatilization of lithium during the calcination process. At the same time, a faster heating rate can also reduce the volatilization of Li during the calcination process. The surface of the calcined LATP sheet is polished and coated with conductive glue. The LATP sheet is subjected to electrochemical AC impedance testing. The test results are as follows: Figure 2As shown, the ionic conductivities of LATP calcined at 800 °C and 900 °C are 1.63×10 −4 S·cm -1 and 1.77×10 −4 S·cm -1 . Example 2

[0040] A preparation method of LATP solid electrolyte specifically includes the following steps: (1) Charge lithium carbonate, titanium dioxide, aluminum hydroxide and ammonium dihydrogen phosphate in a ratio of 0.65:1.7:0.3:3, with lithium carbonate being 15% in excess. In addition, add 2% of Bi 2 O 3 as a flux. Initially mix the raw materials through a powder grinder, and then ball mill them in a planetary ball mill at a rate of 350 r / min for 10 h. The ball mill tank and balls are made of zirconia, the dispersant is isopropanol, and the ratio of raw materials, balls, and isopropanol is 1:1:1.5. Dry the ball-milled slurry through a rotary evaporator.

[0041] (2) Place the uniformly mixed raw materials in a sintering furnace, heat them to 600 °C at a rate of 2 °C / min and hold for 4 h to promote the release of NH 3 and CO 2 in the raw materials to avoid the expansion of the final sintered product.

[0042] (3) Crush the pre-calcined materials through a powder grinder, and screen the crushed materials through a 100-mesh sieve. Place the sieved powder in a planetary ball mill and ball mill it at a rate of 500 r / min for 20 h. Dry the ball-milled slurry through a rotary evaporator.

[0043] (4) Place the dried powder in a sintering furnace, heat it to 800 - 900 °C at a rate of 5 °C / min, set the holding time to 8 h, and cool it naturally.

[0044] (5) Crush the calcined materials through a crusher, grind the chunks into powder through a powder grinder and pass through a 200-mesh sieve. Refine the sieved materials through a planetary ball mill, with a ball mill rate of 500 r / min and a time of 20 h. Dry the ball-milled slurry through a rotary evaporator, and conduct XRD phase analysis on the dried LATP powder. The XRD analysis results are as Figure 3 shown. When the calcination temperature is 800 and 900 °C, the main phase of the obtained product is LiTi 2 (PO 4 ) 3The standard spectrum (PDF: 35-0754) was consistent with that of the standard spectrum, indicating that pure LATP was obtained.

[0045] Compared with Example 1, Bi 2 O 3 After sintering the additive, pure phase LATP can be generated at 800℃, which indicates that Bi 2 O 3 The sintering aid effectively lowers the melting point of the raw materials, which inhibits the volatilization of local Li and thus reduces the generation of impurity phases. Example 3

[0046] A method for preparing a LATP solid electrolyte specifically comprises the following steps: (1) Lithium carbonate, titanium dioxide, aluminum hydroxide, Se powder, and ammonium dihydrogen phosphate were prepared in a ratio of 0.65:1.68:0.3:0.02:3, with an excess of 15% lithium carbonate. The raw materials were preliminarily mixed by a powder grinder, and then ball milled in a planetary ball mill at a rate of 350 r / min for 10 h. The ball milling jar and balls were made of zirconium oxide, the dispersant was isopropanol, and the ratio of raw materials, balls, and isopropanol was 1:1:1.5. The milled slurry was dried by a rotary evaporator.

[0047] (2) Place the mixed raw materials in a sintering furnace, heat them to 600 °C at a rate of 2 °C / min and keep them at that temperature for 4 h. Pre-sintering promotes the NH 3 and CO 2 to avoid expansion of the final sintered product.

[0048] (3) The pre-burned material is crushed by a powder grinder, and the crushed material is sieved through a 100-mesh screen. The sieved powder is placed in a planetary ball mill and ball-milled at a rate of 500 r / min for 20 h. The ball-milled slurry is dried by a rotary evaporator.

[0049] (4) Place the dried powder in a sintering furnace and heat it to 800 °C at a rate of 5 °C / min. Set the holding time to 8 h and cool it down naturally.

[0050] (5) The calcined material was crushed by a crusher, and the broken pieces were powdered by a powder grinder and passed through a 100-mesh sieve. The sieved material was refined by a planetary ball mill at a ball milling rate of 500 r / min for 20 h. The ball-milled slurry was dried by a rotary evaporator, and the dried LATP powder was subjected to XRD phase analysis. The XRD analysis results are shown in Figure 4 As shown in the figure, the generated LATP powder still contains AlPO 4 The existence of mixed phases.

[0051] (6) Add the refined LATP powder to PVB as the binder, then place the powder in a mold with a diameter of 16 mm and press it under a tablet press at 100 MPa for 5 min. Place the thin sheet in a small crucible, cover it with a layer of mother powder on the outside and calcine it. The calcination temperature is 1000 °C, the heat preservation time is 10 h, and the heating rate is 10 °C / min. The main significance of the buried powder is to inhibit the lithium volatilization during the calcination process. Polish the surface of the calcined LATP sheet and apply conductive glue, and conduct electrochemical impedance spectroscopy detection on the LATP sheet. The detection results are as Figure 5 shown. The ionic conductivity of this LATP sheet is 5.11×10 −4 S·cm -1 。

[0052] Compared with Example 1, the doping of Se significantly improves the ionic conductivity of LATP. Example 4

[0053] A preparation method of an LATP solid electrolyte specifically includes the following steps: (1) Weigh lithium carbonate, titanium dioxide, aluminum hydroxide, Se powder, and ammonium dihydrogen phosphate in a ratio of 0.65:1.68:0.3:0.02:3, with lithium carbonate being 15% in excess. Initially mix the raw materials through a powder grinder, and then ball-mill them in a planetary ball mill at a rate of 350 r / min for 10 h. The ball mill tank and balls are made of zirconia, and the dispersant is isopropanol. The ratio of raw materials, balls, and isopropanol is 1:1:1.5. Dry the ball-milled slurry through a rotary evaporator.

[0054] (2) Place the uniformly mixed raw materials in a sintering furnace, heat them to 600 °C at a rate of 2 °C / min and hold for 4 h to promote the release of NH 3 and CO 2 in the raw materials to avoid the expansion of the final sintered product.

[0055] (3) Crush the pre-calcined material through a powder grinder, and screen the crushed material through a 100-mesh sieve. Place the sieved powder in a planetary ball mill and ball-mill it at a rate of 500 r / min for 20 h. Dry the ball-milled slurry through a rotary evaporator.

[0056] (4) Place the dried powder in a sintering furnace, heat it to 800 °C at a rate of 5 °C / min, set the heat preservation time to 8 h, and cool it naturally.

[0057] (5) The calcined material is crushed by a crusher, and the fragments are ground into powder by a pulverizer and passed through a 100-mesh sieve. The sieved material is refined by a planetary ball mill at a ball-milling rate of 500 r / min for 20 h. The ball-milled slurry is dried by a rotary evaporator, and the dried LATP powder is subjected to XRD phase analysis. The XRD analysis results are as Figure 6 shown, and the main phase of the obtained product is consistent with the LiTi 2 (PO 4 ) 3 standard spectrum (PDF: 35-0754) card, indicating that pure-phase LATP is obtained.

[0058] (6) The refined LATP powder is added with PVB as a binder, and then the powder is placed in a mold with a diameter of 16 mm and pressed at 100 MPa for 5 min under a tablet press. The thin sheet is placed in a small crucible and covered with a layer of mother powder for calcination. The calcination temperature is 1000 °C, the holding time is 10 h, and the heating rate is 10 °C / min. The significance of the buried powder is mainly to inhibit lithium volatilization during the calcination process. The surface of the calcined LATP sheet is polished and coated with conductive glue, and the LATP sheet is subjected to electrochemical impedance spectroscopy detection. The detection results are as Figure 7 shown, and the ionic conductivity of this LATP is 7.17×10 −4 S·cm -1 .

[0059] Compared with Example 3, adding Bi 2 O 3 sintering aid on the basis of Se doping can further improve the ionic conductivity of LATP, indicating that the Bi 2 O 3 flux coupling Se doping technology can effectively improve the ionic conductivity of LATP.

[0060] In summary, it can be seen that in Example 1, no additives were used, in Example 2, Bi 2 O 3 was added as a flux, in Example 3, Se powder was added, and in Example 4, both Se powder and Bi 2 O 3 were used. In Example 1, there were AlPO 4 impurity phases after calcination at 800 °C and 900 °C, and the ionic conductivity was low. In Example 2, by adding Bi 2 O 3 , pure-phase LATP can be formed at 800 °C without impurity phases. In Example 3, the ionic conductivity was improved by Se doping, but there was still an AlPO 4 impurity phase. In Example 4, Se doping and Bi 2 O3 The flux not only produced a pure phase of LATP but also further increased the ionic conductivity. These differences indicate that the introduction of additives (such as Bi 2 O 3 and Se powder) and the optimization of sintering conditions have a significant impact on the purity and ionic conductivity of the LATP solid electrolyte.

Claims

1. A method for preparing a LATP solid electrolyte, characterized in that: The steps include: The lithium source, the aluminum source, the titanium source, the phosphate, and the modifier are mixed and then ball-milled; The ball-milled material is sintered and then ball-milled; The modifier is one or both of selenium and / or flux.

2. The method for preparing the LATP solid electrolyte according to claim 1, characterized in that: The weight ratio of lithium source, aluminum source, titanium source and phosphate is prepared according to the molecular formula, and the lithium source is in excess of 5-25%; the molecular formula is;;; ； d=3; 。 3. The method for preparing the LATP solid electrolyte according to claim 2, characterized in that: The mass percentage of flux in the solid electrolyte is in the range of 2-4%, and the stoichiometric number of selenium in the molecular formula of the solid electrolyte is 0.01-0.

05.

4. The method for preparing the LATP solid electrolyte according to claim 1, characterized in that: The flux is Bi2O3.

5. The method for preparing the LATP solid electrolyte according to claim 1, characterized in that: The lithium source is one or a mixture of lithium carbonate, lithium hydroxide, lithium oxide, lithium nitrate, lithium dihydrogen phosphate, oxalic acid, and lithium halide.

6. The method for preparing the LATP solid electrolyte according to claim 1, characterized in that: The aluminum source is aluminum hydroxide, aluminum chloride or a mixture of the two.

7. The method for preparing the LATP solid electrolyte according to claim 1, characterized in that: The titanium source is one of titanium dioxide and tetrabutyl titanate or a mixture of several of them.

8. The method for preparing the LATP solid electrolyte according to claim 1, characterized in that: The sintering conditions are 700-950°C and the time is 5-20h.

9. The solid electrolyte obtained by the preparation method according to any one of claims 1 to 8.

10. A lithium ion battery, characterized in that: It contains the above-mentioned solid electrolyte.

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