docs: Add async batch case (#19686)

docs/docs/expression_language/why.ipynb

@@ -323,6 +323,58 @@
     "```"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "id": "1f282129-99a3-40f4-b67f-2d0718b1bea9",
+   "metadata": {},
+   "source": [
+    "</Column>\n",
+    "</ColumnContainer>\n",
+    "\n",
+    "## Async Batch\n",
+    "\n",
+    "<ColumnContainer>\n",
+    "<Column>\n",
+    "\n",
+    "#### Without LCEL\n",
+    "\n"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "1933f39d-7bd7-45fa-a6a5-5fb7be8e31ec",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import openai\n",
+    "\n",
+    "\n",
+    "async def abatch_chain(topics: list) -> list:\n",
+    "    coros = map(ainvoke_chain, topics)\n",
+    "    return await asyncio.gather(*coros)\n"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "90691048-17ae-479d-83c2-859e33ddf3eb",
+   "metadata": {},
+   "source": [
+    "```python\n",
+    "await abatch_chain([\"ice cream\", \"spaghetti\", \"dumplings\"])\n",
+    "```\n",
+    "\n",
+    "</Column>\n",
+    "\n",
+    "<Column>\n",
+    "\n",
+    "#### LCEL\n",
+    "\n",
+    "```python\n",
+    "await chain.abatch([\"ice cream\", \"spaghetti\", \"dumplings\"])\n",
+    "```"
+   ]
+  },
   {
    "cell_type": "markdown",
    "id": "f6888245-1ebe-4768-a53b-e1fef6a8b379",